Proteins are made up of twenty amino acids or building blocks that are linked together in different ways. Your body can produce half of its amino acids but the other half are from special foods. Different proteins serve different functions. They help form parts of structure of muscle, hair, skin, nails, connective tissue, and glands. The main use of protein is to help build working body tissue.
Fats supply the body with energy.
They are a major source of calories. It is not good though to eat to many fatty foods if your body can't burn it in activity. It will then be stored as fat. If you have to much fat you will became overweight. Being overweight like being under weight is not good for your body.