Orthorexia — an unhealthy fixation on eating only healthy or "pure" foods — was originally defined as a disordered eating behavior in the '90s, but experts believe it has been gaining steam in recent years, fed by the profusion of foods marketed as healthy and organic, and by the media's often conflicting dietary advice. Like anorexia nervosa, orthorexia is a disorder rooted in food restriction. Unlike anorexia, for orthorexics, the quality instead of the quantity of food is severely restricted.

"Orthorexia starts out with a true intention of wanting to be healthier, but it's taken to an extreme," says former Academy of Nutrition and Dietetics Spokesperson Marjorie Nolan, MS, RDN, CDN, ACSM-HFS, who specializes in working with eating disorder clients. "If someone is orthorexic, they typically avoid anything processed, like white flour or sugar. A food is virtually untouchable unless it's certified organic or a whole food. Even something like whole-grain bread — which is a very healthy, high-fiber food — is off limits because it's been processed in some way."

Orthorexics typically don't fear being fat in the way that an anorexic would, but the obsessive and progressive nature of the disorder is similar. Orthorexics may eliminate entire groups of food — such as dairy or grains — from their diets, later eliminating another group of food, and another, all in the quest for a "perfect" clean, healthy diet. In severe cases, orthorexia eventually leads to malnourishment when critical nutrients are eliminated from the diet.