April 22, 2025

Why the carnivore diet is so risky

Norman Swan: Tegan, what’s the weirdest diet you’ve ever been on?

Tegan Taylor: I have only ever adhered directly to the Mediterranean diet, or a diet exclusively of sour lollies and individually wrapped easter eggs. 

Norman Swan: You’re so sensible.

Tegan Taylor: So sensible. How about yourself? 

Norman Swan: Probably best not admitted to. But you know, these days I do adhere to the…

Tegan Taylor: Oh, you’ve got me reaching for my Mediterranean diet bell over here. 

Norman Swan: Yeah. And I must admit I’ve done all sorts of weird diets over the years. Not too weird, but weird enough. 

Tegan Taylor: Have you ever done the carnivore diet?

Norman Swan: A version of it. It’s what we’ve actually been discussing because we covered it on our recent live show as part of the World Science Festival in Brisbane.

Tegan Taylor: Which you get to listen to right now here on What’s That Rash?.

Norman Swan: The podcast where we answer the health questions that everybody’s asking.

Tegan Taylor: So you’re familiar with my favourite artefact…I need some help today, I’ve got bells, we’ve got bells, and I need three volunteers. Producer Shelby, who you will have heard of as well if you’ve listened before, is going to hand out some Med diet bells for your ringing pleasure, only when we say the words, you know the rules. 

Norman Swan: I was actually doing a recorded interview with somebody for the Health Report, and he brought a bell into the studio, hoping I’d say it.

Tegan Taylor: I love it, it’s catching on. Also I need a couple of volunteers to help read out some of our questions as the show progresses. If someone in the room would read us our first question?

Audience member: Hi Norman, hi Tegan. Over the past couple of years I have seen a number of people migrate to a complete carnivore diet, only eating animal products, like cavemen. From my understanding, the carnivore diet suggests that fruits, nuts, seeds and vegetables are poisonous long-term to humans. I don’t know how someone can survive long-term without these things; would you not develop scurvy? I personally would find this diet incredibly boring. What puzzles me the most is that the people I know personally who follow this diet look the most energetic, fit, lean and healthy I have ever seen them. What are the health benefits and consequences of this type of diet? — Anonymous.

Tegan Taylor: A big clap for…I’ve got to know, is anyone in this room on a carnivore diet? Has anyone tried it before? That’s called selection bias.

Norman Swan: How many here are on the Mediterranean diet?

Tegan Taylor: Have you ever tried the carnivore diet?

Norman Swan: I tried it occasionally without realising what it was before, in the days of the ketogenic diet, and I was trying to lose weight and I went on a meat diet. I felt terrible. 

Tegan Taylor: Meat diet. Okay, so I think it would be useful for us to take a look at a day in the life of someone on the carnivore diet. And, I mean, it sounds like this is a pretty safe room, not huge carnivore diet fans here, but there are lots of people who say they feel better on it. Should we have a look at what a day in the life of a carnivore diet would look like? So this is just sample size of one, I guess. But breakfast; bacon and eggs. That feels fine, right? Unless you’re vegan, maybe. No toast…

Norman Swan: So, just in the way of background, almost no carbohydrates, very high fat, like 60%, 70% fat, and the rest protein. 

Tegan Taylor: All right, so breakfast…I’m giving that like a six out of ten on my own personal appetising scale. What do you reckon? 

Norman Swan: I don’t mind it every so often.

Tegan Taylor: Yeah, we’ve got some bacon fans here. Okay, what about lunch? Lunch is just a big old frypan of ground beef.

Norman Swan: Yum. 

Tegan Taylor: What’s our macro breakdown here, Norman?

Norman Swan: The macro breakdown is…it depends on the beef, but if it’s lean beef, not too much fat but a lot of protein in there. 

Tegan Taylor: Do you know what I really like about that pan of ground beef is a complete lack of the Maillard reaction, like not even a crispiness piece in sight, just brown.

Norman Swan: As far as the eye can see.

Tegan Taylor: All right, so that’s lunch. We’re feeling pretty satisfied. Let’s have some dinner. Dinner is just some steak with salt.

Norman Swan: With the fat still on. 

Tegan Taylor: What do you reckon? 

Norman Swan: What do I reckon? I reckon, you know, that’s pretty high in fat. It’s got marble fat. It’s probably wagyu, looking at the marbling there, so we’re talking high fat, a bit of protein.

Tegan Taylor: That’s a high cost also, I think that would be quite expensive. So I feel like if all I was eating was bacon and eggs for breakfast, ground beef for lunch and a steak for dinner, I might feel peckish throughout the day.

Norman Swan: Yeah, you’d need a snack.

Tegan Taylor: Okay, let’s have a look. Just a stick of butter?

Norman Swan: Yeah, so some people on the carnivore diet will put the stick of butter in their coffee.

