A study from the Journal of the American Dietetic Association hit the press in April of 2009 with a rather provocative association - young adult and adolescent vegetarians have an increased risk of eating disorders.
Let's examine the data for a moment. 2516 participants from Minnesota schools (in 1999 and 2004) aged 15-18 and 19-23 answered questionnaires regarding food, exercise, weight, binge eating behaviors, dieting behaviors, demographics, and substance abuse. A huge cohort was originally recruited in ethnically diverse high schools, but many of them (around 50-60%, depending on the cohort) were lost to follow up. The "EAT-II" sample (of 2516 participants) who answered both surveys were more likely to be female and were less ethnically diverse than the overall study sample, which is important to know, as the EAT-II folks were used for the article I'm reviewing here.
Of the 2516 folks, about 15% labeled themselves as current or former vegetarians, but very few were vegan, as 95% of them consumed milk products, 87% consumed eggs, 46% consumed fish, and 25% consumed chicken. Most were vegetarian because they wanted a more healthful diet, and a slightly lesser percentage didn't want to kill animals, didn't like meat, wanted to help the environment, to lose or maintain weight, or were vegetarian for family or religious reasons. In the older cohort, vegetarians were thinner (not true of the younger ones), and all of the vegetarians tended to eat more fruits and vegetables and ate less fat than non-vegetarians. Overall exercise patterns were about the same between vegetarians and non-vegetarians, and younger vegetarians were less likely to drink or smoke cigarettes, but more likely to use "non-marijuana" drugs than non-vegetarians.
Here's where it gets interesting - vegetarians were more likely to engage in "extreme unhealthful weight control behaviors" (p<0.005) and "binge eating with loss of control" than the nonvegetarians (p<0.001). The extreme weight control behaviors included use of vomiting, diet pills, laxatives, and diuretics, and approximately 1 in 4 current adolescent and young adult vegetarians admitted to using one or more of those methods to lose weight. Only 1 in 10 of never-vegetarians admitted the same.
So what comes first - the decreased consumption of chicken or the semi-avoidance of eggs? Well, this article (or the abstract anyway - the original article is in Hebrew!) suggests that vegetarianism precedes eating disorders, though if one talks to patients with eating disorders, many will explain that they told people they were vegetarians so they could avoid eating in social situations.
The authors of the 2009 study, in an editorial in the same issue, expressed their belief that vegetarianism did not cause eating disorders, but could be used as a marker by concerned parents and health care practitioners to be more suspicious of an eating disorder in a young adult or teenager who is vegetarian. Lierre Keith (not surprisingly) has a different view in her book, The Vegetarian Myth: Food, Justice, and Sustainability (p230-4) Nutrition therapists at eating disorder clinics in in Indiana, Boston, and Los Angeles reported that between 30-50% of their patients were vegetarian. Julia Ross, a nutrition writer, thought the reason might be due to lower amounts of tryptophan in a vegetarian diet (1). Recall that tryptophan is the precursor to serotonin, so that without enough of it, we are vulnerable to anger, anxiety, depression, and addictive behaviors. Zinc is a mineral tough to come by in a vegetarian diet (it is found mostly in egg yolks and red meat), and zinc deficiency is known to cause depression, obsessive and compulsive behavior, and eating disordered behavior. Supplementation with zinc is a known and extremely helpful treatment for anorexia nervosa, helping sufferers regain weight faster than those without the supplement (2). Binging and vomiting can trigger an endorphin rush, which can temporarily mask anxiety and depression (bulimics given an opiate blocker, naltrexone, report symptoms of opiate withdrawal, according to Ross). Fasting and extreme dieting lower other vitamins, like thiamine, which can cause loss of appetite, making it easier to fast, on and on and on.
Lierre Kieth has her axe to grind, but I do think her book is an important counterpoint to the milder view (and worth a read for vegetarians and meat-eaters alike). Julia Ross' theories and her clinical experience are also intriguing. Vegetarians tend to be healthier and thinner than those who eat a standard American diet (which I'll say is not saying much), but there may be a hidden cost, and when a young person is a vegetarian, it seems that one should be somewhat suspicious that there is a darker reason than not wanting to kill animals.