Impact of diet, microbiome and environmental factors on Inflammatory Bowel Disease

Inflammatory Bowel Disease is a chronic immune mediated disorder characterized by relapsing and remitting course. The etiopathogenesis of IBD is complex and involves genetic, environmental, microbial and immunological factors working in tandem.

Epidemiologic and laboratory data suggest that environmental factors (through their interaction with the host and the possible agent) play an important role in influencing the risk, presentation and natural history of the disease.  The rapidity of the increase in incidence of IBD in countries where IBD was previously considered uncommon—in many cases, paralleling industrial development—also points to a potential role of environmental factors that are associated with the westernization of lifestyle. Diet is the fundamental environmental factor implicated in the pathogenesis of IBD as it is intricately involved in maintaining homeostasis of the gut, preserving the gut barrier and mucosal permeability and regulating the physiological secretion of hormones in the gastrointestinal tract. Diet is also an important determinant of gut microbial composition and host immune responses. Broadly, the dietary patterns across the world have been divided into two types: Westernized diet and Mediterranean diet. While westernized diet is predominantly animal-based diet rich in xenobiotics, carbohydrates, refined sugar and ultra-processed foods, the Mediterranean diet is commonly plant-based diet rich in fibre, fruits, vegetables, nuts, dairy and fish. High prevalence of IBD in areas consuming westernized diet suggests a possible link between the two. Although high quality and in-depth studies are lacking, it is becoming increasingly evident that westernized diets have an impact on risk as well the clinical course of IBD.  A shift to westernized diet is associated with increase in pathobionts belonging to pro-inflammatory phyla Actinobacteria and proteobacteria, and decrease in anti-inflammatory genera like Faealibacterium and Roseburia. With globalization and cultural influences of western lifestyle on more traditional Indian/Oriental/Mediterranean cultures, westernized diet has overshadowed the traditional healthy diets of these regions, leading to emergence of IBD.

Other environmental factors that have been studied in association with risk of development of IBD are urban residence, hygiene including availability of protected drinking water and toilet facilities, presence of cattle in the house compound, smoking, breastfeeding, pollution, use of antibiotics and NSAIDs, stress, and physical inactivity. Vast differences in the genetic makeup and environmental factors in different geographical locations make it necessary that descriptive epidemiology be studied in populations from different regions and locations.