Tegan Taylor: Yeah, I’ve heard, the bulletproof coffee thing.

Norman Swan: There is one more slide, just part of the carnivore diet. So the carnivore diet can be a bit of a strain. And for those listening to What’s that Rash?, we just put up a photograph of a toilet.

Tegan Taylor: A very clean toilet, not having much use at the moment. Okay, break down why, please; why is this toilet so sparkling clean?

Norman Swan: Well, it’s sparkling clean because you’re constipated and you never use it. Constipation is one of the problems of a carnivore diet.

Tegan Taylor: Because there’s just zero fibre in it.

Norman Swan: To the extent that some people say, well, the solution for your constipation; why don’t you just eat more fat?

Tegan Taylor: Oh, what, it just slides out of you? How does that work?

Norman Swan: Well, it works just because the fat doesn’t get absorbed.

Tegan Taylor: Yikes, okay.

Norman Swan: So your scientific hypothesis is probably correct. 

Tegan Taylor: So when we heard the question that was read out so beautifully before, the claims that were made by the friends of the person asking the question were that these people were eating like cavemen, and that perhaps fruit, vegetables, nuts, or whatever had poisons in them. There’s sort of two claims there. Let’s talk about the cavemen thing first. What did cavemen actually eat, and cavewomen? 

Norman Swan: Well, ‘cavewomen’ is a really important caveat here. So it depends where you were as an early human and which environment you were in. So if you were in the far northern reaches of the world and a cold climate, you probably did eat very few vegetables and were mostly eating blubber and seal. But for most of the world, you had carbohydrates, and the women would go out foraging for really quite complex carbohydrates. The mystery is why it took so long for agriculture to develop, but they were pretty good at finding complex carbohydrates, and they had tools to pound them and make them more digestible. So every Palaeolithic diet pretty much had complex carbohydrate in it, just of different kinds depending on availability. 

Tegan Taylor: The thing that I find really interesting about the idea of going back to hunter gatherer societies, and I can see the logic, basically humans were evolving for 1 million, 2 million years to get to what we would recognise today, Homo sapiens, and then we’ve had a lot of a lot of change in the last 50,00, 60,000, years. 

Norman Swan: We actually haven’t had that much change, so human genes have not changed that much, it’s our environment that’s changed.

Tegan Taylor: Exactly, and so are we really evolved to the lifestyles that we live in today, is the question that I think underpins these sorts of things. The thing that I find really interesting is we actually have quite a lot of information about how humans lived before the agricultural revolution, and there’s also still lots of hunter gatherer societies that still exist in the world today that we can look at, and none of them, as far as I’m aware, eat nothing but beef and salt, which is what the most extreme version of some of the carnivore diets are, partly because cattle weren’t domesticated paleolithically. And the parts of the world where cattle are…bovine ancestors are from places like modern day Iran. We have really good evidence about what people ate there back then. Like you say, it was quite varied. 

I also found a really interesting article about pre-agricultural remains in North Africa. They found teeth and bones and also preserved pieces of food in this cave entrance in Morocco, found sweet acorns, pine nuts, pistachios, oats and legumes, much more starchy plants and fewer aquatic species than the researchers expected to find in that particular environment.

Norman Swan: And the teeth, they were ground down from eating the rough carbohydrate.

Tegan Taylor: And had decay, showing that there were starches in it. So there’s these hints that there were carbohydrates in that diet in that site. We obviously also have Australian Aboriginal and Torres Strait Islander societies that follow traditional parts of their diet, very diverse, humans are omnivores. The thing that I always take away from these sorts of discussions is that humans are actually incredibly adaptable and able to live under a lot of different conditions and a lot of different diets.

Norman Swan: Omnivorous. 

Tegan Taylor: We are omnivorous, indeed.

Norman Swan: Which is part of our survival.

Tegan Taylor: The other question that was part of that question was the idea of plants and plant foods having toxicness. Is there anything in that?

Norman Swan: Yeah. So you can have legumes which are required to be soaked, otherwise you get alkaloids. So plant foods do have risks attached to them in terms of spoilage, mould, that sort of thing. But so do meats, meats can be contaminated as well, particularly faecal contamination if you haven’t…

Tegan Taylor: I mean, anything can have poo on it, if you just believe. Plants can too, Norman.

Norman Swan: True. 

Tegan Taylor: So one of the key words that piqued my interest in that question was ‘scurvy’. Everyone knows what scurvy is, it’s a vitamin C deficiency, it causes all sorts of skin and other conditions. Like you said before, there are some traditional societies that did have very, very high meat intake. Why didn’t they get scurvy? I’m thinking of the Innuits that ate mostly seal and seal oil for most of the year. 

Norman Swan: Well, the evidence suggests that people on a carnivorous diet are low in vitamin C, so you are lower than probably we are, because you’re all on the…[bells ring]…

Tegan Taylor: Even I missed that one.

