Responses of Gut Microbiota to Diet Composition and Weight Loss in Lean and Obese Mice

Maintenance of a reduced body weight is accompanied by a decrease in energy expenditure beyond that accounted for by reduced body mass and composition, as well as by an increased drive to eat. These effects appear to be duein part- to reductions in circulating leptin concentrations due to loss of body fat. Gut microbiota have been implicated in the regulation of body weight. The effects of weight loss on qualitative aspects of gut microbiota have been studied in humans and mice, but these studies have been confounded by concurrent changes in diet composition, which influence microbial community composition. We studied the impact of 20% weight loss on the microbiota of dietinduced obese (DIO: 60% calories fat) mice on a high- fat diet (HFD). Weight- reduced DIO (DIO- WR) mice had the same body weight and composition as control (CON) ad- libitum (AL) fed mice being fed a control diet (10% calories fat), allowing a direct comparison of diet and weight- perturbation effects. Microbial community composition was assessed by pyrosequencing 16S rRNA genes derived from the ceca of sacrificed animals. There was a strong effect of diet composition on the diversity and composition of the microbiota. The relative abundance of specific members of the microbiota was correlated with circulating leptin concentrations and gene expression levels of inflammation markers in subcutaneous white adipose tissue in all mice. Together, these results suggest that both host adiposity and diet composition impact microbiota composition, possibly through leptin- mediated regulation of mucus production and/ or inflammatory processes that alter the gut habitat.