There are tens of trillions of microbes in our guts, which are important for our digestion and our health. The antibiotics that we take to kill off disease-causing bacteria also indiscriminately nuke these beneficial bugs. Now, a new set of experiments in mice have shown that low, regular doses of antibiotics at an early age can disrupt these microbe communities, leading to weight gain later in life. The increase in body weight was small, but compounded by a high-fat diet. If the results apply to humans, they would add to the large body of evidence suggesting that antibiotics should be used more carefully in infants and children.

“I’m not saying people should never take antibiotics,” says Martin Blaser from