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