Interactions between diet and gut microbes affect how quickly food moves through the gut.

To simulate dietary changes that occur when people travel to places with different cuisines, Jeffrey Gordon at Washington University in St Louis, Missouri, and his team took germ-free mice and transplanted them with gut microbes from people consuming one of five different diets from around the world. They then fed the mice a series of all those diets and measured transit times of dye-stained food through the gut. They found that transit time varied with different combinations of diet and microbial community, and that it correlated with certain metabolites produced by some bacteria.

Turmeric (pictured), a common ingredient in Bangladeshi food, in particular decreased gut motility in mice carrying microbes and eating food from Bangladesh — in part by increasing the production of bile acid, which was converted by microbes into compounds that slow down gut movement. The approach could be used to identify components of different diets that affect gut health, the authors say.

Cell 163, 95–107 (2015)