The carnivore diet exposed: Healthful or harmful?

0:00Hello, and welcome to Zoe's 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.

0:33So what's on our plate today, Christopher? In episode four, Jonathan, we're dishing up some succulent steaks with a pairing of absolutely nothing else. Okay, Christopher, I'm intrigued by this one. What is the name of this diet that seems to be made up entirely of meat? The carnivore diet. Well, that's certainly an unusual choice. And I'm surprised that this is something that people would actually go for in real life. But it turns out, we did a little bit of research, that the carnivore diet has become increasingly popular in no small part due to a rather famous podcaster. So why, other than celebrity endorsement, might someone go for this diet?

1:17My only impression here that I can take away is people like the taste of meat and they want an excuse to eat it. Done. Hi, I'm thrilled that you're here to find out if cutting out all plant foods really could have health benefits. If you haven't already, please hit follow in your podcast player so you'll know whenever a new episode arrives. This will help us to continue our mission to improve the health of millions. So what exactly are people eating on this diet? Yeah, actually, I don't, I've never seen a formal write-up of this. So could you eat eggs? So eggs aren't meat. So is it really? And no dairy, because that's not carnivorous.

1:58It's really just meat. So that does sound pretty tough. What would happen if you ate this way? So if I got to do a study, I would certainly want to look at the microbiome. So the microbiome gets fed by... Which is all the bacteria in our gut. Indigestible carbohydrates don't get digested in our upper small intestine, and they all go to our colon where the bacteria of the microbiome, the main source of bacteria in our body, eat that fiber for fuel. And it has, ah, we're learning all about the microbiome and the potential health benefits. We've been doing a lot of studies on this. Meat, by definition, has no carbohydrate at all and no fiber.

2:42Fibers are carbohydrate-like substances. So you would get none. You'd probably be pretty constipated. And could you live on this diet for six months or a year? Does it give you all the essential nutrients that you need? Yeah, I don't understand how that's possible. So of all the food groups, if you look at our U.S. dietary guidelines, it sort of outlines here's all the vitamins, here's all the minerals, Here's different types of carbs and proteins and fats. You get that from a varied diet. The more restrictive your diet is, the more likely you will have nutrient deficiencies. None of those, fruits, grains, vegetables, none of them have all the nutrients.

3:31You need a variety in your diet, and you could not get that from a meat-only diet. The most commonly cited claim for why you should follow this diet is apparently improvements in autoimmune conditions and type 2 diabetes. And there are also claims around weight loss. What are your thoughts on that? Weight loss would be easier to answer because when you have such a restrictive diet, you might be hungry for a piece of bread. Nope, can't have that. Hungry for some beans. Nope, can't have that. Hungry for some vegetables. Nope, can't have that. Are you hungry for another piece of steak? Got it. I can definitely see like you go into a coffee shop or something and there's like all of these pastries and you're like, no, I can only have steak.

4:12And they're like, we're a coffee shop. We don't have any steak. So you just have to be hungry for a few more hours. So I can see how in the short term you're going to restrict. How will that play out in the long term? So in the long term, the balance that we're not getting here is that's excess protein and excess fat. The excess protein is going to get turned into carbohydrate. rate. The fat from meat is going to be a lot of saturated fat. So in the world of people with diabetes, it's well recognized that they have three times the heart disease rate of people without diabetes. Three times the heart disease rate, so a huge increase.

4:49And heart disease is the number one cause of death in the U.S. So if you're addressing the diabetes by avoiding the carbs and having the saturated fat, you're setting yourself up for other health consequences as a result of your strategy. At this time of year, many of us focus on supplements, quick fixes, or food fads to stay healthy. But one of the most powerful tools we have is something much simpler, sharing food with other people. The science is really clear on this. Eating with others naturally encourages us to slow down, which supports better digestion. People also tend to choose more nutritious, balanced foods when they eat together.

