I did become vegan/vegetarian to lose weight, and it didn't work. Instead, I gained 15 pounds! My theory is that while this high carb diet DOES work for some people to lose weight, other people- like me- do not lose weight because of it.
Nontheless, my skin has cleared considerably, I have more energy (when I'm eating a PROPER vegan diet) and I am the healthiest I have ever been. If you feel that you want to lose weight, I would contact a nutritionist or other healthcare professional who can help you do it in a responsible manner....500 calories is clearly a disordered eating pattern and being thin is not, not, not, NOT worth it. Please read up on veganism and see its other benefits in addition to possible weight loss- vegan is truly a healthy lifestyle that is highly beneficial to the earth.