A new study in the Journal of Bacteriology suggests that bacteria in the human gastrointestinal tract may have some control over our appetites.
This hypothesis, proposed by Vic Norris of the University of Rouen, France, is based in large part on observations of the number of roles bacteria are already known to play in host biology. "Bacteria both recognize and synthesize neuroendocrine hormones," Norris explained. "This has led to the hypothesis that microbes within the gut comprise a community that forms a microbial organ interfacing with the mammalian nervous system that innervates the gastrointestinal tract."
Norris says the gut microbiota respond both to the nutrients consumed by their hosts and to the state of their hosts as signaled by various hormones. "That communication presumably goes both ways," suggests Norris. "They also generate compounds that are used for signaling within the human system, including neurotransmitters such as GABA, amino acids such as tyrosine and tryptophan - which can be converted into the mood-determining molecules, dopamine and serotonin."
The new work builds on other studies that have linked gut bacteria to diseases such as cancer and metabolic syndrome, as well as mood disorders. The gut bacterium, Campilobacter jejuni, has been implicated in the induction of anxiety in mice, according to Norris.
But do our gut flora influence our choice of food? Norris proposes a variety of experiments that could help answer this question, including epidemiological studies, and "experiments correlating the presence of particular bacterial metabolites with images of the activity of regions of the brain associated with appetite and pleasure."
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Source: American Society for Microbiology