Fat (definition): one of the three main classes of foods and a source of energy in the body.  Fats help the body use some vitamins and keep the skin healthy.  They also serve as energy stores for the body.  In food, there are two types of fats, saturated and unsaturated (NASM, 2008).

Fat (function): serve as an energy source and facilitate the use of vitamins by the body. They also provide satiety and warmth for the body (NASM, 2008).

Protein (definition): Amino Acids linked by peptide bonds, which consist of carbon, hydrogen, nitrogen, oxygen and usually sulfur and that have several essential biological bonds (NASM, 2008).

Protein (function): build and repair body tissue and structure, synthesis of hormones, enzymes and peptides and serve as a secondary energy source (NASM, 2008).

Carbohydrates (definition): neutral compounds of carbon, hydrogen, and oxygen (such as sugars, starches and celluloses) which make a large portion of animal foods (NASM, 2008).

Carbohydrate (function): the chief form of energy for all body functions and muscular exertion.  They also help to regulate digestion and utilization of protein and fat (NASM, 2008).