Monday, June 21, 2010

Effects of Whey Protein Supplementation on Muscle Protein Synthesis and Hypertrophy


If you work out with weights and you want to feed your muscles so that they will grow stronger and bigger, then you likely use some form of protein supplement. Whey protein (one form of milk protein, the other being casein) is probably the most popular protein supplement.

This is yet another research article looking at the impact of whey protein on muscle protein synthesis (repairing the damage caused by weight training) and hypertrophy (muscle growth). The full article (provisional) is available as a PDF.

In the past, the research has been overwhelming that protein supplementation supports weight training efforts, and in general, whey has been demonstrated to be the best source of amino acids, especially post-workout when the muscle will be most in need of protein synthesis for recovery. This meta-study confirms that earlier research.

Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein

Juha J Hulmi email, Christopher M Lockwood email and Jeffrey R Stout email

Nutrition & Metabolism 2010, 7:51 - doi:10.1186/1743-7075-7-51

Published: 17 June 2010

Abstract (provisional)

Regardless of age or gender, resistance training or provision of adequate amounts of dietary protein (PRO) or essential amino acids (EAA) can increase muscle protein synthesis (MPS) in healthy adults. Combined PRO or EAA ingestion proximal to resistance training, however, can augment the post-exercise MPS response and has been shown to elicit a greater anabolic effect than exercise plus carbohydrate. Unfortunately, chronic/adaptive response data comparing the effects of different protein sources is limited. A growing body of evidence does, however, suggest that dairy PRO, and whey in particular may: 1) stimulate the greatest rise in MPS, 2) result in greater muscle cross-sectional area when combined with chronic resistance training, and 3) at least in younger individuals, enhance exercise recovery. Therefore, this review will focus on whey protein supplementation and its effects on skeletal muscle mass when combined with heavy resistance training.

Net protein balance (NPB) is defined as muscle protein synthesis (MPS) minus muscle protein breakdown (MPB), or NPB = MPS – MPB. Thus, a significant rise in skeletal MPS (anabolism) and/or reduction in MPB (catabolism), such that NPB remains positive can result in increased skeletal muscle mass accretion. Conversely, a negative NPB, arising from a reduction in MPS and/or increase in MPB, will result in a loss of skeletal muscle. It has clearly been demonstrated that an acute bout of heavy resistance exercise – intermittent exercise of repeated short, highintensity (60-90% 1RM) bouts [1] – stimulates a significant increase in MPS. However, NPB remains negative due to a concomitant rise in MPB when resistance exercise and recovery occur under fasted conditions [2-4]. Pre- or post-exercisise ingestion of protein (PRO) or essential amino acid (EAA) can increase MPS and result in a positive NPB [3,5-11]. Furthermore, the majority of studies in humans suggest that PRO/EAA ingestion in the context of a resistance training session can enhance skeletal muscle hypertrophy in response to chronic resistance training [12-20]. More specifically, PRO/EAA intake around the time of resistance exercise, as opposed to nutrient ingestion at times distal to exercise, may be more beneficial for promoting muscle hypertrophy [21,22].

Milk contains two categories/fractions of PRO – whey and casein. About 20% of the total PRO in commercial bovine milk comes from whey [23-25]. Direct and indirect evidence suggests that whey may be an especially suitable PRO to be used in conjunction with resistance exercise to stimulate muscle hypertrophy [9,20,26,27]. If correct, this may contribute to the observed widespread use and sales of whey PRO amongst sports nutrition consumers. This review will, therefore, focus on whey PRO supplementation and resistance training as it pertains to muscle mass adaptations in healthy adults. Some general effects of PRO/EAA will, however, be reviewed first.

Effects of PRO/EAA supplementation on MPS and skeletal muscle hypertrophy
Heavy resistance training has a well documented positive effect on skeletal muscle size [20,28-31], whereas ingestion of sufficient amounts of PRO/EAA also plays an important role in muscle adaptations. For example, in young men, PRO/EAA supplementation in combination with resistance training has been shown to significantly increase myofiber cross-sectional area greater than a non-energetic or carbohydrate placebo [12-15]. Additionally, PRO/EAA has been shown to be more effective than carbohydrate or non-energetic placebo at increasing lean or fat-free body mass and whole muscle cross-sectional area [14-20,32]. Contrary to the aforementioned, some studies have reported that PRO/EAA ingestion provides no significant effect on myofiber size or lean body mass during resistance training [33-36]. Overwhelmingly, however, in young males, PRO/EAA has been shown to positively augment the physiological adaptation to exercise. For instance, Andersen et al. [12] investigated the effects of a mostly whey-containing PRO blend versus an isoenergetic carbohydrate, consumed before and after resistance exercise for 14 weeks, in previously untrained young men. Only the PRO group showed type I and II myofiber hypertrophy (18% and 26%, respectively). Similarly, Hartman et al. [15] reported that consumption of fat-free milk after resistance exercise, for 12 weeks, increased lean mass and type II myofiber crossectional area more than consuming soy or carbohydrate in previously untrained young males. Candow et al. [17], on the other hand, found that both whey and soy PRO increased lean tissue mass more than an isocaloric carbohydrate placebo in healthy, young men. Hulmi et al. [20,37] has also reported that combined PRO ingestion and resistance training in previously untrained males, following an ad libitum diet, provides an augmented physiological adaptation to training. Specifically, ingestion of 15 g of whey PRO isolate (WPI) immediately before and after resistance exercise, for 21 weeks, increased skeletal muscle cross-sectional area [20] and seemed to accelerate increases in muscle thickness [37] more than ingestion of a non-energetic placebo. No significant effects between groups on direct measures of myofiber size were observed [37]. However, this non-effect may be due to large variation inherent within the measurement. Interestingly, the significant differences observed between groups occurred despite both groups consuming a relatively large habitual ingestion of PRO from diet alone (~1.4-1.5 g/kg bodyweight /day).

Read the whole study.

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