March 12, 2025 • 37 mins
It's a rule that has frustrated kids everywhere. But is it a myth, or is there real science behind it? Jorge finds out if it passes the float test.
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Speaker 1 (00:01):
Hey, welcome to Sign Stuff, a production of iHeartRadio. My
name is Hoorge Champ, and today on the program, we
are tackling a question that has poured cold water on
the fund of countless children here in the US and
across the world. Do you have to wait thirty minutes
after eating before you can go swimming? We've all been there.
It's a hot day and you're eager to get back
(00:23):
into the cool and inviting pool, but you've just had
lunch and some adult is telling you you're supposed to
just sit there and do nothing for thirty minutes before
you can rejoin your friends in the water. Now, as
I'll mentioned in a minute, this is a very personal
question for me, and so it was very eager to
put this advice to the float test to see if
it sinks or swims. We're going to be doing that
(00:45):
by talking to a medical doctor and also a physiologist
will take us on a deep dive into the topic
of digestion and exercise. So put your floaties on, because
we are going to the deep end of science to
find out do you really have to wait thirty minutes
after eating to go swimming? Don't worry if anything happens.
(01:07):
I know CPR, which in this case stands for Certified Podcasts, Researching, Enjoying. Okay,
so the first thing I did was to try to
figure out where this piece of advice about eating and
swimming came from, but it seems nobody could figure it out.
The earliest mentioned that anyone can find about this is
(01:29):
in the Boy Scout Manual from nineteen oh eight. A
lot of people don't know this, but the boy Scout
movement actually started in England, who was started by a
British Army general called Robert Baden Powell, who fought in
a bunch of wars in Africa. So when he came
back he wrote a book called Scouting for Boys, which,
according to the Telegraph newspaper, is one of the top
(01:52):
four best selling books of the twentieth century. Apparently, the
only books that have sold more copies are the Bible,
the Quran, and the Thoughts of Chairman mal Sittung. This book,
Scouting for Boys contains advice, of course about scouting, like
how to start a campfire or how to deal with
the stink bite, but it also has some weird pieces
of advice, like the rule that you shouldn't trust men
(02:14):
with waxed mustaches. And then in a section called keep
yourself Clean, it's a little bit of advice. It says, quote,
never bathed in deep water very soon after a meal.
It is very likely to cause cramp, which doubles you
up and so you get drowned. End quote. Now nobody
can tell if this is the actual origin of that advice,
but after that it definitely seems to have seeped into
(02:35):
the culture. But is it actually true. To get to
the bottom of this, I decided to call doctor Matthew Badgett,
who is a doctor of internal medicine and pediatric primary
care at the Cleveland Clinic. Now, he's spoken about this
before on the internet, and he was also a high
school competitive swimmer, so I thought he was the perfect
person to call. So here's the first part of my
chat with doctor Matthew badget All Right, well, thank you
(02:59):
doctor badget for joining us today.
Speaker 2 (03:00):
Yeah, thank you for having me excited to be here.
Speaker 1 (03:03):
Okay, so today we're tackling a very important question that
a lot of kids are asking and have been asking
for decades, and that is can you go swimming after eating?
Or do you have to wait thirty minutes, as most
parents would say. And I should just tell you this
is a bit of a personal question for me. So
I grew up in Panama. I was born and raised there,
and I spent a lot of time in swimming pools
because my favorite aunt would take us swimming, and she's
(03:26):
a doctor, and she would always tell us that we
had to wait thirty minutes after eating before we could
go swimming, and it was the worst part of the day.
You know, you're excited, you want to go into the
swim pool, but you can. You just have to sit
there and be totally bored for thirty minutes. So basically,
doctor Badget was my aunt lying to me.
Speaker 2 (03:45):
I don't think she was lying to you because she
believed she was telling the truth. But I do think
she's wrong, right, you know, from my own history, I
remember when I was at the pool, i'd lie to
my mom about when I last.
Speaker 1 (03:56):
Ate so I could go back, incause I'd have thought
of that before.
Speaker 2 (04:01):
Yeah, but you know, this is a long standing thing
where it's growing up. This made no sense to me
because you know, like, well, you can't eat and then
go swimming. But you go to a soccer game and
there's like oranges and caprice suns everywhere, and they're like,
if you don't eat this orange, you're going to get
a cramp. But then they say that if you go
swimming and if you do eat, you'll get a cramp.
And I'm like, being my like opinionated self at ten,
(04:21):
I was like, this is stupid, right, Like this makes
no sense because they're telling you some physical activities require
eating to prevent cramps, while they're telling you that other
physical activities you need to not eat.
Speaker 1 (04:32):
To prevent that. Wait, so you're ten years old and
you've reasoned this, like you figured this out?
Speaker 2 (04:38):
Yeah, yeah, I don't know. Maybe I always had a
strong barometer for hypocrisy, but I always thought this rules
really made no sense to me. I remember this is
I would have been at the end of high school.
But when like Michael Phelps was really big and they
really showed what he would eat.
Speaker 1 (04:51):
Right, like a billion calories, But.
Speaker 2 (04:54):
It wasn't just a billion calories. You know, his pre
morning swim meet meal was like eggs, toast and four shakes.
Four shakes but not one or two. Know, he had
four energy eatings.
Speaker 1 (05:06):
Right, did do you think he waited thirty minutes or
do you think he ate those four shakes and jumped
into the pool.
Speaker 2 (05:10):
Well, I mean he probably waited a little bit, but
like he had a ob scene him out. But if
you ask, like what people are doing before swimmings or
what they're doing in before morning practices, I could physically
tell a difference if I had two pieces of toast
and then went and swam an hour at five thirty
six am in high school versus if I didn't eat it,
I would be dragging like that workout would definitely feel
you know, you.
Speaker 1 (05:29):
Would feel the difference.
Speaker 2 (05:30):
Yeah, indeed, you know, like other sports, I think this
is more commonly understood. It's you go to a five
k race nowadays, right, and they're handing out snacks everywhere, right, right,
So it's well understood that we need to be doing
these we need to be eating. And there's better evidence
for running and bicycling because I think this's is easier
to control for studies that giving carbohydrates before an exercise
improves endurance, improves energy, and prove speed and strength. Now,
(05:54):
of course, most people that are going in the pool
don't necessarily need optimal physical performance.
Speaker 1 (05:59):
I know, I know, But you know, if you're playing
marco polo. Those are high stakes.
Speaker 2 (06:02):
You know that's true, though, I mean marco polo is
more about strategy and holding your breath underwater and other
other nuances then.
Speaker 1 (06:10):
Right, right, other performance issues.
Speaker 2 (06:12):
Yeah, But the point is that we know that for
optional physical performance we need some amount of carbohydrates or calories.
You know, if you're doing a really long physical activity
in the pool, like if you're doing like a couple
of mile swim, like, it's probably reasonable to stop after
half an hour, take like a goo or a piece
of fruit and eat it and then keep swimming if
you really want to be physically optimal.
Speaker 1 (06:32):
In which case you're eating into the exercise.
Speaker 2 (06:35):
Yeah. If people are doing half marathons, they're taking fluids
and carbohydrates during the race. If they're doing marathons, they're
doing that, they're doing one hundred mile bike rides. They're
doing these things, right And once again, we're telling these
kids to eat oranges during the soccer game, right right,
because we think it helps their physical performances and prevents cramps,
right right, right, So we're already telling the kids to
do these things.
Speaker 1 (06:54):
Uhuh, just not in the pool, Just not in the pool.
Speaker 2 (06:56):
And that that really pissed me off.
Speaker 1 (06:58):
When I was like, who would you direct this anger at?
I guess the adult who was telling you.
Speaker 2 (07:04):
I think I argue with my mom about it once.
She wasn't very interested, but she also didn't feel strongly
enough to stop me from eating and swimming, So like.
Speaker 1 (07:15):
I see, So, doctor Badgett definitely has some strong opinions
about this, but his general point is that on the
one hand, we're telling kids that they should eat some
food before they exercise, like, for example, they should eat
some orange slices or drink some juice before they play soccer.
And in some sports you actually want to be eating
during the exercise, like if you're doing a really long
(07:36):
run or really long swim. But at the same time,
we seem to be telling kids not to eat anything
at all right before going swimming because it might cost cramps.
Of course, you're probably thinking, well, maybe swimming is different
than playing soccer, and that's what I thought too, So
I asked them directly if swimming and eating can be
a dangerous combination. This is what he said, but I
(07:58):
just want to double check. So in your medical school
education as a pediotician, when you go to School for Pediatrics. Yeah,
they never mentioned this.
