Summary: Vegan diets are one popular intervention for IBD, and for good reason – a well-designed vegan diet may confer beneficial effects on intestinal health via modulation of the microbiome, increased nutrient density, and elimination of food irritants. However, diets completely devoid of animal products are not viable long-term for the vast majority of people, and nutritional deficiencies are a serious risk. All the potential health benefits of a vegan diet can still be leveraged within an omnivorous diet, but for those who are vegan for ethical or sustainability reasons, careful supplementation or strategic inclusion of certain nutrient-dense animal foods (such as bivalves) are potential options for avoiding some of the pitfalls.
This article is part of the IBD Index. Last updated on March 16, 2022.
It is well known that high intakes of meat have been associated with IBD (example source; there are many!). And while yes, these are epidemiological studies and no, correlation does not equal causation, I’d consider it a bit disingenuous to brush off these results as a mere artifact of the “healthy user bias” (as many in the keto, carnivore, and paleo communities are wont to do).
I’ll say right at the outset that, on the basis of anthropological, biological, and other scientific knowledge and data, I don’t believe a strict vegan diet to be viable for the vast majority of humans. That said, many people have anecdotally had astonishing success managing their IBD with a vegan diet, and considering those experiences in light of the epidemiological evidence I mentioned above, I think it would behoove us to pay attention to what this information could teach us about the disease processes involved in IBD, and how to best address them.
Table of Contents
What is a vegan diet?
How might a vegan diet help with IBD?
Is there any clinical evidence to support a vegan diet for IBD?
Are there any risks to a vegan diet?
The bottom line
Bonus content! A blast from the past
What is a Vegan Diet?
The term “vegan” refers to any diet that excludes all products of animal origin, including dairy, eggs, and honey. You may also see people use the term “plant-based,” although that one is more ambiguous; some people use it to mean strict vegan, while others use it to mean an omnivorous diet that is mostly based on plants. Of particular note in the context of this website, one group of Japanese researchers has devised a semi-vegetarian diet for the treatment of IBD that they refer to as a “plant-based diet.”
There are a couple of popular sub-classifications of vegan diet as well, including raw vegan (only eats uncooked plant food) and fruitarian (only eats fruit). There may be others I’m unaware of as well. If I had unlimited time, I would do a thorough analysis of raw vegan and fruitarian health claims, but I don’t, and I’m sure the topic has been dealt with extensively elsewhere. For the purposes of this post, suffice it to say that neither of these dietary approaches are supported by science, and both are risky long-term. For a short period of time (on the order of a month or less), they’re probably harmless.
How Might a Vegan Diet Help with IBD?
The commonly cited rationale for going on a vegan diet to treat IBD is that all foods of animal origin are in some way unhealthy, toxic, etc. There’s nuance here that could be explored, but for all practical purposes, that is simply untrue.
However, there’s a lot to recommend a well-designed vegan diet, and the below are some of the likely contributing factors for those who do find relief on such a diet:
- Improved microbiome health: The average vegan diet will likely be higher in fiber than the average omnivorous diet, including prebiotic fibers that feed beneficial bacteria in the gut. It’s fairly well established that generally, diets high in prebiotic fibers improve the health of the microbiome and increase production of butyrate and other SCFAs, which feed colonocytes and support healthy gut function.
- Elimination of many food irritants: Although dairy is not an intrinsically unhealthy or toxic food, many people with IBD have difficulty digesting lactose and/or are sensitive to casein or other components of dairy, so removing it from the diet could provide relief. And assuming someone is following a whole-foods-based vegan diet (ie, not eating a bunch of processed junk), they’ve probably also removed many other potential irritants, such as food additives, gums, etc.
- Improved nutrition: Although a well-designed vegan diet is less nutritionally complete than a well-designed omnivorous diet, switching from a Standard American Diet (or similarly unhealthy diet) to a vegan diet may improve certain aspects of nutritional status, although nutrients found primarily in animal foods may quickly become a concern.
- Higher concentration of beneficial polyphenols: A fair bit of evidence (review article here) indicates that polyphenols (such as quercetin, resveratrol, caffeic acid, etc) have beneficial effects on health in general, and gut health in the context of IBD specifically.
- Reduction of protein fermentation in the colon: Animal studies and other preliminary evidence indicates that the byproducts of protein fermentation (such as hydrogen sulfide, which I’ve discussed a bit here) can compromise the structure and function of colonic epithelial cells, lead to thinning of the mucus barrier, and increase intestinal permeability (two review articles here and here). Much of the research thus far on this topic makes it difficult to parse out effects related to availability of fermentable carbohydrates/fiber vs. effects related to availability of protein in the large intestine, but either way, a vegan diet is likely to reduce bacterial fermentation of proteins.
All of these factors will be magnified if someone switches to a vegan diet straight from an extremely processed and nutrient-poor diet, so in those cases especially, it’s not a surprise at all if a vegan diet confers significant health improvements.
However, all of these potential mechanisms can easily be leveraged without eliminating animal products from the diet.
Is There Any Clinical Evidence to Support a Vegan Diet for IBD?
No; I haven’t been able to find any clinical trials that have tested a vegan diet as an intervention for IBD. The mechanisms I mention in the previous section are certainly evidence-based though, and I’ll discuss them in greater detail in future articles.
But again, there’s no evidence (aside from anecdotal) that a strict avoidance of all animal products is more beneficial for IBD patients than a similar diet that contains some nutrient-dense animal products. In fact, the opposite is true – there’s plenty of evidence that including animal products is more beneficial.
For an example of a plant-based (but still omnivorous) diet for IBD that is supported by clinical evidence, check out this post: Semi-Vegetarian/Plant-Based Diet for Ulcerative Colitis.
Are There Any Risks to a Vegan Diet?
Yes. Specifically, the risk of nutrient deficiencies. And when I say “risk” – for the average person, it’s not a matter of “if,” but a matter of “when” (for a vegan diet with no supplements, that is).
An extensive review of why a strict vegan diet is not suitable for most people is outside the scope of this post, but if you’re interested in 19-year-old Alyssa’s take, check out the links at the bottom of this page.
But if you’re committed to a vegan diet, I recommend reading this post from Denise Minger, where she gives advice on how to avoid some of the common pitfalls that strict vegans face. Her own health suffered terribly on a vegan diet, but she’s long since recovered and still feels best eating mostly plants, so she brings an excellent perspective to the topic. Strategies she discusses include supplementation, food preparation methods, and thoughtful incorporation of certain animal foods that may have fewer sustainability and/or ethical concerns.
The Bottom Line
I would not recommend a vegan diet long-term due to the risks associated with nutrient deficiencies. All of the above-mentioned beneficial mechanisms (improved microbiome health, improved nutrient density, elimination of food irritants, high concentration of beneficial phytonutrients, and reduced microbial protein fermentation) can be leveraged in a diet that includes animal foods.
If someone has tried and failed other approaches and/or is particularly drawn to a vegan approach, then it could be worth experimenting with temporarily. But even then, I would urge you to consider whether there are any nutrient-dense animal products you could strategically include in your diet to improve nutritional completeness (bivalves in particular might be worth considering, from nutritional, ethical, and environmental standpoints; Denise Minger discusses this in the article mentioned above).
Bonus Content! A Blast From the Past
Almost a decade ago, back when I first thought it would be nifty to blog regularly, I wrote a series of posts about veganism. My knowledge of health and nutrition has grown tremendously since then, and my overall philosophy of health has evolved considerably, but upon re-reading the posts today (almost a decade later), much of what I had to say back then still rings true. So if you’re interested in 19-year-old Alyssa’s take on veganism – well, here you go!
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