This is a helpful review of the literature on nutrition and inflammatory bowel disease: https://www.tandfonline.com/doi/pdf/10.1080/17474124.2020.1733413?needAccess=true
While there is much research yet to be done, ample observational and some experimental data has associated plant-based eating patterns with prevention of / remission from IBD. These aren’t always exclusively plant-based diets, but the more diverse plant compounds consumed and the fewer animal products and processed foods consumed, the better for any inflammatory condition.
The low FODMAP (fermented oligo- di-, and mono-saccharides and polyols) diet has been associated with alleviation of IBD symptoms. These are poorly absorbed compounds which seem to aggravate symptoms. But a low FODMAP diet is even more restrictive than a generally plant-based eating pattern and presents challenges for adherence.
Dietary fiber is overall associated with positive results when it comes to IBD. The varied fibers in a plant-based diet spawn beneficial intestinal flora whose byproducts like short-chain fatty acids reduce local and systemic inflammation. A subset of IBD patients with intestinal stenosis may have to restrict fiber until that process resolves.
We can also consider the benefits via prevention of colorectal cancer. There is impressive data associating plant-based eating patterns with reduced risk of colorectal cancer, which becomes particularly important for IBD patients (eg, observational studies have associated ulcerative colitis with a 30% increased risk of developing colorectal cancer).
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