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Protein

Introduction

Research indicates that athletes require more protein than the general population; specifically that strength athletes need between 1.4 and 1.8 grams of protein per kilogram body weight per day (g/kg/d) and endurance athletes between 1.2 and 1.4g/kg/d. The recommended intake for non-athletes 19 years and older is 0.8 g/kg/d. It should be noted that the estimated protein requirement for athletes makes two important assumptions: adequate calorie intake and a diet that provides both animal and plant proteins. Negative energy balance will increase protein requirements because of increased protein used as an energy substrate. Biological value of the protein consumed also affect requirements; recommendations for protein are based on studies in which the subjects consumed approximately 65% of their protein as animal protein. Thus, a strict vegetarian will have a higher per kilogram body weight requirement for protein than the athlete who eats meat, fish, eggs, or diary products. This is due mainly to differences in the digestibility and the amino acid composition of plant protein versus animal protein. Research on populations consuming diets high in plant protein show that athletes require more than 2.0g/kg/d.

Effects on Health

Although consuming protein equal to 175% to greater than 200% of the current RDA may appear excessive, there is no indication of any adverse health effects unless there is some pre-existing complicating factor such as abnormal kidney function or fat metabolism. Moreover, these quantities of protein can be obtained without consuming special protein supplements, assuming total food (energy) intake is adequate. This latter point is critical because, as a result of dieting or extremely high expenditures caused by exercise training, it is likely that some athletes under eat and consequently consume inadequate protein. The highest risk individuals are those who are growing, especially girls and young women who, in comparison to males, have a far greater tendency to consume insufficient energy to cover their training expenditures.

Effects on Performance

Suboptimal protein intakes can adversely affect exercise performance in a variety of ways. Examples include: impaired muscle development, prolonged repair of exercise-induced muscle damage, delayed replenishment of muscle energy stores after exercise, altered substrate use during prolonged exercise, and perhaps even increased injury incidence/severity, and/or compromised immune function. Individually or in combination these effects could also minimize training adaptations secondary to a reduction in the training stimulus that can be tolerated. Consequently, adequate protein intake for athletes and perhaps even timing of intake relative to the exercise session is likely to enhance performance in many athletic events.

Dietary Recommendation

During training and competition, 1.2 to 2.0 g/kg/d is recommended. Protein intake can be reduced during off-season or other times when not training.

Supplement Range

The amount of protein supplement recommended is the amount that results in a total intake (diet and supplement) of 1.2- 2.0 g/kg/d. This recommendation assumes adequate calories and a diet containing some foods of high biological protein value. If a supplement is needed to meet these levels, a low-fat milk-based product is recommended.

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