#55 The 5" food rule: safe to eat? Or misguided?

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Be honest—have you ever rescued a French fry from the floor? In this bite-size myth episode, I test the famous “5-second rule.” I walk through what actually transfers to your food (fast), when that matters, and why a little microbial exposure isn’t always the villain—while drawing a hard line for high-risk settings and situations.

Key Topics & Takeaways

• The verdict meter: The 5-second rule is false—bacteria can transfer in <1 second. In a Rutgers lab study, juicy foods like watermelon picked up the most, gummies the least; tile/steel transferred more than carpet (Applied and Environmental Microbiology / PubMed
  ).
• Foodborne illness is common: ~48M illnesses/year in the U.S., ~128k hospitalizations, ~3k deaths. Usual suspects include Salmonella, E. coli, Campylobacter, Listeria, and norovirus. Symptoms are typically GI, but severe cases occur—especially in the very young, elderly, pregnant, or immunocompromised (CDC overview
  ).
• Context matters: Moisture and surface trump “time.” High-moisture foods collect more microbes; visibly dirty or high-traffic floors (think convenience stores) raise risk—regardless of seconds.
• When to skip the floor food—no debate: If you’re immunocompromised, pregnant, very young/elderly, or you’re in a hospital/clinical setting, don’t eat it. Full stop.
• Nuance: Are microbes always bad? Early, diverse exposure to benign environmental microbes associates with more resilient immunity. Farm-exposed kids had lower asthma/atopy rates (≈20–40%) versus city peers (NEJM
  ). Greening urban daycare yards (adding soil/plant matter) increased skin/gut microbial diversity and shifted immune markers in a favorable direction (Science Advances
  ). This doesn’t mean “eat off the floor”—it means the bigger story is about exposure diversity and context.
• My practice: At home, I don’t stress over a quick drop on a clean surface; out in public or medical settings, I pass.

Bottom Line
Microbes hop on fast; the “rule” doesn’t save you. But danger depends on what fell, where, and who is eating it. Be smart, especially if you or your environment are higher risk.

Call to Action
What health saying should I myth-test next? Text me your favorites (include your email so I can reply), and please rate the show on Apple/Spotify. Want my newsletter on practical, science-backed longevity? Join me at DrBobbyLiveLongAndWell.com.

Episode Transcript

SPEAKER_00 (00:00):
Have you ever eaten a French fry off the floor and
told yourself, well, it's stillsafe.
It was less than five seconds,so sure it must be okay.
And even if bacteria got on thefood, is that absolutely such a
bad thing?
I really do want that Frenchfry.

(00:20):
Well, what does the evidencetell us?
Let's find out.
Hi, I'm Dr.
Bobby Du Bois, and welcome toLive Long and Well, a podcast
where we will talk about whatyou can do to live as long as

(00:43):
possible and with as much energyand vigor that you wish.
Together we will explore whatpractical and evidence-supported
steps you can take.
Come join me on this veryimportant journey, and I hope
that you feel empowered alongthe way.
I'm a physician, Iron Mantriathlete, and have published

(01:07):
several hundred scientificstudies.
I'm honored to be your guide.
Welcome, my dear listeners, toepisode 55, the five second food
rule.
Safe to eat or misguided.
There are so many wonderfulhealth sayings like the five

(01:30):
second rule.
Well, chicken soup can cure yourcold.
Starve a cold feed a fever.
Or is it the other way around?
Don't swim after eating oryou'll drown.
If your feet are cold, put on ahat and so many, many more.
Are these true or false?

(01:52):
Today I start a new episode typeto answer questions like these.
These episodes, these funepisodes, will be sprinkled in
with my usual topics.
Of course, I need feedback fromyou.
Let me know if you enjoy theseepisodes.
They're likely to be shorterthan my usual ones and a bit

(02:13):
bite-sized, and definitely witha more limited amount of
critical evidence to answer someof these questions.
As always, I love feedback.
Include your email when you sendme a text or otherwise, and do
tell others about the podcast.
If you have some favoritesayings or myths to explore, by

(02:38):
all means, send them my way.
Now, this fascination ofquestions like this is not new
for me.
When I went to medical school, Iwas fascinated by quirks of the
human body.
Like, why do we hiccup?
What is your funny bone?
What happens when your footfalls asleep?

(03:00):
So as I went through each of theclasses in medical school and
there were professors talkingabout related topics, I would
interview them and find out whatwas the answer to these
questions.
I even started writing a book.
This was a long, long time agowhere you didn't have Chat GPT
or anything else to help you.

(03:21):
But I never really got too farwith the book.
Medical school took its toll andaway I went on my career.
But I've always been fascinatedby common things that affect us.
Now, if you would like, I caninclude some of these episodes
as well about what is going onin our body.

