Protein--along with carbohydrates and fat--are called the 'energy nutrients.' The energy they provide is used by the body to fuel the billions of chemical reactions that sustain life each day. The primary role of protein is to build tissues and other essential compounds. Small amounts of protein are enough to satisfy the daily minimal requirement for the average adult--two ounces, or 60 grams. The sources of protein that provide your body with the most efficient fuel and the least waste and damage are those that are lowest on the 'food chain.' The primary source of energy is the sun, which is turned into energy by plants, which are then eaten by plant-eating animals, which are eaten by carnivores. The higher you eat on the food chain, the more fat and toxins you ingest. If you haven't done so already, you may want to begin replacing animal protein in your diet with soy products, grains, legumes, and non-fat dairy. You'll get just as much protein and get carbohydrate and fiber along with the protein.
