Gut bugs, which play a vital role in the biology of human beings and animals, could also be driving appetite, say researchers in France.
"The gut microbiota (bugs) respond both to nutrients consumed by their hosts and to the state of their hosts as signalled by various hormones," write Vic Norris and colleagues from the University of Rouen, France.
Gut microbes are thought to comprise a community that interacts with the mammalian nervous system, also called the enteric nervous system, to stimulate the gastrointestinal tract, says Norris, the Journal of Bacteriology reports.
This enteric system contains half a billion neurons, compared with 85 billion neurons in the central nervous system, according to a Rouen statement.
It is also becoming clear that gut bugs may be linked with cancer, metabolic syndrome, and thyroid disease. They may even influence mood disorders, through the action on dopamine and peptides involved in appetite.
The gut bacterium, Campilobacter jejuni, has been implicated in the induction of anxiety in mice, adds Norris.