In that diet and nutritional status are among the most important modifiable determinants of human health, and the nutritional value of food is influenced in part by a person’s gut microbial community (microbiota) and its component genes (microbiome), Jeffrey I. Gordon, from Washington University School of Medicine (Missouri, USA), and colleagues conducted studies on mice, feeding them the animal equivalent of a Western diet filled with sugars and carbohydrates.  The researchers observed a near-instantaneous change in the gut flora, whereby the structure of the microbial community changed dramatically and very rapidly, not only in terms of species of organisms but their proportional representations.  As a consequence, the mice became obese on Western diets.