First off, for all you semantics sticklers, the answer to the question in the title is, strictly speaking, no. (If it were bad for your health it wouldn't be healthy, right? And let's not get started on the healthy/healthful distinction.) However, contrary to the popular saying, you can be too thin. And if an obsession with eating "pure" and ostensibly healthy foods means you aren't eating enough, or are eating an unbalanced diet, it can be dangerously unhealthy.
According to a recent article in The Guardian, an eating disorder called orthorexia nervosa, which can lead to malnourishment and, in rare cases, starvation, is on the rise, particularly among "middle-class, well-educated people who read about food scares in the papers." In contrast to anorexia nervosa, which is an obsession with being thin, usually characterized by controlling caloric intake, orthorexics are so concerned with what they believe to be the optimum healthy diet that they unreasonably restrict what they eat.
"Orthorexics commonly have rigid rules around eating," the article explains. "Refusing to touch sugar, salt, caffeine, alcohol, wheat, gluten, yeast, soya, corn and dairy foods is just the start of their diet restrictions. Any foods that have come into contact with pesticides, herbicides or contain artificial additives are also out."
The disorder was named in 1997 by a California doctor, Steven Bratman, who wrote a book called Health Food Junkies. As Bratman explains on his Web site, he was once an "evangelical" advocate of healing through food. But he became disillusioned while serving as head chef on a commune by the abundance of competing dietary theories—vegan, raw, macrobiotic, Ayurvedic, etc.—with each adherent convinced that his or her way was the only path to ultimate health.
"Orthorexia begins, innocently enough, as a desire to overcome chronic illness or to improve general health," he writes. "But because it requires considerable willpower to adopt a diet that differs radically from the food habits of childhood and the surrounding culture, few accomplish the change gracefully. Most must resort to an iron self-discipline bolstered by a hefty dose of superiority over those who eat junk food. Over time, what to eat, how much, and the consequences of dietary indiscretion come to occupy a greater and greater proportion of the orthorexic's day."
As I write this I am digging into a pint of Ben & Jerry's S'mores ice cream, so I'm pretty sure I am not afflicted by orthorexia. As a migraine sufferer, though, I can understand the lure of seeking a cure through dietary restrictions. You hear an acquaintance (or read a writer in a magazine) talk about how great they feel after an extended juice fast, or following an "alkaline" diet, and are tempted to try it yourself.
Even if orthorexia is becoming a more common mental health diagnosis, it's probably fair to say that far more people in this country fall at the other end of the spectrum—they could stand to obsess just a little bit about the healthfulness of what they eat.