Ron is right. The way to maximize weight loss on a vegan diet is to:
1. Make sure you create well-combined meals that will give you the full 9 amino acids. This usually means a legume (black beans, white beans, garbanzo beans, green beans, kidney beans) and a grain (corn, wheat, kamut, millet, rice, oats), but you can also do it with squash (winter is the most filling) and mushrooms.
2. Avoid things made with flour, and/or sugar/high fructose corn syrup. This includes everything like soda, bakery goods, crackers made with white flour, etc. But to maximize weight-loss any baked goods, even vegan ones made with organic flours and raw sugar, or maple syrup have too high a glycemic index.
3. Avoid foods high in fat, and cook with less fat. We need some fat to be healthy, but there's naturally occuring fat in foods like bananas, olives, and avocadoes. Some good substitutes for fat include vegetable broth made with good vegan boullion, and prune puree (in baked goods). You can save 100 calories every time you use 1 tbsp of oil to saute instead of 2.