April 8, 2025 • 13 mins
Here is a link to the article that I discuss: https://pmc.ncbi.nlm.nih.gov/articles/PMC8541481/
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Episode Transcript
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Speaker 1 (00:09):
Hey, everybody, Welcome to another edition of Wisdom Wednesdays. Today,
I want to do a bit of a deep dive
into a topic that is so controversial in nutrition, it's
almost not how controversial is and that is about our
intake of saturated fats, should we have any and how much?
Speaker 2 (00:32):
And I'm actually going to be a sist on a really.
Speaker 1 (00:35):
Really good peer reviewed articles that was published in the
journal Nutrients in twenty twenty one, and the title of
it is Dietary Saturated Fats and Health. Are the US
guidelines And in brackets what they don't say is and
Australian and British and New Zealand and et cetera, et cetera.
(00:58):
Are they evidence best a good place to start obviously,
or what are.
Speaker 2 (01:04):
The recommended guidelines?
Speaker 1 (01:06):
So in the United States, the doger guidelines are for
Americans are recommended that saturated fat intake should be less
than ten percent of daily calories. And in the UK,
the UK's NTS follows suit and the guidelines there are
to keep saturated fat to a minimum, ideally below ten percent.
(01:26):
And in Australia it is the same thing, limiting saturated
fat as part of heart healthy eating and keeping it
below ten percent. So where did we get this idea from. Well,
this is about something called the diet heart hypothesis. So
back in the nineteen fifties, there's a physiologist named Ansel
(01:48):
Keys and he was the first to propose the heart
that are the diet heart hypothesis, and he suggested that
saturated fat raises total serum cholesterol, which increases the risk
for heart disease. And the idea took off, especially after
he presented his very famous seven country study and to
(02:10):
the American Cardiology Society meeting. And this study that he
had published link saturated fat to heart disease across populations
in seven different countries, and he showed in these seven
countries that greater intakes of saturated fat were associated with
greater intakes of or sorry, greater incidents of heart disease.
(02:34):
But here's something that's really important. A couple of things
that are really important. It wasn't a clinical trial. It
was observational, but it only collected detailed dietary data on
less than five percent of the participants, right, and it
was fewer than one hundred people per country, And that's
(02:54):
not exactly a strong foundation for decades of global nutrition policy.
And what we now know is that ansel Keys didn't
just study seven countries. He studied twenty two countries, but
fifteen of them didn't fit his hypothesis, so he left
(03:15):
it out. Now, that is not poor research.
Speaker 2 (03:18):
That is fraudulent research. There's nothing.
Speaker 1 (03:21):
I just finished my PhD and we I had to
redo something on ethics and ethical research. And it's very
clear that ansel Keys conducted unethical research. And if I
had a present of that in my PhD, I wouldn't
have just feel I would have just been kicked off
the course for doing something like that. Now, despite all
(03:46):
of this, right, and despite the fact that even his
study that he produced and had fewer than one hundred
people per country, so.
Speaker 2 (03:54):
It's a very.
Speaker 1 (03:57):
Low participant of observational study. Despite all of this, saturated
fat became public enemy number one, especially after President Eisenhower
had a heart attack. So there was this big drive
to reduce heart disease. And then in nineteen early nineteen eighties,
the first Diarty Guidelines for Americans recommended limiting It was
(04:22):
about cholesterol in then and and the early nineteen nineties,
it was to limit your intake of saturated fats and
ten percent was the hardcap, and that.
Speaker 2 (04:33):
Has actually stayed to this day.
Speaker 1 (04:36):
Now, if you go and you look back the sixties
and seventies, there were several large randomized control trials testing this,
this diet heart hypothesis. And these randomized control trials, which,
as you'll know if you listen to this, are the
best form of evidence.
Speaker 2 (04:53):
They included around.
Speaker 1 (04:54):
Sixty seven thousand participants and ran for up to seven years,
so long enough to track hard outcomes like heart attacks
and death.
