Can you be a vegan and still be overweight?

Possibly, but not necessarily. A standard, balanced vegan diet is going to include fewer calorically dense foods (such as high-fat meats, cheeses, milk and the like) and more low caloric density foods (such as fruits and vegetables). However, this isn't to say being vegan will make you lose weight- consuming fewer calories will make you lose weight. A vegan could scarf down sugar-coated,chocolate-covered almonds all day long, and like anyone else, gain weight. There's nothing magical about being vegan that suddenly makes weight disappear, it's simply that what most vegans eat contains fewer calories per gram than the standard American diet.

If you do decide to become vegan, it's very important that you monitor what you eat more closely, not just to verify that what you're eating is actually vegan, but also to make sure that you're consuming a balanced diet. Bad as the standard American diet may be, it's very unlikely that someone encounter a protein deficiency. But in a vegan diet, without many common protein sources (such as fish,eggs,dairy and lean meats) it's very important to make sure you are consuming enough complete proteins, likely through soy. Taking an additional B-vitamin supplement might also be helpful.