In metabolism, the body harnesses energy from carbon compounds by adding Oxygen to them. This means they attract much less water, and are therefore a good storage system for energy in the body. Note that if the body consumes excess carbohydrate, it will convert it into fatty acids for storage. Cholesterol is also a lipid that shares a similar structure with many hormones. Too much Cholesterol can lead to plaque formation in arteries which can cause heart attacks.
Proteins carry out the vast majority of functions in the body.
Amino acids will link together to form chains, or polypeptides. Since proteins carry out most of the body's functions, small problems with proteins create big problems for people. For example, Hemoglobin is a protein that carries oxygen in the blood from the lungs to the tissues of the body. Carbon Monoxide will bind hemoglobin much more tightly than will oxygen, such that every hemoglobin protein that binds carbon monoxide is essentially rendered useless to the body. Each gram of fat contains about 9 calories, each gram of protein and carbohydrate contain about 4 calories per gram.