Speaker 2 (05:04):
What did these trials show.
Speaker 1 (05:05):
Well, certainly not what you expect if you support the
ditary guidelines or believe in them. The totality of evidence
did not support the idea that lowering saturated fat reduces
cardiovascular risk. Yet, and this is crucial, these trials were
largely ignored in the shaping of official dietary guidelines, and
(05:28):
in fact, at twenty eighteen, Citation network analysis showed very
clear bias in the literature, with eighty two percent of
supportive reviews. These are reviews that support reducing saturated fat
only cite one positive trial while ignoring others with contradictory findings.
(05:49):
So there was very clear bias right now going on
about saturated fat. So let's revisit the evidence. That's fast
forward and now to twenty ten. And by the way,
what tends to happen with these things When they get
enshrined in the recommendations, it becomes very hard to shift
(06:12):
them out of it. And then you have people who've
based their whole career on this who tend to sit
and influence the diactary guidelines, and that's how it becomes
very hard to shape.
Speaker 2 (06:23):
But let's talk about the evidence. Now.
Speaker 1 (06:25):
Since twenty ten, we've seen a wave of systematic reviews
and meta analysis on this topic, including from heavyweights like
the Cochrane Collaboration. So if you know anything about researcher,
you can just google it. Anything that the Cochrane Collaboration
puts out tends to be the.
Speaker 2 (06:45):
Strongest form of evidence.
Speaker 1 (06:46):
These our meticulously done reviews, and these reviews find that
reducing saturated fats does not significantly impact mortality, heart attacks.
Speaker 2 (06:58):
Or strokes.
Speaker 1 (07:00):
And the twenty twenty Cochrane review, which was considered very
very rigorous, found no significant benefit when trials that less
successfully reduced saturated fat were analyzed separately and on the
observational front. Out of at least eight large meta analysis
(07:21):
most found no association between saturated fat and cornary heart disease,
and one twenty twenty Umbrella review, which is a review
of reviews, concluded that the diet heart hypothesis is of
uncertain validity. So let's talk about this word is this idea?
(07:44):
Why is it still so pervasive? Well, the whole basis
of this is about LDL cholesterol. So there is a
big are's a well documentary mack documented fact that saturated
fat can increase ld L cholesterol, often dubbed the bad cholesterol.
Right now, there are a couple of things on this. Firstly,
(08:07):
saturated fat does increase your total cholesterol, increases LDL cholesterol
and increases hates the L cholesterol, which is her brackets
the good cholesterol. But it's the detail that's really important.
Saturated fats mainly rese large LDL particles. So just to
take a step back, when you look at LDL, they
(08:30):
are particles of different size, And what we now know
is that large LDL particles and these particles are not pathogenic,
and it's the small, dense LDL that is the issue.
And saturated fats mainly real is large LDL particles, the
(08:54):
non pathogenic ones and don't affect your small dense LDL particles,
And at the same time saturated fat raises. As I
said earlier, they hates DL right, and proving the total
cholesterol ratio. That's a better marker of risk, but a
much better marker of your overall risk than just LDL
(09:16):
particles is the amount of small dense LDL particles. So
in short, using LDL as a proxy for heart disease,
it is overly.
Speaker 2 (09:27):
Simplistic, very very clearly.
Speaker 1 (09:30):
And half of all people who die from heart disease
have got normal levels of LDL. So if it was
such an issue, that really wouldn't be the case now.
The twenty twenty Datary Guidelines for Americans committee excluded nearly
twenty review papers by external scientists, and they instead relied
(09:53):
on in house USDA reviews, and of the thirty nine
studies that they cite as support for keeping saturated fats low,
eight percent of those thirty nine studies had null or
negative finding. Yet the guidelines still recommend capping saturated fat
at ten percent of total calories. And about the food
(10:16):
they found that diry including butter, was either neutral or
beneficial for heart disease risk. These are these reviews and
meat had mixed findings, but again most of the studies
showed no consistent harm from saturated fat rich studs and
another noteworthy study, there's this influential what's called Pure study,
(10:38):
which followed over one hundred and thirty five thousand people
across five continents, and it found no link between saturated
fat and heart disease and a lower risk of stroke
in those who had higher levels of saturated fat. Now,
there's also something that's really important to understand, and we
eat food.
