The microbes in your stomach seem to hijack a hormone system that signals the brain to stop eating.
Hear that little voice in your head telling you to skip a second slice of pumpkin pie? It might be coming not from your conscience, but from the masses of bacteria in your stomach.
Experiments in mice and rats suggest that certain microbes living in your body as part of the gut microbiome have ways of letting the brain know when they’ve received enough nutrients to reach their goal—creating a billion more of their kind. Those signals seem to turn hunger on and off in their hosts.
The findings build on a bounty of evidence that microbes play a key role in the physiology of appetite—and perhaps could help people with eating disorders.
“We have long known that after eating we get a feeling of fullness. Most have assumed that it is because our stomach or intestines are stretched,” says Martin Blaser, director of NYU’s Human Microbiome Program and author of Missing Microbes. “We never thought that the bacteria we were carrying could be part of that signal, but this new work provides evidence that that is what is occurring.”
In recent years scientists have been exploring the many ways the microbiome may affect its animal host’s feelings and behaviors. To test its influence over appetite, Serguei Fetissov and his team looked at proteins produced by the common intestinal bacteria Escherichia coli.
The team noticed that about 20 minutes after feeding and multiplying their numbers, E. coli switch from pumping out one set of proteins to another. So Fetissov, of Rouen University, and his team injected tiny doses of those post-meal proteins into rats and mice.
They found that the injected rodents reduced their food intake whether they’d previously been freely fed or kept hungry. Further analysis showed that one protein stimulated the release of a hormone associated with satiety. Another of the chemicals found in the animals’ bloodstream appears to increase the firing of brain neurons that diminish appetite, the team reports this week in Cell Metabolism.
Many studies suggest that our gut produces hormones that tell our brain to either grab some more grub or stop eating. Fetissov thinks that E. coli may be hijacking this molecular pathway to produce the signals that make animals feel full, and that doing so may be a way for the bacteria to self-regulate their populations …
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