The bodybuilding community is deeply intertwined with that of the sports supplement world a look into any bodybuilding or fitness magazine will reveal a wealth of protein and supplement advertisements (Rankin 1995). Bodybuilders and other strength athletes have tended to always eat well above the normal RDA (Recommended Daily Allowance) of 0.8g per kilogram of bodyweight on the rational that resistance exercise increases their protein needs substantially (Wilson and Wilson 2006). The purpose of this article is to look at these anecdotal recommendations and to contrast that with current scientific literature.
Protein consumption and muscle growth.
Bodily proteins are constantly being made and degraded this constant process is termed as protein turnover figure 2 shows a schematic of this process (Phillips 2004).
Figure 1 – Schematic of protein turnover and various fates of amino acids in skeletal muscle (Phillips, 2004).
Resistance exercise is followed by a period of up to 48 hours when rates of protein synthesis are greater than resting. The interaction between the chronic applications of resistance exercise and the infusion or ingestion of amino acids (protein) gives us a basis of understanding for muscle growth (Phillips, 2004). Bodybuilders are synonymous with high volume resistance exercise and high levels of dietary protein (Rankin 1995). The application of these two protocols may induce an increase in protein synthesis, overall protein turnover and muscle accretion (Phillips, 2004). This may more typical of novice bodybuilders as elite bodybuilders show much less response to resistance training stimulus (Tarnopolsky et al, 1992).
Bodybuilder’s Dietary Habits.
The primary goals of the competitive bodybuilder are to increase muscle mass and symmetry whilst decreasing body fat (primary pre-contest) which they obtain through high volume resistance exercise and dietary manipulation (Rankin 1995). There exist a limited number of dietary studies on the habits of bodybuilders however the majority of studies before 1989 do not take into account the time of season participants are in (Heyward et al 1989) this omission of the participants’ state of completive readiness is a serious handicap to their validity. In the preseason bodybuilders typically eat in excess of all RDAs (Kcal/Protein/Fat/Carbohydrate) in order to allow them to train at higher volumes and put on muscle mass typically termed as “bulking” (Heyward et al 1989). In contrast the pre-contest portion of the season which may last up to three months is a period of major Kcal and Fat restriction by these athletes in an attempt to decrease adipose tissue in order to increase muscle definition; commonly referred to as “cutting” (Rankin 1995). Dietary studies carried out on dietary habits of national level bodybuilders typically found their dietary intake to have been up to two to four times the RDAs with protein consumption making a larger contribution to the diet in the pre-competition phase (Heyward et al 1989). In a ten week dietary survey and blood analysis of a pre-competition bodybuilder Too et al 1998 found the participant’s dietary protein intake to be as high as 5g per kilogram of body weight (thus kg/BW) with a macronutrient split of 71% Protein, 16% Carbohydrates and 13% Fat. Blood analysis showed the athlete to be hyperglycaemic with high levels of creatine in blood samples being attributed to the athletes’ high protein intake. It is quite clear from dietary analysis carried out in both surveys and experimental studies (see figure 3) that these athletes consume protein levels well above the current RDA (0.8g per kg/BW) established for their sedentary counterparts. This article shall try and establish what evidence there is for this practice and what rationale may lie behind such a large increase in their RDA.
Figure – 2 reported habitual protein intake of resistance athletes (Phillips, 2004)
Dietary Protein Manipulation.
Controversy has existed over dietary protein needs of athletes being greater than current RDAs for sedentary individuals (Campbell et al 2007). Protein needs are typically measured using nitrogen balance and amino acid tracer techniques (Campbell et al 2007). The nitrogen balance technique involves quantifying how much dietary protein is entering the body and how much nitrogen is being excreted (Campbell et al 2007). When a person is in negative nitrogen balance they are said to be in a state of catabolism, when in a neutral state they are said to be in a state of equilibrium when they are in a positive nitrogen state they are thought to be in a state of anabolism (Wilson and Wilson 2006). There however exist quite a few methodological issues with the nitrogen balance technique such as increased leucine oxidation during exercise not recorded in urine excretion as well as nitrogen loss through excessive sweating and breathing (Wilson and Wilson 2006). These methodological issues aside nitrogen balance remains the basis for all dietary recommendations for protein intake even though it has been suggested that a mixed approach of amino acid tracing and nitrogen balance techniques should be used (Phillips, 2004). In one of the earliest studies of protein dietary manipulation using bodybuilding athletes Tarnopolsky et al 1988 assessed the effects of protein intake and training status on lean body mass comparing three groups (sedentary controls, elite endurance athletes and elite bodybuilders n = 6) using both high protein and low protein conditions all diets where isocaloric. There was a ten day adaptation period and three days of nitrogen balance measurement for both conditions. Despite of the studies age it offers a well controlled example of the nitrogen balance technique, during the thirteen day of low protein diet (1.05g per kg/BW) bodybuilders showed a positive nitrogen balance and no loss of lean body mass leading the author to extrapolate that elite level bodybuilders have a dietary protein requirement only 12% greater than their sedentary controls (1.2g per kg/BW). The conclusions that may be drawn from this study are limited due to the short term of intervention, the nature of the exercise (maintenance) which may not have induced a hypertrophy response in the bodybuilding group as well as the small sample size. In another of the few experimental studies carried out on bodybuilders Tarnopolsky et al (1992) found that 1g per Kg/BW was insufficient to maximise muscle gain and recommended 1.43 – 1.6g per Kg/BW to maximise training effects in novice bodybuilders. The greater protein needs in this study where justified by greater levels of muscle accretion and the large amount of stress that new exercise protocols put on individuals which has also observed in endurance athletes. This study however may not be applicable to elite level athletes; this may be attributed to the likely hood of elite athletes reaching a plateau in their training. Hakkinen et al 1988 showed elite level strength athletes making modest gains of 4% in strength and 5.9% in muscle hypertrophy over a two year period whilst comparatively novice trainees during a month of resistance training gained 7.9% and 8.8% gains in strength and fibre cross sectional area respectively (Tarnopolsky et al, 1992). It may prove prudent to keep in mind that nitrogen balance techniques are limited in the conclusions that may be drawn as shown by high nitrogen balance in protein intakes similar to habitual diets of bodybuilders (2.8g per kg/BW) showed high nitrogen balances (12 – 20g of nitrogen a day) which should of attributed to a lean mass gain of 400-500g per day in these bodybuilders which obviously did not happen (Phillips, 2004). This data could be wrongly used to recommend very high levels of dietary requirements in bodybuilders. In a review of the available literature on protein requirements of strength athletes Phillips 2004 showed that an intake of 1.19g per kg/BW of protein (49% greater than current RDA) was required to maintain zero nitrogen balance which is demonstrated by figure 4.
