Dietary Relationships between Obesity and Inflammatory Bowel Diseases: A Narrative Review of Diets Which May Promote Both Diseases.

Purpose of review: The pandemic of obesity preceded global spread of Inflammatory Bowel diseases by almost 2 decades. A pathogenic relationship has been described between obesity and inflammatory bowel diseases, but Crohn`s disease may be selectively impacted. The role of diet in pathogenesis has also gained significant support in the last few decades. This review explores dietary relationships to account for epidemiological observations. Quantifiable indices for diets have been described including a glycemic index, inflammatory indices and levels of food processing. Meta-analyses have been published which examine each for effects on obesity and co-morbidities as well as Crohn's disease and ulcerative colitis. This review suggests that ultra-processed foods provide the best link between obesity and Crohn's disease explaining epidemiological observations. However, the other 2 types of dietary indices likely contribute to ulcerative colitis as well as to co-morbidities related to both obesity and inflammatory bowel diseases. The term ultra-processed foods cover a large number of additives and extensive work is needed to define individual or combined harmful effects. Furthermore, the interactions among the 3 main indices need clarification in order to precisely apply therapeutic diets to both diseases (obesity and inflammatory bowel disease).