Protein Supplementation

In terms of nutritional requirement, it appears that protein supplementation by increasing daily protein intake to a level higher than 12-15 en% will be too high for most athletes. Since a higher daily energy intake in endurance athletes will result in higher protein intake, as well, the value of protein supplementation for endurance sport can be questioned. Based on the observed relationship between energy consumption and protein consumption, athletes expending and eating 5000 kcal/day will ingest twice as much protein as people not involved in exercise and expending/ingesting only 2500 kcal/day. Protein intake for any endurance athlete will thus be sufficient as long as the diet is well composed and contains a variety of protein sources such as lean meat, fish, dairy products, eggs and vegetable protein. Supplementation may be warranted for athletes who compete in weight classes and combine intensive training with weight reduction programmes. Also vegetarian athletes, who consume low energetic and low protein diets (55, 141), or athletes who for any reason are unable to ingest sufficient protein, may benefit from some protein supplementation with the goal to achieve an intake of 1.2-1.8 g/kg body weight a day. Ingesting a moderate amount (10-30 g) of protein powder, e.g. mixed in a liquid, can do this. Examples of supplementation are all categories that are at risk for a marginal nutrient intake as described in Chapter 1 (Table 1), especially those ingesting < 1500 kcal/day (23, 176). Basically the protein sources used for supplementation or as part of replacement meals, taken during 'prolonged endurance exercise days', should be low in fat, easily digestible and of appropriate quality. Milk protein, milk protein hydrolysates and their combinations with whey protein or soya protein are appropriate for these purposes. These protein sources are very low in fat, cholesterol free and do not increase purine intake and uric acid levels in blood. From a health point of view such supplements may also replace a substantial part of the high daily animal protein intake and very frequent egg consumption in high weight strength in order to reduce the atherogenic character of their diets (62).

It should not be overlooked that meals ingested during ultra-endurance events, such as the triathlon, multi-day cycling races and high altitude climbing, and which replace normal meals, may be composed of CHO, fat and protein in a ratio of 60 - 70 en% CHO, 10-15 en% protein, 25-30 en% fat.

Aspects of amino acid supplementation can be found in Chapter 10. Recent reviews presenting more detail on protein and exercise metabolism can be found in references 224 and 225.

Key points

  • Sufficient protein consumption is required for optimal muscle growth and exercise-related repair of muscle damage and enzymatic adaptations.
  • The protein requirement of athletes is increased and, according to present knowledge, amounts to approximately 1.2-1.8 g/kg body weight for endurance athletes and about 1.0-1.2 g/kg body weight for strength athletes. The reason for this increase is enhanced utilization of amino acids in oxidative energy production during physical exercise—a process which is known to be intensified at higher endurance work levels and in a state of carbohydrate store depletion.
  • There is a close relationship between energy intake and protein consumption. Accordingly, endurance athletes generally ingest a protein quantity that is larger than their required amount. On the contrary, athletes who ingest low caloric diets may also have low protein intakes, which may not compensate for the net nitrogen loss from the body. This may influence protein synthesis processes and training adaptations negatively. To these categories belong bodybuilders, weight class athletes, gymnasts, dancers, female long distance runners and under some circumstances vegetarian athletes.
  • Protein intake/supplementation above levels that are normally required will not enhance muscle growth or performance. The building blocks of protein, amino acids, are also involved in numerous metabolic pathways and processes. Some of the amino acids are known to influence hormone secretion and neurotransmission.
  • Exercise-induced impairments in neurotransmission are speculated to influence fatigue/performance. However, data that support beneficial effects of single amino acids as present in currently available food supplements are generally lacking.
  • The use of single amino acids, to influence metabolic pathways involved in fatigue development and hormone production, needs further research before athletes should be informed positively about benefits (see also Chapter 10).

II Aspects of Dehydration and Rehydration in Sport

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