Recommended Protein Intake to Build Muscle Mass

Optimum protein intake levels for athletes and when to take protein to build muscle

Article at a glance:
  • The issue of optimum protein intake levels for athletes seeking muscle mass gains is addressed and some of the myths are dispelled;
  • Protein quality and the role of the essential amino acids (particularly leucine) is discussed;
  • The importance of timing of protein ingestion is emphasised.

All athletes know that adequate protein is vital to build lean muscle mass. However, according to Dr Kevin Tipton, the latest research indicates that more is not necessarily better when it comes to optimum protein intake for maximising muscle mass

The metabolic basis for changes in muscle mass is net muscle protein balance (NBAL). Muscle proteins, in fact all body proteins, are constantly being synthesised and degraded; these processes are concurrent. The balance between these two processes determines the amount of proteins in muscle.

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Myofibrillar proteins
Proteins found in muscle and other tissues that provide structure and size and which are necessary for muscle

More specifically, changes in muscle mass are due to changes in the balance of the synthesis and breakdown of muscle contractile, ie myofibrillar proteins. Over any given time, the quantity of muscle protein is due to a change in NBAL. Accretion of muscle proteins occurs during periods of positive balance and muscle proteins are lost during periods of negative balance (see figure 1). Nutritional intake and exercise both have profound influences on the duration and magnitude of these periods of positive and negative net muscle protein balance.

The amount of muscle mass gains possible by any individual is ultimately determined by genetics. So, those who gain mass easily may want to thank their parents first. However, environmental influences, such as exercise and nutrition, have a profound impact on muscle mass and will determine what mass within this range will be expressed at any given time. The type, volume, intensity and duration of the exercise training will have by far the largest influence on muscle mass. No matter what or how much is eaten, gains in muscle mass will be minimal without the proper training load.

Exercise and nutrition influence muscle mass through changes in muscle protein synthesis and breakdown that will increase (or decrease) NBAL. On a daily, or even hourly, basis NBAL can be either positive or negative, depending on feeding and exercise situations. The length and duration of these periods of positive and negative balance determine the net loss or gain of muscle mass(1). Consequently, in healthy, mass-stable adults, periods of positive and negative NBAL will be equal, and no growth occurs. Muscle growth only results when a cumulative positive protein NBAL prevails (see figure 1).

Figure 1: Net Muscle Protein Balance

Figure 1: Net Muscle Protein Balance

Figure 1: Muscle protein gains are due to the accumulation of muscle protein in response to each individual bout of resistance exercise plus nutrient (amino acid) intake. For illustration purposes, the theoretical daily response to resistance exercise plus ingestion of a meal at weeks 1, 12 and 24 of training is depicted. There is no change in basal NBAL or in the response to a meal plus exercise over time, but instead muscle hypertrophy results from an accumulation of proteins due to the response to each individual exercise bout. The positive area in response to exercise plus nutrient intake is greater than the negative areas during fasting.

Nutritional influences on muscle mass have received a great deal of attention lately. Protein and amino acids in various forms are generally thought to be the most important nutrient for muscle building. As such, many athletes consume very large amounts of protein. In a recent article, scientists at McMaster University in Canada gathered data from many published papers. They determined that strength athletes consume well above 2.0g protein per kg body mass per day (g/kgBW/d) on average and many consume up to 3.5-4.0g/kgBW/d(2). That equates to as much as 400g protein consumed per day!

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How much protein?

The question is whether that much protein is necessary or even desirable for increasing muscle mass and strength? It is clear that protein ingestion is critical for increased muscle mass. Resistance exercise increases muscle protein synthesis resulting in improved muscle protein balance(3). However, without a source of amino acids, muscle protein balance will not reach positive levels – ie muscle anabolism(4).

Protein ingestion before or after exercise clearly results in positive muscle anabolism. Proteins, particularly myofibrillar proteins, accumulate over time in response to each exercise bout and associated protein intake, resulting in increased muscle mass. However, the amount of protein necessary to stimulate muscle anabolism in association with exercise is relatively small – as little as 6g of essential amino acids consumed either before or after exercise result in positive net balance(5).

