Adding to a growing understanding of the role the microbiome plays in our metabolism, a new study from Australian and Canadian researchers has discovered how gut bacteria can directly influence blood sugar levels by promoting the synthesis of gut-derived serotonin.

Serotonin is probably best known as the neurotransmitter that influences feelings of happiness and regulates mood, but the molecule actually has incredibly broad effects across the entire body. In fact, over 90 percent of serotonin produced by a human body is located in the gut. Scientists are only just now learning about the roles these intestinal serotonin secretions play in regulating everything from our gastrointestinal movements, to our general metabolism.

As serotonin cannot cross the blood-brain barrier, these intestinal secretions are not thought to directly influence our brain. Instead, gut and blood serotonin levels seem to play a significant role in our overall metabolic profile. In obese subjects for example, circulating serotonin has been detected at higher levels than in normal weight subjects suggesting the molecule can influence weight regulation.

This new research set out to investigate the relationship between the gut microbiome, serotonin synthesis, and blood sugar levels. The hypothesis was that gut bacteria may be a factor in regulating intestinal serotonin production, and subsequently glucose metabolism.

Using both genetic and pharmacological animal models the research discovered gut microbiome perturbations did indeed result in disruptions to intestinal serotonin synthesis, and these factors could be correlated with improvements in glucose handling. So essentially, the higher the gut and blood serotonin levels, the worse a body's glucose handling.

“We found that the microbiome worsens our metabolism by signaling to cells in the gut that produce serotonin,” says Damien Keating, from Australia’s Flinders University, and corresponding author on the new study. “They drive up serotonin levels, which we previously showed to be increased in obese humans, and this rise in blood serotonin causes significant metabolic problems.”

The study perhaps raises as many questions as it answers, paving the way for a great deal more research. Keating is very clear in where the next stage of the research project is going: exploring exactly how this microbiome-induced mechanism is taking place.

“This is an exciting revelation that can one day have direct implications for human health disorders such as diabetes, but much more research like this is required in the years to come,” says Keating. “The next step will be to understand exactly which bacteria do this, and how, in the hope that this could lead to new approaches to regulating blood sugar levels in humans.”

The new research was published in the journal PNAS.

Source: Flinders University via Eurekalert