Skinny men have new reason to celebrate. Well, kind of. Beefcakes may be able to attract women by rippling their muscles, but the downside of all that brawn is a poor immune system and an increased appetite, a new study finds.

Such evolutionary costs could explain why males of our species do not all look like He-Man, according to William Lassek, an evolutionary psychologist at the University of Pittsburgh, Pennsylvania, who led the new study. "In some respects I was surprised at how big the costs were… something I hadn't anticipated," he says.

Many other studies have shown that women tend to prefer more toned men, and muscle-bound men tend to have more sexual partners than slender men, when other factors are controlled for.

Previous research has also suggested that musculature comes with a cost. Testosterone, a hormone that promotes secondary muscle growth, suppresses the immune system of all animals, including people.