Obesity Has a Microbial Component With Therapeutic Implications

Increasing ‘lean microbiota can help in reducing obesity. Scientists have found that the proportion of beneficial intestinal Bacteroidetes is lower in obese people than in lean people. Conversely, the proportion of the other dominant beneficial gut bacteria, Firmicutes, is higher in obese people. However, these proportions shift as weight is lost on low-calorie diets.

Dr. Jeffrey I. Gordon and colleagues from Washington University School of Medicine report, "Our findings suggest that obesity has a microbial component, which might have potential therapeutic implications.

The way it works, said Jeffrey I. Gordon, M.D., of Washington University, and colleagues, is that when an overweight person goes on a diet, one group of efficient bacteria moves out of the gut and another less-efficient group moves in to fill the void.

To explore the relation between gut microbial ecology and body fat, the investigators randomly assigned 12 obese individuals to either a fat-restricted or carbohydrate-restricted low-fat diet. For the next year, the investigators monitored the composition of their gut microbiota, including beneficial bacteria that help breakdown otherwise indigestible food.

Before the diet, obese people had fewer Bacteroidetes (p < 0.001) and more Firmicutes (p = 0.002) than did lean controls.
Over the next year, the abundance of Bacteroidetes increased (p < 0.001) and the abundance of Firmicutes decreased in the obese subjects, regardless of which low-fat diet they were on. The increase in Bacteroidetes correlated with percentage loss of body-weight.

Studies in mice, reported in a companion paper in Nature by the St. Louis team suggest a possible explanation for these findings. They found that gut microbes in genetically obese mice have 50% fewer Bacteroidetes, and correspondingly more Firmicutes, compared with lean mice.

They also observed that the gut microbiota of obese mice have an increased capacity to harvest energy from the diet. And the effect is transmissible, Dr. Gordon and colleagues report, noting that "colonization of germ-free mice with an ‘obese microbiota’ results in a significantly greater increase in total body fat than colonization with a ‘lean microbiota.’"

"The dynamic linkage between adiposity and gut microbial ecology described here, together with our results in mice, indicates that manipulation of gut microbial communities could offer another approach in the treatment of obesity," they conclude.
Nature 2006;444:1022-1023,1027-1030.