Loading ...

BERLIN — Adherence to a healthy plant-based diet is associated with a reduced risk of developing inflammatory bowel disease (IBD), whereas an unhealthy plant-based diet is linked to an increased disease risk and worse outcomes, according to the results of a large cohort study.

The study, which included both Crohn’s disease (CD) and ulcerative colitis (UC), also showed that diet quality may affect disease progression and surgery risk for individuals already diagnosed with IBD.

“Not all plant-based foods are equal — they don’t all have the same effect on health outcomes,” said study researcher, Judith Wellens, MD, PhD, gastroenterology resident at Leuven University Hospital, Leuven, Belgium.

“We need to look at what people are eating more carefully because it isn’t black and white, with all plant-based food being good and animal-based food being bad,” said Wellens, who presented the data at the European Crohn's and Colitis Organisation (ECCO) 2025 Congress.

Although she advocates for plant-based diets, Wellens stressed that “they need to be individualized to ensure the overall dietary quality is good. Just cutting out meat products is not very helpful. We think it is the unhealthy additions to some plant-based diets that drive the IBD risk.”

Is It the Plants or the Processed Ingredients? 

“Preclinical studies have already taught us that plant-based diets alter the gut microbiota in a beneficial way. However, many diets promoted for IBD — for example the Crohn’s disease exclusion diet — contain ingredients that are animal based. This is confusing for patients and for clinicians,” said Wellens.

To look more closely at the question, she and her colleagues analyzed data for 187,888 participants from the UK Biobank and 341,539 participants from across eight European countries from the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort. None of the participants had IBD at baseline.

Based on participant 24-hour dietary recalls, the researchers constructed plant-based diet indices (PDIs) with diets categorized as healthy (eg, whole grains, fruits, vegetables, legumes, and vegetarian protein alternatives) or unhealthy (eg, emulsifiers, refined grains, fries, fruit juices, sweets, desserts, sugar-sweetened beverages, and processed foods).

The primary outcome was the incidence of IBD (either CD or UC), whereas the secondary outcome was IBD-related surgery, thereby marking disease progression. Cox regression analysis estimated IBD risk and progression. Incidences of IBD were similar between the two cohorts.

In the UK Biobank cohort, 925 participants developed IBD over a median follow-up of 11.6 years. Participants who followed a healthy PDI had a 25% reduced IBD risk, whereas those who followed an unhealthy PDI had a 48% increased risk for disease development. Both CD and UC showed similar outcomes.

The EPIC cohort had a longer median follow-up time of 14.5 years, during which 548 people developed IBD. Healthy PDIs were linked to a 29% reduced risk for IBD, whereas unhealthy PDIs were associated with a 54% increased risk.

A healthy PDI halved the risk for surgery in participants from the UK Biobank, whereas an unhealthy PDI was associated with a twofold higher risk for surgery.

There were no significant associations between PDIs and other outcomes, such as cardiovascular disease, diabetes, or all-cause mortality.

The researchers also looked at the interactions between genetics and plant-based diets, but those results were not presented here in Berlin.

However, Wellens told Medscape Medical News that people with a moderate to high risk for IBD based on their polygenetic risk score showed increased odds for IBD risk.

“We don’t test people for their genetic risk of IBD, but if people have close relatives with IBD, then there is probably an increased genetic risk of its development,” she added.

Commenting on the findings, delegate James Lindsay, professor of inflammatory bowel disease, Queen Mary University of London, London, England, said that several recent epidemiological studies have highlighted “the negative impact of ultra-processed foods on increasing the risk of developing Crohn’s disease.”

Based on these studies, “one might assume that plant-based diets would be protective,” he said, however, the current study shows us “that plant-based diets are not all equal and there are unhealthy aspects to some.”

“Of course, showing that a diet is associated with an outcome is not the same as knowing that changing a diet will reduce the risk,” Lindsay added. “That requires a well-designed, carefully controlled trial.”

Wellens and Lindsay reported no relevant financial disclosures.