Orthorexia is an eating disorder, coined in 1997 by Steven Bratman, MD, that is defined as an obsession with "healthy or righteous eating." It often begins with someone's simple and genuine desire to live a healthy lifestyle.
An individual dealing with Orthorexia fixates on defining the "right" foods, foods that can be safely eaten.
They will spend just as much time and energy thinking about food as someone with Bulimia or Anorexia. They may not think about calories, but they think about the overall "health benefits" and how the food was processed, prepared, etc. Individuals with Orthorexia tend not to eat out as much because they do not trust the preparation of foods other than what they have prepared.
The obsession for healthy foods could come from a number of sources such as family habits, society trends, economic problems, recent illness, or even just hearing something negative about a food type or group, which then leads them to ultimately eliminate the food or foods from their diet.
Something to keep in mind: The severe restrictive nature of Orthorexia has the potential to morph into Anorexia.