a lot of males are just fine at low body fats that allow their abdominals to show, some are even genetically predisposed to have higher metabolisms and lower body fats. many body builders do dehydrate themselves down before competition, but those guys are in a whole other world, their life is revolved around bulking and leaning and seeing the aesthetic results. Also a lot of folks will eat a lot and highly specialied meals and supplements during the day and "balance" their caloric intake with exercise to see those results. To me its just exercise bullemia, but some people are happy with that lifestyle.
plus, look at sully, he is a fine example of genetics and also training and diet, I don't think he is starving, just very muscular in comparison to fat %.
I think its different for women. Ive known a few girls in my life who were slender enough growing up to have visable ab muscles without excessive exercise or close attention to diet. but most do not have this or have to try extremely hard for this. since a lower body is not typical for women and can put stress on the endocrine system. strong bodies for women is super important though, lifting, squats, all kinds of body weight exercises, sprints, flexibility and just movement in general.
