Americans are fat and getting fatter. Obesity rates among U.S. adults doubled between 1980 and 2004. Currently, more than one-half of the U.S. population is overweight, and more than one-third of U.S. adults, or over 72 million people, are obese (BMI>30).

The obvious question—why? The obvious answer—too much food and too little exercise.

Experts, however, agree that body weight—both composition and distribution—is likely influenced by a wide range of genetic, social, cultural, behavioral, and environmental factors. Recently, Dr. John DiBaise and colleagues examined the evidence for a link between obesity and bacteria in the gastrointestinal tract (gut microbiota). The full report can be found in the April 2008 issue of Mayo Clinic Proceedings.

The marked difference in gut microbiota between fat and thin people raises the possibility that gut microbiota play a role in regulating weight and may be partly responsible for the development of obesity in some people. If the hypothesis proves to be true (and much more research is needed), then modifying the bacteria in the gut could one day be a treatment for obesity.

The difference in gut microbiota seen in bottle-fed and breastfed babies, may partly explain why breastfed babies are less likely to become overweight children.