Surgically bypassing the stomach is not the only reason that patients this surgery quickly begin to drop pounds. Changes to the microbial make-up of their intestines also play a big role, according to a paper published in Science Translational Medicine yesterday (March 27): A.P. Liou et al., “Conserved shifts in the gut microbiota due to gastric bypass reduce host weight and adiposity,” Sci. Transl. Med. 5, 178ra4, 2013.
Gastric bypass surgery was originally thought to work by forcibly reducing a person’s capacity for food, but the effects are more complicated than they first seemed, Lee Kaplan director of the Massachusetts General Hospital Weight Center in Boston and a senior author of the study explained. “We began to see, in patients that got bypass surgery, that they were not hungry and that they were not craving what they used to crave.”
It is known that patients having gastric bypass surgery also have altered gut microbial profiles. Kaplan and his team have now observed similar bypass-induced microbial changes in obese mice. Within 1 week of surgery, three phyla of microbes were significantly enriched in the mice. The mice lost 30 percent of their body weight, and exhibited metabolic changes—their blood glucose levels lowered and insulin sensitivity improved.
To determine if these microbial and metabolic changes shared a causal relationship, Kaplan’s team transplanted the microbial community from the guts of these mice into microbe-free, normal-weight mice.
“What we saw in the normal-weight recipients that were given gastric bypass microbiota was that their food intake was not altered, but they had less body fat and they lost about 5 percent of their body weight,” said lead author Alice Liou, a research scientist at Massachusetts General Hospital.
It is not yet clear whether such microbial transfers would be effective in humans, but the results imply that a probiotic that replicates the effect of gastric bypass surgery is possible, and may contribute to weight loss. Wouldn’t it be wonderful if medicine could identify supplements to achieve the same effects as a bypass, but without the risk of surgery?!