Gut bacteria may be affecting both our cravings and moods to get us to eat what they want, and often drive us towards obesity, a new study suggests.
US researchers concluded from a review of scientific literature that microbes influence human eating behaviour and dietary choices to favour consumption of the particular nutrients they grow best on, rather than simply passively living off whatever nutrients we choose to send their way.
Bacterial species vary in the nutrients they need. Some prefer fat, and others sugar, for instance.
But they not only vie with each other for food and to retain a niche within their ecosystem - our digestive tracts - they also often have different aims than we do when it comes to our own actions, according to senior author Athena Aktipis.
While it is unclear exactly how this occurs, researchers believe this diverse community of microbes, collectively known as the gut microbiome, may influence our decisions by releasing signalling molecules into our gut.
Because the gut is linked to the immune system, the endocrine system and the nervous system, those signals could influence our physiologic and behavioural responses.
"Bacteria within the gut are manipulative," said Carlo Maley, director of the University of California - San Francisco (UCSF) Center for Evolution and Cancer.
"There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals, and others not," said Maley, corresponding author on the paper.
We can influence the compatibility of these microscopic, single-celled house-guests by deliberating altering what we ingest, Maley said, with measurable changes in the microbiome within 24 hours of diet change.
"Our diets have a huge impact on microbial populations in the gut. It's a whole ecosystem, and it's evolving on the time scale of minutes," Maley said.
Research suggests that gut bacteria may be affecting our eating decisions in part by acting through the vagus nerve, which connects 100 million nerve cells from the digestive tract to the base of the brain.
"Microbes have the capacity to manipulate behaviour and mood through altering the neural signals in the vagus nerve, changing taste receptors, producing toxins to make us feel bad, and releasing chemical rewards to make us feel good," said Aktipis, co-founder of the Center for Evolution and Cancer with the Helen Diller Family Comprehensive Cancer Center at UCSF.
The research was published in the journal BioEssays.