Speaker 2 (08:06):
No, I never heard it come up for or against. Right,
I was never taught that we need to The number
one thing that I got about pools in pediatric training
is fences, fences, fences, fences, fences and fences, which is,
if you have a pull at your house, always put
a fence up to reduce the chance that your child
drowns in it. Most of the training, you know it
(08:27):
is around, and there's evidence of that, right, putting a
fence up reduces depths, so it's recommended.
Speaker 1 (08:32):
But in your years and years of being a pediatrician,
and nobody has ever come in or no cases have
come through your office of parents saying something out of
either kid because they swim too soon after eating.
Speaker 2 (08:42):
No, And have I told patients that it's okay to
eat during swieing. Not often, because it doesn't come up.
We have so many things we want to talk about
in a limited visit and so many issues. Now. It's
actually interesting you bring this up because I was at
talking with some residents when I got interviewed for this
article a couple of months ago, and a good number
of them are for medical grads.
Speaker 1 (09:00):
You mean foreign like from another country.
Speaker 2 (09:02):
And so the American ones were like, yeah, no, you
don't wait to swim, and all the foreign medical grads
they're all from Europe or the Middle East, They're like,
we don't know this rule.
Speaker 1 (09:12):
They don't even have this rule.
Speaker 2 (09:14):
So so so like how universal is it? Right? Like
you know where I couldn't find where culturally got started.
Speaker 1 (09:19):
Right, Well, it's interesting you said that there's this push
for evidence based medicine. Yeah, you would think this is
maybe high on the priority list of things to figure
out the answer to.
Speaker 2 (09:31):
I mean not really, because it's a I mean it's
a it's probably not very harmful, right, Waiting to swim
is not harming people. Now, I'm sure you were very
upset by it, right, like when you're younger and that
you had to wait. It's not you know, I think
very rarely are we actually putting people in danger by
doing this, because you know, it's a situation where like, yeah,
(09:51):
kids might have to not get as much swimming time in,
but is that actually harmful? There's so there's a thousand
and one.
Speaker 1 (09:56):
Issues, right, not harming anyone, and in fact, it's maybe
just teaching kids to sit still for thirty.
Speaker 2 (10:01):
Minutes which might have a benefit. Right.
Speaker 1 (10:05):
Okay, So to recap my conversation with doctor Badget, medical
doctors are not taught at eating before swimming is dangerous,
and in fact, in lots of other sports you actually
eat while you're doing the exercise. Now, is this based
on heart science? Well, like doctor Badget said, this is
not a high priority issue for the medical community. But
they did manage to find some scientific studies that look
(10:28):
at this question. For some reason, in the nineteen sixties,
a whole bunch of scientists got really interested in the subject,
and so there was a small flurry of experiments that
were done, and they all sort of go something like this.
The scientists grabbed a bunch of people, usually college students
because these were all mostly done at universities, and then
they had the subject to a bunch of laps on
a swimming pool. In one study, they would have the
(10:50):
college student swim two hundred yards freestyle, and another they
would swim one hundred yards, and then another they would
swim a whole mile. Now, the scientists would also have
the swimmers eat a small meal at different times before
they went swimming, So some of the swimmers would eat
a small meal three hours before they went swimming. Some
of the swimmers would eat a meal one and a
half hours before swimming, and some of the swimmers would
(11:12):
eat a small meal half an hour before going swimming.
And then the scientists would see how well the swimmers swam,
Did they have the same times, did they report feeling
any struggle or nausea or cramps, did any of them drown?
And across the board pretty much, they all found the
same thing. They found that how much time passes between
(11:32):
eating a meal and swimming has no effect on how
well the swimmers swam. They all swam at the same speed. Basically,
the students who ate a meal half an hour before
swimming swam just as well as the students who ate
three hours before swimming. And also nobody drowned. In fact,
there were no reported cases in the studies of anyone
even having cramps. But still it seems like the myth persisted.
(11:55):
I mean, I was born way after the nineteen sixties,
and my aunt was still giving that advice. So it
got to the point where even the Red Cross had
to intervene. So in twenty eleven, the American Red Cross
Scientific Advisory Committee issued a special scientific review on the
issue of eating before swimming, which they published in the
International Journal of Aquatic Research and Education. It reads, quote
(12:19):
this review services a scholarly literature to investigate whether there
is any correlation between eating and fatal or non fatal
drowning events, and to establish whether it is safe to
swim after eating end quote. At the end, they concluded,
quote there are no reported cases of eating before swimming
costing or contributing to fatal or non fatal drowning in
(12:41):
any of the literature search. Currently available information suggests that
eating before swimming is not a contributing risk for drowning
and can be dismissed as a myth. Food intake restrictions
prior to swimming are unnecessary. End quote. That's right, kits everywhere,
you can eat whatever you want before going swimming, the
American Red Cross says, So, so question answered, or is
(13:06):
it there is something that was found in those swimming
studies that was not covered in the Red Cross report.
So when we come back, we're going to look into that,
and also we're going to tackle the general issue of
digestion and swimming. What's actually happening to that food you eat?
How does it affect your body, you're listening to sign stuff,
(13:31):
welcome back to sigence stuff. So to recap. Even the
Red Cross has concluded you don't have to wait thirty
minutes after eating before you can go swimming. There's no
evidence that it leads to any danger. But there is
one thing that several of the swimming studies found. They
found that the swimmers who went swimming thirty minutes or
less reported a significant amount of discomfort and nausea. It
(13:57):
was not a good swimming experience for them. And I
think that's something that maybe some of us can relate to,
which is going swimming after a meal and then feeling
like you're going to throw up. So now the question
is what's going on there, what is it about swimming
and eating that causes that discomfort, and how is it
tied to the thirty minute mark? And so I called
an expert. Professor. Stephen Ives is an associate professor of
(14:20):
Health and Human Physiological Sciences at Skidmore College, and he
studies how our bodies respond to exercise and how we
adapt to exercise long term. So I told him about
my experiences with my aunt, and then I asked him
to break it all down for us. So here's my
chat with Professor Steven Ives. Thanks so much for joining
(14:40):
us here today. What are your thoughts on the question
of whether, one sh you'd wait thirty minutes after eating
before going swimming.
Speaker 3 (14:47):
Yeah, that's a great question, and I think your scenario
is one we can all relate to. I also rope
roundwater pools and lakes, etc. And I had that same
blore given to me as well. And now it's the
same thing, but with sunscreen. You gotta put your sun
screen on, then you got to wait until that track.
So we've traded one for the other.
Speaker 1 (15:04):
I suppose in thirty years our kid's going to be
complaining about us and that advice perhaps perhaps.
Speaker 3 (15:11):
So the interesting thing about this is, you know, when
you look into it, there's no real evidence to suggest
that there's any real threat or danger. So I don't
think there's a cute risk there. That said, we can
talk a little bit more about is it wise to
eat before swimming?
Speaker 1 (15:31):
I see, so it's not a safety issue, but it
does maybe affect your swimming experience.
Speaker 3 (15:37):
Yeah, I think it's more of a comfort issue or
a discomfort issue that we're more likely to encounter than
a safety issue. So there's two main categories that I
would talk about with regards to this question. That is
the process of digestion and the swimming. So we can
use a technique clinically that's called gastric emptying studies, and
(15:59):
that allows us to assess how long it takes to
begin the process of digestion in the stomach for that
food to leave the stomach.
Speaker 1 (16:09):
Maybe steak is a step back. So when I eat
something I quew, it goes down my throat lands in
my stomach. What happens to that food afterwards.
Speaker 3 (16:18):
Well, it actually starts before that. So you as soon
as you see that food or you smell that food,
the whole process of digestion starts right So you smell
the food, you see the food, you begin to salivate,
and that's really the first step in the digestive process.
The chewing helps start to break down the food, but
(16:39):
there's also enzymes in saliva that help to start the
digestive process and breaking down our starches, our larger carbohydrate molecules.
That goes down the esophagus and that food gets sensed
by the esophagus and that triggers this rhythmic muscle contraction.
That moves the food down into the stomach, and the
(17:02):
stomach actually begins to pulverize it a little bit. We
don't think of the stomach as doing any mechanical digestion,
but it.
Speaker 1 (17:09):
Does what My stomach will actually start contracting and massaging
the food.
Speaker 3 (17:15):
It is a muscular organ, so it'll start to sort
of grind that food down a bit more. And interestingly enough,
it starts to analyze it, right. So you know, we
think about our dishwashers as being smart detecting how much
dirt is on your dishes. The stomach is a little
bit the same. Starts to detect the composition of the
(17:35):
meal and how big the meal is. The meal will
stretch the stomach and depending on the stretch, that tells
you about the size of the meal. But it's also
looking at the composition and then that's going to dictate
some of the digestive response.
Speaker 1 (17:48):
How does it analyze it? Does it have like sensors?
