Extra winter pounds got you down? Good news. According to two new studies released Thursday, the bacterial makeup of our intestines may be a key factor in determining whether we lose or gain weight. The research, conducted on both humans and mice, suggests that gastric bypass surgery—a now ubiquitous weight-loss operation—is successful in part because it “shifts the balance of bacteria in the digestive tract” by rearranging the intestines. The groundbreaking research suggests at some point treatment may be available to adjust the “microbe levels” in the guts and help people lose weight—without surgery.