Optimising muscle mass is a primary goal for many athletes involved in strength and power sports, bodybuilders and recreational gym-goers.
From a health perspective, we know that the risk of muscle mass loss and function decreases with age, so it becomes even more important as we get older to focus on muscle mass and to mitigate this age-related loss.
One of the key nutritional considerations for optimising muscle mass is protein, the building block for muscle. And it’s not just a case of making sure an athlete eats enough protein in a day. Sure, this is the most important factor in the hierarchy of protein for skeletal muscle hypertrophy but there are other factors to consider, especially as we deal with high-performance athletes.
Total daily protein intake
Muscle protein synthesis (MPS) is the primary determinant of skeletal muscle hypertrophy – this is the main measure researchers are interested in. Morton et al performed a segmental linear regression analysis between relative total protein intake and the change in fat-free mass using 42 study arms, which included 723 young and old participants who performed resistance training at least twice per week with protein intakes ranging from 0.9-2.4 g/kg body weight/day (g/kg/day) (1). They found that the benefit from protein in terms of changes in fat-free mass starts to plateau at 1.6 g/kg/day, suggesting that in most cases this level is sufficient and effective at increasing MPS and optimising muscle mass gains from resistance training.
While this is a good starting point, let’s not forget that it’s an average as science mainly looks at averages. I believe that some individuals require over 1.6 g/kg/day to observe meaningful hypertrophic adaptations. In fact, an isolated study demonstrated that a level of 3.4 g/kg/day was actually safe and more effective than 2.3 g/kg/day in terms of changes in fat-free mass and body fat percentage (2). The total amount also depends on the individual’s caloric intake – if they’re also in a caloric deficit to lose fat mass, amounts higher than 1.6 g/kg/day are likely required to mitigate muscle mass loss and support satiety.
Protein quality
The key amino acid that triggers the increase in MPS via the mTOR pathway is leucine, so focusing on whole-food protein sources and isolated protein sources with a high leucine content is essential (3).
We usually eat mixed meals that contain protein, carbohydrate, fibre and fat (the food matrix). This typically translates into a more moderate but prolonged MPS response than from an isolated protein source. More evidence suggests that the micronutrient component of a whole-food protein source may also enhance the MPS response (4).
As for isolated protein sources, although whey proteins are the gold standard in terms of leucine content, certain protein sources such as plant-based proteins can be optimised either by consuming greater amounts of them or by mixing different sources.
Then again, trained individuals seem to get away with a bit less leucine than untrained or bed-rest individuals since their muscles are more ‘sensitised’. To get the same anabolic response as a trained individual, untrained individuals would need to either engage in resistance training or consume more leucine.
Protein distribution
Athletes should aim for an even protein distribution throughout the day instead of typically leaving most of their protein intake for dinner time (Figure 1).
Figure 1: Skewed vs Balanced daily distribution for the same amount of protein (140g). Adapted from Egan (5).
This concept was first shown in a key study by Areta et al. In this study, 24 healthy non-smoking young males, who had done at least two years of resistance training, were randomly assigned to one of three groups: 8 x 10g of whey protein isolate, 4 x 20g of whey protein isolate or 2 x 40g of whey protein isolate (6). Note that the total amount was the same (80g), but the pattern of consumption over 12 hours was different. They found that the repeated consumption of 20g of protein over 12 hours was better at stimulating MPS than the other patterns of consumption. This also translated into a superior anabolic molecular signalling compared to the other two patterns of consumption.
To optimise MPS, aim for a protein intake target of at least 0.4g/kg body mass at each meal or snack. As practitioners, it’s important to consider the practicalities of introducing protein distribution into an athlete’s daily eating plan while considering their training regime, life commitments and preferences – this is where individuality comes into play. Although we should take a whole-food approach, the convenience of good-quality protein supplementation is sometimes appropriate to ensure that an athlete is meeting their overall needs and is obtaining a balanced protein distribution.
