There are millions of people who have issues with healthy body image and struggle with eating/food on a daily basis.  However some of these people never get help because they don't necessarily fit into any one category of an eating disorder.  Though anorexia and bulimia are most talked about, there are millions of women and men who do not fit the classical defenitions of an eating disorder.  In some places, such as sororities, as much as 80 percent of women may have some form of distorted eating. 
Distored eating patterns do not always turn into full-blown eating disorders, but they can still cause major distress, disrupt people's lives, and lead to psychological issues.  Perhaps most dangerous, the symptoms can go unchecked for years because the symptoms may never reach a level of severity that triggers professional or family attention. 

Are you talking about like extreme dieting..?  Some of my friends are obsessed with dieting because they feel like they could lose 5-10 pounds, but starving yourself and cutting out whole food groups is actually really bad for your health.