Hi there, it's Mary here... 

First, let me start by saying that plant-based diets are not right for everyone and that you have to work at it in order for the diet to be beneficial. A plant-based diet comprises only plant foods, including fruit, vegetables, grains, and legumes, and avoids meat, dairy, and eggs.

It's harder to get calories through vegetables and fruits. This means it's harder to gain weight as well. That's why most vegetarians are thinner.