Food, immunity, and the microbiome.

There is increasing evidence that ingested diet-borne components are involved in the pathogenesis of disorders such as inflammatory bowel diseases, atherosclerosis, and type 2 diabetes. Nutrients can have short- and long-term effects in shaping the composition of the microbiota. Western diets (enriched in fat, phosphatidylcholine, and L-carnitine) promote inflammation and atherosclerosis through specific fatty acids and degradation products such as trimethylamine N-oxide. Other dietary factors such as carbazoles or tryptophan-enriched proteins have anti-inflammatory properties-partly via activation of aryl hydrocarbon receptors. The microbiota and its metabolic machinery produce a myriad of metabolites that serve as important messengers between the diet, microbiota, and host. Short-chain fatty acids affect immune responses and epithelial integrity via G-protein-coupled receptors and epigenetic mechanisms. By increasing our understanding of interactions between diet, immunity, and the microbiota, we might develop food-based approaches to prevent or treat many diseases. There now is scientific evidence to support the adage "we are what we eat," and this process begins in early life.