New study says keeping fit really about gut instinct

By Stephen Beech via SWNS

Keeping fit really is a gut instinct, according to a new study.

Researchers found that certain microbes in the gut can boost the motivation to exercise.

The American team explained that some species of gut-dwelling bacteria activate nerves to promote the desire to get physically active.

The study in mice, led by researchers at the Perelman School of Medicine at the University of Pennsylvania, revealed the gut-to-brain pathway that explains why some bacteria boost exercise performance.

The team found that differences in running performance within a large group of lab mice were largely attributable to the presence of certain gut bacterial species in the higher-performing animals.

The researchers traced the effect to small molecules called metabolites that the bacteria produce - metabolites that stimulate sensory nerves in the gut to enhance activity in a motivation-controlling brain region during exercise.

Study senior author Dr. Christoph Thaiss, of Penn Medicine, said: “If we can confirm the presence of a similar pathway in humans, it could offer an effective way to boost people’s levels of exercise to improve public health generally."

The team set up the study to search broadly for factors that determine exercise performance.

They recorded the genome sequences, gut bacterial species, bloodstream metabolites, and other data for genetically diverse mice.

Researchers then measured the amount of daily voluntary wheel running the animals did, as well as their endurance.

They analyzed the data using machine learning, seeking attributes of the mice that could best explain the animals’ sizable differences in running performance.

The researchers were surprised to find that genetics seemed to account for only a small portion of the performance differences -whereas differences in gut bacterial populations appeared to be "substantially" more important.

They observed that giving mice broad-spectrum antibiotics to get rid of their gut bacteria reduced the mice’s running performance by about half.

The researchers eventually found that two bacterial species closely tied to better performance, Eubacterium rectale and Coprococcus eutactus, produce metabolites known as fatty acid amides (FAAs).

The latter stimulate receptors called CB1 endocannabinoid receptors on gut-embedded sensory nerves, which connect to the brain via the spine.

The stimulation of the CB1 receptor-studded nerves causes an increase in levels of the neurotransmitter dopamine during exercise, in a brain region called the ventral striatum.

The researchers explained that the striatum is a "critical node" in the brain’s reward and motivation network.

The team concluded that the extra dopamine in this region during exercise boosts performance by reinforcing the desire to exercise.

Study co-authorProfessor Nicholas Betley said: “This gut-to-brain motivation pathway might have evolved to connect nutrient availability and the state of the gut bacterial population to the readiness to engage in prolonged physical activity.

“This line of research could develop into a whole new branch of exercise physiology.”

The team say their findings, published in the journal Nature, open up many new avenues of scientific investigation.

They are planning further studies to confirm the existence of the gut-to-brain pathway in humans.

The researchers believe exploration of the pathway might also yield easier ways to modify motivation and mood in areas such as addiction and depression.