A surprising new study published in the journal Brain, Behavior and Immunity found that rodents injected with a micro-organism found in cow’s milk and soil didn’t gain weight even when fed a junk food diet. The results suggest that a shot that contains Mycobacterium vaccae (M. vaccae) could be the answer to those struggling with obesity who can’t afford weight loss drugs such as Wegovy.

According to the New York Post, researchers divided mice into groups. One group ate a healthy diet while the other consumed a diet high in fat and sugar for 10 weeks. Half of each group received a weekly injection of M. vaccae, which researcher Christopher Lowry, of the University of Colorado in Boulder, had previously determined could reduce stress-induced inflammation in mice.

The untreated mice who ate junk food weighed 16% more than the healthy eaters and had more visceral fat at the end of the study. That’s the bad fat that accumulates around organs and boosts the risk for heart disease and diabetes, says a University of Colorado news release. Surprisingly, the mice who ate the rodent equivalent of a Big Mac and fries during the study period and received the injection of M. vaccae, also called a “good” bacterium, did not gain any more weight than the healthy eaters. The inoculated mice also had less visceral fat.

The study is the latest to report the benefits of boosting our consumption of healthy forms of bacteria that were cast aside as we moved from farms to more sterile, urban environments.

“This finding suggests that M. vaccae effectively prevents excessive weight gain induced by a Western-style diet,” said Lowry. He speculates that M. vaccae may act directly on the immune system to reduce inflammation, make fat healthier and boost metabolism. The scientist plans to do further studies on whether taking M. Vaccae orally has the same effect in preventing weight gain and promoting health, but in the meantime, he suggests that we spend more time in nature, work in the garden and eat a variety of fresh vegetables that have soaked up the healthy microbes from the soil.