Are the Bacteria in Your Gut Making You Fat?

By David Shultz
BU News Service


As you wait in line for fast food, it’s not only your taste buds that are looking forward to the juicy burger. Deep in your intestines a hundred trillion bacteria cells are licking their proverbial bacteria lips in anticipation—worst of all though, these gut microbes could be making you fat.

According to new study published in Science, your fatty diet could be sustaining a population of obesity-promoting bacteria. In a collaborative effort, researchers from University of Washington and University of Colorado discovered that the type of bacteria living in the human gut may contribute to obesity. Furthermore, the composition of these microbial populations depends on their host’s diet.

High fat diet vs low fat diet in mice with different microbial profiles. ©Geoff Glocke
Image created by Geoff Glocke

Researchers began by culturing gut-bacteria from twins, one obese and the other healthy.  Despite the genetic similarities between twins, it became evident that  the genetic makeup of their gut bacteria could vary dramatically. In order to test whether these variations could be a contributing factor in obesity, Jeff Gordon and his team at University of Washington transplanted samples of bacteria from each twin into germ-free mouse pairs. As suspected, the mice receiving the microbes from the obese twin gained significantly more fat mass and began to display other biological markers of obesity.

The researchers then housed both the obese and lean mice together to allow their gut bacteria to interact. If the mice were fed a diet low in fat, the lean profile bacteria replaced their obesity-linked brethren. However, if the mice were fed high fat diets, this protective effect was lost; the bacteria cultured from the obese twin continued to survive in the mouse’s guts.

It seems that the specific profile of bacteria living in the GI tract play at least some role in the development of obesity. Furthermore, the profile of these bacteria can be altered by changes in diet. While this certainly isn’t a magic cure to the obesity epidemic, it certainly sheds light on just how complex this issue is. “We’re very optimistic but it is hard to say how long before [these findings] can be applied in humans, especially due to regulatory obstacles,” cautions Knight, lead researcher from University of Colorado.

Jacques Izard, an instructor in immunology at Harvard’s Forsyth institute echoed Knight. “At this point in time, only very small numbers of subjects have been included in the microbiome/obesity investigations,” Izard said. “The results are however so significant that a new field is being created as we speak. It opens new doors of treatment that go beyond probiotics and prebiotics.”

The bacteria in your body out number your own cells about ten to one. The food we eat is the food they eat, and these results suggest we can alter their population for our benefit… if we can just manage to resist that double cheeseburger. So maybe the bacteria in your gut are making you fat, but if they are, it’s because you’re enabling them.