I've suspected for a long while now that those prone to eating disorders would be attracted to vegetarianism, so I am not surprised at all to find ED positively correlates with veganism. The entire concept of restricting normal consumption due to a feeling of worthlessness, immorality, guilt or gluttony is the definition of having an ED. Many of these feelings overlap with and are the catalyst for vegetarianism (especially the guilt/morality issue).

Ever read the PeTA message boards? Many who post there are kids with overt eating disorders. If you listen to how they speak about eating and food, you can see their thought processes and perceptions aren't right. They equate everything they consume with morality (or lack of it). Some of them refuse to eat anything but only fruit, because (in their minds) all other foods destroy the planet. IMO, it's not physically or mentally healthy.

Animal rights activists often say vegans and vegetarians are lower weight than omnivores in defense of the healthfulness of their diets, but I wonder if this is a cause or effect. I think the sort of person who would become a vegetarian is going to be someone with marked ED tendencies already... or at the very least, someone who doesn't fancy food much or who finds eating disgusting/unenjoyable for any number of reasons. Naturally, they aren't going to eat enough to maintain even an average weight, nevermind gain weight.

However I think if an average-dispositioned person (a non-moral vegetarian) were forced to subsist on a diet of no animal products, they would most certainly gain weight (or at the very least not lose any weight). Unless they consciously and carefully planned their diet before hand to avoid it, they would undoubtedly end up replacing animal protein and fat with less satiating, metabolic disorder inducing grains and other high glycemic load carbohydrates... which, as we all know, are not conducive to maintaining balanced energy, balanced consumption, and healthy weight.