Well, who knew that there was a polite term that refers to people who eat so much of small number of things that end up suffering from malnutrition? From Wikipedia
Orthorexia, or orthorexia nervosa is a term coined by Dr. Steven Bratman, a Colorado MD, to denote an eating disorder characterized by a fixation on eating what the sufferer considers to be healthful food, which can ultimately lead to early death.
Bratman coined the term in 1997 from the Greek orthos, "correct or right", and orexis for "appetite". Literally "correct appetite", the word is modeled on anorexia, "without appetite". Bratman describes orthorexia as an unhealthy obsession (as in obsessive-compulsive disorder) with what the sufferer considers to be healthy eating. The subject may avoid certain foods, such as those containing fats, preservatives, or animal products, and suffer malnutrition. Dr. Bratman asserts that "emaciation is common among followers of health food diets."
Suffer the orthorexics, for they must not inherit our mirth. Qualms v. 1
Thanks to Gary Allen for leading us to this refreshing intermezzo of contemporary psycho-speak.