Nanocolloids in drinking water increase the risk of obesity in mice by modulating gut microbes

[Display omitted] •Nanocolloid-pattern contaminations in drinking water are found in a national scale.•Concentrations of nanocolloids are at mg/L level.•Nanocolloids induce obesity in mice by regulating gut microbes.•The ratio of Firmicutes to Bacteroidetes is upregulated by nanocolloids.•Nanocolloids affect long-chain fatty acids, lipid metabolites and lipid synthesis. Both gut microbes and environmental contamination may cause metabolic disorders and obesity. However, the relationships among gut microbes, environmental contamination and obesity remain obscure. The drinking water on a national scale (31 cities in China) contained nanocolloid-pattern contamination at the mg/L level, a concentration that is 10- to 100-fold higher than commonly reported pollutants. Exposure to nanocolloids (environmentally related dose, 0.15 mg/kg) for three weeks increased the body weight and leptin levels of mice and decreased the expression of adiponectin. Nanocolloids increased the ratio of Firmicutes to Bacteroidetes, a typical obesity-related phenomenon, in the obese individuals. Oral administration of resveratrol verified the role of gut microbes in the tendency toward obesity induced by nanocolloids. The ratio of Firmicutes to Bacteroidetes is positively correlated with body weight and leptin levels. Compared to the control, the levels of triglycerides and high-density lipoprotein cholesterol were up- and downregulated by the tested nanocolloids at 0.15 mg/kg, respectively. Long-chain fatty acids, lipid metabolites and the expression of lipid synthesis-related genes (Fas, Srebp-1 and ACC-1) were also significantly increased by nanocolloids. The present study provides new insights that improve our understanding the risks of obesity associated with drinking water contamination that are mediated by gut microbes.