Speaker 2 (10:59):
We don't eat nets.
Speaker 1 (11:00):
I don't know the last time you've gone up and
you've ordered a serving of saturated fat or polyphenols are
a serving of fiber. We eat the food matrix, and
it's how these nutrients are packed together that plays a
big role in our health effects. So, for instance, the
saturated fat in cheese behaves very differently in your body
(11:24):
than the saturated fat in process meats.
Speaker 2 (11:27):
And even more.
Speaker 1 (11:28):
Than that, it's our overall diet that matters. So, for instance,
if you look at the evidence low carb diets, saturated
fat is burned for fuel when you have a low
carb diet rather than stored and can actually lead to
improved cardio metabolic health when you're having a low carb diet.
What is clear from some other studies it's saturated fat
(11:52):
in the presence of carbohydrate and especially sugar that actually
becomes slightly more damaging. Right, But this move away from
isolated nutrients and that's been embraced for total fat and
ditary cholesterol. Yet the whole guidelines are insaturated fat remain
pretty much stuck in the past.
Speaker 2 (12:13):
So is it time for a rethink?
Speaker 1 (12:15):
I think any rational scientist who has looked at the
studies and particularly the totality of evidence, including looking at
high quality randomized control trials, and then looking at meta
analysis and umbrella reviews of meta analysis and real world
(12:36):
observational studies would say an overwhelming yes, it is at
least time to reevaluate it. And as I'm just going
to leave you on this one with a quote from
the authors of a comprehensive twenty twenty one review put it.
They said, making a strong recommendation based on weak and
(12:58):
contradictory evidence does not meet scientific standards for guidelines. Yet,
and we have these guidelines in many many countries around
the world, and they are based on very flawed evidence.
That's it for this week.
Speaker 2 (13:14):
Folks, catch you next time.
Hey, everybody, Welcome to another edition of Wisdom Wednesdays. Today,
I want to do a bit of a deep dive
into a topic that is so controversial in nutrition, it's
almost not how controversial is and that is about our
intake of saturated fats, should we have any and how much?
Speaker 2 (00:32):
And I'm actually going to be a sist on a really.
Speaker 1 (00:35):
Really good peer reviewed articles that was published in the
journal Nutrients in twenty twenty one, and the title of
it is Dietary Saturated Fats and Health. Are the US
guidelines And in brackets what they don't say is and
Australian and British and New Zealand and et cetera, et cetera.
(00:58):
Are they evidence best a good place to start obviously,
or what are.
Speaker 2 (01:04):
The recommended guidelines?
Speaker 1 (01:06):
So in the United States, the doger guidelines are for
Americans are recommended that saturated fat intake should be less
than ten percent of daily calories. And in the UK,
the UK's NTS follows suit and the guidelines there are
to keep saturated fat to a minimum, ideally below ten percent.
(01:26):
And in Australia it is the same thing, limiting saturated
fat as part of heart healthy eating and keeping it
below ten percent. So where did we get this idea from. Well,
this is about something called the diet heart hypothesis. So
back in the nineteen fifties, there's a physiologist named Ansel
(01:48):
Keys and he was the first to propose the heart
that are the diet heart hypothesis, and he suggested that
saturated fat raises total serum cholesterol, which increases the risk
for heart disease. And the idea took off, especially after
he presented his very famous seven country study and to
(02:10):
the American Cardiology Society meeting. And this study that he
had published link saturated fat to heart disease across populations
in seven different countries, and he showed in these seven
countries that greater intakes of saturated fat were associated with
greater intakes of or sorry, greater incidents of heart disease.