Norman Swan: But they are lower than average, so they’re teetering. And there is evidence that some meat and fat diets preserve vitamin C, so they actually slow down the metabolism of vitamin C or provide alternative pathways and so on. So it’s likely that you get a little bit of vitamin C from the meat that you’re eating, but also that there’s something in some of these diets which preserves…in other words it conserves your vitamin C, you are not burning it up, and it’s the overall nutrition. And remember that the sailors who got scurvy…and there are reports, by the way, of scurvy…not very many, but there are reports of people with scurvy who are on very strict carnivorous diets. 

Tegan Taylor: I found a case study called Scurvy in an Unrepentant Carnivore, which I just loved as a title. He had it twice. Both times they went through a barrage of tests to try to figure out what it was and it was scurvy both times.

Norman Swan: And they treated him with vitamin C, he went home, and then he came back with scurvy again because he went back on his diet.

Tegan Taylor: Just eat a vegetable, mate.

Norman Swan: So it’s not guaranteed that you will not become vitamin C deficient, but your vitamin C will go down.

Tegan Taylor: So the question then is what other health effects do we have? We’ve talked about, yes, plants can have poisonous alkaloids in them, but we cook them and that basically deals with it. Perhaps humans haven’t eaten a lot of red meat a lot of the time for a lot of history, but there are people who do report having great results on a carnivorous diet. What is happening? If people have felt like they’ve had chronic health conditions, which is often the story with these sorts of diets, people have had thing after thing that they’ve basically felt like they’ve been brushed off by the medical society, and they found something that they feel really good on. What could be happening there?

Norman Swan: Well, this is a ketogenic diet. So you are producing ketone bodies, these alternate sources of energy which come from metabolising fat, rather than glucose and glycogen for your energy. Well, you use glucose, but the route to glucose is different, and you use these ketone bodies, which also replaces normal carbohydrate metabolism. So basically you’re ketogenic, and you’ve got these ketone bodies going around. And after a little while on a ketogenic diet, most people report feeling quite energised. The first couple of days are a bit rough. You feel quite energised. You feel quite good, and that’s what people are reporting here. Your breath also smells, you do tend to constipation, but the ketogenic diet is associated with feeling quite good. There have not been very good studies…just before we go on, life expectancy in the Stone Age was 28, so just be careful what you wish for.

Tegan Taylor: I think that had more to do with infections and lions than heart disease though, right? 

Norman Swan: It wasn’t heart disease, that’s right. So the studies that have been done, some of the bigger studies, at least one that we’ve come across, not very well conducted in terms of it’s self-reported rather than objective measures of how they’re going. Some objective measures have looked at blood fats, for example. And so if you look at, again, in a self-reported study, they’re trucking along at an LDL of…

Tegan Taylor: No, stop. I want to know, before you start saying numbers, we need context, because we’re not all…I mean, maybe you guys are all doctors, I’m certainly not. What’s normal? What do I want to be getting when I go to my doctor and they take the blood out and they’re like, ‘Tegan, you’re so healthy, I can’t believe these numbers, they’re so good, they’re…’?

Norman Swan: It’s not a straightforward question. We probably evolved to have a total cholesterol of two or three. If you look at some hunter gatherer societies, not carnivorous, but just regular hunter gatherer societies, they truck along at very low total cholesterol levels. But we have come to an average cholesterol that we think is reasonably acceptable in a western society, but probably even that is too high for what we’ve evolved to, which is why heart disease is so common, dementia and so on. So total cholesterol, 5, 5.5. The bad form of cholesterol, LDL, 2. If you’ve had coronary heart disease, it should be less than 1.7. And HDL, over 1, and triglycerides under 1. These are millimoles per litre. 

Tegan Taylor: So, for example, if we had a patient whose dietary habits included a high intake of fat consisting of six to nine pounds of cheese, sticks of butter and additional fat incorporated into daily hamburgers, I will say this person reported weight loss, increased energy and improved mental clarity, their total cholesterol levels exceeded 25, significantly higher than his baseline level of 5 to 7 millimoles per litre. And it came out in an unusual way, literally. What’s this called?

Norman Swan: Well, it’s either called xanthoma or xanthelasma.

Tegan Taylor: Xanthos being the Greek word meaning yellow.

Norman Swan: Yeah, so it’s basically fat coming out in your hands, and it comes out in your eyes, all of your body. 

Tegan Taylor: So this is an unusual case study, of course. If that’s what’s coming at your hands, what is happening inside your body?

Norman Swan: You’re screwed.

Tegan Taylor: But he said he felt good, he’d lost weight, he said he felt really good, he said mental clarity.

Norman Swan: So there’s a paper out today or yesterday showing that the lower your LDL, the less likely you are to develop dementia. So his LDL was what, 12, wasn’t it?