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Essential amino acids
Amino acids found in body proteins that are not synthesised in the body and must be ingested in foods

Furthermore, recent data presented at the latest American College of Sports Medicine Conference in New Orleans earlier this year demonstrate that the anabolic response to protein ingestion following exercise demonstrates a ceiling effect. Consumption of more than 10g protein results in diminishing increases in muscle anabolism following exercise. Thus, it appears that large amounts of protein are unnecessary. The excess protein is simply oxidised for energy and not used for muscle building.

Protein requirements for athletes are a somewhat controversial topic in the scientific community(6). Protein requirements are typically determined by measuring nitrogen balance. This technique is based on the fact that protein is unique among nutrients in that it contains nitrogen. Thus, if one measures the amount of nitrogen consumed and how much is excreted, the gain or loss of body (not necessarily muscle) protein may be determined. This method is commonly used to determine protein requirements for various populations. Several well-controlled studies show that nitrogen balance is attained in highly trained athletes at the levels of protein intake mentioned above –
ie approx 1.2-1.6g/kgBW/d(1,6,7).

Nitrogen balance conundrum

So, why do many athletes and coaches maintain that much higher protein intakes are desirable for increased muscle mass? The answer probably lies in the nitrogen balance method. Athletes desiring increased muscle mass should be in positive nitrogen balance, thus the conclusion is that protein intakes above 1.6g/kgBW/d are considered necessary. Furthermore, when nitrogen balance is measured in athletes, the greater the protein intake, the greater the nitrogen balance(2), thus athletes conclude that the more protein they eat, the bigger they’ll get.

Unfortunately, the increase in muscle mass that would be associated with these very high nitrogen balances is simply not possible (see box 1), even if anabolic drugs were administered. If this level of nitrogen were actually incorporated into muscle, these athletes would gain around 100kg of muscle mass in a year(1,7)! Clearly, there are problems with this method for determining nitrogen balance, especially at high levels of protein intake.

Box 1: Why positive nitrogen balance is not the same as muscle gain

  • Suppose an athlete eats 2.5g protein/kg/d; this would result in a positive nitrogen balance of around 15g of nitrogen per day;
  • But nitrogen constitutes only around 16% of protein by weight, therefore actual protein gain = 15g N x 1g protein/0.16g N = around 94g of protein per day;
  • Since muscle is 75% water, amount of muscle accretion per day = 94g protein x 25% protein in muscle (75% water) = 282g muscle per day;
  • Per year = 282g protein per day x 365 days = 102930g/yr or 103kg of muscle gained in one year!

More direct evidence that high positive nitrogen balance is disassociated from gains in lean mass has accumulated. Several studies demonstrate that athletes may have a very high nitrogen balance, but lean body mass does not increase(1,7). Thus, the basis for very high levels of protein intake is unsound.

Recently, two studies from McMaster University in Ontario nicely show why it is not necessary to ingest large amounts of protein during training designed to increase muscle mass(8,9). Athletes in these studies consumed between 1.2 and 1.6g/kgBW/d of protein for 12 weeks. Muscle mass and strength increased during training on what may be considered – at least by many athletes and coaches – a relatively modest level of protein intake.

These studies clearly demonstrate that the anabolic nature of training actually decreases the requirement for protein and that muscle mass and strength increase on ‘normal’ levels of protein intake; extremely large amounts of protein (above 2.0g/kgBW/d) are unnecessary and do not increase strength and mass gains. The excess protein is simply oxidised and the nitrogen likely ends up in the urea pool to ultimately be excreted.

“The main problem with high protein intakes is that other nutrients must be supplanted if energy intake is not to be increased”

Protein dangers?

On the other hand, is there any harm in consuming excess protein? Many scientists and physicians have warned against high protein intakes due to potential health consequences. In particular kidney problems and loss of bone are given as adverse effects of high protein intakes. However, there has never been a documented case of kidney problems in otherwise healthy individuals.

Similarly, bone loss with high protein intake seems to be overstated. The main problem with high protein intakes is that other nutrients must be supplanted if energy intake is not to be increased. Thus, it is likely that carbohydrate intake will go down. Carbohydrates are critical to performance, especially in endurance exercise, but also for maintenance of high-intensity resistance training. Thus, care should be exercised to avoid increasing protein intake at the expense of other nutrients, particularly carbohydrates.

