Protein Goals

Protein accounts for about 15% of a person's body weight and except for water is the largest component in human bodies. Protein performs the same functions in sedentary and physically active individuals. However, protein requirements of athletes are increased above those of sedentary people due in part to changes in amino acid metabolism induced by exercise. A small amount of protein is used as fuel during endurance exercise. Extra protein is needed by strength-trained athletes to repair injuries to muscle fibers and to remodel muscle tissue in response to strength training.

In addition, muscle and whole-body protein synthesis is suppressed during exercise. For example, running for an hour may reduce muscle protein production in the liver by 20%. Increases in exercise intensity and duration further depress protein synthesis. Catch-up occurs after exercise. Protein synthesis increases once endurance or strength exercise has ended. Also, several studies indicate that protein synthesis during recovery is enhanced when the recovery meal contains both carbohydrate and protein.

Protein needs are related to caloric intake. Consuming sufficient calories to maintain energy balance improves nitrogen balance and decreases protein requirements. When energy intake is low, protein is broken down to meet energy needs. Using protein as an energy substrate increases protein requirements. Factors associated with increased protein requirements include the following:

Vegetable proteins are less digestible and their amino acid composition is somewhat different from animal proteins. Protein needs (g/kg BW) increase as the amount of vegetable protein goes above about one third of the total protein in a person's diet.

Protein Recommendations

Protein intake equal to 10-20% of total calories will meet the protein requirements of most athletes. The type of sport and total calorie intakes influence protein requirements. For example, cross country skiing and ice hockey both require a high level of energy intake to meet energy expenditures. Eating sufficient food to meet high energy demands while balancing food selections from the five major food groups nearly always ensures that these athletes will meet their protein requirements.

Unlike carbohydrate or fat, amino acids are not stored. Most amino acids function as part of protein structures, enzymes, or are used as precursors to form hormones, neurotransmitters, or nucleic acids. A pool of free amino acids accounts for no more than 1.0% of all amino acids in the body. Free amino acids that are not used for protein synthesis can be broken down and their carbon skeleton used to make glucose, oxidized for energy or stored as fat. The amino portion ends up as urea which is excreted in urine or sweat. Research on strength athletes indicates that at a daily protein consumption of 2.4 g/kg BW, amino acid oxidation increases and no further protein synthesis occurs. Consuming more protein than is needed promotes protein oxidation, urea formation, diuresis, and can increase risk for dehydration.

Do some athletes eat too little protein? Inadequate protein intake can occur in athletes, particularly among athletes whose energy demands are low or those who overemphasize carbohydrate in daily eating patterns. Athletes who do not consume enough protein to meet their requirements risk being unable to maintain muscle tissue and to repair muscle damage that occurs during exercise.

Protein Considerations

Ice Hockey High intensity, intermittent activity that incorporates strength training in the exercise program. Resistance exercise provides the stimulus for gains in muscle size and strength. Strength training relies on anaerobic metabolism for energy production. The primary fuel for resistance exercise is muscle glycogen. Amino acids are not used as energy substrates for either strength training or ice hockey competition activity. Building muscle is energy intensive. The primary nutritional need is to meet total energy requirements. For each day of strength training, an athlete may need more than 40 kcal/kg BW just to maintain muscle mass. Combined with appropriate resistance training, additional calories are required to build muscle. Protein turnover (synthesis and degradation) is elevated in strength athletes.Protein requirements are increased to supply amino acids to maintain nitrogen balance and to support enhanced rates of protein synthesis.