This article is part of the IBD Index. Last updated on April 15, 2022.
The carnivore diet is like the sexier, more exciting cousin of the ketogenic diet (which I covered in the linked post). Rather than hewing to a certain macronutrient ratio, a carnivore diet simply eliminates any food that comes from a plant, only including foods that come from animals. This makes it far simpler to follow, and also more fun (if you’re the type of person who enjoys all the connotations of being a “carnivore” and feeling superior for eschewing lame plant foods).
Many people with IBD have reported miraculous results from adopting a carnivore diet, but many also claim that a stint of carnivore dieting ruined their health. So what are the considerations surrounding a carnivore diet in the context of IBD?
Table of Contents
What is a carnivore diet?
Are humans carnivores?
How might a carnivore diet be beneficial for IBD?
Are fruits and vegetables actually bad for you?
Is there any clinical evidence to support a carnivore diet for IBD?
Are there any risks to a carnivore diet?
The bottom line
What is a Carnivore Diet?
A carnivore diet is exactly what it sounds like: only eating animals. No plants. Easy.
However, there are a few different breeds of carnivore, so to speak. The strictest carnivore diet includes only meat (including seafood and organ meats), eggs, and water, even discouraging seasonings aside from salt. A more liberalized carnivore diet will also include dairy products, and I’ve even seen some allow for honey (hey, it’s from an animal!).
Major public proponents of the diet include Shawn Baker and Paul Saladino, both MDs, who have both published books about the carnivore diet. Saladino has a history of making authoritative claims and then totally changing his tune at a later date (as this very measured Amazon review of his book points out), so it’s a bit difficult to follow what exactly a “carnivore diet” is at any given time.
Are Humans Carnivores?
One argument proponents make in favor of the carnivore diet is that such a diet is the most appropriate for our genes on the basis of our evolutionary history. Is that true?
The short answer is that different populations of humans have adapted well to a wide variety of environmental niches and their associated foods, from high-carb and plant‑heavy to mostly carnivorous.
Dr. Georgia Ede wrote a post summarizing populations who have traditionally consumed mostly carnivorous diets, including the Inuit and Chukotka in the Arctic, the Maasai, Samburu, and Rendille in East Africa, the steppe nomads of Mongolia, the Sioux of South Dakota, and the Brazilian Gauchos. I’ve also seen mentions of Native Americans being mostly carnivore.
However, to my knowledge, no human population has ever survived exclusively on animals. And if you read about the mostly-carnivorous ones, you’ll notice that they often have very specific dietary practices that the average modern carnivore likely does not replicate.
Allow me to let Weston Price, dentist-turned-anthropologist extraordinaire, paint a picture:
He writes in Nutrition and Physical Degeneration that “among the Indians in the moose country near the Arctic Circle a larger percentage of the children were born in June than in any other month. This was accomplished, I was told, by both parents eating liberally of the thyroid glands of the male moose as they came down from the high mountain areas for the mating season, at which time the large protuberances carrying the thyroids under the throat were greatly enlarged.”
They also had the wisdom to prevent scurvy (which they called a “white man’s disease”) by divvying up the adrenal glands from each moose killed so that everyone in the tribe got a piece. We now know the adrenal glands are the richest source of vitamin C in an animal. (p. 69)
Of the Inuit, he writes that “seal oil provides a very important part of their nutrition. As each piece of [dried] fish is broken off, it is dipped in seal oil.” (p. 63)
And “the eggs of the salmon are dried and stored as an important item of nutrition for both children and adults. They are also used to increase the fertility of the women. From a chemical standpoint, they are one of the most nutritious foods I have found anywhere.” (p. 65)
And “the food of these Eskimos in their native state includes caribou, ground nuts which are gathered by mice and stored in caches, kelp which is gathered in season and stored for winter use, berries including cranberries which are preserved by freezing, blossoms of flowers preserved in seal oil, sorrel grass preserved in seal oil, and quantities of frozen fish. Another important food factor consists of the organs of the large animals of the sea, including certain layers of the skin of one of the species of whale, which has been found to be very high in vitamin C.” (p. 65)
The Maasai notoriously survived mostly on meat, milk, and blood from cattle, although their diet was also supplemented with plant foods. Weston Price writes “the blood is defibrinated by whipping in the gourd. The fibrin is fried or cooked much as bacon or meat would be prepared. The defibrinated blood is used raw just as the milk is, except in smaller quantities. When available, each growing child received a day’s ration of blood as does each pregnant or lactating woman. Formerly, the warriors used this food exclusively.” (p. 123)
You may notice some trends here.
