When Jill Miller reflects on her long, painful dance with veganism, anorexia, and bulimia, she remembers standing alone in her kitchen, binge-eating a tofu-cream pie.

These episodes of stuffing herself with whipped soy—when what she really wanted was a pint of Ben & Jerry’s—stand out in her mind as a sign that her commitment to veganism was a cover for something darker. As do the many times that she turned down food with the seemingly innocent, even noble excuse that no one could argue with: Oh, sorry. I can’t eat that—I’m vegan.

“No prime rib and Yorkshire pudding at New Year’s with Grandpa,” says Miller. “This happened at every family event.”

The shame, discomfort, and self-loathing represented by her eating habits defined much of her early life. When she was just 13, Miller became a vegetarian, in part for philosophical reasons, but mainly as an excuse to avoid her mom’s New Orleans-style chicken-fried steak and jambalaya. As she forged a career in yoga instruction, she further restricted her diet by going vegan, all the while struggling with an eating disorder that she kept under wraps.

“I seized on the food theory of veganism to justify my desire to restrict,” she told The Daily Beast. “It was a convenient way to eliminate fat and calories.”

A breakthrough came shortly after she turned 30. She realized that the only way to fight her illness—and be happy—was to stop saying “no” to so many foods, and begin saying “yes.” She’s now an omnivorous yoga guru, starring in dozens of instructional DVDs, and she’s never felt better.

As veganism moves from the fringes to the mainstream of American culture, with A-listers like Natalie Portman and Jonathan Safran Foer loudly endorsing it, more Americans are giving it a whirl. Five percent of people in this country identify as vegan, according to a 2002 Time/CNN poll. And for most, becoming vegan can mark a healthy shift toward wholesome eating and concern for the welfare of animals. But for those at risk of developing an eating disorder, it can mask or trigger an illness, providing a socially conscious excuse not to partake in family barbeques or dinners out with friends.

According to Dr. Angela Guarda, director of the Johns Hopkins Eating Disorders Program, many vegans (and vegetarians) who enter her treatment center initially deny an underlying problem—only to later confess that their efforts to avoid animal products were really an effort to avoid food in general. “In most of our patients, the vegetarianism is in the service of the eating disorder,” she said.

For this reason, Guarda and her staff try to dissuade patients from observing any form of vegetarianism while undergoing treatment, encouraging them to broaden their food repertoire to include some meat. Other eating disorder and nutrition specialists report similar approaches.

Dr. Marcia Herrin, founder of the Dartmouth College Eating Disorders Prevention, Education and Treatment Program and now a dietician in private practice, takes a stricter (if potentially problematic) approach: Herrin tells parents not to let their kids be vegetarian until they go to college, echoing that the diet can create a “ruse” that loved ones can’t see through. “Most families don’t have the time to prepare vegetarian entrées,” she said. “What’s at risk is the child’s growth and development, and potentially an eating disorder.”

Herrin may be onto something: A 2009 study in the Journal of the American Dietetic Association revealed that young adults ages 15 to 23 who reported being vegetarian were, at some point, more likely to have also engaged in unhealthy weight-loss behaviors like bingeing, purging, and using diet pills or laxatives. And surveys show that the prevalence of vegetarianism among eating-disorder patients is higher than in the general population.

It’s important to note that for most of the country’s roughly 3 million vegans, who don’t consume or wear any animal products, their eating habits never veer into mental illness. Many consider veganism a lifestyle, says Annie Hartnett, an animal-rights activist and blogger for Change.org, or a protest against cruel farming practices. And studies have found that the physical benefits of veganism, when observed in a healthy way, are extraordinary, including lowered risk of chronic disease, improved heart health, and increased energy.

