Apparently, hormones are involved

How Women Work Lots of intriguing anecdotal tidbits here, like:

the amygdala of the brain processes emotions like fear and anxiety. In men, the amygdala communicates with organs that take in and process visual information, like the visual cortex. In women, though, it communicates with parts of the brain that regulate hormones and digestion. This may mean that stress responses are more likely to cause physical symptoms in women than in men

Or this:

one study has suggested that toys with unattainable proportions might affect a person’s self-image. But the study didn’t involve Barbie — it involved male subjects and Ken dolls as well as action figures like the Hulk and G.I. Joe. The men in the study reported a more negative self image after playing with hyper-muscular action figures than after playing with Ken

Yep. You can probably say that superhero comics made me hate my body. Although they did fill me with hope of a super-serum, radioactive accident or some other miracle that would enact a magical transformation upon it.

Turns out that science might help in that regard: there’s this magical drug that convinces your muscles that you’ve been exercising.