Gut microbes signal when dinner is done

Gut bacteria are not polite dinner guests. They fill up fast and tell their host to quit eating, too.

After only 20 minutes, helpful E. coli populations that live in animal guts produce proteins that can curb how hungry its animal partner is, researchers show November 24 in Cell Metabolism. In mice and rats, the proteins stimulated brain-body responses that led the animals to eat less. The new findings indicate that gut microbes could be more involved with regulating food intake in animals, including humans, than previously thought.

“It suggests that the growth and activity of the microbiome might specifically regulate appetite and feeding behavior,” says Kevin Murphy, an endocrinologist at Imperial College London not involved with the study.

Food provides loads of nutrients to the gut. There, microbes use the nourishment to maintain population size. In the lab, Sergueï Fetissov and colleagues found that E. coli populations stopped growing 20 minutes after receiving nutrients. Upon hitting the 20-minute mark, the microbes also made some different proteins than before and boosted production of the protein ClpB, which mimics a hormone in humans that acts on appetite. When the E. coli stopped growing, they produced “two times as much of this protein,” says Fetissov, a physiologist at Rouen University in France.

Proteins from the E. coli no-growth stage were then injected in rats and mice. Compared with rodents that didn’t receive the proteins, those that did ate less and had higher levels of ClpB in their guts. The researchers also found that the protein encouraged the release of peptide YY — a hormone associated with reduced appetite — and stimulated nerve cells that decrease hunger levels.

 The E. coli proteins seem to influence feeding behavior in the rats and mice. But it’s too soon to say whether the results are applicable to humans. “Further work is required to determine how physiologically relevant the findings are,” Murphy says.

The interaction between gut microbes and host organisms isn’t well understood, Fetissov says, so it’s important to study pathways and mechanisms that relate to food intake. Human gut microbes, for instance, may play a role in obesity, and he says that studies like this could help explain links between microbes and human health.