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Hello and welcome to Zoe Science and Nutrition and our special daily series about diets. Each day this week we're examining one of the world's most popular diets, putting the latest scientific evidence under the microscope. We'll find out these diets true impact on your health. I'm your host Jonathan Wolfe and I'll be joined throughout this series by Professor Christopher Gardner.
Hello, Christopher. Good to be here, Jonathan. Christopher is a professor of medicine at Stanford University and the director of nutrition studies at the prestigious Stanford Prevention Research Center. He's one of the world's leading researchers on how our diet impacts our health. So what's on our plate today, Christopher? In episode two, Jonathan, we're removing a major food group from our plate in favor of a very starchy lunch. So Christopher, which food group gets the chop today and how low are we talking?
We're not talking all that low. We're talking 30%, 25%. It's the saturated fat in, for example, whole fat dairy or fatty meats, ice cream, things like that. And so what diet is this? The low-fat diet, which really its name got tarnished over the last couple of decades in a backlash. So let's get into that. Hi. I love that you're here to find out if low-fat diets are healthy after all.
If you haven't already, please hit follow in your podcast player so you'll know whenever a new episode arrives.
This will really help us to continue our mission to improve the health of millions. Brilliant. Well, look, I think for people who've listened to this podcast quite often, they'll know that fat was really demonized by the American Heart Association sort of starting in the 1960s. And I believe this was based on research that at the time showed that eating too much fat seemed to increase heart disease. And so it makes sense that, you know, in the past, people
this idea of low fat being really supported. But we now know that a lot of the basis of that research didn't really add up and that actually not all fat is bad. And so there's been a big shift here. So why are people still following these low fat diets today in 2024?
It's pretty funny how sort of culturally ingrained that has become after many, many years. We actually did a weight loss study in men and women. And culturally, we wrote a separate paper on how the women had a problem doing low fat or high fat when they got assigned to this. They got assigned to low carb. And you could see there was actually a gender difference. And I just, I'm trying to avoid body fat. I'm going to avoid fat in my diet.
So there's a sort of, it's still hanging on, which by the way, it's really interesting. I see this with, you know, my mother-in-law, for example, like a lot of people who you grew up with this very strong public health messaging, right? Saying you must eat low fat. It's hardly surprising if you're surrounded by that for like 30 or 40 years. And then the scientists come back and say, oh no, no, fat is fine. You can see why this might be hard to adjust to. Not fair, not fair. So if you really went back and look, so some of the oldest data on this go back to the seven country study by Ancel Keys.
And what he found was, oh, there's a lot of heart disease out there. And of all the countries that I've looked at, it seems to be in the saturated fat group. And if you really look at his study, there was a Mediterranean group that had low heart disease when they had high fat, but unsaturated and low saturated. And there was an Asian group that had very low fat, both unsaturated and saturated.
And so as they tried to make a public health message out of this, they thought, do we really think the public will understand mono and poly and saturated? How about if we just say low total fat and then saturated fat will be part of what gets lower? And that was a mistake. That oversimplification was a mistake. Hi, I hope you're enjoying the show so far and learning a lot. If you're not already a regular listener, I hope you feel like you might come back.
Okay, let's get back to the show. ♪
So coming back, I guess, to what's going on, therefore, for people following this low-fat diet today, what happens in the body if you cut out fat? So if you cut out fat, it's another one of these issues where your calories are from carbs, fats, and proteins. If you cut out fat, what do you eat more of?
I have a rant to go on about protein to show you that there's actually a lot of data to show you how little variability there is in protein on wildly different low-carb and low-fat diets. If you cut back on your fat, you're going to eat more carbs. And at least in the U.S., boy, we eat a lot of crappy carbs. And so one of the issues here is, yes, we would love you to cut back on saturated fat sources, meat and dairy and things like that.
and have more beans and whole grains and fruits. But at that time, the food industry caught this and ran with it and said, ah, we're going to make low-fat cookies, low-fat chips, low-fat desserts, low-fat crappy carbs. So there were a lot of things out there that were very low in fat, but very high in refined grains and added sugars. And that's a problem for the body. And so what I think you're saying is,
When I get told that I need to move to low fat, I will eat less fat. So I do make that change. And what I eat is a lot of very refined carbohydrates as a result. So what does that mean for my health? Have I made myself healthier by following this shift to this sort of low fat and high, you know, high carb diet? So the high added sugars and refined grains are absorbed very quickly in the body.
So they create an insulin spike. So, oh my gosh, this is the hormone that puts away glucose when it hits the bloodstream. Glucose being your blood sugar. Yep. So that's the concern. And so you're going to put a lot of carbohydrate into fat storage. Right.
This actually is related. Just to clarify, I've eaten all these carbs because I've eaten low fat. And what is it that my body's just done to those carbs? So as soon as you've met your immediate needs for carbohydrate and then stored a little as what's called glycogen, a little bit in your liver and a little bit in your muscle, all the rest of the carbs get turned into fat.
and stored as fat in your body. - I found this incredibly depressing the first time that someone explained this to me, Christopher, 'cause after all, you buy all the stuff in the store that says low fat, people buying that because they're thinking, "Well, I wanna be healthier, "and I don't wanna put on weight," and all these other things.
