TORONTO -- While we should all strive for a balanced diet, York University researchers say the extreme pursuit of healthy eating can be a sign of mental-health struggles.

Jennifer Mills, an associate professor in York's psychology department, co-wrote a recent paper on orthorexia nervosa, which she describes as an unhealthy obsession with healthy eating, published in the journal Appetite.

In reviewing academic literature on the subject, the authors found that people with a history of eating disorders, obsessive-compulsive tendencies, perfectionism and other psychological and behavioural tendencies were at higher risk of developing orthorexia.

"There is nothing wrong with healthy eating. Healthy eating is something we should all aspire to," Mills said in an interview. "But (we need) to be aware that mental-health difficulties can manifest through food."

Orthorexia has not been recognized in the standard manual psychiatrists use to diagnose mental disorders, and the York study found research on the subject is limited.

But as so-called clean diets have picked up steam, Mills said there's been growing interest in medical and research circles about the social and psychological side-effects of a "pathological" preoccupation with healthy eating.

While there's overlap between the risk factors for orthorexia and certain eating disorders -- such as poor body image, a drive for thinness and dieting -- Mills said the conditions differ in key ways, particularly their motivations.

People with a restrictive eating disorder like anorexia will typically reduce their food intake in order to reach a low body weight or change their appearance. But for those with orthorexia, Mills said the focus on food is about quality rather than quantity.

Many people with orthorexia are proud of their bodies, she said, but are decidedly picky about what they put in them.

This often involves eliminating certain types of food from their diets, such as sugar, saturated fat, gluten, animal products, artificial flavours and preservatives.

For some, she said, the list of forbidden foods can grow so long that their diet may be lacking in essential nutrients, which in severe cases can lead to health hazards such as anaemia, vitamin deficiencies or excessive weight loss.

But Mills said one of the reasons orthorexia tends to go overlooked, including by medical professionals, is that many people with the condition are physically healthy, even though they may be suffering psychologically.

"When people go to their doctors and say, 'I eat really healthy,' the most typical response they'll get is, 'That's great... Keep doing what you're doing,"' said Mills.

"But they may be struggling more privately with just this sense that they're starting to lose control, that this is actually taking away from their life."

For individuals with orthorexia, eating foods that conflict with their diets is likely to cause extreme guilt or anxiety, said Mills. This distress is usually bound up in perceived risks of disease or physical impairment. But in treating their bodies as temples of health, some may lose sight of their mental welfare, she said.

They may spend a lot of time and money planning and preparing meals, and can find it difficult to eat food made by others, Mills said.

Some strict dieters find these sacrifices are worth it given the health benefits, Mills acknowledged. But people with orthorexia may feel their fixation on food is so all-consuming that it interferes with their work, family and social activities, she said.

"When we're extremely stressed or overwhelmed, we look for ways of coping. And for some people, having very, very tight control over their eating is a way for them to feel like they're in control, but then the irony is that they're not," she said.

"Being healthy mentally means having flexibility, and having time and mental space freed up for other kinds of things, and not having your world revolve around food."

Mills said one of her research team's most surprising findings was that orthorexia occurs in relatively equal rates between men and women. This suggests the condition may be less like an eating disorder, which disproportionately affect women and girls, and more like anxiety or obsessive-compulsive disorder, which are similarly prevalent across genders, she said.

She said diagnosing orthorexia can be slippery, because it isn't defined by specific eating habits, but rather, a pattern of problematic thoughts and behaviours that detract from a person's quality of life.

Mills hopes the study increases awareness about orthorexia, a condition she believes is on the rise, fuelled by a culture that prizes healthy eating and wellness among its ultimate virtues.

"It's all around us: messages about how we should be doing better; we should be eating better; we should be constantly striving to improve ourselves," she said.

"I think it has a way of encouraging black-and-white thinking about food ... and (that) can make people feel worse about themselves."