Girls grow up mostly having concerns about being too large. Although testosterone does decrease in males with eating disorders, especially anorexia, there is no clear marker of hormonal dysfunction like there is with females. Women with anorexia or excessive exercise problems develop amenorrhea or loss of menses. In the gay male community it appears that body image is often more important for being attractive than it is in the lesbian community. Boys with eating problems seem to have more gender conflicts.
Male anorexics seem to have anxieties about masculinity and athletic performance.
Boys seem to have more of a history of being overweight than girls. Underscore with your son the negative social pressures that the media places on males to be buff and sculpted. Help you child understand that acceptance of natural body shape is important, even if it means having a culturally disapproved weight or shape. Point out to your son that Luke, Hans, GI Joe and many of the most popular action figures have grown significantly more muscular over time. Your son will benefit from knowing that he has been exposed to unrealistic cultural expectations to acquire the physique and musculature of superhumans.