Food cravings determined by gut microbes’ activity
Substances secreted by gut microbes in mice have been found to influence what they choose to eat, providing a sort of explanation into food cravings and associated behaviour. Animals with different compositions of gut microbes do change their preferred diet, said Kevin Kohl, an assistant professor in the Department of Biology in the Kenneth P. Dietrich School of Arts and Sciences, the University of Pittsburgh.
Kohl and colleagues at the university gave 30 mice that lacked gut microbes a cocktail of microorganisms from three species of wild rodents with very different natural diets, later noticing that the mice chose food rich in different nutrients, according to the molecules produced by the given gut microbes.
Unbeknownst to many, the microbes in the gut can produce some of the same molecules as those from the brain, changing the meaning of the brain-gut message to benefit themselves. One such messenger is tryptophan.
“Tryptophan is an essential amino acid that’s common in turkey but is also produced by gut microbes. When it makes its way to the brain, it’s transformed into serotonin, which is a signal that’s important for feeling satiated after a meal,” said postdoctoral student Brian Trevelline. “Eventually that gets converted into melatonin, and then you feel sleepy.”
In their study, Kohl and Trevelline showed that mice with different microbiomes had different levels of tryptophan in their blood, even before they were given the option to choose different diets; those with more of the molecule in their blood also had more bacteria that could produce it in their gut.
“There are likely dozens of signals that are influencing feeding behaviour on a day-to-day basis. Tryptophan produced by microbes could just be one aspect of that,” Trevelline added.
The study has established a plausible way that microscopic organisms could alter what we want to eat – however, more studies testing the idea in humans are needed before determining diet.
“Humans have way more going on that we ignored in our experiment. But it’s an interesting idea to think about,” said Kohl.
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