I believe that diet has an effect on character and also that character has an effect on diet.
For example when someone becomes more and more compassionate a vegetarian type diet becomes natural for them.
On the other hand, a vegetarian diet, a diet that includes lots of fresh and wholesome food, will have a positive effect on character, helping one to live virtuously.
I agree vegetarianism is inherently more virtuous -- but some vegetarians take an arrogant attitude to non-vegetarians and it becomes an expression of pride, which seems to me from a character point of view, to negate the benefits. Richard