People who have higher levels of a certain metabolite in the gut microbiome are more prone to engage in “hedonic” eating, or eating for pleasure rather than hunger, according to a new study published in the journal PLOS One.
The research is the first in humans to show a link between specific metabolites produced by gut bacteria and overeating behaviors.
The study of 63 healthy people revealed that those with elevated microbiome levels of the metabolite indole — produced when gut bacteria break down the amino acid tryptophan — had stronger function and connectivity in specific areas of the brain’s reward network.
This type of brain activity indicates that a person is more prone eating for pleasure. In fact, the participants with higher levels of indole were more likely to have food addiction, as determined by questionnaires they completed.
Researchers have long known that certain areas of the brain’s reward network tend to drive eating behaviors. In particular, the nucleus accumbens (a brain region which processes reward stimuli such as food) and the amygdala (which helps regulate emotions) are activated when people are hungry or eating. In this study, people with greater levels of the metabolite indole exhibited stronger function and connectivity in these two brain regions.
Greater function and connectivity in these parts of the brain could indicate an overactive reward system that continuously promotes and reinforces overeating. In fact, previous studies have shown this type of reward system overactivity in obese individuals who struggle with food addiction.
For the study, the researchers analyzed functional MRI brain images taken of the healthy participants, and collected and analyzed participant fecal samples in order to determine the presence of particular gut metabolites. The participants also answered questionnaires that measured their propensity for food addiction.
The findings suggest that indole — or our gut bacteria’s ability to produce it — could contribute to food addiction behaviors in humans. The study adds to the growing body of evidence that our gut microbiome has a significant impact on our health, moods and behaviors.
The new study also opens the door to future research which will focus on whether specific interventions, such as changes to diet, can impact brain function and thus affect the desire to overeat or to eat when not hungry.
The senior author of the study is Dr. Emeran Mayer, director of the G. Oppenheimer Center for Neurobiology of Stress and Resilience and co-director of the CURE: Digestive Diseases Research Center at the University of California-Los Angeles (UCLA).