I agree that sugar and processed foods probably have way more of an effect. My understanding is a vegetarian diet can set you up for nutritional deficiencies. Beans and grains are not good for your gut, so if you focus your vegetarian diet on those things you can disrupt your gut bacteria which DOES have a negative effect on mood. There is a gut/brain connection and I have tried my darndest to heal my bp through food, but I am just not disciplined enough. My healthiest eating would be whole30/paleo, but I would much rather not eat meat. Bottom line, if you can make your eating like 80% veggies and a little fruit and 20% other, you will probably be doing good.