SOURCE: Komaroff AL. The microbiome and risk for obesity and diabetes. JAMA 2017;317:355-356.

Apparently, the gut bacteria — currently called the microbiome — are much more than simple innocent bystanders. There are two primary families of intestinal microbiota: Bacteroidetes and Firmicutes, which comprise approximately 90% of all gut bacteria. Recently, it has been appreciated that the microbiome actually generates proteins, hormones, neurotransmitters, and inflammatory molecules. These products of the microbiome may enter the circulation and produce far-reaching effects.

For instance, obese persons are populated with greater numbers of Firmicutes, which are more efficient in providing energy sources than Bacteroidetes. Confirming the causal role of this relationship, transplantation of gut microbiota from obese mice promptly converts lean mice into obese ones. Equally remarkable, and much more hopeful, is the observation that transplantation of microbiota from lean mice into obese ones produces a favorable effect on weight.

The story is complicated even further by the observation that the microbiome is capable of remodeling: When obese persons consume weight-reducing diets, the disproportion of Firmicutes declines, and it resumes when excess calories are again introduced. We are only beginning to understand the magnitude of the role the microbiome plays in health and disease.