Speaker 3 (17:51):
Yep. Wherever you have a response, you have to have
a sensor and an integrator, right, So there's something that's
sensing the composition and the meal, and there's various so
it's analyzing the content of the meal, and then that
information gets integrated by the nervous system and then we
generate a response which will help dictate the hormonal response,
(18:15):
the enzyme response, the stomach acid response.
Speaker 1 (18:19):
Whoa. So then the food lands in there and it
sits in the stomach for a while, or it depends
on what's in it.
Speaker 3 (18:26):
It depends, That's what I'm saying it. So the size
of the meal matters. The contents of the meal matters.
So the larger the meal, it could alter the rate
of digestion. The more calorie dense it is, the longer
it's going to take to digest that Or if it
has more fiber, that could take longer to digest that meal.
(18:48):
So then after it leaves the stomach, it enters into
the small intestine.
Speaker 1 (18:52):
Oh, is there like a little door to the lower
testine that opens little by little or does it lead
the food into it or how does it move the food?
Speaker 3 (19:01):
Again, it depends. If it's more liquid, it's a more
fluid process, you know, no pun intented it's it's going
to be more of a streaming type of effect. But
there is a gatekeeper at the top and bottom of
the stomach. Right, So we have these what we call sphincters,
these muscular parts that help close off or allow both
the entrance to the stomach and the exits to the
(19:23):
stomach to open and close. And we hope those work
well as they're supposed to. And so when people talk
about indigestion, that's the upper sphincter of the stomach perhaps
being dysfunctional and stomach acid can leak back up into
the esophagus and cause that pain in the chest.
Speaker 1 (19:42):
Okay, the food sits in my stomach, at some point
it gets through to the intestine. How fast is that process?
Speaker 3 (19:49):
So we can use a technique clinically that's called gastric
emptying studies, and that allows us to assess how long
it takes to begin the process of digestion in the
stomach for that food to leave the stomach. They use
a meal, but the meal I think is usually egg
(20:11):
whites and barium chloride or something like that, so it's
a radio labeled substance, so it's not a typical meal.
Speaker 1 (20:18):
Wait, radio labeled like it's radioactive.
Speaker 3 (20:22):
Even with that standardized meal, seventy percent is still in
the stomach after thirty minutes.
Speaker 1 (20:29):
So meaning that after thirty minutes seventy percent of the
food you eat is still in your stomach.
Speaker 3 (20:35):
From a gastric emptying or food exiting the stomach as
an indicator of digestion. You know, we still have a
long way to go.
Speaker 1 (20:43):
So there is something to the thirty minute mark.
Speaker 3 (20:46):
Perhaps, but there's still a lot of food to be digested.
So I guess that would be an argument against thirty minutes.
I ice right, Well, depending on whether you're an optimist
or a pestimist, either you're you know, twenty five percent
there or twenty five percent left to go. Yeah, there
you go.
Speaker 1 (21:04):
Okay, so then it goes in my intestine and then
and then what happened?
Speaker 3 (21:08):
So in the small intestine, that's where at least the
beginning part of the small intestine, we have bile that's introduced,
and that's where we're starting to break down the fats
into smaller molecules so then we can chop them up
a little bit more for energy as well. So the
small intestine is mostly the further breakdown of our macro
(21:30):
nutrients and starting to extract those nutrients that is, the fats,
the carbohydrates, the proteins, but also the vitamins, the minerals,
et cetera. So then after that we transition into the
large intestine. There is some extraction of water and nutrients.
Speaker 1 (21:49):
And then it all turns to well, i'd want to
say it P word. I was gonna say the S word,
but uh oh yeah, maybe we'll stick with the P word.
So that's a broad overview of digestion. And what's kind
of interesting there is the idea that your stomach actually
senses what you eat and then it adjusts how it's
(22:11):
going to digest that food and how long it's going
to take. And then when it comes to swimming, it
turns out that your digestion also depends on the exercise
that you're doing, but not in a way that I
think most of us understand it. So I asked professor
iis how swimming affects your digestion? Here's what he said,
all right, So that's what happens to your food when
(22:32):
you eat it. That's super interesting. And you said the
other part of it was the exercise, the swimming.
Speaker 3 (22:38):
Yeah, so then that's the second part, right, So not
all swimming or exercises created equal, and perhaps that's obvious,
but you know, jumping off the diving board and doing
the doggy paddle to the ladder to go out and
do your next jump. That's one thing. But getting ready
to do a couple thousand yards meters in a pool
(22:59):
or sprint interval set for some hardcore swim training, those
are very different things. So interestingly, when we think about activity,
we could think about as light intensity, moderate intensity, and
high intensity, and the light intensity actually can aid in
digestion and likely speeds up gastric emptying.
Speaker 1 (23:23):
Is it like light exercise, like going for a walk exactly?
Speaker 3 (23:28):
And that's actually been in the press a lot lately,
that after dinner walk has been a popular thing of late.
And it's not a new thing, that's for sure, but
that's been popularized because it can aid in digestion, give
you a better feeling it particularly if you overeat, because
it's going to facilitate that gastric emptying.
Speaker 1 (23:48):
Yeah, I've been hearing that a lot. So what's going
on there? Why is going for a walk helping you digest?
Speaker 3 (23:54):
Well, that one's hard to figure out. I think we're
still trying to figure that out. Because the way we
tip do these studies is clinically. They would do the
barium studies and so then you're doing lots of imaging.
So I think it would be almost impossible to do
those studies while exercising, so you can do it before
and see what happens at the end of the day.
(24:17):
Being able to exercise and move is a fight or flight, right,
So light physical activity is likely to help us maintain
an ability to fight or flight. It's going to aid
in digestion, facilitate the mobilization of the nutrients that are
being digested.
Speaker 1 (24:37):
Meaning your body is trying to keep itself ready in
case it needs to run from a line or fight
a hyena.
Speaker 3 (24:44):
Yeah, it probably comes down to blood flow, which we'll
have to come back to that in a moment. But okay,
let's contrast that light physical activity with a high intensity.
So if we think about you know, maximal sprints down
the pool, or thinking about being in the ocean or
a surfer paddling hard out to that wave, that's a
(25:04):
very different situation in the sense that we need to
think about the blood flow that's going around the body
and how it gets distributed. So at rest, we think
about cardiac output, that is, the blood that's pumped out
by the heart per minute, and the relative percentages that
is distributed across all your organs and the tissues. It's
(25:25):
pretty fair. Let's just say that. So your brain's getting
what it's needed, the heart's getting what it needs, the
muscles are getting some, the gut is getting what it needs.
Maybe as much as twenty five percent of the blood
that's pumped out by the heart per minute could be
going to the.
Speaker 1 (25:40):
Gut for digestion, I think.
Speaker 3 (25:43):
But when we start exercising, our cardiac output, or the
blood that's pumped out by the heart per minute, you
can quintuple, right, So we're going from maybe five leaders
per minute that's leaving the heart to twenty five leaders
per minute during exercise, and that'd be during a sort
of high intensity exercise.
Speaker 1 (26:01):
I see, this is your heart just pumping faster, so
it's putting through more blood.
Speaker 3 (26:06):
Yeah, it's squeezing harder, so per beat, it's pushing more
blood out, and it's beating more times per minute. So
you get more bang for your buck, and you get
a lot of blood leaving the heart. Permitut it. But
then the percentage changes too. So the skeletal muscle, all
the muscles that produce the swimming movement, walking, movement, et cetera.
There's a high demand. The muscles want blood flow, they
(26:29):
want the nutrients that you've eaten recently. They could also
be coming from the liver. There's a high demand for
blood flow, for the nutrients, for the oxygen to support
energy production, so the muscles can keep doing their thing
and contracting. That can come at a cost of some
of the other organs. So on a percentage basis, the
gut goes from getting maybe twenty five percent of the
(26:52):
blood that's pumped out by the heart per minute to
maybe a couple percent. It gets cut dramatically.
Speaker 1 (26:59):
Well sage are absolutely like it's getting less or just
less of the blood.
Speaker 3 (27:04):
It's getting less of the pie. It's getting less of
the pie.
Speaker 1 (27:07):
When we come back, we'll talk about how all of
these shenanigans with your digestive system and your muscles, how
that affects your swimming experience and ability to stay afloat.
We'll be right back, and we're back.
Speaker 3 (27:28):
So we've known that for many years, and that was
part of the impetus or the rationale for the waiting
of thirty minutes, is you ate, your gut needs blood flow.
Your muscles may not get enough blood supply while you're swimming.
That could be catastrophic. If you can't support the swimming
(27:50):
motion then you're going to drop or somehow. That was
causing a muscle cramp. But interestingly, on an absolute basis,
the amount of blood flow going to the gut actually
increases because the cardiac out with the total increase, but
percentage wise it went way down.
