This is a question I get all the time, when I am working with someone most of the time they are undereating as an athlete. I share my experience I had with wanting to live in a smaller body and how now I changed the way I think about food. I give you different questions to ask yourself instead of "what if I gain weight?" It will help you change the narrative around fueling yourself like the athlete you are. 

Please DM me if you have any questions on this topic, @serenamarierd.