ok so i want to begin to eat healthier, but there is a problem. my bmi is 18, so i don't want to lose weight, and i have a really fast metabolism, so when i do try to eat healthier, i end up losing a lot of weight. I do want to be healthier because my diet right now is mostly junk food and soda, stuff like that. So, how do i go about eating healthy but not losing weight? thanks!