Plant-based diets and IBD

By Dr. Liji Thomas, MDReviewed by Lily Ramsey, LLMMar 19 2025

Plant-based foods are increasingly being recommended as part of various dietary approaches for patients with inflammatory bowel disease (IBD). A recent study explored the connection between plant-based diets and the incidence and outcomes of IBD.

Study: Composition of plant-based diets and the incidence and prognosis of inflammatory bowel disease: a multinational retrospective cohort study. Image Credit: 5PH/Shutterstock.com

Introduction

IBD is a chronic condition that includes Crohn’s disease and ulcerative colitis, characterized by persistent intestinal inflammation, pain, and diarrhea. With no known cure, it significantly reduces quality of life while imposing substantial financial and social burdens.

Western-style diets, which are high in animal-based foods, have been linked to an increased risk of IBD. Some evidence suggests that plant-based foods can encourage beneficial microbial activity in the gut, potentially producing essential nutrients that support intestinal health.

Plant-based diets vary widely; some are entirely plant-derived, while others include limited animal products. Even therapeutic diets like the Crohn's Disease Exclusion Diet (CDED) incorporate animal proteins.

Research indicates that animal-based foods may reduce beneficial microbial activity in the gut, raising the possibility that modifying dietary patterns could help prevent or manage IBD.

Previous studies on plant-based diets and IBD have not fully accounted for the simultaneous consumption of animal products. This study aimed to address that gap by analyzing data from two large population studies: the UK Biobank (UKB, 2009–2022) and the European Prospective Investigation into Cancer and Nutrition (EPIC, 1991–2010).

The study included 187,888 and 341,539 participants, respectively, all of whom were free from IBD at baseline. The participants were drawn from eight European countries.

Dietary classification and plant-based indexes

Participants' diets were categorized based on plant-based indexes (PDIs), distinguishing between healthy and unhealthy plant-based diets. Dietary patterns were assessed using 24-hour recalls and food frequency questionnaires (for UKB and EPIC, respectively).

PDIs classify dietary habits into three categories:

1. Overall PDI – Includes all plant foods without distinguishing between healthy and unhealthy options.
2. Healthy PDI – Positively scores nutrient-dense plant foods while assigning negative scores to refined grains, potatoes, sugary drinks, and desserts.
3. Unhealthy PDI – Positively scores less nutritious plant foods, while lowering scores for healthier plant-based options.

Animal foods—including eggs, dairy, and fish—were negatively scored in all PDIs. The diet scores ranged from 1 (lowest intake) to 5 (highest intake). Additionally, a “healthy omnivorous diet” was considered in sensitivity analyses, which incorporated healthy plant-based foods along with eggs, dairy, and fish.

Findings: Healthy PDI lowers IBD risk

Over a median follow-up period of 11.6 years for UKB and 14.5 years for EPIC, 925 and 548 new IBD cases were recorded, respectively.

• Participants in the highest quintile of healthy PDI had a 25% lower IBD risk in the UKB cohort and a 29% lower risk in the EPIC cohort compared to those in the lowest quintile.
• Conversely, the highest quintile of unhealthy PDI was associated with a 48% higher IBD risk in the UKB cohort and a 54% higher risk in the EPIC cohort compared to the lowest quintile.
• When individual foods were analyzed, potatoes and sweets were linked to a higher risk of IBD, while fruits and whole grains were associated with a lower risk.

PDI and IBD prognosis

Among 2,133 IBD patients in the study, the risk of IBD-related surgery was more than twice as high in the highest quintile of unhealthy PDI compared to the lowest. Conversely, patients in the highest quintile of healthy PDI had half the risk of requiring surgery compared to those in the lowest quintile.

However, no significant associations were found between PDI scores and long-term complications such as diabetes, cardiovascular disease, or mortality. The impact of PDI appeared most pronounced in individuals with moderate to high genetic susceptibility to IBD, suggesting that the anti-inflammatory effects of plant-based foods might partly explain the observed benefits.

Healthy omnivorous diet and IBD

The healthy omnivorous diet was also associated with a 29% lower IBD risk between the highest and lowest quintiles, even after accounting for ultra-processed food consumption and IBD medication use.

Conclusions

This study underscores the potential benefits of healthy plant-based diets in lowering IBD risk and improving outcomes for those with the disease. The positive effects are likely due to the anti-inflammatory properties of nutrient-rich plant foods, particularly in individuals with a genetic predisposition to IBD.

However, not all plant-based diets offer the same benefits. Some, particularly those high in refined grains, sugary foods, and processed plant products, may actually increase IBD risk. The findings highlight the importance of dietary guidance that promotes awareness of both healthy and unhealthy plant-based diets among IBD patients.

Future research should explore the specific mechanisms driving these differences and assess the impact of various plant-based food categories on gut health and overall metabolic function.