Protein timing
We know that MPS rates are elevated for up to 48 hours after a single bout of resistance exercise, so muscles are sensitive to protein feeding throughout this recovery period. Therefore, the “anabolic window” is not as important as thought, as eloquently discussed by Aragon and Schoenfeld in their 2013 review paper (7).
Still, we must put the athlete into context. A good rule of thumb is that if the athlete goes into a training session fasted, or if they ate their last meal four to six hours ago, it becomes more of a priority to consume protein right after the session (or even during a long session). But if the athlete had a snack before their session that contained some protein, they can afford to delay the post-exercise protein feed by up to two hours. This can be delayed even further if they consumed a protein-rich mixed meal before their session.
That said, there’s no harm in eating a protein-rich snack or meal immediately afterwards: it’s a good strategy sometimes to ensure that athletes are meeting their overall needs by asking them to consume the likes of a post-exercise smoothie. The same applies to pre-sleep protein, which is also a popular timing strategy. Most studies have compared a control group with a group that has consumed extra protein before bedtime, meaning a higher daily consumption, so it’s not really a true comparison in terms of timing. But again, it’s another feeding opportunity for athletes to meet their overall needs and for older individuals or possibly even patients who experience accelerated muscle loss (8).
Protein supplementation
As seen above, protein supplementation has its place at times. Yet the benefits of protein supplementation seem to diminish when total daily protein is at least 1.6 g/kg/day. And the overall effect of protein supplementation isn’t as large as one might think, with a mere 0.30 kg increase in fat-free mass. This was neatly demonstrated in the meta-analysis, systematic review and meta-regression by Morton et al (1).
They also showed that for changes in fat-free mass, protein supplementation was more effective in resistance-trained individuals than untrained individuals (1.05 kg vs 0.15 kg). Morton et al speculated that this may be because resistance-trained individuals have a smaller potential for muscle growth and a lower protein turnover after exercise, which means they may have less flexibility to change with resistance training and have a greater need for protein supplementation.
It also seems less effective with increasing age. This makes sense since older individuals are more anabolically resistant and require more protein per meal to achieve similar rates of MPS than younger individuals. The average supplemental dose in the Morton et al study was relatively low (20±18 g/day), so their finding wasn’t surprising.
Final remarks
The focus of this blog article is protein, with an attempt to contextualise research. We should not forget one important aspect though, and that’s the gut-muscle axis. It’s a topic I’ve written about before (click here) and perhaps the most important consideration. If an athlete presents with gut permeability and dysbiosis, for example, this will likely affect the process of nutrient digestion and absorption, including dietary amino acids needed to fuel skeletal muscle hypertrophy. Gut health should be our first area of focus if an athlete presents with symptoms, even if they’re eating an ideal diet with an adequate amount, distribution and timing of good-quality protein.
References
- Morton et al. (2017). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adult. Br J Sports Med. 52:376-384.
- Antonio et al. (2015). A high protein diet (3.4 g/kg/d) combined with a heavy resistance training program improves body composition in healthy trained men and women – a follow-up investigation. J Int Soc Sports Nutr. 12:39
- Philips (2016). The impact of protein quality on the promotion of resistance exercise-induced changes in muscle mass. Nutr Metab. 13:64.
- Trommelen et al. (2019). The muscle protein synthetic response to meal ingestion following resistance-type exercise. Sports Med. 49:185-197.
- Egan (2016). Protein intake for athletes and active adults: Current concepts and controversies. Nutr Bull. 41:202-213.
- Areta et al. (2013). Timing and distribution of protein ingestion during prolonged recovery from resistance exercise alters myofibrillar protein synthesis. J Physiol. 591(9):2319-2331.
- Aragon & Schoenfeld (2013). Nutrient timing revisited: is there a post-exercise anabolic window? J Int Soc Sports Nutr. 10:5.
- Trommelen & van Loon (2016). Pre-sleep protein ingestion to improve skeletal muscle adaptive response to exercise training. Nutr. 8(12):763.