First, these diets don’t much resemble the modern carnivore diet.
Second, these populations had very specific practices to ameliorate nutritional concerns related to subsisting mostly on meat, such as lack of vitamin C or fertility concerns.
Third, although not mentioned here, many have undergone genetic changes over generations to better adapt to their specific diets.
And fourth, they all ate some plants.
And although the amounts of plant foods are small, there’s no reason to believe they’re insignificant. I came across one interesting study where healthy volunteers were given an animal-based diet with either dried cranberry powder or placebo, and changes in their microbiome were measured.
Only 30g per day of freeze dried cranberry powder (about 1/4 cup, judging by this cranberry powder) was enough to reverse the negative changes in many microbial parameters (including carcinogenic metabolites), and in many cases to fully abrogate them. (Source)
(Full disclosure, this study was funded by the Cranberry Institute, which I think is hilarious. Relevant comedy sketch.)
How Might a Carnivore Diet be Beneficial for IBD?
But when it comes to therapeutic diets for IBD, our primary concern is not whether a diet is ancestrally consistent; it’s whether it works. And there’s no denying that in some cases, a carnivore diet works. So what are the potential mechanisms at play?
Carbohydrate restriction: Unless someone is consuming large quantities of milk and/or honey, a carnivore diet will necessarily be extremely low in carbohydrate, even containing essentially none at all. And as I discuss here in the context of a ketogenic diet, carbohydrates can be problematic for many with digestive issues.
Increased ketone production: Being extremely low in carbohydrates, a carnivore diet will likely increase ketone production, with the extent of ketosis depending on the ratios of fat and protein in the diet. And as discussed in my lengthy article about the ketogenic diet, there are several plausible mechanisms by which ketosis could be beneficial to someone with IBD. (FYI, all of those links direct to specific subsections in that article for easier reference.)
Elimination of fiber: Reducing fiber intake is common dietary advice for people in active IBD flare-ups on the basis of practical experience, although it’s not clinically validated advice and there’s some controversy. (Source)
Aside from some evidence that a low-fiber high-fat diet decreases Bifidobacterium levels and thereby reduces host inflammatory response, I’m not aware of any specific ways that eliminating fiber intake would be beneficial for IBD patients. In fact, the vast majority of research, both human and animal, points to the opposite conclusion.
But given that fiber is one of the most important dietary constituents shaping the microbiome, and that the state of the microbiome heavily influences IBD pathogenesis, I assume there are interesting mechanisms at play in cases where the carnivore diet works well for people. It just appears that we have not yet characterized them.
Elimination of plant toxins: This is the big one that sets the carnivore diet apart from any other therapeutic diet. As part of their defense against insects, animals, and other environmental factors, the plants we eat contain various compounds that can, through a certain lens, be considered “toxic” to humans.
The Paleo movement has historically focused heavily on certain classes of these “anti-nutrients,” such as phytates, lectins, saponins, and protease inhibitors found in grains and legumes.
The Autoimmune Protocol takes this a step further by also drawing attention to phytates in nuts and seeds, and glycoalkaloids in plants of the nightshade family.
Not to be outdone, the “pro-metabolic” crowd takes it a step further than that, demonizing glucosinolates in brassica vegetables and oxalates in other greens.
The carnivore diet simply takes the final step, eschewing even fruits with their pesky flavonoids and fiber.
(An aside: it’s noteworthy that as of this writing in April 2022, the “Carnivore MD” Paul Saladino is now promoting what he’s calling an “animal-based” diet, which includes fruit and looks a heck of a lot like the type of “pro-metabolic” diet that has been promoted by followers of Ray Peat for years.)
Are Fruits and Vegetables Actually Bad For You?
None of these anti-plant arguments are wrong per se, and there’s absolutely an argument to be made that in the context of autoimmune disease, some of these plant compounds could cause problems. As I mention in my Autoimmune Protocol post, Sarah Ballentyne makes these arguments quite thoroughly regarding grains, legumes, nuts and seeds, and nightshades.
Indeed, phytochemicals are generally handled by the body the same way as drugs and other xenobiotics, and some – such as naringin in grapefruit – can impact liver detoxification to such an extent that the metabolism of prescription medications is affected.
