There are two main anabolic stimuli for muscle: exercise and protein intake.
Protein not only provides the building blocks for muscle. It also provides the trigger to stimulate muscle protein synthesis. Muscle protein synthesis (MPS) is the physiological process of adding new amino acids to muscle proteins and is the primary mechanism of muscle growth.
Athletes typically consume a lot of protein to optimize recovery and improve training adaptations. We’re going to take a look at the protein habits of high-level athletes and compare them to evidence-based protein recommendations. In addition, we’ll go beyond the guidelines and discuss my advanced hypotheses to take gains to the next level.
Assessing protein intake in high-level athletes
We recently collected food intake data from 553 Dutch athletes from a wide range of sports (Gillen, 2016). All of these athletes were at least national-level competitors, including several Olympic athletes. Their food intake data were collected using three 24-hour dietary recalls (two on weekdays and one in the weekend). We divided the athletes in strength, team, and endurance athletes. Of note, the strength athletes’ group contained sports like CrossFit and gymnastics but did not include bodybuilders, powerlifters, or Olympic lifters, who might focus more on protein intake. However, you don’t need to worry if you’re a lifter: this article will still be extremely relevant to you.
How reliable are the data?
A 24-hour dietary recall asks specific questions to characterize food intake in the previous day. The advantage of this method over prospective food journals is that the outcome is not affected by awareness and altered food choices. Just having a food journal lying around can make you more aware of what you’re eating and can change your dietary habits, which means the data you provide may not reflect the way you’d typically eat.
However, all dietary assessment methods based on self-reporting are prone to errors. Total energy intake and protein intake normally display less random or day-to-day variation than other nutrients, such as marine fatty acids. Systematic errors – that is, over-reporting or under-reporting of intake – are often due to socially desirable reporting, omitting foods, and underestimating of portion sizes.
However, we have validated protein intake assessed with the 24-hour dietary recalls with 24-hour nitrogen excretions (Wardenaar, 2015). We found a reasonably good correlation between the methods, but the recalls did appear to underestimate protein intake by about 25%. Keep that in mind when looking at the data.
Total daily protein intake
The first thing we looked at was the total daily protein intake in the athletes.
Total daily protein intake was about 1.5g/kg/d. This is nicely in line with protein recommendations for athletes, which are about 1.3-1.8g/kg/d (Phillips, 2011). If we take into account the protein underestimation by the recalls, it appears that on average, athletes even hit the upper limit of the recommendation.
I quickly have to address a recent paper that got a lot of attention on social media in the strength training community. It determined protein needs in bodybuilders and came to an estimated average requirement of 1.7g/kg/d (Bandegan, 2017). They also calculated the 95% CI estimated average requirement to be 2.2g/kg/d, which basically provides a huge safety margin (for the bodybuilders with the ”let’s just go very high to play it safe mentality”). While it’s nice they studied bodybuilders, the actual measurement is not specific to muscle growth and likely overestimates protein needs to maximize muscle mass gains.
Protein recommendations are often expressed in g/kg/d. This seems quite logical, as a heavier person has more muscle mass, and thus might need more protein. However, only one study has directly compared the effect of protein ingestion on MPS in a group of subjects with a high lean body mass versus a group with low lean body mass. The MPS response to protein ingestion was not impacted by the amount of lean body mass of the subjects (Macnaughton, 2016).
This suggests that bigger guys may not need more protein than smaller guys. Therefore, expressing protein recommendations as an absolute amount (e.g. 120g/d) might be more accurate than recommendations expressed per kilogram of bodyweight. For example, a protein intake of 1.5g/kg/d represents 75g protein in a day for a 50kg person which is likely a suboptimal amount despite them being smaller. This might sound counterintuitive, but remember the two functions of protein for muscle: protein provides the building blocks for muscle growth, and it triggers muscle protein synthesis. It appears that even a relatively small amount of protein provides more than enough building blocks for muscle growth, whether you’re big or small. However, you need more protein to maximize the MPS trigger function (so you actually make use of the building blocks), which does not seem to depend much on your size.
There does not appear to be a difference between the sexes in the MPS response to protein ingestion (Smith, 2016). Our data show that females eat almost the same amount of protein as men expressed per unit of body weight, but because their bodyweight is much lower, their total amount of protein per day is much smaller. Therefore, women are potentially at risk of eating suboptimal amounts of protein.
