September 24, 2011
Made of amino acids, proteins are particularly important because they make up our skeletal muscles, which are necessary for physical activity and basic functions. Furthermore, proteins are constantly degraded and synthesized. Degraded proteins are oxidized or converted to glucose, ultimately excreted as urea in our urine. The inability to recycle amino acids means that proteins are required in our diet. There are 20 amino acids, with 9 being essential to our diet. Meats have all 20 (complete protein), while most plant products do not (incomplete protein). Thus, for vegetarians, it is important to combine sources to get a complete protein (i.e. rice and beans).
The Dietary Reference Intake (DRI) for protein is 0.8 g per kilogram body weight per day. However, many individuals get more than this. High protein diets are familiar to many Americans because of the large amount of meat available in this country. In addition, protein supplements are popular among athletes and body builders.
Muscle mass is built when the net protein balance is positive: muscle protein synthesis exceeds muscle protein breakdown. Research shows muscle protein turnover is greatest post-workout (Phillips, et al 1999). Additionally, it has been shown that muscle mass increases over time when resistance exercise (i.e. lifting, body weight exercises, etc) is combined with nutrient intake (Phillips, 2004). The effects of resistance exercise and intaking proper nutrients is also additive, meaning that both are necessary to increase muscle mass and are more effective together than alone—there is an interactive effect. Synthesis of muscle protein following each bout of exercise is small, and these small changes, over time, gradually increase muscle mass. This is why changes in muscle mass are not seen until after months of training (Tipton, et al 2001). Likewise, hypertrophy (increase in muscle volume due to an increase in cell size) is a result of an accumulation of successive periods of positive protein balance after exercise when protein is consumed; hypertrophy takes a while (weeks to months) to attain (Biolo, et al 1995).
There are many factors, however, that come into play in determining if your muscle mass will grow by increasing protein intake through supplements and diet. The bottom line is that no evidence suggests protein supplements work better than protein consumption from a high-quality diet in increasing muscle mass. And there is limited evidence indicating that highly trained athletes require a daily amount of protein much higher than the DRI. Here are some other factors that play a role in building muscle mass and in your protein needs:
- Other nutrients: It has been shown that carbohydrate, in addition to protein, in a post-exercise meal increases muscle protein synthesis and results in net protein synthesis (Miller, et al 2003).
- Timing: Protein synthesis occurs 24-48 hours after exercise; research shows that it is likely that an athlete who consumes protein plus carbohydrate sooner and more often after exercise has a better chance at increasing muscle repair and synthesis (Bohe, et al 2003). However, the rate of protein synthesis has a ceiling, and consuming protein beyond this point has not been shown to stimulate more synthesis (Bohe, et al. 2003).
- History of resistance exercise: Research suggests that needs increase above 0.8g/kg body weight/day for people undergoing acute resistance training. That is, people who have just started resistance training. However, athletes who have been training for long periods of time (months to years) do not need to increase their protein intake because research shows prolonged resistance training attenuates the acute immediate response of muscle protein synthesis to an isolated bout of exercise (Philipps, et al 1999).
- Our current diets: Research shows that most athletes are getting enough protein in their daily diets—from intake of normal foods; in fact, some athletes are getting more protein than necessary for positive net protein balance (Phillips, 2004).
The Bottom Line:
Increased muscle mass results from small amounts of protein synthesis (positive net protein balance) in response to nutrient intake (carb and protein) combined with resistance exercise (Tipton & Ferrando, 2008). Most of us already get the amount of protein we need to maximize our efforts in the gym.
Eating a high-quality diet with good sources of protein is the best thing to do if you’re looking to gain strength and muscle mass. Lean protein, like lentils, beans, grains, chicken, pork, fish, and lean red meat, are great protein sources. Peanut butter, and other nuts/seeds are also good. Eating a snack post-workout is smart for athletes who are undergoing more than an hour of resistance exercise. However, a protein supplement at this time is not necessarily the best bet; instead, try to eat a mixed meal of carb and protein and, additionally, factor this snack into your day’s diet.
By: Kate Sweeney
Editor: Elisha Sum
Biolo, G., Maggi, S., Williams, B., Tipton, K., and Wolfe, R. (1995). Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans. Am. J. Physiol. 268, E514-E520.
Bohe, J., Low, A., Wolfe, R., and Rennie, M. (2003). Human muscle protein synthesis is modulated by extracelluarl, not intramuscular amino acid availability; a dose response study. J Physiology, 552:315.
Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein, and amino acids, part I. Washington, DC: National Academy Press, DC, 2003.
Miller, S., Tipton, K., Chinkes, D., Wolf, S., and Wolfe, R. (2003). Independent and combined effects of amino acids and glucose after resistance exercise. Med. Sci. Sports Exercise. 35, 449-455.
Phillips, S.M. (2004) Protein requirements and supplementation in strength sports. Nutrition 20, 689–695.
Phillips, S., Tipton, K., Ferrando, A., and Wolfe, R. (1999). Resistance training reduces the acute exercise-induced increase in muscle protein turnover. Am J Physiology, 276;E118.
Tarnopolsky, M., Atkinson, S., MacDougall, J., Atkinson, S. (1992). Evaluation of protein requirements for trained strength athletes. J Appl Phyiol, 73;1986.
Tipton, K. and Ferrando, A. (2008). Improving muscle mass: response of muscle metabolism to exercise, nutrition, and anabolic agents. Essays in Biochemistry. 44,85-98.
Tipton, K., Rasmussen, B., Miller, S., Wolf, S., Owens-Stovall, S., Petrini, B., and Wolfe, R. (2001). Timing of amino acide-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am. J.Physiol. Endocrinology Metab. 281, E197-E206.