Eating a diet very low in calories paves way for risky gut bacteria

Weight loss can be a long, often frustrating process, potentially driving some dieters to drastically reduce the number of calories they eat in an effort to burn fat. While eating a very low-calorie diet can help reduce body weight, a new study has found that it may also pave the way for a risky pathogenic bacterium to take hold in the gut.

The new study comes from scientists at the University of California – San Francisco, where it was found that restricting one's self to 800 calories a day can effectively help people lose weight, but with a potentially unwanted effect on gut bacteria. The study involved 80 post-menopausal women who were put on an 800-calorie liquid diet for 16 weeks.

Fecal samples were collected from the participants before and after the dieting period to determine the effects a very low-calorie diet may have on the gut microbiome. The samples were transplanted into mice that had been raised in a sterile environment, revealing one big surprise: the mice that received post-diet transplants lost weight.

When looking into the bacteria profiles in an attempt to determine what may be helping drive the weight loss, the researchers found higher than normal levels of a pathogenic bacteria called C. difficile. This would be due to the decrease in secondary bile acids that ordinarily keep the C. difficile population under control.

Of note, C. difficile can result in severe hard-to-treat intestinal disease — yet it wasn't linked to the presence of colitis or heightened inflammation in the case of this study, indicating that it may also play an important role in metabolism.

However, the researchers caution that more work is necessary and that people desperate to lose weight shouldn't stick to an extremely low-calorie diet in an effort to shed pounds. The study's senior author Peter Turnbaugh, Ph.D., explained, "Let's be clear; we are definitely not promoting C. difficile as a new weight loss strategy. We've got a lot of biology left to unpack here."