If you lose weight before exercise, you'd better not eat anything to achieve the best fat-reducing effect. Eat one hour after exercise. Because your body needs energy badly after exercise, you can absorb everything well.

If you want to gain muscle, you can eat something from protein before running, such as boiled eggs (egg whites).

Do a lot of exercise. I suggest you drink a bag of milk before going to bed at night to supplement calcium. It can make up for your massive loss of calcium and nutrients.