In general, people who are thin don't eat less food than heavier people. Studies have consistently failed to find a difference in eating patterns between thin and heavier people. Genetics and early family habits of eating and activity have a powerful influence on a person's adult weight. A person who loses 100 pounds through dieting typically gains back 125. Strict diets with insufficient carbohydrates cause the body to use protein for energy needs.
Protein is then unavailable to build and repair muscle tissue.
Loss of muscle lowers metabolism. First, remember that healthy bodies come in all shapes and sizes. If your body isn't as healthy as you'd like, talk to a health care provider. With a health care provider, make a plan to improve your health and your satisfaction with your body. You can learn to enjoy foods that will help you to look and feel good.