Protein intake correlates with energy intake
The protein content of a healthy diet typically ranges between 15-25% of total energy intake in the general population (Fulgoni, 2008). This suggests that protein intake is strongly determined by total energy intake. Indeed, we observed a strong positive correlation between protein intake and total energy intake.
These findings are exactly what you would expect. The more you eat in general, the more protein you eat.
This shows that protein intakes tend to be lower when overall energy take is lower. Therefore, a conscious effort should be made to ensure sufficient protein intake when energy intake is low (which is typical in smaller females, weight-conscious sports, and during intentional weight loss). In fact, there is evidence that suggests that protein intakes should be higher during energy restriction (Phillips, 2011).
Protein type and source
The next thing we did was break down the type of protein consumed (animal versus plant-based protein) and the main protein sources for these athletes (the actual food products).
The first thing to note is that plant-based protein made up almost half of total protein intake. This is important because plant-based protein is typically less anabolic than animal-based protein (Van Vliet, 2015). Plant-based protein contains less essential amino acids compared to animal-based protein, and the essential amino acid content is a major determinant of the anabolic response to a protein.
However, you can (largely) compensate for the lower anabolic properties of plant-based protein by simply eating more of it (Gorissen, 2016). However, this means that protein recommendations should not be seen as a number set in stone. The exact amount of protein you need is dependent on the protein quality of diet. If you consume a lot of plant-based protein, you likely need to eat more total daily protein to compensate for the lower protein quality.
The largest food group that contributed to plant-based protein was bread. Bread is a staple in Dutch breakfast and lunch. Other Dutch staples are milk and milk products. It’s likely that the food group breakdown would be different in different cultures, and that the plant-based versus animal-based ratio would also be somewhat different.
We also characterized when protein was consumed.
Most protein was consumed during three main meals: breakfast, lunch, and dinner. Protein intake was skewed toward dinner, which is a typical pattern in the Netherlands and the US. However, in Spain, lunch is the largest meal of the day, for example.
There is research suggesting that protein distribution throughout the day affects the anabolic response (Mamerow, 2014)(Areta, 2013). Therefore, protein recommendations are starting to move to per-meal recommendations instead of just a daily total.
As little as 5g of protein can stimulate MPS. Twenty grams of protein will give a near-maximal increase in MPS and is sometimes referred as the optimal amount per meal. The observation that 20g of protein gives a near-maximal increase in MPS has been shown in rest, post-exercise, the overnight fasted state, four hours following a protein rich meal, and with egg and whey protein (Moore, 2009)(Witard, 2014). However further increasing protein to 40g of protein appears to give a relatively small 10-20% further increase in MPS (Moore, 2009)(Witard, 2014)(Macnaughton, 2016).
Protein intake was below the recommended 20g or 58% of athletes at breakfast, 36% at lunch, and 8% at dinner. Keep in mind that the recommended 20g is based on high-quality protein, while the lower quality plant-based protein contributed about half of the protein at breakfast and lunch. On the other hand, protein intake was underreported by about 25%. So the majority of athletes hit 20g of protein at their main meals, but protein intake at breakfast is at risk of being somewhat low and/or low in protein quality for some athletes.
Remember that increasing protein intake at a meal from 20g to 40g would result in 10-20% higher MPS. In addition, older adults have what we call anabolic resistance. They need more protein to get the same increase in MPS compared to younger adults. Therefore, since older adults need more protein to optimally stimulate MPS, they should aim for at least 40g of protein per meal if they want to maximize gains (Churchward-Venne, 2016). Most athletes and older adults do not eat 40g of protein at the majority of their meals to get the highest possible MPS rates, unfortunately.
Taking a closer look at the protein distribution data, a potential concern is that very little protein is consumed after dinner. It can be questioned whether dinner can maximize MPS until breakfast (easily 10-12 hours later).
We have shown that eating extra protein just before overnight sleep further increases overnight MPS (Res, 2012). In addition, we have shown that over time, this results in additional muscle mass gains (Snijders, 2015). Our work has not compared whether protein pre-sleep is superior to eating the same amount of protein during the day.
