It's no surprise that a lot of Americans watch what they eat. Counting calories, nutrients and fat grams is practically a national pastime.
But what happens when people go over the line, and the pursuit of healthy eating actually becomes unhealthy?
For Johnny Righini, a 26-year-old from California, eating a nutritious lunch is a painstaking ritual.
"Sometimes it takes days to prepare meals, because I have to sprout things, ferment things," he said. "I am constantly thinking about what I am gonna have for my next meal."
Charlotte Andersen, a 29-year-old Minnesota mother of three, says she went through the same thing.
"It really turned into a huge problem, and I think that there are a lot of other people out there that have this issue," she said.
Food took over her life. She compulsively catalogued everything she ate.
"I was obsessed with things like macro-nutrient ratios, numbers, charts," she said.
She realized she had a problem when she started paying more attention to food than to her own children.
What Righini and Andersen are struggling with is a kind of an obsessive compulsive disorder focused on health food called "orthorexia." The term was coined by Dr. Steve Bratman, author of the book "Health Food Junkies."
Bratman spent years in the health food movement, but became one of its critics after he realized he had started to become orthorexic.
"I suffered from a psychological obsession with food," he said. "When I was involved with this, it took up way too much of my life experiences when there were other things I could have been doing."
Orthorexia is different from anorexia, Bratman said.
"Anorexics seem to always think they're fat," he said, but "orthorexics know they're thin, but they want to be pure."
For people like Righini and Andersen, orthorexia is "a disease disguised as a virtue," Bratman said, because society approves of health consciousness. Americans spend millions on diet books hawking things like macrobiotics, the Zone, the Blood-type diet. And dieting is OK, up to a point.
"But when it gets to the point where your health is overtaking your life, I think that's when it gets to be a problem," Andersen said.
Because they pursue purity in the food they eat, orthorexics are disgusted by processed food like macaroni and cheese. And Righini said even something as seemingly innocent as an apple could be toxic, because "if it's not organic, probably what goes into the soil is going go into the food, and then it goes into you."
With toxins lurking everywhere, orthorexics end up avoiding much of what most of us eat.
"I took out tropical fruits, because they were too high in sugar," Andersen said. "I took out root vegetables, because they had too many carbohydrates."
Andersen couldn't eat at restaurants or friends' homes, fearing she would be pressured to eat impure foods.
"I was afraid that if I got anything wrong I was going to get cancer," she said.
And plenty of diet gurus will tell you, Andersen was right to worry.
"You become what you consume. You consume dead food, and death accelerates its presence," diet guru Viktoras Kulvinskas said.
Kulvinskas is a leading advocate of the "raw food" diet.
Raw foodists believe cooking vegetables even a little destroys their nutritional value. And eating meat is even worse, Kulvinskas said, because you eat the animal's fear.