Problems arise when individuals approach veganism primarily as a vehicle for weight loss, and indeed, more than ever, it’s being marketed by certain proponents as an extreme diet. Last month, actress Jessica Simpson tweeted that she’s going vegan, along with drinking a popular weight-loss tea. While she later claimed the veganism isn’t to shed pounds, tabloids have since treated it as if it were the next Atkins Diet. Then there’s the bestselling Skinny Bitch series, a vegan manifesto in diet-book packaging. Even PETA is guilty: This past May, the organization proposed placing an ad on the Great Wall of China, depicting an overweight American tourist, with the caption: “It’s the Wall That We Should See From Space, Not You. Go Vegan.”

At the most toxic end of the eating-disorder spectrum, “ Pro-ana” websites pitch veganism as a trick of the trade, so to speak—as both a weight-loss plan and a front so no one will notice you’re anorexic. When Georgia Hollenbeck, 24, was in her early teens and spiraling into anorexia and bulimia, the veterinary worker decided to give veganism a try after reading about it on one of these sites. “I’m from Michigan, so we eat a lot of meat here,” she said. As such, becoming vegan allowed her to say “no, thanks” to meals much of the time, and allowed her eating disorders to flourish in secret.

Of course, some embark on vegan diets for all the seemingly right reasons, only to find themselves on a slippery slope to disordered eating. As with alcohol or cigarettes, exposure combined with biological predisposition can lead to abuse. “Going on any kind of diet where you’re paying a lot of attention to what you eat or don’t eat puts you at risk for an eating disorder,” says Herrin. “Especially when you label certain foods as ‘bad.’”

Recently, reports of “orthorexia” have captured headlines. Those who suffer from the controversial new disorder compulsively avoid foods thought to be unhealthy or unnatural, including products with trans fats, artificial colors, or flavors, high-fructose corn syrup, and preservatives. Often, orthorexics opt for a strict vegan diet. Some say orthorexia represents this dangerous slide from health to pathology.

To ensure both physical and psychological health, emerging vegans should educate themselves on how to maintain balanced nutrition and weight, says Keri Gans, a spokesman for the American Dietetic Association and a practicing dietician in Manhattan. Replacing meat and dairy with plant-based sources of protein and fat is crucial, as is taking certain vitamin supplements. If they’re not vigilant, vegans can become lethargic and malnourished; they’re particularly at risk for Vitamin B-12 deficiency, which can lead to deterioration of the spinal cord.

“A person who undertakes veganism as a lifestyle, not related to any kind of eating disorder, will know that they have to replace the foods they’ve eliminated with new foods,” says Gans. “If they’re saying to me, ‘Let’s talk about ways to add more foods into my diet, I’m not afraid of healthy fats,’ I’ll say to myself, ‘OK, this person gets it.’” If not, the veganism may be a red flag.

Perhaps counterintuitively, some who are in recovery from an eating disorder say adopting a vegan diet helped to nurse them back to health. After struggling with anorexia and drug use in her 20s, Mandi Babkes embarked on an all-raw, vegan diet. She now runs a holistic health practice and raw-food vegan catering business in Pittsburgh, explaining that while her eating disorders were about self-destruction, her veganism is about self-love. "Being a vegan and raw foodist really helped me to feel better, to feel cleaner, to feel more energized,” she said. “I sleep better, and I have a brighter outlook.”

Still, many dieticians and eating-disorder specialists hesitate to recommend a vegan diet as a path to recovery. “It’s like an alcoholic who likes to spend time in bars,” says Herrin. “It’s very risky to take on any system of eating that’s restrictive and passes judgment on food that’s not founded on health principles.”

Perhaps above all, clinicians and vegan advocates alike emphasize one underlying message: At its most basic level, veganism is about practicing non-violence toward animals. And in keeping with this philosophy, its followers should look out for their own well-being, too.

Danielle Friedman has worked as a nonfiction book editor for Hudson Street Press and Plume, two imprints of Penguin Group. Her writing has been published in the Miami Herald, and on DoubleX and CNN.com. She is a graduate of the Columbia University Graduate School of Journalism.