The RDA for protein is quite specific in its application: Adults with low activity levels who are getting their energy needs met by dietary carbohydrates (CHO) and fat and are not growing or changing. Based upon these criteria, the RDA of .8g/kg BW is sufficient, even providing a margin of safety to ensure enough protein.
However, gym members/recreational athletes generally present a different scenario. They are often active, eating reduced calorie diets (energy needs NOT being met by dietary CHO and fat), or breaking down and rebuilding muscle (physiological adaptations). All of these factors affect protein requirements.
Individual protein requirements are based upon the following factors:
- Weight- the more you weigh the more protein your body requires.
- Calorie intake- when calorie intake is lowered below maintenance, energy needs are not met by carbohydrate and fat, forcing the remaining energy needs to come from protein and related tissues (e.g. muscles).[2,3,4,5,6,7,8] Therefore, the amount of lean body mass lost in exercising or sedentary persons in negative energy balance can be reduced and often eliminated (depending on the size of the calorie deficit) by increasing protein in the diet.[9,10]
- Exercise/Goal- as early as 1981, scientists Lemon and Nagle studied the effect of exercise on protein requirements. Following this review, scientists began to recommend protein intakes for athletes well above the RDA. While the effect of exercise on protein metabolism was found to vary by exercise type, protein can supply from 4 to 10 percent of exercise energy needs. Additionally, exercise increases the oxidation of amino acids and the rate of protein turnover in lean body mass during recovery.[11,12,13,14,15,16,17,18,19,20,21,22,23] Furthermore, cardiorespiratory exercise alone contributes to an increase in protein requirements,[11,12,13,14,15,16,17,18,19,20,21,22] as does resistance training.[11,12,24,25] The needs of those participating in both activities may be greater than the highest recommendation for strength training.[26,27]
Assuming the majority of one’s energy needs are met with carbohydrates and fats, below are the current protein recommendations for active individuals.
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11 Lemon PW, Nagle FJ. Effects of exercise on protein and amino acid metabolism. Med Sci Sports Exer 1981;13(3):141-9.
12 Wolinsky I, Hickson JF, editor. Nutrition in exercise and sport. Boca Raton (FL): CRC Press; 1993. p 317-318, 508 p.
13 Gontzea I, Sutzescu P, Dumitrache S. The influence of muscular activity on nitrogen balance and on the need of man for proteins. Nutr Rep Int 1974;10:35.
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17 Wolfe RR. Does exercise stimulate protein breakdown in humans? Isotopic approaches to the problem. Med Sci Sports Exerc 1987 Oct;19(5 Suppl):S172-8.
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22 Lemon PW. Protein requirements of soccer. J Sports Sci 1994 Summer;12 Spec No:S17-22.
23 Pivarnik JM, Hickson JF Jr, Wolinsky I. Urinary 3-methylhistidine excretion increases with repeated weight training exercise. Med Sci Sports Exerc 1989 Jun;21(3):283-7.
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25 Tarnopolsky MA, Atkinson SA, MacDougall JD, Chesley A, Phillips S, Schwarcz HP. Evaluation of protein requirements for trained strength athletes. J Appl Physiol 1992 Nov;73(5):1986-9.
26 Keul J. The relationship between circulation and metabolism during exercise. Med Sci Sports 1973 Winter;5(4):209-19.
27 Keul J, Doll E, Keppler D. Energy metabolism of human muscle. Baltimore (MD):University Park ;1972. p 111.