And no one says, by the way, if you eat more than you need, your body's going to turn it right back into fat, right? This is sort of one of those hidden secrets that I think most of us didn't really understand. Absolutely. And it's related to something called NAFLD, which is a horrible acronym, non-alcohol fatty liver disease. So as the carbohydrates are going to your liver to get stored as fat, your liver starts accumulating fat. So we have these people who are predisposed to diabetes and
who are taking in all these refined grains, not good for diabetes, not good for insulin, not good for your liver. So there really were a lot of downsides to the way people were trying to follow low-fat. So is it possible to have a healthy low-fat diet? And what would you be saying about that? Yeah, so if you were to have the whole grains, and let's talk about whole grains for a minute. Let's think about white bread, white flour bread.
You might think, ah, I'm going to pat myself on the back. I move to whole wheat flour bread. Well, actually, there's this thing called glycemic index, which is how fast the glucose from the food ends up in your blood. And to be honest, white bread and whole wheat bread are almost the same because they both use flour, which has been ground to a fine, you know, almost dust-like particle. There's not much digestion left. I actually make a fantastic wheat berry salad. What the heck is a wheat berry?
It's the whole wheat kernel. Like if you saw it, it wouldn't look like flour. It's the whole thing. You have to chew it. It's wrapped up in a food matrix. You have to digest it. It takes a long time. So what you want is a slow drip of glucose from your stomach and your intestine.
into your blood. The wheat berry would have that. Beans would have that. But what you're saying, you know, is that if you eat bread or white pasta or rice, actually basically your body turns that into sugar in your blood very fast. It does, although oddly pasta is a little slower than bread. There's something about pasta and the way you cook it and eat it. It's a little slower than bread, but the wheat berry would be best. In the US, we eat almost all wheat. We hardly eat any other grains. But if you were to eat millet or
barley or quinoa or things like that, those all appear more slowly in your blood. So if you did low fat and you did that with veggies and beans and whole grains and you had a slow absorption and drip of glucose, you'd be much better than the low fatters who are achieving that with crappy carbs. And I think you were saying the reason why you might do this in the first place was to get rid of
All fats or just some sorts of fats? And the idea was to lower the saturated fat. And that's coming from dairy and meats, primarily animal foods. So this would be a way, what you're saying is you're saying there is a way to reduce those foods, therefore reducing fat and increasing your carbohydrate. But you need to really pick carefully the carbohydrates that you switch to. How many of the carbohydrates that you switch to are likely to have low fat content?
printed on the label when you buy it in the grocery store. Oh, no. Yeah. That won't be a selling point because it won't be in a package. It'll be a little bag of beans or the vegetables that you're eating. This is one of the things I've been shocked by some of the other podcasts. It's sort of like if you wanted to eat low fat, the first rule is never eat something that says low fat on the package because it's sort of had all... It's very artificial. It's probably ultra processed. It's had all of these changes. Yes. You're saying it is possible. So I guess...
Then the question for us today is if you can, if you can choose these healthy carbs, then is like a low fat diet with healthy carbs, like better than being on a diet that has got more fat in it. Yeah. So if you did it as intended, which was low saturated fat, plenty of unsaturated fat, that's fine. And it was a high carb diet of whole foods. You would be fine.
And how low in fat is that? Because you've had this sort of subtle distinction, but most people listening to this will say, well, you know, one of the first things I do is I make sure I don't cook any food with any oils. Like I remove all the oils from my diet. Obviously I can't eat an avocado. That's high in fat. Like you give up all of these fats, right?
How would you feel about somebody who's really just given up all their fats in order to eat carbs, but they're carefully eating lots of whole grains in their carbohydrates? Well, people aren't very good at counting percentages or calories. But in most cultures, fat might be 30%, 35%, or 40% fat in the Mediterranean diet. And the low-fat group is sort of trying to get you down to 25% or 20%.
You'd have to be careful because by the time you get to 20% fat, it's really hard to eat enough calories of vegetables and beans and things like that. And there's even one more extreme group, the vegan low-fat group that wants to eat all plants and very low fat, not just 20%, but 5% or 10% fat. That is very hard to make palatable. And so what happens to a lot of those people is when they're that extreme in low fat, they
We have a study showing this, that some of the most successful low-fat people did it by having more refined grain and added sugar, even though they were very well counseled on, here's the right way to do it. They just couldn't get that many calories in them by eating all whole foods. And what happens if somehow you manage to remove all fats from your diet? So you took this to the extreme of it being truly like, you know, no fat.
So there's two types that you need to get because instead of using almost all of your fat for energy, some of them get converted to hormone-like substances that help you regulate your metabolism. And those are the unsaturated fats. So you need some unsaturated fat in your diet.
So what's your verdict, Christopher, on low-fat and very low-fat diets? Yeah, I'm not a very big fan of low-fat diets because of the way people tend to follow them. I would be sad if they left out the avocados, the olive oil, the nuts, and the seeds. Some of those have healthy fats in them, and they make food more palatable and more enjoyable, and I want people to enjoy what they're eating. Brilliant.
Thank you, Christopher, for putting fat on the bones of low-fat diets in today's conversation. Part of our special series of daily episodes about diets and our health. I'm Jonathan Wolff. And I'm Christopher Gardner. Join us tomorrow when we'll be traveling back in time to eat the Stone Age way and discussing the paleo diet. As always, the Zoe Science and Nutrition podcast is not medical advice. It's for general informational purposes only. See you next time.