Speaker 1 (28:08):
What does that mean then? Does that mean that your
muscles are getting less blood if you're trying to digest
something at the same time.
Speaker 3 (28:16):
The muscles, again, they're a hungry beast. They will steal
rub and sheet from everybody else, which is a survival mechanism.
Speaker 1 (28:27):
Right, that's the most important thing at the moment.
Speaker 3 (28:30):
The fight or flight. You got to fight off that
lion or run away from it, and so your muscles
have evolved to be able to steal blood to support
that activity. Yeah, it's an interesting thing. So even during
exercising in the heat, your muscles are so profound in
their demand for blood they will steal it from the skin.
(28:52):
And when you're exercising in the heat, that can predispose
you to heat related illness or heat stroke. Whoamuscle doesn't care,
it's just you want to exercise, you want to keep
running at a certain speed. It'll take the blood from
somewhere else, just to give an example. So it'll steal
from the skin, and it'll steal from the gut, and
(29:12):
it's all trying to produce that exercise or that physical activity.
Speaker 1 (29:17):
Okay, I think you're telling me that we don't have
to worry about your muscles not getting enough nutrients just
because you just ate before going swimming.
Speaker 3 (29:24):
The muscles are going to get what they need no
matter what. So your muscles aren't. They're not magically not
going to get enough blood. We know that that's a
fallacy at this point, but there's a competition a little
bit between blood going to the gut and the muscle.
The muscle's going to win. And so if you just
ate a big meal that is very calorically dense, the
has a lot of fat in it, that's going to
(29:46):
be uncomfortable because that food is going to tend to
sit in the stomach and the digestive process is overall
going to be slower. If you've ever atened and tried
to go for a run, a lot of people know
that feeling. It's pretty uncomfortable. Swimming can be the same.
And interestingly, if we think about running versus swimming, position
(30:10):
can also influence gastric emptying. So if you're sitting or
you're standing, our gastric emptying rate is higher than when
we're lying down. So swimming, of course, we do in
what we call prone or supine position, laying down basically
uh huh exactly, either on our stomach or our back,
(30:30):
and that actually slows down gastric emptying.
Speaker 1 (30:34):
Oh, because you don't have gravity pulling the food towards
the hole at the bottom of the stomach. Probably, So
does it slow down? Is it partly because the muscles
are pulling all of the blood that it slows indigestion
or is it just because it knows it needs to
sit in your stomach longer?
Speaker 3 (30:51):
Yeah, I mean in terms of the swimming question, there's
a couple of things going on. Is you know, if
you eat a large meal, that's a greater challenge for
your digestives system. But that would be true of any exercise.
I think swimming interestingly has that position component, which could
make the situation worse. Another factor to consider is the temperature.
(31:12):
When are we typically.
Speaker 1 (31:13):
Swimming summer, I guess.
Speaker 3 (31:15):
Yeah, it's in Panama, where it's warm most.
Speaker 1 (31:18):
Of the summer all year round. Yeah, but when it's
warm out.
Speaker 3 (31:22):
But when it's warm out there can also be a
greater challenge because we need to thermo regulate so the skin.
Taking it back to blood flow, the skin needs greater
blood flow to be able to support thermal regulation. Make
sure we're not getting too hot. You get some sweat
production going on, you get vase dilation of the skin,
so our skin appears a little bit more flushed. That's
(31:44):
all trying to get rid of heat, but it's due
to increased blood flow to the skin. Again, then we're
thinking about a competition for blood flow. So blood needs
to go to the skin, it needs to go to
the muscle, and it needs to go to the digestive system.
If we're thinking about eating before swimming in a warm environment.
Speaker 1 (32:02):
Are you saying that the digestive system basically loses.
Speaker 3 (32:05):
Kind of yes, it's going to take third place to
the skin, certainly to the muscle.
Speaker 1 (32:12):
So it's kind of opposite of the lore. Right, The
lore was that the stomach would suck blood flow from
your muscles. But it's the opposite. It's going to lose
and therefore it's going to take longer to digest and
even more because you're laying down when you're assuming, and
that's going to cause you discomfort.
Speaker 3 (32:27):
That's really I think this story. It's a comfort or
discomfort issue.
Speaker 1 (32:31):
I see, And where does a discomfort come from? Why
doesn't your body like having food around belong?
Speaker 3 (32:36):
That's a that's a good question. It could be the
distension of the stomach. Right, so use a large meal.
Oh I feel, I feel really full. That's not a
comfortable feeling. It's probably the mechanical stension and the sensory
neurons are detecting that and letting you know, hey, you're
really full, don't eat more, right, So that's that's part
(32:59):
of it is, is trying to regulate energy intake.
Speaker 1 (33:02):
Like you had a full meal, whoa, whoa, you know,
don't need anymore.
Speaker 3 (33:07):
That allows time for your digestive system to interpret the
meal and go to the brain and say, slow down,
you're starting to get full. So it does take time
those signals to happen.
Speaker 1 (33:20):
Did discomfort is a signal that your stomach's trying to
tell your brain, hey, stop eating. But I wonder if
it's also trying to tell you to not exercise because
it knows that your stomach needs the blood flow.
Speaker 3 (33:32):
Right, What does this all orchestrator are controlled by is
the autonomic nervous system. Always tell my students autonomic is automatic.
So it's the nervous system that is dealing with controlling
our internal environment. So when we think about fight or
flight or rest and digest. So I think you're right.
I think that makes intuitive sense that some of that
(33:55):
signal is rest and digests. Let's process this meal, Let's
get the nutrients from it so that way we can
do the next thing. There's no need to go out
and hunt and gather, so just relax.
Speaker 1 (34:07):
What about cramps? I know crams was sort of in
that Boyscout report, like if you eat it before swimming,
you might get cramps and then you'll drown. What causes cramps.
Speaker 3 (34:17):
Believe it or not, there's things that we still don't
know the answer to, we don't have the final answer to,
or we're still trying to better understand. So muscle cramps,
those are very likely the result of two things, one
a water electrolyte imbalance and two neural dysregulation. So obviously
(34:38):
our body has a significant portion that is water, right,
something like seventy percent of our body is made up
of water. We also have electrolytes. These are basically salts,
and when there is not good harmony between the amount
of water that we have in the amount of electrolytes
that we have, they can create very serious problems. But
(35:00):
that wouldn't be recency to a meal. That would be
too much time from a meal with some electrolytes.
Speaker 1 (35:08):
Oh, because when you eat, you're bringing in those electrolytes
that you need, and if you haven't eaten in a while,
you're gonna your body's going to run out of them.
Speaker 3 (35:15):
Exactly. That's sort of our number one hypothesis, along with
something going on with a neuro muscular system.
Speaker 1 (35:23):
All right, So it sounds like you don't want to
eat too close to swimming, but you do want to
eat something beforehand at some point. Interesting. All right, So
then I guess the final question, Steve is was my
aunt lying to me.
Speaker 3 (35:37):
Yes, Oh, you should thank her for taking your swimming
every day. Yeah, it's an interesting question. But at the
end of the day, I think, as we've hit on
a couple of times, it's not really a safety issue.
I would say under nutrition is probably more of a
safety issue. It's more of a comfort issue.
Speaker 1 (35:56):
I see. Maybe that's why my aunt was really trying
to help me avoid was the discomfort?
Speaker 3 (36:02):
Probably not.
Speaker 1 (36:05):
Or just not me throwing up from the pool. Well,
there you have it. The answer to the question is
you don't have to wait thirty minutes after eating before
you can go swimming, but you probably should. Thanks for
joining us, you've been listening to Science Stuff. The production
of iHeartRadio written and produced by me Or hitch Ham,
(36:28):
executive producer Jerry Rowland, an audio engineer and mixer Casey Peckram.
You can follow me on social media to search for
PhD comics and the name of your favorite platform. Be
sure to subscribe to Sign Stuff on the iHeartRadio app,
Apple Podcasts or wherever you get your podcasts, and please
tell your friends we'll be back next Wednesday with another episode. Okay, Well,
(36:54):
what if your niece or nephew orview if you have
do you have kids? Yeah? Yeah? Or let's say, like
what if your kids had two cheeseburgers and then they
wanted to jump into the pool. Would you be like, yes,
go for it, or like maybe have a seat for
a second.
Speaker 2 (37:08):
So first of all, my said two and a half.
So our policies we do not feed him before going
into the pool because we do not want him pooping
in the pool because he is not potty trade, completely
different conversation. It's a different strategy we're approaching in that situation.
We feed him unch, he goes down for nap time,
we wake up, we change his diaper, and we take
him to the pool.