One recent study compared the ingestion of pre-sleep protein compared to extra protein in breakfast (Antonio, 2017). While there was no statistically significant difference, the study had a quite small number of subjects, studied trained subjects, was short, and didn’t have the most sensitive measurements of muscle mass, all of which make it very difficult to obtain a statistically significant difference. In fact, subjects did not even make “statistically significant” lean body mass gains during eight weeks of training on a very high protein diet. Statistics aside, it did appear the pre-sleep protein group outperformed the morning supplementation group: +1.2kg increase in fat-free mass versus +0.4kg increase in fat-free mass, respectively. Larger studies are required to confirm if this was just coincidence, or whether pre-sleep protein timing might be more effective compared to protein supplementation earlier in the day.
Of course, the question of whether pre-sleep protein is better than protein at a different time during the day is not necessarily practically relevant. Eating extra protein earlier during the day may also increase muscle growth, but it obviously wouldn’t do so by stimulating overnight MPS. So, even if protein supplementation in the morning would be as effective as pre-sleep protein, the effects would likely be additive, and you should do both if your goal is to maximize gains.
Each protein meal appears to be a unique window of opportunity and does not negatively impact the next protein meal (Wall, 2016). Your body does not suddenly say: Well, you had an awful lot of protein early in the day, so I’m not going to use that pre-sleep protein for muscle growth. Each meal should maximize muscle protein synthesis until the next meal. Given the long period between dinner and breakfast, an extra pre-sleep protein meal in between just seems smart. We do not suggest there is something magic about pre-sleep protein. We just promote pre-sleep protein intake as it’s a commonly missed feeding opportunity.
Once it’s time to go to bed, the relevant question is: Should I consume some pre-sleep protein? Yes, you probably should, regardless of the amount of protein you ate earlier during the day if your goal is to maximize gains. Unless you are on some weird protein ration, additional pre-sleep protein only has a potential upside for muscle growth. You increase total protein intake AND improve protein distribution.
So how much pre-sleep protein do you need? While 20g of protein gives a near-maximal increase in MPS during the day, it appears you need at least 40g of protein to get a robust increase in overnight MPS (Trommelen 2017, Res 2012, Trommelen 2016). We speculate that the need for a larger pre-sleep protein dose is related to the longer nature of the overnight period. It appears that you simply need more protein to sustain MPS over a longer period.
Minimal and optimal recommendations
Not everyone has the same goals, priorities, time, budget, etc.; therefore, I like to provide different levels of protein recommendations.
Minimalists want to do as little as possible, while still getting a decent chunk of the results. Minimalists want fitness to enrich their lives, not be a slave to it. My recommendation is a daily protein intake of at least 120g. That should give pretty good results, without worrying about small incremental gains by further increasing protein intake and worrying about quality or distribution.
Optimalists are willing to put in more effort if there is enough evidence that indicates their effort will produce reasonable additional results. My recommendation is four meals spaced throughout the day (e.g. breakfast, lunch, dinner, and pre-sleep) that contain 40g of protein, with most protein coming from animal-based sources. Compared to the minimalists, this is a higher daily total protein intake and includes attention to protein quality and distribution.
The amount of protein, quality of protein, and distribution of protein are all important variables that determine the anabolic effect of protein. Of these, the amount of protein is likely the most important. This makes sense, of course. By increasing the amount of protein you eat, you’ll eat more essential amino acids and therefore can (partly) compensate for lower quality protein. Additionally, a meal with a huge amount of protein will take longer to digest, thereby providing amino acids over a longer period and (partly) compensate for a low meal frequency.
However, that does not mean that total daily protein intake is the be-all-end-all. There are good reasons to assume that even large amounts of total daily protein intake may not maximally stimulate MPS throughout the day.
That’s where my advanced hypotheses come in the picture. Let me start by saying that for the vast majority of people, the optimal recommendations provided above are more than enough. The optimal recommendations should give you near-maximal results. These advanced hypotheses sections are basically me speculating about protein metabolism and making recommendations for those who are absolutely obsessed with making the best possible gains and want every potential competitive edge. Whether it’s worth the effort and money are not considered; we’re only talking about whether it may increase results (and has little potential to be detrimental).
