Can too much of a good thing actually be harmful?
When it comes to eating healthy foods, the answer may be yes.
We are all encouraged to follow a healthy diet, but some people take it too far, limiting their diets to food that they consider to be pure to the exclusion of everything else. Some of them end up with orthorexia, a severe eating disorder.
Kristie Rutzel, a Richmond, Va., woman in her mid-20s, said she nearly died because of her obsession with healthy food.
"I stayed away from restaurants," she told "Good Morning America." "It took me, maybe two or three hours for me to figure out what my next meal was going to be."
She said she started out at 120 pounds, and dropped 60 pounds because of her rigid diet.
It was so serious that doctors told her parents that she was going to die, and advised them to prepare for her funeral, she said.
Orthorexia is an obsessive-compulsive disorder that creates severe phobias about eating impure, unhealthy food.
Most experts still think orthorexia is part of anorexia nervosa, an eating disorder whose sufferers obsess about the amount of food they eat and their body weight, rather than an independent disorder.
But Rutzel said her fear wasn't about gaining weight. It was about wanting to avoid eating anything that was impure.
There are no hard data on the incidence of orthorexia.
"We do know what we're seeing in the clinic," said Cynthia Bulik, director of the eating disorders program at the University of North Carolina at Chapel Hill. "We are seeing more people really worrying about what's in their food."
But doctors are not sure why people are experiencing these concerns, she said.
"One of the things we think is that there might be an anxiety component to this, so people may feel that this is a way to control their anxiety," Bulik said.
Dr. Marie Savard, an ABC News medical contributor, said people who have orthorexia have a distortion of thinking about what constitutes good health and an unhealthy obsession with eating only healthy foods. That can lead to severe weight loss and emaciation.
Savard said most experts believe orthorexia is a serious eating disorder or obsessive compulsive disorder.
It may seem counter-intuitive, but limiting one's diet to certain foods can be dangerous, she said.
For example, one of the common tendencies is to eliminate meat from a diet. Savard said meats have the full balance of amino acids, which contain the building blocks for muscle and tissues in the body. Those are very hard to come by on a strict vegetable diet, she noted.
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Similarly, eliminating fats can be harmful. The body needs fatty acids to keep the brain and nerves healthy. Those fats come from cold water fish and nuts. Those who cut out fats from their diets won't get those essential nutrients, she said.
Excessive worrying or stress about eating certain foods is a warning sign of orthorexia, Savard said.
Other symptoms include eating the same foods prepared in the same way, increased time spent on food shopping and reading food labels, social isolation, weight loss or emaciation, and withdrawing from friends to eat -- usually at home or away from others.