(02:34):
But here's something that's really important. A couple of things
that are really important. It wasn't a clinical trial. It
was observational, but it only collected detailed dietary data on
less than five percent of the participants, right, and it
was fewer than one hundred people per country, And that's
(02:54):
not exactly a strong foundation for decades of global nutrition policy.
And what we now know is that ansel Keys didn't
just study seven countries. He studied twenty two countries, but
fifteen of them didn't fit his hypothesis, so he left
(03:15):
it out. Now, that is not poor research.
Speaker 2 (03:18):
That is fraudulent research. There's nothing.
Speaker 1 (03:21):
I just finished my PhD and we I had to
redo something on ethics and ethical research. And it's very
clear that ansel Keys conducted unethical research. And if I
had a present of that in my PhD, I wouldn't
have just feel I would have just been kicked off
the course for doing something like that. Now, despite all
(03:46):
of this, right, and despite the fact that even his
study that he produced and had fewer than one hundred
people per country, so.
Speaker 2 (03:54):
It's a very.
Speaker 1 (03:57):
Low participant of observational study. Despite all of this, saturated
fat became public enemy number one, especially after President Eisenhower
had a heart attack. So there was this big drive
to reduce heart disease. And then in nineteen early nineteen eighties,
the first Diarty Guidelines for Americans recommended limiting It was
(04:22):
about cholesterol in then and and the early nineteen nineties,
it was to limit your intake of saturated fats and
ten percent was the hardcap, and that.
Speaker 2 (04:33):
Has actually stayed to this day.
Speaker 1 (04:36):
Now, if you go and you look back the sixties
and seventies, there were several large randomized control trials testing this,
this diet heart hypothesis. And these randomized control trials, which,
as you'll know if you listen to this, are the
best form of evidence.
Speaker 2 (04:53):
They included around.
Speaker 1 (04:54):
Sixty seven thousand participants and ran for up to seven years,
so long enough to track hard outcomes like heart attacks
and death.
Speaker 2 (05:04):
What did these trials show.
Speaker 1 (05:05):
Well, certainly not what you expect if you support the
ditary guidelines or believe in them. The totality of evidence
did not support the idea that lowering saturated fat reduces
cardiovascular risk. Yet, and this is crucial, these trials were
largely ignored in the shaping of official dietary guidelines, and
(05:28):
in fact, at twenty eighteen, Citation network analysis showed very
clear bias in the literature, with eighty two percent of
supportive reviews. These are reviews that support reducing saturated fat
only cite one positive trial while ignoring others with contradictory findings.
(05:49):
So there was very clear bias right now going on
about saturated fat. So let's revisit the evidence. That's fast
forward and now to twenty ten. And by the way,
what tends to happen with these things When they get
enshrined in the recommendations, it becomes very hard to shift
(06:12):
them out of it. And then you have people who've
based their whole career on this who tend to sit
and influence the diactary guidelines, and that's how it becomes
very hard to shape.
Speaker 2 (06:23):
But let's talk about the evidence. Now.
Speaker 1 (06:25):
Since twenty ten, we've seen a wave of systematic reviews
and meta analysis on this topic, including from heavyweights like
the Cochrane Collaboration. So if you know anything about researcher,
you can just google it. Anything that the Cochrane Collaboration
puts out tends to be the.
Speaker 2 (06:45):
Strongest form of evidence.
Speaker 1 (06:46):
These our meticulously done reviews, and these reviews find that
reducing saturated fats does not significantly impact mortality, heart attacks.
Speaker 2 (06:58):
Or strokes.
Speaker 1 (07:00):
And the twenty twenty Cochrane review, which was considered very
very rigorous, found no significant benefit when trials that less
successfully reduced saturated fat were analyzed separately and on the
observational front. Out of at least eight large meta analysis
(07:21):
most found no association between saturated fat and cornary heart disease,
and one twenty twenty Umbrella review, which is a review
of reviews, concluded that the diet heart hypothesis is of
uncertain validity. So let's talk about this word is this idea?
