[1457389]

I remember this study doing the rounds a few weeks ago. The consensus back then was that there were significant confounding factors. For one thing, you can't be sure that the vegetarians you include in the set didn't become vegetarian specifically to address some lifestyle problem or health issue. Based on my anecdotal experience of vegetarians in wealthy first world nations, a large proportion include health concerns as part of their justification for vegetarianism.

Might have been useful to only include vegetarians who had been on their diet for a minimum length of time, or exclude those who said they had health issues.

Another issue someone already noted below, but the cherrypicking involved in going from thousands of survey responses to the few hundred they actually used must have been enormous.

[mazuhl]

Another aspect might be that people with mental/eating disorders might be more attracted to vegetarianism, rather than vegetarianism causing those. I can see good reasons for this: vegetarianism is a good mask for being a "picky" eater, it's got strong issues you can be concerned/depressed about (animal suffering, environmental destruction, being a social outcast in certain areas), etc.