Although protein can be used for energy, it is the least efficient source and is converted for fuel only if there are insufficient calories in the rest of the diet. Most Americans eat too much protein under the mistaken impression that it builds muscle. Muscle mass is increased only by exercising the muscle. Excess protein must be either converted to urea and excreted, a process that puts undue strain on the kidneys, or converted to fat and stored.
Protein comes from both animals and vegetables, although in the average American diet 60 to 80 percent comes from animals. The problem is that animal sources of protein are usually laden with generous portions of fat and cholesterol, both of which can contribute to heart disease. The fat is often hidden in poultry skin or embedded (marbled) in red meat and thus is hard to detect and remove.
Suzanne was eating plenty of protein with her bacon, sausage, and fried chicken, but she consumed a tremendous amount of calories as fat at the same time. At home they had always baked or broiled chicken after removing the skin, reducing the fat calories 50 percent simply by the method of cooking, while preserving the original protein source.
The components of protein are amino acids, which are essential to maintaining and developing muscle, bone, cartilage, blood, and skin. Of the 22 different amino acids, 14 can be synthesized by the body. The remaining 8 (for adults, 9 for infants), the so-called essential amino acids, cannot be made by the body and must be eaten on a regular basis. Protein from animal sources, which are called complete protein sources, is rich in these 8 essential amino acids.
If you restrict yourself to vegetable sources for protein, you are confronted with a different set of problems. Most vegetables are not complete protein sources, meaning they do not have all the essential amino acids and must be complemented with another protein source that supplies the missing amino acids. A diet of beans, for example, must be supplemented with rice, corn, wheat, or some other grain to supply your body with complete protein. Or you can combine a little fish, chicken, or meat with rice to get complete protein. Your body uses amino acids to build new cells, but it can only use the amino acids if all of the essential amino acids are there at the same time.