However, all of this begins to make sense if we look at the effects of these phytochemicals through the lens of hormesis, and it’s now well accepted that many of the thoroughly‑documented beneficial effects of polyphenols, flavonoids, and other phytochemicals do operate through a hormetic mechanism. (Source 1, 2, 3)
In other words, the body responds to a stressor – in this case, a plant toxin – in an adaptive way that ultimately promotes health.
Taking into account the reams of preclinical, clinical, epidemiological, and anthropological evidence for the health benefits of plant foods, there’s no question that plant foods are extremely beneficial to human health as a general rule.
But that doesn’t mean that they can never be harmful in individual cases, especially in disease states such as IBD where the body’s normal adaptive mechanisms are out of whack.
Is There Any Clinical Evidence to Support a Carnivore Diet for IBD?
Unsurprisingly, no clinical trials have yet tested a carnivore diet for the treatment of ulcerative colitis or Crohn’s disease. And I kind of doubt any such trials are forthcoming, since most of our epidemiological data indicates that a high-meat, low-fiber diet is a significant risk factor for IBD.
However, we do have one relevant case study from Tóth et al. published in 2016: Crohn’s disease successfully treated with the paleolithic ketogenic diet. Of note, the authors are part of a Hungary-based clinical research group called Paleomedicina where they treat various chronic illnesses using a “paleolithic ketogenic” diet. Their website is a bit sketchy-looking, especially for a clinical research group, but they have a number of publications reporting successful cases (such as this one!).
The report describes the case of a 14 year old boy with Crohn’s disease who had severe inflammation of the terminal ileum and mild to moderate inflammation in the colon and elevated CRP. After diagnosis, the patient had rapidly progressed through the stages of traditional medical treatment without success: from anti-inflammatories with antibiotics and probiotics to immunosuppressant therapy to biologics, and finally to formula feeding.
The report title is a bit of a misnomer, because while the diet was ketogenic, it was specifically a carnivore diet, consisting of “animal fat, meat, offal and eggs with an approximate 2:1 fat:protein ratio,” with an emphasis on red and organ meats over poultry. He reportedly ate very small amounts of honey as well.
Apparently he began eating small amounts of vegetables and fruits after a few months on the diet, but removed them again at the suggestion of his doctors because he still had persistent mild anemia. Within 10 months, he achieved full remission from symptoms as well as normalization of intestinal inflammation, evidenced by imaging data and normalization of laboratory parameters. His intestinal permeability also resolved.
From the report, it sounds like plant foods were indeed a trigger for this patient. In addition to the failed addition of fruits and vegetables at the beginning, the report also discusses one instance where the patient ate a paleo cake and had a significant disease flare-up as a result.
Are There Any Risks to a Carnivore Diet?
As with any “extreme” diet, there’s always the risk of getting caught up in the dogma and ignoring your body’s signals that it’s not doing well. It doesn’t help that some of the prominent leaders of the carnivore movement have repeatedly made authoritative extreme health claims and then totally changed their story without acknowledging the implications to their thousands of followers.
One common criticism of a carnivore diet is the lack of vitamin C-containing foods, since humans cannot synthesize their own vitamin C. I haven’t looked into this topic in depth, because I don’t think a strict carnivore diet should be maintained long-term anyway, but I found this twitter thread from Amber O’Hearn tackling the topic.
You could also do as the Indians did and eat adrenal glands regularly, or eat whale skin like the Inuit.
Some other pertinent risks, which I covered here in the IBD Index article about ketogenic diets, include increased absorption of lipopolysaccharides (also known as endotoxin) from the higher saturated fat content of the diet; adverse effects on the gut microbiome from lack of fiber; increased hydrogen sulfide production from increased fat and protein content and no fermentable carbohydrate; and adverse effects on muscle growth, bone density, cognitive performance, thyroid health (don’t forget to eat your moose thyroid!), and overall metabolism.
I won’t rehash what I wrote in the keto article, but I do want to add a little extra color to the microbiome/hydrogen sulfide discussion, since unlike a ketogenic diet, a carnivore diet necessarily contains zero fermentable carbohydrates.
In the David et al. study I referenced in the keto article, the “animal-based” diet was in fact totally devoid of plant foods, consisting of bacon, eggs, coffee, cream, spare ribs, brisket, salami, prosciutto, pork rinds, and cheeses.
Kind of a junk carnivore diet if you ask me, but probably not too off-base from what a modern carnivore diet might look like for someone just hopping on the bandwagon.
