Mice That Eat Yogurt Have Larger Testicles: Scientific American

More important, that masculinity pays off. In mating experiments, yogurt-eating males inseminated their partners faster and produced more offspring than control mice. Conversely, females that ate the yogurt diets gave birth to larger litters and weaned those pups with greater success. Reflecting on their unpublished results, Erdman and Alm think that the probiotic microbes in the yogurt help to make the animals leaner and healthier, which indirectly improves sexual machismo.