By Registered Dietitian
on August 06, 2009
Protein provides amino acids, the building blocks of all structures and organs. Besides providing the materials needed for building muscle, protein is required More...

Nutrition Myth - The RDA for protein (.8g/kg BW) is all you need

 

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.[1]
  • 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.

 



References

1  Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber,Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: National Academies Press, 2005.
2  Knapik J, Meredith C, Jones B, Fielding R, Young V, Evans W. Leucine metabolism during fasting and exercise. J Appl Physiol 1991 Jan;70(1):43-7.
3  Youn VR. Metabolic and nutritional aspects of physical exercise. Fed Proc 1985;44:341.
4  Allison JB, Bird JC. Elimination of nitrogen from the body. In: Munro HN, Allison JB, editors. Mammalian protein metabolism. Vol 1. New York: Academic Press;. 1964. Chapt 11.
5  Munro HN. Historical introduction: the origin and growth of our present concepts of protein metabolism. In Munro HN, Allison JB, editors. Mammalian protein metabolism. Vol 1. New York: Academic Press;. 1964. Chapt 1.
6  Waterlow JC, Garlick PJ, Millward DJ. Protein turnover in mammalian tissues and in the whole body. New York:North-Holland; 1978. p 179.
7  Kurzer MS, Calloway DH. Nitrate and nitrogen balances in men. Am J Clin Nutr 1981 Jul;34(7):1305-13.
8  Piatti PM, Monti F, Fermo I, Baruffaldi L, Nasser R, Santambrogio G, Librenti MC, Galli-Kienle M, Pontiroli AE, Pozza G. Hypocaloric high-protein diet improves glucose oxidation and spares lean body mass: comparison to hypocaloric high-carbohydrate diet. Metabolism 1994 Dec;43(12):1481-7.
9  Farnsworth E, Luscombe ND, Noakes M, et al. Effect of a high-protein, energy restricted diet on body composition, glycemic control, and lipid concentrations in overweight and obese hyperinsulinemic men and women. Am J Clin Nutr 2003;78:31
10  Pikosky MA, Smith TJ, Grediagin A, Castaneda-Sceppa C, Byerley L, Glickman EL, Young AJ. Increased protein maintains nitrogen balance during exercise-induced energy deficit. Med Sci Sports Exerc. 2008 Mar;40(3):505-12.
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.
14  Gontzea I, Sutzescu P, Dumitrache S. The influence of adaptation to physical effort on nitrogen balance in man. Nutr Rep Int 1975;11:231.
15  Felig P, Pozefsky T, Marliss E, Cahill GF Jr. Alanine: key role in gluconeogenesis. Science 1970 Feb 13;167(920):1003-4.
16  Felig P, Wahren J. Amino acid metabolism in exercising man. J Clin Invest 1971 Dec;50(12):2703-14.
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.
18  Dohm GL, Williams RT, Kasperek GJ, van Rij AM. Increased excretion of urea and N tau -methylhistidine by rats and humans after a bout of exercise. J Appl Physiol 1982 Jan;52(1):27-33.
19  Dohm GL. Protein nutrition for the athlete. Clin Sports Med 1984 Jul;3(3):595-604.
20  Burke LM, Read RS. Sports nutrition. Approaching the nineties. Sports Med 1989 Aug;8(2):80-100.
21  Lemon PW, Proctor DN. Protein intake and athletic performance. Sports Med 1991 Nov;12(5):313-25.
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.
24  Tarnopolsky MA, MacDougall JD, Atkinson SA, Influence of protein intake and training status on nitrogen balance and lean body mass.  J Appl Physiol 1988 Jan;64(1);187-93.
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.

 

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