Speaker 1 (37:27):
I see it's more important to time than diaper change.
Speaker 2 (37:31):
But very different. Yeah,
Hey, welcome to Sign Stuff, a production of iHeartRadio. My
name is Hoorge Champ, and today on the program, we
are tackling a question that has poured cold water on
the fund of countless children here in the US and
across the world. Do you have to wait thirty minutes
after eating before you can go swimming? We've all been there.
It's a hot day and you're eager to get back
(00:23):
into the cool and inviting pool, but you've just had
lunch and some adult is telling you you're supposed to
just sit there and do nothing for thirty minutes before
you can rejoin your friends in the water. Now, as
I'll mentioned in a minute, this is a very personal
question for me, and so it was very eager to
put this advice to the float test to see if
it sinks or swims. We're going to be doing that
(00:45):
by talking to a medical doctor and also a physiologist
will take us on a deep dive into the topic
of digestion and exercise. So put your floaties on, because
we are going to the deep end of science to
find out do you really have to wait thirty minutes
after eating to go swimming? Don't worry if anything happens.
(01:07):
I know CPR, which in this case stands for Certified Podcasts, Researching, Enjoying. Okay,
so the first thing I did was to try to
figure out where this piece of advice about eating and
swimming came from, but it seems nobody could figure it out.
The earliest mentioned that anyone can find about this is
(01:29):
in the Boy Scout Manual from nineteen oh eight. A
lot of people don't know this, but the boy Scout
movement actually started in England, who was started by a
British Army general called Robert Baden Powell, who fought in
a bunch of wars in Africa. So when he came
back he wrote a book called Scouting for Boys, which,
according to the Telegraph newspaper, is one of the top
(01:52):
four best selling books of the twentieth century. Apparently, the
only books that have sold more copies are the Bible,
the Quran, and the Thoughts of Chairman mal Sittung. This book,
Scouting for Boys contains advice, of course about scouting, like
how to start a campfire or how to deal with
the stink bite, but it also has some weird pieces
of advice, like the rule that you shouldn't trust men
(02:14):
with waxed mustaches. And then in a section called keep
yourself Clean, it's a little bit of advice. It says, quote,
never bathed in deep water very soon after a meal.
It is very likely to cause cramp, which doubles you
up and so you get drowned. End quote. Now nobody
can tell if this is the actual origin of that advice,
but after that it definitely seems to have seeped into
(02:35):
the culture. But is it actually true. To get to
the bottom of this, I decided to call doctor Matthew Badgett,
who is a doctor of internal medicine and pediatric primary
care at the Cleveland Clinic. Now, he's spoken about this
before on the internet, and he was also a high
school competitive swimmer, so I thought he was the perfect
person to call. So here's the first part of my
chat with doctor Matthew badget All Right, well, thank you
(02:59):
doctor badget for joining us today.
Speaker 2 (03:00):
Yeah, thank you for having me excited to be here.
Speaker 1 (03:03):
Okay, so today we're tackling a very important question that
a lot of kids are asking and have been asking
for decades, and that is can you go swimming after eating?
Or do you have to wait thirty minutes, as most
parents would say. And I should just tell you this
is a bit of a personal question for me. So
I grew up in Panama. I was born and raised there,
and I spent a lot of time in swimming pools
because my favorite aunt would take us swimming, and she's
(03:26):
a doctor, and she would always tell us that we
had to wait thirty minutes after eating before we could
go swimming, and it was the worst part of the day.
You know, you're excited, you want to go into the
swim pool, but you can. You just have to sit
there and be totally bored for thirty minutes. So basically,
doctor Badget was my aunt lying to me.
Speaker 2 (03:45):
I don't think she was lying to you because she
believed she was telling the truth. But I do think
she's wrong, right, you know, from my own history, I
remember when I was at the pool, i'd lie to
my mom about when I last.
Speaker 1 (03:56):
Ate so I could go back, incause I'd have thought
of that before.
Speaker 2 (04:01):
Yeah, but you know, this is a long standing thing
where it's growing up. This made no sense to me
because you know, like, well, you can't eat and then
go swimming. But you go to a soccer game and
there's like oranges and caprice suns everywhere, and they're like,
if you don't eat this orange, you're going to get
a cramp. But then they say that if you go
swimming and if you do eat, you'll get a cramp.
And I'm like, being my like opinionated self at ten,
(04:21):
I was like, this is stupid, right, Like this makes
no sense because they're telling you some physical activities require
eating to prevent cramps, while they're telling you that other
physical activities you need to not eat.
Speaker 1 (04:32):
To prevent that. Wait, so you're ten years old and
you've reasoned this, like you figured this out?
Speaker 2 (04:38):
Yeah, yeah, I don't know. Maybe I always had a
strong barometer for hypocrisy, but I always thought this rules
really made no sense to me. I remember this is
I would have been at the end of high school.
But when like Michael Phelps was really big and they
really showed what he would eat.
Speaker 1 (04:51):
Right, like a billion calories, But.
Speaker 2 (04:54):
It wasn't just a billion calories. You know, his pre
morning swim meet meal was like eggs, toast and four shakes.
Four shakes but not one or two. Know, he had
four energy eatings.
Speaker 1 (05:06):
Right, did do you think he waited thirty minutes or
do you think he ate those four shakes and jumped
into the pool.
Speaker 2 (05:10):
Well, I mean he probably waited a little bit, but
like he had a ob scene him out. But if
you ask, like what people are doing before swimmings or
what they're doing in before morning practices, I could physically
tell a difference if I had two pieces of toast
and then went and swam an hour at five thirty
six am in high school versus if I didn't eat it,
I would be dragging like that workout would definitely feel
you know, you.
Speaker 1 (05:29):
Would feel the difference.
Speaker 2 (05:30):
Yeah, indeed, you know, like other sports, I think this
is more commonly understood. It's you go to a five
k race nowadays, right, and they're handing out snacks everywhere, right, right,
So it's well understood that we need to be doing
these we need to be eating. And there's better evidence
for running and bicycling because I think this's is easier
to control for studies that giving carbohydrates before an exercise
improves endurance, improves energy, and prove speed and strength. Now,
(05:54):
of course, most people that are going in the pool
don't necessarily need optimal physical performance.
Speaker 1 (05:59):
I know, I know, But you know, if you're playing
marco polo. Those are high stakes.
Speaker 2 (06:02):
You know that's true, though, I mean marco polo is
more about strategy and holding your breath underwater and other
other nuances then.
Speaker 1 (06:10):
Right, right, other performance issues.
Speaker 2 (06:12):
Yeah, But the point is that we know that for
optional physical performance we need some amount of carbohydrates or calories.
You know, if you're doing a really long physical activity
in the pool, like if you're doing like a couple
of mile swim, like, it's probably reasonable to stop after
half an hour, take like a goo or a piece
of fruit and eat it and then keep swimming if
you really want to be physically optimal.
Speaker 1 (06:32):
In which case you're eating into the exercise.
Speaker 2 (06:35):
Yeah. If people are doing half marathons, they're taking fluids
and carbohydrates during the race. If they're doing marathons, they're
doing that, they're doing one hundred mile bike rides. They're
doing these things, right And once again, we're telling these
kids to eat oranges during the soccer game, right right,
because we think it helps their physical performances and prevents cramps,
right right, right, So we're already telling the kids to
do these things.
Speaker 1 (06:54):
Uhuh, just not in the pool, Just not in the pool.
Speaker 2 (06:56):
And that that really pissed me off.
Speaker 1 (06:58):
When I was like, who would you direct this anger at?
I guess the adult who was telling you.
Speaker 2 (07:04):
I think I argue with my mom about it once.
She wasn't very interested, but she also didn't feel strongly
enough to stop me from eating and swimming, So like.
Speaker 1 (07:15):
I see, So, doctor Badgett definitely has some strong opinions
about this, but his general point is that on the
one hand, we're telling kids that they should eat some
food before they exercise, like, for example, they should eat
some orange slices or drink some juice before they play soccer.
And in some sports you actually want to be eating
during the exercise, like if you're doing a really long
(07:36):
run or really long swim. But at the same time,
we seem to be telling kids not to eat anything
at all right before going swimming because it might cost cramps.
Of course, you're probably thinking, well, maybe swimming is different
than playing soccer, and that's what I thought too, So
I asked them directly if swimming and eating can be
a dangerous combination. This is what he said, but I
(07:58):
just want to double check. So in your medical school
education as a pediotician, when you go to School for Pediatrics. Yeah,
they never mentioned this.
Speaker 2 (08:06):
No, I never heard it come up for or against. Right,
I was never taught that we need to The number
one thing that I got about pools in pediatric training
is fences, fences, fences, fences, fences and fences, which is,
if you have a pull at your house, always put
a fence up to reduce the chance that your child
drowns in it. Most of the training, you know it
(08:27):
is around, and there's evidence of that, right, putting a
fence up reduces depths, so it's recommended.