(03:42):
You know, what is a burp?
What are all these things youmight be interested in?
Let me know.
I can sprinkle them in anytimeas well.
So the plan for the day on thefive-second rule is part one.
What is the evidence on thistopic?
What does happen when food fallsfor five seconds or less?

(04:05):
Second part.
Well, yeah, but are floorbacteria a problem, even if it
picked up some of those bugs?
Might those bugs actually bebeneficial in some way?
Now, jumping ahead, thefive-second rule does not apply
if you are immunocompromised,pregnant, or the French fry

(04:29):
falls to the floor in ahospital.
These can be scary bugs in thehospital that all of us need to
worry about.
So food and food safety isreally important.
There are 48 million uhfood-borne illnesses every year.
About 128,000 people gethospitalized with one of them,

(04:53):
and about 3,000 people die eachyear.
Now, typically, the bugs youhear about are salmonella, E.
coli, campylobacter,toxoplasmosis, uh listeria, and
norovirus.
Now, for most people, when theyhave a foodborne illness, it's
going to be a GI problem.

(05:14):
You're going to have diarrhea,cramps, vomiting.
But for some people, if you geta severe case, it can be
systemic.
You can have fever, you can havesepsis, and again, even death
can occur, especially in theelderly, the very, very, very,
very young, and theimmunocompromised.
Keep in mind that food doesn'tneed to fall on the floor.

(05:39):
Even the kitchen counter canhave some of these contaminants,
as we'll talk about.
If the chicken's raw, uh, ifthere's other raw meats, uh, and
even tainted vegetables have uhbeen problematic at times.
So the five-second rule,although it's humorous at some
level, is also very important toexplore.

(06:02):
Okay, part one, the evidence.
What do we know?
Now, for these health sayings,these little episodes we're
going to do together, therelikely won't be perfect
evidence.
And they're likely to be smallerstudies.
So unlike when we talk about uhsleep or we talk about the

(06:23):
impact of sauna, where there'slots of studies, often big
studies, these kind of funtopics.
I don't anticipate there'll be ahuge body of evidence about
chicken soup or things likethat.
But as always, I will review theevidence that's there, and I'll
try to summarize it in ways thatmight be useful for you.

(06:45):
Okay, so in this area, there area few studies.
The classic study that everybodyrefers to is called the, well,
they call it the Rutgers studybecause it was done at Rutgers.
The study, as we might hope,took various foods and dropped
them on surfaces.
Then they put them in petridishes to see what grew.

(07:08):
Did any bacteria grow?
And they varied theirexperiments by contact time,
meaning what happens in lessthan a second, what happens at
five seconds, 30 seconds, 300seconds.
They also varied the type ofsurface.
Well, maybe it fell on tile,maybe it fell on wood, maybe it

(07:29):
fell on stainless steel orcarpet.
So they tested those variousthings.
And then they varied the foods,wondering if certain foods
picked up bacteria more readilythan others.
Things like watermelon, bread byitself, bread with butter, and
gummy candy.
I, of course, would have beenfascinated by bread with peanut

(07:52):
butter, since that's one of myfavorites.
Uh, but we just have toextrapolate from bread with
butter.
All right, what do they find?
And really the study asked thequestions I would want it to.
Now, obviously, if it had beenduplicated in three or four or
five other labs around thecountry and published, that
would have been better.
But what do we learn?

(08:14):
We learn that the five-secondrule is not correct, that plenty
of bacteria will transfer to thefood within a second.
Now, if you leave it on theground longer, more bacteria
will go on to the food.
But within five seconds, a wholelot gets transferred.

(08:34):
So the five-second rule is notcorrect.
I'm starting something new.
If you guys have a better name,let me know.
For the moment, I'm calling itthe verdict meter.
So, on this issue of whether thefive-second rule means that
bacteria won't get on your breador whatever, the verdict meter

(08:56):
says a resounding false.
Turns out, when you dig belowthe surface, watermelon was the
worst, probably because it had alot of moisture.
Bread and bread and butter werethe same, so the butter didn't
seem to make it worse than justbread by itself.
And gummies caught the leastamount of bacteria.

(09:19):
And carpet might be safer thanthese other surfaces.
So if you drop a gummy oncarpet, perhaps go for it.
Again, the caveats I saidearlier still apply.
Okay, so now we know thefive-second rule doesn't work.
Bacteria will absolutely get onyour food.

(09:40):
Part two, is that such a badthing if in fact bacteria get on
our food?
In prior episodes, we talkedabout peanuts and how the
pendulum swung from peanuts arefine in kids when they're very
young to, oh no, no, no, thatcauses peanut allergies.

(10:02):
Don't give your kids peanuts.
Well, then we had a whole uhdecade of kids with peanut
allergies who weren't exposed topeanuts, and now the pendulum's
gone back to, you know, youought to expose your kid to
peanuts.
So there may be something aboutearly exposure that is
potentially beneficial.