We’ve discussed that the essential amino acid content of a protein source is a major determinant of its anabolic potential. Of the essential amino acids, leucine is especially potent at stimulating MPS. However, it’s not necessarily the amount of leucine in a protein source/meal that is important; what really matters is the level of leucine that is reached in your blood. The plasma leucine level will obviously partly depend on the leucine content of your protein source/meal, but if a protein is slowly digested, the leucine never reaches high plasma levels.
Fast-digesting protein sources are typically more anabolic than slowly digesting protein sources. This was shown in a nice study in which the fast-digesting whey protein was tested when given as a bolus or as pulses (West, 2011). A bolus of whey results in high but also transient increases in plasma amino acids levels. Giving the same amount of whey in small pulses with some time in between results in only a small but prolonged increase in plasma amino acid, reflecting the digestion of slow protein. The advantage of this bolus versus pulse comparison is that this controls for differences in amino acid content, which may not be equivalent if just comparing a fast- versus slow-digesting protein. The bolus resulted in a greater MPS response, indicating that protein digestion and absorption speed are important for muscle anabolism.
It’s the combination of the leucine content in a protein source/complete meal and the protein digestion and absorption rate which together determine the peak plasma leucine levels. And these peak leucine levels are a major determinant of the MPS response to protein (Pennings, 2011), though it should be noted that higher plasma leucine levels do not always result in higher MPS (Gorissen, 2014).
So, we eat protein to provide amino acids as building blocks for muscle, and because eating protein produces a plasma leucine peak, that triggers MPS (this basically tells the body to actually do something with the building blocks). The building block function is often not the rate-limiting factor in muscle growth. A relatively small amount of protein will already provide enough amino acids to build muscle at a high rate. This is illustrated in the following study.
Note that the bars do not represent MPS. We built tracers into the protein that the subjects ingested. You can imagine the tracers as tracking devices in the protein. By taking muscle biopsies, we could see how much of the protein had been incorporated into muscle tissue a few hours later (we call this de novo muscle protein synthesis). In the group that only got protein, some of the protein was incorporated into muscle tissue, but when supplemental leucine was added to the protein, more of the amino acids from the protein were incorporated into the muscle tissue. There wasn’t suddenly more protein available, but the additional leucine provided the trigger, telling the muscle to actually start putting those amino acids to good use. This suggests that it’s not the available building blocks, but the leucine trigger function that is the limiting factor for the MPS response. It should be noted that in this study, supplemental leucine was added to a relatively small 20g protein dose in older adults. (Wall, 2013).
Leucine supplementation, or simply eat more protein?
Could you not simply eat more protein to get a higher leucine peak instead of using supplemental leucine? Unfortunately, eating more protein may not necessarily result in higher plasma leucine levels. When eating more protein, it simply takes longer before the protein is completely digested and absorbed, meaning plasma leucine levels will remain elevated longer, but the peak doesn’t increase very much. You won’t reach the same peak plasma leucine levels you could by taking free supplemental leucine, which doesn’t require digestion.
Eating a small amount of protein is only going to produce a small leucine peak. Eating a larger amount of protein will produce a larger plasma leucine peak and result in higher MPS. But if you increase the amount of protein even further, it will take you longer to digest and absorb all that protein. It will only produce a minimal further increase in plasma leucine and MPS rate, although MPS may remain elevated longer. The latter would be beneficial if you won’t be able to eat anytime soon (represented by the area right of the dotted line). On the other hand, it won’t be of benefit if your next meal will follow soon. In contrast to consuming more protein, leucine supplementation would drastically increase peak plasma leucine levels and may increase MPS.
Note that if you would eat more of a fast protein (whey protein or hydrolyzed protein), it would result in higher plasma leucine levels instead of a more prolonged response. But whey and hydrolyzed protein are supplements, not foods and thus behave more like supplemental leucine than actual food.
Mixed meals may reduce peak plasma leucine levels
It should be noted that most protein research has been done with protein supplements, not complete meals consisting of meat with added carbohydrates and vegetables, for example.
Supplements are just much more convenient to really isolate the effect you’re studying. Whole protein sources are much more difficult to accurately dose, the exact cooking protocol will always have some variance, the number of chews will differ, some people eat their plate in a few minutes while others would take much longer, etc. But the anabolic response to a mixed meal could be somewhat different than what is seen with protein supplements.