The authors first framed the observed microbiome shift as evolutionary adaptation:
“Our findings that the human gut microbiome can rapidly switch between herbivorous and carnivorous functional profiles may reflect past selective pressures during human evolution. Consumption of animal foods by our ancestors was probably volatile, depending on season and stochastic foraging success, with readily available plant foods offering a fall-back source of calories and nutrients. Microbial communities that could quickly, and appropriately, shift their functional repertoire in response to diet change would have subsequently enhanced human dietary flexibility.” (Source)
However, they then note that certain observed changes, such as an increase in sulfate-reducing bacteria, could be problematic:
“Mouse models have also provided evidence that inflammatory bowel disease can be caused by B. wadsworthia,* a sulphite-reducing bacterium whose production of H2S is thought to inflame intestinal tissue. Growth of B. wadsworthia is stimulated in mice by select bile acids secreted while consuming saturated fats from milk. Our study provides several lines of evidence confirming that B. wadsworthia growth in humans can also be promoted by a high-fat diet. This Bilophila-containing cluster also showed significant positive correlations with both long-term dairy and baseline saturated fat intake, supporting the proposed link to milk-associated saturated fats.
“Second, the animal-based diet led to significantly increased faecal bile acid concentrations. Third, we observed significant increases in the abundance of microbial DNA and RNA encoding sulphite reductases on the animal-based diet. Together, these findings are consistent with the hypothesis that diet-induced changes to the gut microbiota may contribute to the development of inflammatory bowel disease.” (Source)
*If I may be so bold, this statement is rather misleading. No mouse model is a good enough model for human IBD that the term “inflammatory bowel disease” is appropriate in statements of causality like this. Note that in the study referenced, an IL10 knockout model was used, and control mice still developed spontaneous colitis at a rate of 25-30%.
There certainly may be something to this connection, and if it’s relevant to any population, it’s probably those with IBD.
But to give a little context, another study in mice found that when comparing three high-fat diets, the milk fat diet promoted a microbial profile reflective of a homeostatic inflammation-resolution cycle between microbe and host, predicting an increased inflammatory response to infection but also robust compensatory mechanisms in the host for immune suppression and tissue healing.
We also have at least one large-scale prospective observational study linking dairy consumption to a decreased risk of developing Crohn’s disease.
So the cautions about hydrogen sulfide that I raised in the keto article are absolutely something to keep in mind, but the dot-connecting from David et al. between an “animal-based” diet and IBD pathogenesis is far from being conclusive.
The Bottom Line
Carnivore diets are increasingly trendy in the health-sphere, and numerous anecdotal reports indicate that such a diet could be therapeutic for people with ulcerative colitis or Crohn’s disease. We even have one published case report of a boy with Crohn’s disease who achieved remission on a strict carnivore diet.
Aside from potential therapeutic benefits from increased ketone production, someone with IBD may see improvement on a carnivore diet due to the elimination of carbohydrates such as FODMAPs, or other plant compounds like lectins or phytates.
However, it must be emphasized that although plant foods may be problematic in certain contexts and eliminating them could provide relief, there’s no question that plants are generally extremely beneficial to health, and every population that has traditionally eaten a mostly-carnivore diet has still included some plant foods.
These populations also maintain specific dietary practices aimed at abrogating some of the potential detriments associated with limited plant foods, such as lack of vitamin C or fertility issues, so just because their diets work for them doesn’t mean a modernized carnivore diet is totally safe.
For a healthy person, the microbiome effects associated with a carnivore diet could potentially be chalked up to simple adaptation, although we have evidence that even small amounts of plant foods (which again, traditional “carnivorous” populations did include) go a long way towards preventing shifts that are widely associated with disease and considered undesirable.
For a person with IBD, such shifts (including increased hydrogen sulfide production) are particularly relevant, so for certain people a carnivore diet could cause more harm than good. Other potential risks common to very low-carb diets, such as issues with metabolism, should be kept in mind as well.
From a practical standpoint, my assessment is that a carnivore diet is a worthwhile approach to try for refractory IBD, but I’d be inclined to experiment with other less‑extreme measures first, and certainly work with a healthcare provider to monitor for potential hydrogen sulfide overproduction.
I also think it could be a good idea to strategically include small amounts of plant foods (such as cranberries) that have been shown to support a healthy gut microbiome in this context. And playing with the fat-to-protein ratio to maximize ketogenesis could help increase the therapeutic value of the diet as well.
And finally, as with any therapeutic diet, but especially for an extremely restricted one such as this, it should be a temporary intervention, working towards a more balanced diet that can be maintained long-term.