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Obesity as measured by BMI is not associated with the development of incident UC or CD. Alternative measures of obesity are required to further investigate the role of obesity in the development of incident IBD.

Crohn's disease and ulcerative colitis, collectively known as IBD, are chronic inflammatory disorders of the gastrointestinal tract. Although the aetiopathogenesis of IBD is largely unknown, it is widely thought that diet has a crucial role in the development and progression of IBD. Indeed, epidemiological and genetic association studies have identified a number of promising dietary and genetic risk factors for IBD. These preliminary studies have led to major interest in investigating the complex interaction between diet, host genetics, the gut microbiota and immune function in the pathogenesis of IBD. In this Review, we discuss the recent epidemiological, gene-environment interaction, microbiome and animal studies that have explored the relationship between diet and the risk of IBD. In addition, we highlight the limitations of these prior studies, in part by explaining their contradictory findings, and review future directions.

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ObjectiveTo examine the relationship between Mediterranean diet and risk of later-onset Crohn’s disease (CD) or ulcerative colitis (UC).DesignWe conducted a prospective cohort study of 83 147 participants (age range: 45–79 years) enrolled in the Cohort of Swedish Men and Swedish Mammography Cohort. A validated food frequency questionnaire was used to calculate an adherence score to a modified Mediterranean diet (mMED) at baseline in 1997. Incident diagnoses of CD and UC were ascertained from the Swedish Patient Register. We used Cox proportional hazards modelling to calculate HRs and 95% CI.ResultsThrough December of 2017, we confirmed 164 incident cases of CD and 395 incident cases of UC with an average follow-up of 17 years. Higher mMED score was associated with a lower risk of CD (Ptrend=0.03) but not UC (Ptrend=0.61). Compared with participants in the lowest category of mMED score (0–2), there was a statistically significant lower risk of CD (HR=0.42, 95% CI 0.22 to 0.80) but not UC (HR=1.08, 95% CI 0.74 to 1.58). These associations were not modified by age, sex, education level, body mass index or smoking (all Pinteraction >0.30). The prevalence of poor adherence to a Mediterranean diet (mMED score=0–2) was 27% in our cohorts, conferring a population attributable risk of 12% for later-onset CD.ConclusionIn two prospective studies, greater adherence to a Mediterranean diet was associated with a significantly lower risk of later-onset CD.

Background and AimsPopulation-based prospective cohort studies investigating fibre intake and development of inflammatory bowel disease are lacking. Our aim was to investigate the association between fibre intake and the development of Crohn’s disease [CD] and ulcerative colitis [UC] in a large European population.MethodsIn total, 401326 participants, aged 20–80 years, were recruited in eight countries in Europe between 1991 and 1998. At baseline, fibre intake [total fibres, fibres from fruit, vegetables and cereals] was recorded using food frequency questionnaires. The cohort was monitored for the development of inflammatory bowel disease. Each case was matched with four controls and odds ratios [ORs] for the exposures were calculated using conditional logistic regression. Sensitivity analyses according to smoking status were computed.ResultsIn total, 104 and 221 participants developed incident CD and UC, respectively. For both CD and UC, there were no statistically significant associations with either quartiles, or trends across quartiles, for total fibre or any of the individual sources. The associations were not affected by adjusting for smoking and energy intake. Stratification according to smoking status showed null findings apart from an inverse association with cereal fibre and CD in non-smokers [Quartile 4 vs 1 OR = 0.12, 95% confidence interval = 0.02–0.75, p = 0.023, OR trend across quartiles = 0.50, 95% confidence interval = 0.29–0.86, p = 0.017].ConclusionThe results do not support the hypothesis that dietary fibre is involved in the aetiology of UC, although future work should investigate whether there may be a protective effect of specific types of fibre according to smoking status in CD.

Article first published online 25 September 2014.Supplemental Digital Content is Available in the Text.

BACKGROUND AND AIMS We aimed to investigate the association between protein intake and risk of inflammatory bowel disease (IBD) in the European Prospective Investigation into Cancer and Nutrition. METHODS 413 593 participants from eight European countries were included. Dietary data were collected at baseline from validated food frequency questionnaires. Dietary data were calibrated to correct errors of measures related to each country-specific questionnaire. Associations between proteins (total, animal, and vegetable) or food sources of animal proteins, and IBD risk were estimated by Cox proportional hazard models. RESULTS After a mean follow-up of 16 years, 177 patients with Crohn's disease (CD) and 418 with ulcerative colitis (UC), were identified. There was no association between total protein, animal, or vegetable protein intakes and CD or UC risks. Total meat and red meat intakes were associated with UC risk (HR for the 4 thvs. 1 st quartile = 1.40; 95% CI = 0.99-1.98; P-trend = 0.01; and 1.61; 95% CI = 1.10-2.36, P-trend = 0.007, respectively). There was no association between other food sources of animal protein (processed meat, fish, shellfish, eggs, poultry) and UC. We found no association between food sources of animal proteins and CD risk. CONCLUSION Meat and red meat consumptions are associated with higher risks of UC. These results support dietary counseling of low meat intake in people at high-risk of IBD.