Proteins are chain-like molecules, and the links of protein chains are called amino acids. About 20 different amino acids occur in human proteins. Twelve of these can be made within the body. The other eight are called “essential amino acids” because they cannot be made by the body; therefore, it is essential that they be obtained from the diet. The proteins you eat as food are not directly incorporated into your body tissues. Instead, the protein chains are digested to yield short fragments (peptides) and individual amino acids which are absorbed into the bloodstream. The individual amino acids then serve as building blocks your body uses to build its own proteins. If any one of the amino acids is deficient, your body can’t make new protein molecules. They all have to be there at the same time.

Protein is required in the diet to maintain tissues and organs and to supply building blocks for growth. Proteins from animal sources such as meat, eggs, and milk, are called “complete” proteins because they supply all the essential amino acids. Animal proteins provide a balance of amino acids similar to that of human tissues. Plant proteins have a profile of amino acids different from human proteins. For this reason animal proteins are considered to be higher quality protein foods. Most vegetable proteins are deficient in one or more of the essential amino acids and are therefore called “incomplete” proteins. However, if vegetable proteins are combined properly, the balance of amino acids in the combination can approach the amino acid profile found in animal proteins.

While animal proteins are generally high quality protein foods, a problem arises in that many of them also contain a lot of fat. You must be selective when using animal proteins to avoid the fat that comes along with them. Good lean protein sources include skinless turkey breast, skinless chicken breast, fish, and egg whites. Occasional red meat is fine, as long as you consume the leanest cuts. Always trim all visible fat.

There has been a lot of debate about the protein requirements of athletes. Historically, nutritionists assert that athletes do not require any more protein than sedentary people. Athletes, however, believe they need more. There is some reason behind both points of view. On one hand, it is well known that weight lifting causes damage to muscle tissue (1). So it makes sense that someone who lifts weights would have to eat more protein than a sedentary person because his body has to repair that damage. Furthermore, if you want to increase the amount of muscle mass on your body, it seems obvious that you would have to eat some extra protein to support this growth. On the other hand, nutritionists point out that this increase need for protein is offset by increased efficiency of protein utilization in the trained athlete (1). If your body utilizes its protein food more efficiently, then it may not need any extra after all. Furthermore, eating excess protein does not in itself make you more muscular. If it did, we would just eat more protein food and get more muscular. Unfortunitely, it’s not that easy.

The National Research Council sets the recommended daily allowance (RDA) for protein intake at 0.8 grams protein per kg body weight per day (g/kg/day). This works out to be 0.36 grams per pound body weight each day (g/pound/day), which is 56 grams per day for a typical male and about 72 grams per day for a 200 pound bodybuilder. This value for the RDA was determined to be the amount required by most of the average population—not for athletes or other very active people. Recently, a new way of measuring the protein status of the body has been developed—the metabolic tracer technique. Using this method, protein requirements are seen to be 23-178% greater than estimated by the nitrogen balance technique (2), a conventional method of measurement.

Much modern research indicates that the protein needs of athletes range from 1-2g/kg/day (0.45-0.9g/pound/day)—about twice the RDA (3). Other studies suggest that some hard training strength athletes require in excess of 2g/kg/day (0.9 g/pound/day) to maintain nitrogen balance (4) and that as much as 3.5g/kg/day (1.6g/pound/day) may be beneficial in maximizing gains in strength and mass (5). Apparently, the increase in efficiency of protein utilization which has been reported to occur during adaptation to exercise may not always be enough to offset the increase protein demand. In other words, the RDA for protein may not always be enough even if it is utilized with 100% efficiency. The RDA protein recommendation may be enough for sedentary people but endurance athletes and very muscular athletes need more.

REFERENCES 1. Hickson JF and Wolinsky I. Human protein intake and metabolism in exercise and sport. In: Nutrition in exercise and sport, eds. Hickson JF and Wolinsky I, p. 5-36. CRC Press, 1989.

2. Lemon PWR. Protein and Amino Acid Needs of Strength Athlete. Internation Journal of Sport Nutrition 1: 127-145, 1991.

3. Lemon PWR. Protein and Exercise: update 1987. Med Sci Sports Exercise 19: S179-A190, 1987.

4. Celejowa I and energy balance in Polish weight lifters during training camp. Nutr Metab 12: 259-274, 1970.

5. Dragen GI, Vasiliu A, Georgescu E. Effect of increased supply of protein on elite weight lifters. In: Milk Proteins, eds. Gasesloot TE and Tinbergen BJ, p. 99-103. The Netherlands: Wageningen, 1985.