Does our intestinal microbiota make us food-dependent?
Could intestinal bacteria have an impact on the risk of food addiction and obesity? To find this out, the gut-brain communication pathway was investigated by an American team, who established a relationship for the first time.
Fighting an irresistible desire to tickle the taste buds sometimes proves very difficult. In some people, the impulse is such that we speak of a true ‘addiction’. By analyzing the fecal matter of 63 volunteers in good health, their BMI, and brain imaging, scientists have brought to light a link between food-related behavior and substances produced in the intestines (metabolites), which are thought to act on key areas of the brain.
From the intestines to neurons
The substances in question are produced during the degradation of tryptophan, an amino-acid provided by certain foods (meat, peanuts, chocolate, bananas…). In degrading, a small proportion of the tryptophan is transported to the brain and is transformed into serotonin and other substances. Serotonin is a neurotransmitter known to specifically regulate mood and behavior. Most tryptophan degradation is completed within fecal matter after having been converted by intestinal bacteria into indole, a metabolite which is thought to be involved in the gut-brain axis. To obtain accurate results, the researchers combined their initial results with questionnaires evaluating the anxiety of the participants and their relationship to food.
A more “active” brain
Result: the presence in the stools of indole-derived metabolites is indeed thought to be associated with changes in the brain of volunteers, who displayed a larger number of connections to the “reward pathway” composed by several brain areas involved in the sensation of pleasure, motivation… but also dependence. A link between these substances and a tendency to food addiction was also observed. For the moment, these results do not allow a causal relationship to be established. But the researchers put forward an avenue for research: these changes could have an impact on appetite–mediated by intestinal hormones–or on the taste of food. However, this needs to be confirmed by larger scale studies.
* BMI = body mass index
Osadchiy V, Labus JS et al., Correlation of tryptophan metabolites with connectivity of extended central reward network in healthy subjects, PLoS One, 6 août 2018