Gut Bacteria Can Alter Energy Efficiency

Why do some people seem to stay thin no matter what they eat, whereas others struggle with obesity despite trying to limit their caloric intake? One factor is genetics; you're stuck with the genes and hence (at least in general terms), the same body type and energy metabolism that you inherited from your parents. Another factor, it seems, is the bacteria in your gut.

A key experiment showing the role of gut bacteria in nutrient absorption was published several years ago (see this blog, Sept. 11, 2013). The authors of the study wondered why twins sometimes were discordant for obesity (showed different tendencies toward obesity), and they suspected that gut bacteria were involved. To find out, they took samples of the gut bacteria from twins discordant for obesity, and gave those samples to mice. Lo and behold, the mice that received bacteria from an obese twin gained more weight than mice given bacteria from the non-obese twin.

Experiments published recently in Cell take the gut bacteria affect energy efficiency hypothesis one step further. In these experiments, researchers exposed mice to either a normal temperature environment (22 degrees Centigrade) or a cold environment (6 degrees C). Both groups were fed exactly the same number of calories per day. As expected, the mice in the cold environment initially lost weight as they burned fat to stay warm. But then something interesting happened; they began to gain weight again. When researchers examined the feces of both groups, they found that the cold mice had become 50% more efficient at absorbing nutrients from their food. Further examination revealed that the cold mice lacked a particular strain of gut bacteria. When mice in a normal temperature environment were given those bacteria, they gained weight.

Bottom line; it's possible that your ability to gain or lose weight may be influenced by gut bacteria. Although I pooh-poohed the idea back in 2013, there may just be the possibility that in the future, modifying your gut biome might actually become an effective dieting tool. We'll see; more research is needed.