Speaker 1 (08:32):
But in your years and years of being a pediatrician,
and nobody has ever come in or no cases have
come through your office of parents saying something out of
either kid because they swim too soon after eating.
Speaker 2 (08:42):
No, And have I told patients that it's okay to
eat during swieing. Not often, because it doesn't come up.
We have so many things we want to talk about
in a limited visit and so many issues. Now. It's
actually interesting you bring this up because I was at
talking with some residents when I got interviewed for this
article a couple of months ago, and a good number
of them are for medical grads.
Speaker 1 (09:00):
You mean foreign like from another country.
Speaker 2 (09:02):
And so the American ones were like, yeah, no, you
don't wait to swim, and all the foreign medical grads
they're all from Europe or the Middle East, They're like,
we don't know this rule.
Speaker 1 (09:12):
They don't even have this rule.
Speaker 2 (09:14):
So so so like how universal is it? Right? Like
you know where I couldn't find where culturally got started.
Speaker 1 (09:19):
Right, Well, it's interesting you said that there's this push
for evidence based medicine. Yeah, you would think this is
maybe high on the priority list of things to figure
out the answer to.
Speaker 2 (09:31):
I mean not really, because it's a I mean it's
a it's probably not very harmful, right, Waiting to swim
is not harming people. Now, I'm sure you were very
upset by it, right, like when you're younger and that
you had to wait. It's not you know, I think
very rarely are we actually putting people in danger by
doing this, because you know, it's a situation where like, yeah,
(09:51):
kids might have to not get as much swimming time in,
but is that actually harmful? There's so there's a thousand
and one.
Speaker 1 (09:56):
Issues, right, not harming anyone, and in fact, it's maybe
just teaching kids to sit still for thirty.
Speaker 2 (10:01):
Minutes which might have a benefit. Right.
Speaker 1 (10:05):
Okay, So to recap my conversation with doctor Badget, medical
doctors are not taught at eating before swimming is dangerous,
and in fact, in lots of other sports you actually
eat while you're doing the exercise. Now, is this based
on heart science? Well, like doctor Badget said, this is
not a high priority issue for the medical community. But
they did manage to find some scientific studies that look
(10:28):
at this question. For some reason, in the nineteen sixties,
a whole bunch of scientists got really interested in the subject,
and so there was a small flurry of experiments that
were done, and they all sort of go something like this.
The scientists grabbed a bunch of people, usually college students
because these were all mostly done at universities, and then
they had the subject to a bunch of laps on
a swimming pool. In one study, they would have the
(10:50):
college student swim two hundred yards freestyle, and another they
would swim one hundred yards, and then another they would
swim a whole mile. Now, the scientists would also have
the swimmers eat a small meal at different times before
they went swimming, So some of the swimmers would eat
a small meal three hours before they went swimming. Some
of the swimmers would eat a meal one and a
half hours before swimming, and some of the swimmers would
(11:12):
eat a small meal half an hour before going swimming.
And then the scientists would see how well the swimmers swam,
Did they have the same times, did they report feeling
any struggle or nausea or cramps, did any of them drown?
And across the board pretty much, they all found the
same thing. They found that how much time passes between
(11:32):
eating a meal and swimming has no effect on how
well the swimmers swam. They all swam at the same speed. Basically,
the students who ate a meal half an hour before
swimming swam just as well as the students who ate
three hours before swimming. And also nobody drowned. In fact,
there were no reported cases in the studies of anyone
even having cramps. But still it seems like the myth persisted.
(11:55):
I mean, I was born way after the nineteen sixties,
and my aunt was still giving that advice. So it
got to the point where even the Red Cross had
to intervene. So in twenty eleven, the American Red Cross
Scientific Advisory Committee issued a special scientific review on the
issue of eating before swimming, which they published in the
International Journal of Aquatic Research and Education. It reads, quote
(12:19):
this review services a scholarly literature to investigate whether there
is any correlation between eating and fatal or non fatal
drowning events, and to establish whether it is safe to
swim after eating end quote. At the end, they concluded,
quote there are no reported cases of eating before swimming
costing or contributing to fatal or non fatal drowning in
(12:41):
any of the literature search. Currently available information suggests that
eating before swimming is not a contributing risk for drowning
and can be dismissed as a myth. Food intake restrictions
prior to swimming are unnecessary. End quote. That's right, kits everywhere,
you can eat whatever you want before going swimming, the
American Red Cross says, So, so question answered, or is
(13:06):
it there is something that was found in those swimming
studies that was not covered in the Red Cross report.
So when we come back, we're going to look into that,
and also we're going to tackle the general issue of
digestion and swimming. What's actually happening to that food you eat?
How does it affect your body, you're listening to sign stuff,
(13:31):
welcome back to sigence stuff. So to recap. Even the
Red Cross has concluded you don't have to wait thirty
minutes after eating before you can go swimming. There's no
evidence that it leads to any danger. But there is
one thing that several of the swimming studies found. They
found that the swimmers who went swimming thirty minutes or
less reported a significant amount of discomfort and nausea. It
(13:57):
was not a good swimming experience for them. And I
think that's something that maybe some of us can relate to,
which is going swimming after a meal and then feeling
like you're going to throw up. So now the question
is what's going on there, what is it about swimming
and eating that causes that discomfort, and how is it
tied to the thirty minute mark? And so I called
an expert. Professor. Stephen Ives is an associate professor of
(14:20):
Health and Human Physiological Sciences at Skidmore College, and he
studies how our bodies respond to exercise and how we
adapt to exercise long term. So I told him about
my experiences with my aunt, and then I asked him
to break it all down for us. So here's my
chat with Professor Steven Ives. Thanks so much for joining
(14:40):
us here today. What are your thoughts on the question
of whether, one sh you'd wait thirty minutes after eating
before going swimming.
Speaker 3 (14:47):
Yeah, that's a great question, and I think your scenario
is one we can all relate to. I also rope
roundwater pools and lakes, etc. And I had that same
blore given to me as well. And now it's the
same thing, but with sunscreen. You gotta put your sun
screen on, then you got to wait until that track.
So we've traded one for the other.
Speaker 1 (15:04):
I suppose in thirty years our kid's going to be
complaining about us and that advice perhaps perhaps.
Speaker 3 (15:11):
So the interesting thing about this is, you know, when
you look into it, there's no real evidence to suggest
that there's any real threat or danger. So I don't
think there's a cute risk there. That said, we can
talk a little bit more about is it wise to
eat before swimming?
Speaker 1 (15:31):
I see, so it's not a safety issue, but it
does maybe affect your swimming experience.
Speaker 3 (15:37):
Yeah, I think it's more of a comfort issue or
a discomfort issue that we're more likely to encounter than
a safety issue. So there's two main categories that I
would talk about with regards to this question. That is
the process of digestion and the swimming. So we can
use a technique clinically that's called gastric emptying studies, and
(15:59):
that allows us to assess how long it takes to
begin the process of digestion in the stomach for that
food to leave the stomach.
Speaker 1 (16:09):
Maybe steak is a step back. So when I eat
something I quew, it goes down my throat lands in
my stomach. What happens to that food afterwards.
Speaker 3 (16:18):
Well, it actually starts before that. So you as soon
as you see that food or you smell that food,
the whole process of digestion starts right So you smell
the food, you see the food, you begin to salivate,
and that's really the first step in the digestive process.
The chewing helps start to break down the food, but
(16:39):
there's also enzymes in saliva that help to start the
digestive process and breaking down our starches, our larger carbohydrate molecules.
That goes down the esophagus and that food gets sensed
by the esophagus and that triggers this rhythmic muscle contraction.
That moves the food down into the stomach, and the
(17:02):
stomach actually begins to pulverize it a little bit. We
don't think of the stomach as doing any mechanical digestion,
but it.
Speaker 1 (17:09):
Does what My stomach will actually start contracting and massaging
the food.
Speaker 3 (17:15):
It is a muscular organ, so it'll start to sort
of grind that food down a bit more. And interestingly enough,
it starts to analyze it, right. So you know, we
think about our dishwashers as being smart detecting how much
dirt is on your dishes. The stomach is a little
bit the same. Starts to detect the composition of the
(17:35):
meal and how big the meal is. The meal will
stretch the stomach and depending on the stretch, that tells
you about the size of the meal. But it's also
looking at the composition and then that's going to dictate
some of the digestive response.
Speaker 1 (17:48):
How does it analyze it? Does it have like sensors?