In fact, energy intake is the most important nutritional factor for increasing muscle mass. It is very difficult, if not impossible, to gain muscle mass if energy balance is negative, ie energy intake is less than expenditure. Indeed, it is impossible to maintain positive nitrogen balance in the face of energy deficits; even given high protein intakes(10).

On the other hand, if energy balance is positive, then athletes may gain muscle mass on a wide range of protein intakes. About 100 years ago, it was demonstrated that soldiers in training will gain muscle at relatively low levels of protein intake – around 1.0g/kgBW/d(11).

A more recent study demonstrated that increased muscle mass during resistance training was equivalent when athletes were fed 2,000 extra calories on top of their normal dietary intake in the form of either carbohydrate alone or carbohydrate plus protein(12). Taken together, these studies suggest that when adequate protein (as little as 1.0g/kgBW/d) is consumed, muscle hypertrophy is dependent on provision of sufficient energy.

Furthermore, by consuming the calories needed to provide the energy necessary to support training, most athletes will automatically consume ample protein without having to resort to supplementary sources. Resistance training at high volumes and intensities is common and necessary to support increased mass and strength. This level of training requires high energy intakes to support it(13). Therefore, even if protein is a relatively low proportion of the diet (eg around 12%), there will be ample protein ingested to meet the higher estimates of protein requirements for muscle growth based on nitrogen balance.

Since it is clear that muscle mass accumulates in response to each individual exercise session (see figure 1), investigations of the acute response of muscle protein synthesis to exercise and nutrient intake provide valuable information for delineation of important strategies for increasing mass and strength.

One important consideration that this research illustrates is that it is rather nonsensical to recommend a general amount of protein to all athletes as the optimal amount to increase muscle mass. Since various factors, such as timing of intake, type of protein and other nutrients ingested with protein influence the overall response, two athletes consuming the same amount of protein will not necessarily experience the same muscle growth.

“This research illustrates that it is rather nonsensical to recommend a general amount of protein to all athletes”

Studies have demonstrated that the type of protein will influence the anabolic response. Recent research shows that milk ingestion stimulates muscle anabolism following exercise and that response is greater than that generated by soy ingestion(14). These results may be used to make two important points: 1) protein in foods works just as well as that in supplements and, 2) animal proteins seem to engender a superior anabolic response following resistance exercise.

A subsequent training study from the same research group supported the results of the acute metabolic study – confirming that acute metabolic studies do represent the potential for longer-term muscle gains(15).

Essential amino acids

The important component of the protein seems to be the essential amino acid content. It is now clear that muscle anabolism occurs with ingestion of only the essential amino acids – ie the non-essential amino acids are unnecessary to stimulate muscle growth following exercise(4). However, this doesn’t mean that essential amino acid supplements are superior to non-essential or to whole proteins. It simply means that essential amino acids can stimulate muscle protein synthesis and there are ample non-essentials to support the elevated levels of synthesis.

Leucine may be the most important amino acid for stimulation of muscle protein synthesis. Leucine, along with isoleucine and valine, is a branched-chain amino acid (BCAA). BCAAs are often touted as the most anabolic amino acids and many BCAA supplements are sold and consumed.

In animal studies leucine stimulates pathways inside the muscle cells that result in increased muscle protein synthesis in rats following intense exercise that would otherwise decrease synthesis(16,17). Thus, in a catabolic exercise model, leucine ingestion may be very effective as an anabolic agent. However, the evidence in humans is less clear, particularly following resistance exercise.

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Catabolic exercise model
An experimental model that results in a reduction in muscle protein synthesis
Pre-hormones
Compounds that may be used by the body to manufacture hormones
Metabolite
A substance produced during metabolism of another compound

Researchers in the Netherlands found that protein ingestion, in addition to carbohydrates, stimulated muscle protein synthesis more than carbohydrate alone(18). However, additional leucine ingested with the protein and carbohydrate did not result in further stimulation of muscle protein synthesis.

Similar results were found in a recent study from a research group in Galveston, Texas. There is evidence that leucine may decrease the amount of muscle protein breakdown in humans, but these studies did not involve exercise(19). The Galveston results demonstrated that the NBAL was not improved with additional leucine, thus casting doubt on the efficacy of leucine supplementation following anabolic exercise in humans. However, it should be noted that few studies have actually examined this issue and a systematic evaluation may be required before leucine can be dismissed as an anabolic agent.

