I think this very much depends on why these people are vegetarians in the first place. The people who are vegetarians because they think it's a healthier diet, or think it helps them losing weight, will probably look thin because they mean to be. However, I have met many vegetarians that are vegetarians because of their religious beliefs, those usually aren't thin.They tend to eat a lot of other junks to make up for what they're missing from eating meat. For example, they tend to replace the lack of protein with bean products, sugar, or even fats.
