Can gut bacteria influence one’s sense of fair play?

Health in a Heartbeat

The microscopic hitchhikers in our gut might be doing more than catching a ride. They could, on occasion, be driving the car.

Each of us hosts trillions of microbes in our gut. They’re essential for a healthy life, helping us digest food and maintain immunity. But do they have more than a physical impact on our bodies?

Do they also influence our notion of fair play?

That might seem like a stretch. But not to European researchers who investigated whether the bacteria, fungi and other residents of our gut could change social behavior.

They separated 101 participants into two groups. Half played the Ultimatum Game before and after taking probiotics and nutrients for several weeks that promote healthy gut bacteria. The others took a placebo.

The Ultimatum Game is a contest in which one player decides how to split a sum of cash with a second player. The second player can reject or accept the offer. So, one person given $10 might decide to give the second player $2.

Each gets the proposed cash split if the offer is accepted. If it’s rejected, neither gets a penny.

The study found participants taking the probiotic were much more likely to reject an offer than they were before taking the supplement. Not so for the placebo group.

Tests confirmed that the probiotic players had a different ratio of two key bacteria in their gut compared with the control group. Researchers think the altered gut influenced players’ brains, making them more likely to reject a sure cash payment to punish a cheapskate.

The work is a reminder of the complex internal chemistry that affects the mind and body — perhaps with a little help from our friends.