Figure 3 – taken from Phillips (2004).
Wilson and Wilson 2006 conducted a large literature review addressing the protein requirements of strength athletes they identified a number of different measures used including nitrogen balance, amino acid tracing, performance based and body composition measurements. They suggest that studies using the nitrogen balance technique have lead to protein requirements ranging 1.2g – 2.2g per kg/BW to retain a positive nitrogen balance in strength athletes (appendix 1) these nitrogen balance techniques seem to be backed up by similar values in amino acid tracer studies (Wilson and Wilson, 2006). The studies involving both body composition and performance measures where typically longitudinal (6 months) these seem to indicate that higher protein diets (2.0g per kg/BW) lead to greater strength gains and improvements in body composition (see figure 5). It would seem that the lower value set at 1.2g per kg/BW has a sound basis in experimental studies however the value of 2.2 as the upper limit is slightly dubious as there may be health issues with high protein diets (Metges and Barth 2000 (see appendix 2)) however little or no supporting evidence exists for the negative effect of high protein diets on healthy athletic populations (Cambell et al 2007) there may a need for future investigation into optimal upper levels of protein consumption.
Figure 4 effects if high protein diet (2.0g per kg/BW) and low protein diet (1.0g per kg/BW) on strength Vukovich et al 2004 (Taken from Wilson and Wilson 2006)
Other Factors effecting protein consumption
It is impossible to talk about protein consumption and not include some of the spectrum of factors effecting protein use in the body. One of the biggest factors in protein use is the total calorie content of a diet; bodybuilders may require more protein in a calorie restricted diet due to the increasing oxidisation of amino acids (leucine) as an energy substrate (Wilson and Wilson 2006, Rankin 1995). Millward 2004 found that protein requirements for zero nitrogen balance at daily energy intakes of 30, 45, and 60 kcal/kg were 1.42, 0.87, and 0.32g/kg/d, respectively (Wilson and Wilson 2006). Protein timing, quality and feeding quantities have also been looked at in recent research and may affect overall RDAs (Campbell et al 2007). Carbohydrates seem to have a protein sparing effect and interact with protein to effect insulin secretion since all macronutrients interact it may prove prudent to take carbohydrate levels into account when assessing overall dietary intake of protein (Wilson and Wilson 2006). Overall training volume will also affect protein needs due to increased oxidisation and damage typical nitrogen balance studies have used sessions lasting around 75mins (Wilson and Wilson 2006) whilst studies on elite weight lifters using much higher volumes have shown protein requirements as high as 3.0g per kg/BW (Tarnopolsky et al 1992) more research is required on athletes who perform high volumes of resistance training.
Conclusion and practical applications for bodybuilders.
Current evidence seems to support the anecdotal recommendations that bodybuilders do require higher levels of dietary protein. However their reported habitual diets 2.8 – 5g per kg/BW are excessive even in light of recent studies and reviews (1.4 – 2g per kg/BW recommended in Cambell et al 2007). Due to the use of high volume exercise and severe calorie restriction during pre-competition diets (1000 – 1500 Kcal below maintenance, Heyward et al 1989) bodybuilders may need to vary protein intake in respect to contest readiness. Pre-Competition phases may need to include higher than normal levels of protein intake in an effort to preserve lean mass. Bodybuilders should also look closely at their overall Macronutrient profiles and calorie levels since increasing carbohydrate and fat intake whilst keeping a modest calorie restriction may help spare dietary and muscle amino acids leading to increased preservation of muscle loss (Rankin 1995).
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2 – Heyward V. H., Sandoval W. M. and Colville B. C. Anthropometric Body Composition and Nutritional Profiles of Bodybuilders During Training. Jornal of applied Sports Science Research, Volume 3, Number 2.
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6 – Tarnopolsky MA, Atkinson SA, MacDougall JD, et al. Evaluation of protein requirements for trained strength athletes. Journal of Applied Physiology 1992;73:1986
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8 – Wilson J., Wilson G. J., Contemporary Issues in Protein Requirements and Consumption for Resistance Trained Athletes. Journal of the International Society of Sports Nutrition 3(1);7-21,2006 (www.theissn.org)
9 – Metges C. C., Barth C. A., Metabolic Consequences of a High Dietary Intake in Adulthood: Assessment of Available Evidence. Journal of Nutrition 130. 886-889, 2000.