Speaker 3 (17:51):
Yep. Wherever you have a response, you have to have
a sensor and an integrator, right, So there's something that's
sensing the composition and the meal, and there's various so
it's analyzing the content of the meal, and then that
information gets integrated by the nervous system and then we
generate a response which will help dictate the hormonal response,
(18:15):
the enzyme response, the stomach acid response.
Speaker 1 (18:19):
Whoa. So then the food lands in there and it
sits in the stomach for a while, or it depends
on what's in it.
Speaker 3 (18:26):
It depends, That's what I'm saying it. So the size
of the meal matters. The contents of the meal matters.
So the larger the meal, it could alter the rate
of digestion. The more calorie dense it is, the longer
it's going to take to digest that Or if it
has more fiber, that could take longer to digest that meal.
(18:48):
So then after it leaves the stomach, it enters into
the small intestine.
Speaker 1 (18:52):
Oh, is there like a little door to the lower
testine that opens little by little or does it lead
the food into it or how does it move the food?
Speaker 3 (19:01):
Again, it depends. If it's more liquid, it's a more
fluid process, you know, no pun intented it's it's going
to be more of a streaming type of effect. But
there is a gatekeeper at the top and bottom of
the stomach. Right, So we have these what we call sphincters,
these muscular parts that help close off or allow both
the entrance to the stomach and the exits to the
(19:23):
stomach to open and close. And we hope those work
well as they're supposed to. And so when people talk
about indigestion, that's the upper sphincter of the stomach perhaps
being dysfunctional and stomach acid can leak back up into
the esophagus and cause that pain in the chest.
Speaker 1 (19:42):
Okay, the food sits in my stomach, at some point
it gets through to the intestine. How fast is that process?
Speaker 3 (19:49):
So we can use a technique clinically that's called gastric
emptying studies, and that allows us to assess how long
it takes to begin the process of digestion in the
stomach for that food to leave the stomach. They use
a meal, but the meal I think is usually egg
(20:11):
whites and barium chloride or something like that, so it's
a radio labeled substance, so it's not a typical meal.
Speaker 1 (20:18):
Wait, radio labeled like it's radioactive.
Speaker 3 (20:22):
Even with that standardized meal, seventy percent is still in
the stomach after thirty minutes.
Speaker 1 (20:29):
So meaning that after thirty minutes seventy percent of the
food you eat is still in your stomach.
Speaker 3 (20:35):
From a gastric emptying or food exiting the stomach as
an indicator of digestion. You know, we still have a
long way to go.
Speaker 1 (20:43):
So there is something to the thirty minute mark.
Speaker 3 (20:46):
Perhaps, but there's still a lot of food to be digested.
So I guess that would be an argument against thirty minutes.
I ice right, Well, depending on whether you're an optimist
or a pestimist, either you're you know, twenty five percent
there or twenty five percent left to go. Yeah, there
you go.
Speaker 1 (21:04):
Okay, so then it goes in my intestine and then
and then what happened?
Speaker 3 (21:08):
So in the small intestine, that's where at least the
beginning part of the small intestine, we have bile that's introduced,
and that's where we're starting to break down the fats
into smaller molecules so then we can chop them up
a little bit more for energy as well. So the
small intestine is mostly the further breakdown of our macro
(21:30):
nutrients and starting to extract those nutrients that is, the fats,
the carbohydrates, the proteins, but also the vitamins, the minerals,
et cetera. So then after that we transition into the
large intestine. There is some extraction of water and nutrients.
Speaker 1 (21:49):
And then it all turns to well, i'd want to
say it P word. I was gonna say the S word,
but uh oh yeah, maybe we'll stick with the P word.
So that's a broad overview of digestion. And what's kind
of interesting there is the idea that your stomach actually
senses what you eat and then it adjusts how it's
(22:11):
going to digest that food and how long it's going
to take. And then when it comes to swimming, it
turns out that your digestion also depends on the exercise
that you're doing, but not in a way that I
think most of us understand it. So I asked professor
iis how swimming affects your digestion? Here's what he said,
all right, So that's what happens to your food when
(22:32):
you eat it. That's super interesting. And you said the
other part of it was the exercise, the swimming.
Speaker 3 (22:38):
Yeah, so then that's the second part, right, So not
all swimming or exercises created equal, and perhaps that's obvious,
but you know, jumping off the diving board and doing
the doggy paddle to the ladder to go out and
do your next jump. That's one thing. But getting ready
to do a couple thousand yards meters in a pool
(22:59):
or sprint interval set for some hardcore swim training, those
are very different things. So interestingly, when we think about activity,
we could think about as light intensity, moderate intensity, and
high intensity, and the light intensity actually can aid in
digestion and likely speeds up gastric emptying.
Speaker 1 (23:23):
Is it like light exercise, like going for a walk exactly?
Speaker 3 (23:28):
And that's actually been in the press a lot lately,
that after dinner walk has been a popular thing of late.
And it's not a new thing, that's for sure, but
that's been popularized because it can aid in digestion, give
you a better feeling it particularly if you overeat, because
it's going to facilitate that gastric emptying.
Speaker 1 (23:48):
Yeah, I've been hearing that a lot. So what's going
on there? Why is going for a walk helping you digest?
Speaker 3 (23:54):
Well, that one's hard to figure out. I think we're
still trying to figure that out. Because the way we
tip do these studies is clinically. They would do the
barium studies and so then you're doing lots of imaging.
So I think it would be almost impossible to do
those studies while exercising, so you can do it before
and see what happens at the end of the day.
(24:17):
Being able to exercise and move is a fight or flight, right,
So light physical activity is likely to help us maintain
an ability to fight or flight. It's going to aid
in digestion, facilitate the mobilization of the nutrients that are
being digested.
Speaker 1 (24:37):
Meaning your body is trying to keep itself ready in
case it needs to run from a line or fight
a hyena.
Speaker 3 (24:44):
Yeah, it probably comes down to blood flow, which we'll
have to come back to that in a moment. But okay,
let's contrast that light physical activity with a high intensity.
So if we think about you know, maximal sprints down
the pool, or thinking about being in the ocean or
a surfer paddling hard out to that wave, that's a
(25:04):
very different situation in the sense that we need to
think about the blood flow that's going around the body
and how it gets distributed. So at rest, we think
about cardiac output, that is, the blood that's pumped out
by the heart per minute, and the relative percentages that
is distributed across all your organs and the tissues. It's
(25:25):
pretty fair. Let's just say that. So your brain's getting
what it's needed, the heart's getting what it needs, the
muscles are getting some, the gut is getting what it needs.
Maybe as much as twenty five percent of the blood
that's pumped out by the heart per minute could be
going to the.
Speaker 1 (25:40):
Gut for digestion, I think.
Speaker 3 (25:43):
But when we start exercising, our cardiac output, or the
blood that's pumped out by the heart per minute, you
can quintuple, right, So we're going from maybe five leaders
per minute that's leaving the heart to twenty five leaders
per minute during exercise, and that'd be during a sort
of high intensity exercise.
Speaker 1 (26:01):
I see, this is your heart just pumping faster, so
it's putting through more blood.
Speaker 3 (26:06):
Yeah, it's squeezing harder, so per beat, it's pushing more
blood out, and it's beating more times per minute. So
you get more bang for your buck, and you get
a lot of blood leaving the heart. Permitut it. But
then the percentage changes too. So the skeletal muscle, all
the muscles that produce the swimming movement, walking, movement, et cetera.
There's a high demand. The muscles want blood flow, they
(26:29):
want the nutrients that you've eaten recently. They could also
be coming from the liver. There's a high demand for
blood flow, for the nutrients, for the oxygen to support
energy production, so the muscles can keep doing their thing
and contracting. That can come at a cost of some
of the other organs. So on a percentage basis, the
gut goes from getting maybe twenty five percent of the
(26:52):
blood that's pumped out by the heart per minute to
maybe a couple percent. It gets cut dramatically.
Speaker 1 (26:59):
Well sage are absolutely like it's getting less or just
less of the blood.
Speaker 3 (27:04):
It's getting less of the pie. It's getting less of
the pie.
Speaker 1 (27:07):
When we come back, we'll talk about how all of
these shenanigans with your digestive system and your muscles, how
that affects your swimming experience and ability to stay afloat.
We'll be right back, and we're back.
Speaker 3 (27:28):
So we've known that for many years, and that was
part of the impetus or the rationale for the waiting
of thirty minutes, is you ate, your gut needs blood flow.
Your muscles may not get enough blood supply while you're swimming.
That could be catastrophic. If you can't support the swimming
(27:50):
motion then you're going to drop or somehow. That was
causing a muscle cramp. But interestingly, on an absolute basis,
the amount of blood flow going to the gut actually
increases because the cardiac out with the total increase, but
percentage wise it went way down.