(10:23):
Obviously, we've got to find theevidence not just for peanuts,
we need to go other things.
Okay, so here's the question.
Perhaps early exposure, meaningearly exposure by young kiddos
to diverse bacteria.
So they are exposed to a lot ofdifferent bugs.
Now, these are not cholera bugs,these are just regular garden

(10:47):
variety bugs that you might runacross.
And um, is it good for you to beexposed when you are young?
Now, we we think we want adiverse microbiome, lots of
different bugs all playingnicely together on our skin, in
our gut, in our mouth.

(11:08):
So, what do we know?
Well, first, there was a NewEngland Journal of Medicine
study that compared kids whogrew up on farms with kids who
grew up in the city.
And you might think that kidsthat were growing up on the farm
were exposed to all sorts oforganisms if they're caring for

(11:28):
the chickens or being exposed tothings like that.
So, in this study, theycollected dust samples and
mattress samples from the kidsthat were living in the city and
the kids that were living on thefarm.
So, what did they find?
They found that the farm kidswere exposed to a lot more

(11:48):
biodiversity.
So, you know, the dust and otherthings had lots of different
bacteria and things in it, moreso than the kids that lived in
the cities.
But what did that mean?
Well, when they looked at thosekids later on, there was a lower
risk of asthma and uh eczema andother atopic illnesses in those

(12:12):
kids who lived on the farm.
So they had a 20 to 40 percentlower rate of these illnesses
having grown up on the farm.
Is this cause and effect?
We don't know, but it's aninteresting study.
And it would suggest that beingexposed to a diversity of

(12:33):
non-life-threatening bugs mightbe a good thing when you're
young.
Okay, second study.
And I was just amazed thatsomebody had done this study
because it's exactly what youmight want to do, and somebody
actually did it.
So this is a set ofinvestigators in Finland, and

(12:54):
they found 10 daycare centers.
Some were in an uh an urbanenvironment that had not a
grassy play area for the kids,but you know, maybe it was
cement or other kinds of things.
So they took half of these urbancenters and removed the old play

(13:17):
area and replaced it with dirtand with sod, with grass.
So now we have half of thedaycare centers having the more
traditional, non-kind of uhoutdoorsy um environment, and
ones now that had the dirt andthe sod.

(13:37):
And they measured bacteria ontheir skin and their gut, and
they also looked at bloodsamples and immune blood
markers.
What did they find?
Well, the kids in the daycarecenter where they replaced the
play area with dirt and sod andgrass, found they had more

(14:00):
bacterial diversity on theirskin, they had more gut bacteria
diversity, and even their immunemarkers changed, suggesting a
more stimulated immune set ofpathways.
Now, they didn't look at who gotmore infections later in life,

(14:20):
but this was very interestingthat again being exposed to
benign non-pathogenic bacteriamight be helpful.
All right, part three.
What the heck do I take from allof this?
My take, look, I wouldn't eatfood that dropped on a hospital

(14:41):
floor for all the pathogens thatmight be there.
I wouldn't eat food that droppedat a 7-Eleven because there's a
lot of traffic of people comingfrom the outdoors with their
shoes and everything else.
And absolutely be really carefulif you're immunocompromised or
pregnant or very elderly orvery, very young.

(15:02):
Otherwise, what do I do?
I follow personally thefive-second rule.
I'll even stretch it to a20-second rule.
Um, we have three Vishla dogs.
So I know there's a lot of dirton the floor at times, and
there's a lot of stuff theyprobably track in.
And we live at Madrone SpringsRanch, our exotic animal bed

(15:25):
breakfast uh place, where wehave also a lot of guests.
So I know I'm probably exposedto a lot of stuff.
In spite of that, I don't worrytoo much when food drops at
home.
Now, when I'm out in some of theplaces I talked about, okay,
different, different story.
Wrap-up time.
The verdict meter for thefive-second rule is a resounding

(15:50):
false bugs transfer almostinstantaneously.
But the interesting question isso what?
Perhaps having some bacteria oror such on your food might not
necessarily be a bad thing.
Again, the studies were mostlydone around kids in this regard.
So we don't really know for thestandard American adult what

(16:13):
that means.
Tell me what you think and whatyou do about all of this.
Do you live by the five-secondrule or not?
Until next time, I hope you livelong and well and you enjoy your
food.
And may your favorite food notfall on the floor where you will

(16:38):
have to make that difficultdecision.
Thanks so much for listening toLive Long and Well with Dr.
Bobby.
If you like this episode, pleaseprovide a review on Apple or
Spotify or wherever you listen.
If you want to continue thisjourney or want to receive my

(16:58):
newsletter on practical andscientific ways to improve your
health and longevity, pleasevisit me at Dr.
Bobby Livelongandwell.com.
That's doctor as the DR BobbyLivelongandwell.com.