Protein Requirements

Protein yields approximately 4 calories per gram, which is the same energy concentration as carbohydrate. The recommended level of protein intake for the general population is 12 to 15 percent of total calories. Therefore, someone consuming 2,000 calories per day has an energy equivalent of 240 to 300 calories (60 to 75 grams) of protein per day. Most nonathletes do well with .8 grams of protein per kilogram of body weight. Using this guideline, a 165-pound (75 kilogram) nonathlete has a protein requirement of 60 grams per day. On a per kilogram basis, athletes have a higher protein requirement because of a greater lean mass, a greater need for tissue repair, and because a small amount of protein is burned during physical activity.

This increases the protein requirement for athletes to approximately double that of nonathletes (1.2 to 1.7 grams per kilogram). Therefore, a 165-pound (75 kilogram) athlete has a protein requirement of 120 grams (480 calories) per day. Although 120 grams of daily protein may seem high, it represents a relatively small proportion of total daily calories and is easily obtained by following the Dietary Guidelines for Americans (2005). These guidelines focus on the premise that nutrient needs can and should be met mainly through food consumption. By comparison, the minimum recommended intake for carbohydrate is 30 calories per kilogram of body weight, so this 165-pound person has a requirement of 2,250 calories from carbohydrate alone.

Athletes require a higher protein intake than non-athletes for a number of reasons:

• Amino acids (from protein) contribute 5 to 15 percent of the fuel burned during exercise. The amount of protein used for energy rises as muscle glycogen decreases. It is generally thought that endurance exercise is more glycogen depleting than power exercise, so endurance activities are likely to cause a higher proportionate usage of protein.
• Exercise may cause muscle damage, which increases the protein requirement for tissue repair.
• Endurance exercise may cause a small amount of protein to be lost in the urine (where there is typically none or very little without exercise).

Despite the increased protein requirement for athletes, most athletes consume much more protein (from food alone) than they require. A look at the protein content of some commonly consumed foods demonstrates this point. Although most athletes have no difficulty consuming sufficient protein, the following groups of athletes should monitor protein intake carefully because it may be difficult for them to get enough:

• Young athletes who have the combined demands of muscular work and growth
• Athletes who are restricting food intake in an attempt to achieve a desirable weight or body profile
• Vegetarian athletes who do not eat meat, fish, eggs, or dairy foods
• Athletes who restrict food intake for religious or cultural reasons

As mentioned earlier, we can derive energy (calories) from protein. However, burning protein as a fuel is a bit like sprinkling your family diamonds on your breakfast cereal because you think it improves the texture. It's a complete waste of resources. Protein is so important for building and maintaining tissues and for making hormones and enzymes that burning it up as a fuel is wasteful. Besides, when protein is burned as a fuel, the nitrogen must be removed from the amino acid chains and excreted. When you increase the excretion of nitrogenous wastes, you also must increase the amount of water lost as urine. Thus, two undesirable things occur: You waste valuable protein by burning it up, and you increase the risk of dehydration because of the increased volume of water that is lost when nitrogenous wastes are excreted. In addition, high-protein diets are shown to increase the excretion of calcium in the urine (a clear problem for females who are at risk for bone disease later in life). Another potential problem is that high-protein diets tend to also be high in fat, which may increase the risk of cardiovascular disease. Therefore, the best way to make certain your protein needs are met is to consume a sufficient amount of food that focuses on carbohydrates but also contains small amounts of dairy products and meats (or plenty of legumes if you're a vegetarian).

Meats and dairy products provide all the essential amino acids in a single food, but plant sources of protein do not. Therefore, vegetarians should be careful to combine foods in a way that optimize essential aminio acid availability. The general rule for ensuring a good distribution of all the essential amino acids is to combine cereals and legumes at the same meal. Both cereals and legumes are good sources of valine, threonine, phenylalanine, and leucine. Corn and other cereal grains are poor sources of isoleucine and lysine but are good sources of tryptophan and methionine. By contrast, legumes are good sources of isoleucine and lysine but poor sources of tryptophan and methionine. By combining cereal grain grains and legumes, the amino acid weakness of one food is complemented by the amino acid strength of the other food to provide a good quality protein.