(07:44):
Why is it still so pervasive? Well, the whole basis
of this is about LDL cholesterol. So there is a
big are's a well documentary mack documented fact that saturated
fat can increase ld L cholesterol, often dubbed the bad cholesterol.
Right now, there are a couple of things on this. Firstly,
(08:07):
saturated fat does increase your total cholesterol, increases LDL cholesterol
and increases hates the L cholesterol, which is her brackets
the good cholesterol. But it's the detail that's really important.
Saturated fats mainly rese large LDL particles. So just to
take a step back, when you look at LDL, they
(08:30):
are particles of different size, And what we now know
is that large LDL particles and these particles are not pathogenic,
and it's the small, dense LDL that is the issue.
And saturated fats mainly real is large LDL particles, the
(08:54):
non pathogenic ones and don't affect your small dense LDL particles,
And at the same time saturated fat raises. As I
said earlier, they hates DL right, and proving the total
cholesterol ratio. That's a better marker of risk, but a
much better marker of your overall risk than just LDL
(09:16):
particles is the amount of small dense LDL particles. So
in short, using LDL as a proxy for heart disease,
it is overly.
Speaker 2 (09:27):
Simplistic, very very clearly.
Speaker 1 (09:30):
And half of all people who die from heart disease
have got normal levels of LDL. So if it was
such an issue, that really wouldn't be the case now.
The twenty twenty Datary Guidelines for Americans committee excluded nearly
twenty review papers by external scientists, and they instead relied
(09:53):
on in house USDA reviews, and of the thirty nine
studies that they cite as support for keeping saturated fats low,
eight percent of those thirty nine studies had null or
negative finding. Yet the guidelines still recommend capping saturated fat
at ten percent of total calories. And about the food
(10:16):
they found that diry including butter, was either neutral or
beneficial for heart disease risk. These are these reviews and
meat had mixed findings, but again most of the studies
showed no consistent harm from saturated fat rich studs and
another noteworthy study, there's this influential what's called Pure study,
(10:38):
which followed over one hundred and thirty five thousand people
across five continents, and it found no link between saturated
fat and heart disease and a lower risk of stroke
in those who had higher levels of saturated fat. Now,
there's also something that's really important to understand, and we
eat food.
Speaker 2 (10:59):
We don't eat nets.
Speaker 1 (11:00):
I don't know the last time you've gone up and
you've ordered a serving of saturated fat or polyphenols are
a serving of fiber. We eat the food matrix, and
it's how these nutrients are packed together that plays a
big role in our health effects. So, for instance, the
saturated fat in cheese behaves very differently in your body
(11:24):
than the saturated fat in process meats.
Speaker 2 (11:27):
And even more.
Speaker 1 (11:28):
Than that, it's our overall diet that matters. So, for instance,
if you look at the evidence low carb diets, saturated
fat is burned for fuel when you have a low
carb diet rather than stored and can actually lead to
improved cardio metabolic health when you're having a low carb diet.
What is clear from some other studies it's saturated fat
(11:52):
in the presence of carbohydrate and especially sugar that actually
becomes slightly more damaging. Right, But this move away from
isolated nutrients and that's been embraced for total fat and
ditary cholesterol. Yet the whole guidelines are insaturated fat remain
pretty much stuck in the past.
Speaker 2 (12:13):
So is it time for a rethink?
Speaker 1 (12:15):
I think any rational scientist who has looked at the
studies and particularly the totality of evidence, including looking at
high quality randomized control trials, and then looking at meta
analysis and umbrella reviews of meta analysis and real world
(12:36):
observational studies would say an overwhelming yes, it is at
least time to reevaluate it. And as I'm just going
to leave you on this one with a quote from
the authors of a comprehensive twenty twenty one review put it.
They said, making a strong recommendation based on weak and
(12:58):
contradictory evidence does not meet scientific standards for guidelines. Yet,
and we have these guidelines in many many countries around
the world, and they are based on very flawed evidence.
That's it for this week.
Speaker 2 (13:14):
Folks, catch you next time.
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