Recommended amount: 1.2g/kg of body weight and may benefit from 1.4 to 1.8 g/kg during periods of muscle building. An ↑ in protein intake appears to be more important during early stages of training than later in the training regime. Strength athletes initially require more protein to support ↑ in their muscle mass (the existing muscle fibers become larger).
The increased pro allows for enlargement of muscle cells, particularly fast twitch fibers. The growth that occurs is an ↑ in the contractile proteins, actin & myosin, as well as in enzymes and stored nutrients. There is also a need for proliferation of the connective tissue surrounding the individual muscle fibers. Whether there is an ↑ in the number of cells, still remains a question.
Although strength training may be extremely intense it is brief (each bout), so that it is unlikely that pro plays an important role in providing energy for this type of exercise. Anaerobic glycolysis and ATP-CP are the important energy systems providing energy. However, when glycogen stores (stored form of carbohydrate in the body) are low due to prolonged exercise or a ↓ carbohydrate diet, pro may contribute as much as 10% of the energy needed for exercise.
When muscle glycogen stores are ↑, the contribution of pro for the energy is no more than 5%. Athletes will also use more pro for fuel when they don’t eat enough calories. Consuming a high CHO (carbohydrate) duet during repeated days of heavy training helps maintain muscle glycogen stores and reduces the use of pro as fuel. TH pro guidelines provided assume that the athlete is consuming adequate kcal.
Evaluation of pro needs of athletes should always consider the energy content of the diet. For any given pro intake, increasing energy intake will improve nitrogen balance. Therefore, pro requirements decrease as energy intake increases. If energy intake is sufficient as a result of the increased energy expenditure of training or if food intake is restricted to help reach a specific body weight (for wrestling, dancing, etc.), pro needs may be further elevated.
Athletes can generally obtain 1.2 to 1.8 g/kg when their diet provides 15% of kcals (calories) as pro. The growing athlete needs more pro relative to body weight than does the adult athlete to support growth requirements. However, a diet supplying 15% of kcals as pro should meet the needs of most children and adolescents in sports (1.2-2.0 g/kg).
Potential adverse effects of increased protein intake:
- Athletes who consume adequate kcals generally obtain sufficient pro and amino acids. When athletes eat more pro than required, the excess pro is either burned off for energy or the carbon skeletons are converted to fat and the nitrogen excreted as urea and ammonium in the urine. CHO are a more effective and less costly source of energy.
- Osteoporosis (due to the effect of increasing Calcium excretion that protein has)
Dispelling the benefits of amino acid supplements:
- Substituting amino acid supplements for food may cause deficiencies of nutrients such as iron, niacin, and thiamin found in pro rich whole foods. (Consider the benefit of 1/3 cup dry milk powder = 10 grams high quality protein + other nutrients vs. expensive amino acid supplements.)
- Arginine and ornithine are favorites because they have a reputation of stimulating the secretion of growth hormone and thereby increasing muscle mass and decreasing body fat.
Growth hormone causes muscle hypertrophy (enlargement of a tissue or organ of the body resulting from an increase in the size of its cells), but does not increase in muscle strength. Consuming large amounts of these amino acids may cause a temporary rise in growth hormone levels but there is no proof that this increases muscle mass or reduces fat. Studies on arginine suggest that a minimum of 250 mg/kg is needed to stimulate growth hormone release. Weight lifting and endurance training both significantly increase growth hormone levels. Combining the supplements with exercise. In addition, ornithine supplements can cause mild to severe stomach cramping and diarrhea.
- Single amino acid supplements on large doses can cause amino acid imbalances and toxicities. There have not been studies conducted on human subjects of large doses of amino acid supplements. Therefore, the margin of safety is not known.
- Athletes may hear that only small amounts of the amino acids in foods are digested and absorbed. This is not correct. Approximately 95% of the amino acids from animal sources and 90% of the amino acids for vegetable sources are digested and utilized by the body.
- Athletes may also be told that amino acids do not need to be digested before absorption and so replenish the body’s pro faster than the amino acids form high pro foods. There is no evidence that more rapid absorption is beneficial. It takes hours, not minutes, to rebuild muscle pro damage during intense exercise.