But there are some people dedicated to a controversial concept called "clean eating" that will stand by this disputed practice. This concept, which still remains valid among a small group of dietary fanatics, means being extremely picky in the foods they eat. In other words, they have an excessive liking for only a few types of healthy foods (especially vegetables) to the exclusion of others (especially meat).

"Clean eaters" eat only whole foods in their most natural state. They avoid processed foods such as refined sugar in the earnest hope this healthy choice will improve their health.

A praiseworthy goal in itself, no doubt. But what has given clean eating a less than savory reputation is the insistence of some to take this goal to its obvious extreme. That is, taking the idea of clean eating so far as to make it an eating disorder much the same way anorexia nervosa is an eating disorder. Anorexia nervosa is a well-known eating disorder that causes people to starve themselves to become thin.

For clean eaters, the excessive obsession with clean eating has brought forth a new medical term -- "orthorexia nervosa."

Also known as orthorexia, this proposed eating disorder is marked by an excessive preoccupation with eating healthy food. Dr. Steven Bratman introduced this term in 1997. Orthorexia nervosa, however, is not recognized as an eating disorder by the American Psychiatric Association (APA).

Dr. Bratman suggested that some people's dietary restrictions intended to promote health might lead to unhealthy consequences. Among these consequences are anxiety, social isolation, loss of the ability to eat in a natural, intuitive manner and reduced interest in the full range of other healthy human activities. He noted that in rare cases, orthorexia might lead to severe malnutrition or even death.

Dr. Bratman said many of his patients forsook traditional medicine and believed the key to good health was simply eating the "right" foods. Some of them asked him what foods not to eat.

"People would think they should cut out all dairy and they should cut out all lentils, all wheat ... And it dawned on me gradually that many of these patients, their primary problem was that they were ... far too strict with themselves," he said.

Bratman created the term orthorexia for this new condition. It consisted of the Greek word "ortho" meaning "right" and -orexia meaning "appetite." He added nervosa as a reference to anorexia nervosa.

"From then on, whenever a patient would ask me what food to cut out, I would say, 'We need to work on your orthorexia.' This would often make them laugh and let them loosen up, and sometimes it helped people move from extremism to moderation," he recalled.

Dr. Bratman confessed he had no idea the concept of clean eating would gain the traction it did over the next two decades. But clean eating is still with us and so are its health dangers.

And for hardcore clean eaters, eating only certain foods and avoiding others is a virtue -- and almost a religion.

Sondra Kronberg, founder and executive director of the Eating Disorder Treatment Collaborative outside New York City, and other nutritionists applaud efforts to eat healthily. The problem begins, however, when a person becomes so focused on his diet "it begins to infringe on the quality of your life -- your ability to be spontaneous and engage."

That's when you should start to worry about an eating disorder, she said.

"In the case of orthorexia, it centers around eating 'cleanly' and purely, where the other eating disorders center around size and weight and a drive for thinness."