Scientists at the Massachusetts Institute of Technology were using mice to study how eating yogurt affects weight gain when they noticed something strange. Not only were yogurt-fed rodents noticeably slimmer than their peers, but the males exhibited a distinct sexual "swagger," complete with shinier fur and more pronounced... features. Here, a brief guide to the unexpected development:
What was the original point of the study?
MIT researchers wanted to examine how the healthy microbial bacteria in yogurt fight off age-related weight gain. Mice were divided into three groups and given three different diets: One group was fed a normal diet, another was given a high-fat diet of mostly junk food, and a final group was fed mouse-sized servings of vanilla yogurt.
And what was it that surprised researchers?
"We knew there was something different in the males, but we weren't sure what it was at first," study co-researcher Susan Erdman tells ABC News. "You know when someone's at the top of their game, and they carry themselves differently? Well, imagine that in a mouse."
Why did the male mice behave that way?
One eagle-eyed lab assistant noticed what was giving the males a surplus of machismo. Their testicles were far bigger than those of their peers–5 percent larger than mice who ate a normal diet, and 15 percent bigger than mice who were fed junk food. "The changes were not just superficial," says Shawn Radcliffe at Men's Fitness. "Yogurt-eating mice inseminated their partners faster and produced more offspring." The yogurt-eating male mice were also notably slimmer, with softer and shinier coats, too.
What happened to the female mice?
Females also reaped the mysterious rewards of yogurt. They had healthier fur, and were able to produce bigger litters of offspring.
What caused these changes?
"It's the probiotics in the yogurt," says study co-researcher Eric Alm. "We think the organisms are somehow directly interacting with the mice to produce these effects." At this point its unclear if the same dramatic effects can be achieved in humans, but stocking more probiotic-filled foods in the fridge couldn't hurt. Says Erdman: "When I saw those fur coats, I thought about adding more yogurt to my diet."