BUENOS AIRES — When healthy eating becomes an obsession, it's known as "orthorexia." It affects almost a third of people in advanced countries, and is certainly no stranger here in Argentina, where we have embraced Western values and have a penchant for neurosis.

There's a difference between people who decide to eat healthier and those who turn healthy eating into a life project. The first lot can go to a backyard barbecue, for example, and take their own vegetables to cook over the fire without getting upset about what others are eating or trying to preach to them. But the orthorexia folks obsessively investigate the source and composition of every food, and spend vast amounts of time planning meals. They regard anything with fat, artificial components or preservatives as poison and impose the strictest diets on themselves, refusing to consume anything that isn't "healthy."

The World Health Organization says orthorexia affects three in 10 people in developed countries, where food tribes are proliferating and where veganism is no longer for hippies or anorexics, but instead a gateway to eating disorders.

"With high obesity figures and the constant media bombardment about healthy foods, we see in most cases how orthorexia begins with picking healthy foods," says Marcela Leal, who teaches nutrition at Maimónides University in Buenos Aires. She says that in some cases, "eating healthy becomes so important it becomes an obsession."

What do these people consider to be poisonous foods? Leal says they won't eat foods that have genetically modified organisms (GMOs), artificial substances or pesticides. "Generally, orthorexic people have the misconception that they can prevent all types of disease with just a healthy diet."

Psychologist Marcelo Bregua describes some of their patterns of conduct. "They have increasingly strict rules and spend a lot of time on thinking how they can implement their self-imposed diet plan. The problem is very few people seek help because they don't see this as sick behavior but quite to the contrary, as healthy conduct."

He says some of the patients who attend his therapy group ALUBA, which tackles eating disorders, have said they have fasted when they could not find suppliers of their organic or non-GMO foods. "For example, we treated a man who stopped eating for three days because his supplier was not open," he says.

That's why orthorexia is sometimes seen as a kind of "hidden anorexia." Bregua says people with these disorders share the same control fixation. "If their will power fails, they might impose on themselves a strict penalty or an even more detailed eating plan," he says. Or as Leal puts it, while bulimia and anorexia focus on food quantities, orthorexia "does the same with food quality."

Nutritionist Mónica Katz describes orthorexic people as those who are obsessed with everything that is clean, pure, natural and organic. "They are uncomfortable with people who don't eat like them and can isolate themselves when anything takes them away from their clean, pure and natural dieting," she says. Pleasure, it goes without saying, isn't a key part of their decision-making.

In fact, Leal adds, isolation is one of the danger signs. Additionally, they eat "in the strangest ways, as they eat alone to avoid criticism."

But what's so wrong with eliminating certain foods deemed to be unhealthy? The problem, says nutritionist and physican Silvio Schraier, is that with this perspective, many more, healthy foods are also eliminated. "Removing meats leads to anemia due to iron and Vitamin B12 deficiency," he says. "Not consuming dairy products creates a calcium shortage and can weaken bones or make them brittle."

Leal says orthorexic people often suffer from "a significant loss of body fat and muscle mass, and attain a very low body fat percentage, less than 18, which is similar to anorexics." Excluding salt and sugar from their diets, she adds, can create tension and heart problems.