The bacterial population of the gut changes within twenty four hours of switching from a plant-based diet to a high fat, high sugar Western diet, according to a new study of mice.

This fascinating finding comes from Washington University School of Medicine in St Louis. Human intestinal microbes (obtained from stool samples) were transplanted into sterile mice eating a plant-based diet. After one month half of the mice were fed a Western diet. Compared to mice being remaining on the plant-based diet mice on the Western diet had a significantly higher proportion of two classes of gut bacteria, Erysipielotrichi and Bacilli, and lower levels of another strain known as Bacteroidetes. Additionally the mice eating the Western diet were expressing more microbial genes devoted to breaking down simple sugars and other components of a Western diet. What surprised the researchers was how rapidly these changes occurred: “Assuming it takes four to six hours for microbes to move through the intestine, this means that the initial shift in the microbial community occurred 18 to 20 hours after exposure to a Western diet”.

This is not the first study to raise the possibility that the gut microbiota has an important role in regulating weight and may be partly responsible for the development of obesity in some people. Previous research has indicated that gut microbiota facilitate the extraction of calories from food and influence energy storage. Previous research has also found both that the composition of gut microbiota is different in lean and obese individuals and that it changes when weight is lost.

Use of antibiotics, prebiotics, and probiotics may result in nonspecific modulation of gut microbiota. Although clearly no substitute for proper diet and exercise, manipulation of the gut microbiota may represent a novel approach for treating obesity, one that has few adverse effects.