Lifestyle may not be the only culprit contributing to weight gain. Scientists at Emory University found that the intestines hold bacteria that play an important role in storing or burning extra calories. This gut micro-biota determines how the food gets processed.
Andrew Gerwirtz, the lead scientist, worked with researchers at Emory, Cornell and the University of Colorado in Boulder. This team became interested in intestinal bacteria when they noticed the weight gain patterns of laboratory mice. They noted a relationship between gut bacteria and weight reporting that lab mice lacking toll-like receptor 5 (TLR5) – a protein – had more ‘bugs’ and were about 15 percent heavier. They also had a higher level of inflammation signaling a condition called metabolic syndrome which can cause weight gain and high blood pressure and cholesterol levels.
The overweight mice in the Gerwirtz study were bred to lack the TLR5 protein. This protein has a filtering role which controls the mass of pathogens living in the intestines. When it is missing, the normally harmless gut bacteria overdevelop and multiply.
When this happens an inflammatory state develops and the attempts to respond to the increasing population of ‘bugs’; it also makes cells less sensitive to insulin. In a way, inflammatory factors and insulin compete for the attention of the same intestinal cells; if the cells are busy responding to inflammatory factors, then they are less likely to take up glucose and process it effectively.
"We don't think the bacteria are directly making the mice eat more, but the bacteria are causing low-grade inflammation, which causes insulin resistance and then makes the mice eat more," says Gewirtz.
While these findings are limited to mice, it is believed that this overproduction of gut bacteria is also applicable to humans. "Our results suggest that the tendency to eat more may not only be driven by the fact that food is cheaper and more available, but by a change in the bacteria in the intestines," he says.