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6:03So you don't think this is a good diet for someone with type 2 diabetes? I would not promote this. I would promote less carbs and unsaturated fats. Now, obviously there are animals that do live a carnivore diet, right? So there are probably people hitting here with like their cats wandering around behind them. And I think they are eating something quite similar to this diet. So is it that it's not impossible to imagine an animal that is a carnivore, you're saying basically as human beings, that's not a good diet for us. I'm thinking about like being in the zoo, right? We know all the animals need a different diet.

6:37Yeah. And they have different teeth and a different intestinal tract structure that we don't have. We have omnivorous teeth and omnivorous intestinal tract. The one human population that makes the most sense to me is the Inuits or the native Alaskans who picture frost and ice everywhere. You're in an igloo. There's really nowhere to plant any vegetables or get any fresh fruit. There really are some stories of those folks eating polar bear and seal and just all aquatic or I don't know if you call them livestock, but animals in the winter when for months at a time, you would have access to no plant foods whatsoever.

7:19They actually had a pretty good track record of health, which is fascinating. But part of that, again, goes back to how much physical activity it took for them to retrieve all these foods. They spent a lot of time getting these foods. And maybe at some point, that very extreme level of physical activity is protective of this, but those populations don't eat that way anymore. When they have access to other foods, they enjoy a lot of other foods. That's really interesting. So they can live on this for months of the time through the winter in this extreme. And I'm guessing in the summer, they were like really happy to add some vegetable to their diet.

7:59Not there to ask them, but yeah, that just, again, seems like a very limited diet and humans love variety of taste and texture and type. So it seems too restrictive. And are there any studies about the carnivore diet that tell us what happens when you follow it? So there really aren't any studies. There aren't any large groups of people that have followed this that you could track. We have lots of studies where they've tracked hundreds of thousands of people for a long time. And there's really not very many carnivores to study that way. There was one small study that came out fairly recently in the last few years.

8:37that was a social media study. So they put it out on social media to have people self-report what they were doing. And it had to be people who self-reported being on the diet for at least six months. So there's a problem there because that's fairly short-term. But I think some of the people who wrote in and said, I have been on this diet for years, it's a very self-selected population. Self-report is always a little touchy because were they being completely honest with what they said? So between a lack of accuracy and a lack of generalizability, it is the only study I know of, but it's really, it's not very sound in terms of scientific design.

9:23But it's there because it's in the absence, there were no other studies available. So it's better than the other studies because there aren't any, but it's not very compelling case. And why do you think, it feels like there are so many nutrition science studies, Christopher, of like almost anything you can imagine. So why aren't there any proper studies of this carnivore diet? Oh, you can't. So the kind of study that I do personally is I like the kind where you recruit people, you randomly assign them to A or B, and then you learn because it's a randomized control trial, which one was better. I don't think anybody would fund me for this.

10:00And I don't think I would ever take it on because the recruitment would be virtually impossible. Who's willing to either be a carnivore or the other option? Let's say it's carnivore versus vegan. Sure, that would be a wonderful head-to-head. Ah, I'm absolutely willing to be carnivore or vegan and give up everything else I eat just because you're curious, Professor Gardner. Sure, I will not only happily sign up, I will adhere to that diet, I promise, every single day for months or years to come. Yeah, it's an unanswerable question. I can't get people to sign up for that. And are you worried that without having studied the carnivore diet, actually, it might be a really healthy diet?

10:43There is enough scientific literature to support that you don't need the randomized control trial of carnivores to be able to answer the question, partly acknowledging that you couldn't get a trial like that accomplished. So Christopher, what's your verdict on the carnivore diet? Yeah, my verdict here is not just thumbs down, but double thumbs down. This is just on a par with the most restrictive diet, short of maybe the breathitarian who only breathes air to eat, or the fruitarian who only eats fruit that dropped lovingly from the tree into their hands. It's just not realistic. All right. Well, this one's out.

11:23On to the next one tomorrow. Ready. Thank you, Christopher, for sinking your teeth into the carnivore diet today, part of our special series of daily episodes about diets and our health. I'm Jonathan Wolfe. And I'm Christopher Gardner. Join us tomorrow when we're getting our calculators out and talking about calorie counting. As always, the Zoe Science and Nutrition podcast is not medical advice. It's for general informational purposes only. See you next time.

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