The most significant drawback of a vegan diet is how difficult it can be to maintain and meet your body's nutritional needs. You remove the primary sources of omega-3s and vitamin B12. It tends to take more work and forethought, otherwise you end up just grabbing vegan snack foods, alternative cheeses, and fake meats, which are processed and often high in fat and calories. It can also be a difficult plan to follow when you're out at a restaurant or over at a friend's for a meal, as you sometimes need to pick between sticking to your vegan ideals and eating anything more than a side of french fries.