I've recently written a letter to the editor to the journal Eating and Weight Disorders - and it was (with some good luck) published a few days ago.
Background: Some psychologists have suspected that a vegan diet is very "restrictive" and could by way of this "restrictiveness" cause a mental health condition in the form of an eating disorder, namely orthorexia (technical name: orthorexia nervosa) - which is generally understood to be something like an obsession with healthy eating.
However, there are two problems with this:
1) The definition of orthorexia nervosa is vague and unclear - and therefore it's controversial whether it is an actual illness (eating disorder).
2) The tools (questionnaires) used to assess the "risk" of "orthorexia" are inadequate.
There is no good evidence at all that a vegan diet could increase the risk of "orthorexia".
See the full text (free) of my letter here. It should clarify the most important issues regarding this topic - for vegans as well as for non-vegan researchers in this field. I hope people will read it. Please share - if you find it useful.