Protein timing

The timing of protein and amino acid ingestion has been given a great deal of attention lately. When an essential amino acid plus carbohydrate solution was ingested before resistance exercise, the response of muscle anabolism was greater than when this solution was ingested following exercise(20). Many people interpreted these results to mean that athletes should ingest protein before exercise.

However, a follow-up study by the same research group showed that the difference in the response of muscle anabolism was very little when whey protein was ingested before and after exercise – a completely different result from the free amino acids and carbohydrate mixture(20,21). Thus, there is an interaction of the type of amino acid source and the timing of ingestion, ie not all proteins are created equally.

The difference is probably explained by the time it takes to digest protein. Since free amino acids do not need to be digested in the gut, the appearance of amino acids into the blood is very rapid. So, when free amino acids are ingested immediately before exercise, delivery of amino acids to the muscle is very high during exercise. However, since protein must be digested, amino acid levels in the arterial blood are not increased rapidly enough to increase delivery so that the anabolic response is similar to that when proteins are ingested following exercise. It is possible that ingestion of protein 15, 20 or even 30 minutes prior to exercise may be advantageous, but no study has looked into this possibility.

Ingestion of other nutrients alongside protein and amino acids seems to be advantageous for creation of an anabolic response. Ingestion of carbohydrates and fat along with protein appears to increase the uptake of amino acids into the muscle from the protein (see figure 2)(22,23). These results also support an earlier contention – ie that protein in foods is equally effective as that in supplements for stimulating muscle hypertrophy.

Figure 2: Amino acid utilisation from various sources following resistance exercise

Figure 2: Amino acid utilisation from various sources following resistance exercise

Figure 2: Utilisation of ingested amino acids for muscle protein accretion following resistance exercise. Addition of carbohydrate to an amino acid source increases the utilisation of the ingested amino acids. MAA = mixed amino acids; EAA = essential amino acids only; MAA+CHO = mixed amino acids plus carbohydrates; EAA+CHO = essential amino acids plus carbohydrates; CAS = casein; WHE = whey proteins.

Whereas there is clearly a place for protein supplements (supplements may be much more convenient to use in certain situations) there is no reason that muscle growth can’t be optimised simply by eating food sources of high-quality proteins such as eggs, milk and dairy products and lean meat. This fact should not be particularly surprising. After all, we did not evolve to forage for individual proteins at supplement stores, but we did evolve to utilise the protein from foods to our best advantage!

Dr Kevin Tipton is a senior lecturer in exercise metabolism in the School of Sport and Exercise Sciences at the University of Birmingham UK

References

  1. Applied Physiology, Nutrition and Metabolism 2006; 31:647-654
  2. Nutrition 2004; 20(7-8):689-695
  3. Am J Physiol (Endocrinol Metab) 1997; 273(36):E99-E107
  4. Am J Physiol 1999; 276(4 Pt 1):E628-E634
  5. Am J Physiol Endocrinol Metab 2002; 283(4):E648-E657
  6. Clin Sports Med 2007; 26(1):17-36
  7. Int J Sport Nutr Exerc Metab 2007; in press
  8. Appl Physiol Nutr Metab 2006; 31(5):557-564
  9. J Nutr 2007; 137(4):985-991
  10. J Nutr 1984; 114(11):2107-2118
  11. Chittenden RH: The Nutrition of Man. London, Heinemann, 1907.
  12. J Sports Med Phys Fitness 2002; 42(3):340-347
  13. J Appl Physiol 1992; 72(4):1512-1521
  14. Am J Clin Nutr 2007; 85(4):1031-1040
  15. Am J Clin Nutr 2007; 86(2):373-381
  16. J Nutr 1999; 129(6):1102-1106
  17. Am J Physiol 1998; 274(2 Pt 1):C406-C414
  18. Am J Physiol Endocrinol Metab 2005; 288(4):E645-E653
  19. J Nutr 2005; 135(6 Suppl):1580S-1584S
  20. Am J Physiol Endocrinol Metab 2001; 281(2):E197-E206
  21. Am J Physiol Endocrinol Metab 2007; 292(1):E71-E76
  22. Med Sci Sports Exerc 2003; 35(3):449-455
  23. Med Sci Sports Exerc 2006; 38(4):667-674

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