Speaker 1 (28:08):
What does that mean then? Does that mean that your
muscles are getting less blood if you're trying to digest
something at the same time.
Speaker 3 (28:16):
The muscles, again, they're a hungry beast. They will steal
rub and sheet from everybody else, which is a survival mechanism.
Speaker 1 (28:27):
Right, that's the most important thing at the moment.
Speaker 3 (28:30):
The fight or flight. You got to fight off that
lion or run away from it, and so your muscles
have evolved to be able to steal blood to support
that activity. Yeah, it's an interesting thing. So even during
exercising in the heat, your muscles are so profound in
their demand for blood they will steal it from the skin.
(28:52):
And when you're exercising in the heat, that can predispose
you to heat related illness or heat stroke. Whoamuscle doesn't care,
it's just you want to exercise, you want to keep
running at a certain speed. It'll take the blood from
somewhere else, just to give an example. So it'll steal
from the skin, and it'll steal from the gut, and
(29:12):
it's all trying to produce that exercise or that physical activity.
Speaker 1 (29:17):
Okay, I think you're telling me that we don't have
to worry about your muscles not getting enough nutrients just
because you just ate before going swimming.
Speaker 3 (29:24):
The muscles are going to get what they need no
matter what. So your muscles aren't. They're not magically not
going to get enough blood. We know that that's a
fallacy at this point, but there's a competition a little
bit between blood going to the gut and the muscle.
The muscle's going to win. And so if you just
ate a big meal that is very calorically dense, the
has a lot of fat in it, that's going to
(29:46):
be uncomfortable because that food is going to tend to
sit in the stomach and the digestive process is overall
going to be slower. If you've ever atened and tried
to go for a run, a lot of people know
that feeling. It's pretty uncomfortable. Swimming can be the same.
And interestingly, if we think about running versus swimming, position
(30:10):
can also influence gastric emptying. So if you're sitting or
you're standing, our gastric emptying rate is higher than when
we're lying down. So swimming, of course, we do in
what we call prone or supine position, laying down basically
uh huh exactly, either on our stomach or our back,
(30:30):
and that actually slows down gastric emptying.
Speaker 1 (30:34):
Oh, because you don't have gravity pulling the food towards
the hole at the bottom of the stomach. Probably, So
does it slow down? Is it partly because the muscles
are pulling all of the blood that it slows indigestion
or is it just because it knows it needs to
sit in your stomach longer?
Speaker 3 (30:51):
Yeah, I mean in terms of the swimming question, there's
a couple of things going on. Is you know, if
you eat a large meal, that's a greater challenge for
your digestives system. But that would be true of any exercise.
I think swimming interestingly has that position component, which could
make the situation worse. Another factor to consider is the temperature.
(31:12):
When are we typically.
Speaker 1 (31:13):
Swimming summer, I guess.
Speaker 3 (31:15):
Yeah, it's in Panama, where it's warm most.
Speaker 1 (31:18):
Of the summer all year round. Yeah, but when it's
warm out.
Speaker 3 (31:22):
But when it's warm out there can also be a
greater challenge because we need to thermo regulate so the skin.
Taking it back to blood flow, the skin needs greater
blood flow to be able to support thermal regulation. Make
sure we're not getting too hot. You get some sweat
production going on, you get vase dilation of the skin,
so our skin appears a little bit more flushed. That's
(31:44):
all trying to get rid of heat, but it's due
to increased blood flow to the skin. Again, then we're
thinking about a competition for blood flow. So blood needs
to go to the skin, it needs to go to
the muscle, and it needs to go to the digestive system.
If we're thinking about eating before swimming in a warm environment.
Speaker 1 (32:02):
Are you saying that the digestive system basically loses.
Speaker 3 (32:05):
Kind of yes, it's going to take third place to
the skin, certainly to the muscle.
Speaker 1 (32:12):
So it's kind of opposite of the lore. Right, The
lore was that the stomach would suck blood flow from
your muscles. But it's the opposite. It's going to lose
and therefore it's going to take longer to digest and
even more because you're laying down when you're assuming, and
that's going to cause you discomfort.
Speaker 3 (32:27):
That's really I think this story. It's a comfort or
discomfort issue.
Speaker 1 (32:31):
I see, And where does a discomfort come from? Why
doesn't your body like having food around belong?
Speaker 3 (32:36):
That's a that's a good question. It could be the
distension of the stomach. Right, so use a large meal.
Oh I feel, I feel really full. That's not a
comfortable feeling. It's probably the mechanical stension and the sensory
neurons are detecting that and letting you know, hey, you're
really full, don't eat more, right, So that's that's part
(32:59):
of it is, is trying to regulate energy intake.
Speaker 1 (33:02):
Like you had a full meal, whoa, whoa, you know,
don't need anymore.
Speaker 3 (33:07):
That allows time for your digestive system to interpret the
meal and go to the brain and say, slow down,
you're starting to get full. So it does take time
those signals to happen.
Speaker 1 (33:20):
Did discomfort is a signal that your stomach's trying to
tell your brain, hey, stop eating. But I wonder if
it's also trying to tell you to not exercise because
it knows that your stomach needs the blood flow.
Speaker 3 (33:32):
Right, What does this all orchestrator are controlled by is
the autonomic nervous system. Always tell my students autonomic is automatic.
So it's the nervous system that is dealing with controlling
our internal environment. So when we think about fight or
flight or rest and digest. So I think you're right.
I think that makes intuitive sense that some of that
(33:55):
signal is rest and digests. Let's process this meal, Let's
get the nutrients from it so that way we can
do the next thing. There's no need to go out
and hunt and gather, so just relax.
Speaker 1 (34:07):
What about cramps? I know crams was sort of in
that Boyscout report, like if you eat it before swimming,
you might get cramps and then you'll drown. What causes cramps.
Speaker 3 (34:17):
Believe it or not, there's things that we still don't
know the answer to, we don't have the final answer to,
or we're still trying to better understand. So muscle cramps,
those are very likely the result of two things, one
a water electrolyte imbalance and two neural dysregulation. So obviously
(34:38):
our body has a significant portion that is water, right,
something like seventy percent of our body is made up
of water. We also have electrolytes. These are basically salts,
and when there is not good harmony between the amount
of water that we have in the amount of electrolytes
that we have, they can create very serious problems. But
(35:00):
that wouldn't be recency to a meal. That would be
too much time from a meal with some electrolytes.
Speaker 1 (35:08):
Oh, because when you eat, you're bringing in those electrolytes
that you need, and if you haven't eaten in a while,
you're gonna your body's going to run out of them.
Speaker 3 (35:15):
Exactly. That's sort of our number one hypothesis, along with
something going on with a neuro muscular system.
Speaker 1 (35:23):
All right, So it sounds like you don't want to
eat too close to swimming, but you do want to
eat something beforehand at some point. Interesting. All right, So
then I guess the final question, Steve is was my
aunt lying to me.
Speaker 3 (35:37):
Yes, Oh, you should thank her for taking your swimming
every day. Yeah, it's an interesting question. But at the
end of the day, I think, as we've hit on
a couple of times, it's not really a safety issue.
I would say under nutrition is probably more of a
safety issue. It's more of a comfort issue.
Speaker 1 (35:56):
I see. Maybe that's why my aunt was really trying
to help me avoid was the discomfort?
Speaker 3 (36:02):
Probably not.
Speaker 1 (36:05):
Or just not me throwing up from the pool. Well,
there you have it. The answer to the question is
you don't have to wait thirty minutes after eating before
you can go swimming, but you probably should. Thanks for
joining us, you've been listening to Science Stuff. The production
of iHeartRadio written and produced by me Or hitch Ham,
(36:28):
executive producer Jerry Rowland, an audio engineer and mixer Casey Peckram.
You can follow me on social media to search for
PhD comics and the name of your favorite platform. Be
sure to subscribe to Sign Stuff on the iHeartRadio app,
Apple Podcasts or wherever you get your podcasts, and please
tell your friends we'll be back next Wednesday with another episode. Okay, Well,
(36:54):
what if your niece or nephew orview if you have
do you have kids? Yeah? Yeah? Or let's say, like
what if your kids had two cheeseburgers and then they
wanted to jump into the pool. Would you be like, yes,
go for it, or like maybe have a seat for
a second.
Speaker 2 (37:08):
So first of all, my said two and a half.
So our policies we do not feed him before going
into the pool because we do not want him pooping
in the pool because he is not potty trade, completely
different conversation. It's a different strategy we're approaching in that situation.
We feed him unch, he goes down for nap time,
we wake up, we change his diaper, and we take
him to the pool.
Speaker 1 (37:27):
I see it's more important to time than diaper change.
Speaker 2 (37:31):
But very different. Yeah,
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