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. One in 16 US women were forced into having sex for the first time Albatrosses strapped with sensors help spy on illegal fishing boats. Together, the pluses of sexual benefits and minuses of the energetic costs of being beefy may even out in the end, explaining why men of all shapes and sizes thrive, Lassek contends. The study also showed that more muscled men tended to lose their virginity at a younger age, compared to skinny men. The beefier the man — measured by total fat-free mass, or arm and leg muscle mass — the more sexual partners he had, Lassek confirmed. 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. 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. How to be superhuman: The science behind extraordinary abilities When will we hear from aliens?