Tegan Taylor: No. So there’s a different there’s a different person who posted in a Facebook group called Carnivore Diet For Beginners, this person, their total cholesterol was 15 millimoles per litre. HDL 2.5, LDL 12. ‘The doctor is ordering a calcium test for the arteries. Doc wanted to prescribe a statin right away, but I declined.’

Norman Swan: So the higher your LDL, the higher your risk of coronary heart disease, stroke and dementia, and some studies suggest that on a carnivorous diet…so it’s not all bad, your thiamine levels and vitamin B levels tend to be quite good. And if you look at the fat levels, again, they’re not great studies, but if you look at the fat levels, the LDL looks as if it’s around about 4.5 which is very high, at least twice what you would consider a normal level. But the triglycerides were lower, which surprises me because they’re eating visible fat, and their HDL was a little bit high, which is a good thing. But essentially the picture there is not good. And that’s the problem with the carnivorous diets, is that they’ve not gone on for long enough to know what the problem is, because we know, in an epidemiological sense, when you look at populations, red meat consumption is directly proportional with the risk of colon cancer, large bowel cancer, and a significant part of that is processed meat, but your first slide there was bacon. So it’s not that they’re necessarily eating fresh red meat and they’re not eating lean meat either. So if you talk to the beef industry, they say, oh well, lean red meat is fine. It may or may not be true, but the reality is that red meat is strongly associated with colon cancer.

Tegan Taylor: The other thing that red meat consumption is strongly associated with what these days feels like far-right politics. It feels like this space…and I don’t…like, it’s kind of funny, but it’s also…it seems to be this…there seems to be a real correlation between people who are interested in these sorts of diets and a certain bent of politics. What could be behind that?

Norman Swan: Contrarian? It’s kind of a contrarian view, that we’ve been misled, we don’t believe public health officials anymore, we’ve been fed lies, that it’s a natural male thing to do to eat red meat, grilled usually on the barbecue. And, you know, this is the Andrew Tate, Joe Rogan, kind of kind of story, that real men eat meat and they don’t eat vegetables. 

Tegan Taylor: So as a takeaway to Joe Rogan and Andrew Tate, who I’m sure are listening, as well as everyone else, what can we say about the carnivore diet based in science?

Norman Swan: Based in science? Short-term, like any ketogenic diet, you’re going to feel quite good. You may well lose weight because it’s, again…

Tegan Taylor: It’s so restrictive. 

Norman Swan: Your appetite goes down because you’re eating so much protein, so you’re probably not consuming as many calories. So some people with diabetes might find a short-term benefit there. But in the long term, you’ve got no idea what…well, we’ve got a reasonable idea of what it’s going to do to you; it’s going to clog up your arteries, increase your risk of dementia, and it’s not a healthy way to do a ketogenic diet. You can do a ketogenic diet with high protein, lower levels of fat and some complex carbohydrate, and still have reasonable levels of ketones in your blood. It might not be super high, but it’s enough to help you lose weight, feel a bit better, but very hard to sustain. 

Tegan Taylor: Norman, I feel like I need a palate-cleansing ‘ding, ding’ of the Mediterranean diet bell to round that one out, please. Well, Norman, as you know, we always do a mailbag as part of What’s That Rash?, and we decided to keep this tradition going with our live show with some audience questions.

Audience member: Given what we know now about the link between the microbiome in the gut and general health and the brain and so on, what are the implications for somebody who has had an ileostomy for 40-plus years with no gut, no large colon, and some shortening of the small intestine? 

Norman Swan: Nobody’s properly studied that, and most people with an ileostomy have had something like ulcerative colitis, and therefore the large bowel has been really inflamed, very high risk of colon cancer and perforation. So you remove the large bowel to save their lives, effectively. And then there’s a trade-off in terms of quality of life, loss of fluids and what have you. But nobody’s really, until recently, studied the effects on the microbiome and the fact that you don’t have a large bowel there to deal with that, but you do have a respiratory tract that’s full of organisms. You have a skin that’s got microorganisms on it. It’s not as if you have no microbiome. But I’m not aware of research which looks at people who might…you know, would they feel better if they were actually on a…so the whole thing about this, by the way, is if your microbiome is deficient, what do you do? Do you go into the chemist and buy probiotics? And most people would say there isn’t really a probiotic on the market that covers you fully, and you’re not going to eat somebody else’s poo, so prebiotics are the way to go. And what’s the best prebiotic diet? [bells ring]

Tegan Taylor: Well, that live show was a lot of fun. Thank you so much to World Science Festival Brisbane for having us. This won’t be the last instalment of that live show that you’ll get to hear. We’ll have another one for you in another couple of weeks.

Norman Swan: But keep your comments and questions coming, and the email address is thatrash@abc.net.au. See you next week. 

Tegan Taylor: See you then.


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