For example, we have shown that the addition of carbohydrates to a casein protein shake slows down protein digestion and absorption (Gorissen, 2014). This happened despite the fact that casein protein is already a very slow digesting protein, so there was relatively little to slow down in the first place. In addition, we added a carbohydrate powder, not a real whole-food carbohydrate source such as potatoes or rice, which may slow down protein digestion even more. Therefore, the addition of whole food carbohydrates, fat, and vegetables to protein may slow down protein digestion and absorption rates, reduce plasma leucine levels, and limit the MPS response.
So even when you eat a high-protein mixed meal (whole foods with carbs, fat, and vegetables), you will likely not reach optimal plasma leucine levels or MPS rates. Therefore, leucine supplementation might be an effective strategy to enhance the anabolic response to a mixed meal.
Some support for this concept comes from two studies that investigated the effect of adding supplemental leucine to protein. In the first study, the addition of 2.25g of leucine to 6.25g of protein increased MPS (Churchward-Venne, 2012). In a follow-up study, however, the addition of 2.25g leucine to 6.25g protein did not increase MPS (Churchward-Venne, 2014). So, what’s the difference between studies? In the second study, the protein drink also contained carbohydrates and fat. These data suggest that the addition of carbohydrates and fat can reduce the plasma leucine peak and thereby reduce the increase in MPS.
In the second study, an even higher dose of supplemental leucine (4.25g) was also tested. This higher leucine dose did increase the MPS response. So, this suggests you need more supplemental leucine to stimulate MPS when you also ingest carbs and fat in your meal. This already occurred when carbohydrate powder and some fat were added to a protein shake. A complete mixed meal with complete carbohydrates might reduce protein digestion and absorption speed even further and might make it even harder to reach optimal plasma leucine levels.
Not convinced yet that you may benefit from adding supplemental leucine to meals? I’ve got more.
The anabolic potential of leucine supplementation on MPS was examined by adding leucine to the three main meals. They tested the addition of supplemental leucine to a lower protein diet (0.8g/kg/d) and a higher protein diet (1.2g/kg/d) in older adults.
Five grams of leucine was supplemented at breakfast, lunch, and dinner. The subjects performed unilateral resistance exercise. That way, one leg was in post-exercise condition, while the other leg served as a rested control (Murphy, 2016).
It might surprise you that the higher protein diet did not result in higher MPS rates compared to the lower protein diet. However, the addition of supplemental leucine increased MPS both in the lower protein condition and in the higher condition. It appears that the addition of 3 x 5g of supplemental leucine was effective at stimulating MPS rates, but the addition of about 33g of protein was not (which is approximately the difference in total daily protein between the two diets). The figure shows the data from the rested leg, but the superiority of leucine supplementation compared to more protein appeared even bigger in the post-exercise condition.
Of course, even the higher protein diet in this study is relatively low for athletes (these amounts were chosen because the study was done in older adults). However, I could argue that leucine supplementation would become even more effective compared to eating more protein if protein intakes were higher. Take a look again at the picture with the plasma leucine responses following the ingestion of different amounts of protein and leucine supplementation. On a high protein diet, what is additional protein going to do? You already have more than enough bricks available for muscle growth, and more protein will barely improve the peak plasma leucine levels.
Therefore, supplementing leucine may be more beneficial than simply trying to eat more protein.
It may also be beneficial to ingest the supplemental leucine 15-30 minutes before your meal instead of during your meal. That way, the supplemental leucine would not be slowed down by the macronutrients, and you’d be more likely to reach optimal plasma leucine levels. This will signal your muscles that MPS should be increased as much as possible. Then, 15-30 minutes later, you start with your meal and the other amino acids will come into the plasma, making sure the amount of ‘’bricks’’ available to build muscle does not become a limiting factor. Leucine supplementation alone can stimulate MPS in a fasted state (Wilkinson, 2013), indicating that the other amino acids do not become a limiting factor for MPS right away after leucine ingestion, though it appears that MPS eventually will be limited by the availability of other amino acids (Churchward-Venne, 2012).
Alternative leucine strategies
I quickly want to address two other leucine strategies.
It has been speculated that leucine supplementation between meals might be effective to keep MPS elevated throughout the day. This strategy is based on the muscle full effect, which proposes that protein stimulates MPS for only a short while. After the initial increase, MPS would go back down again even if you still have enough amino acids and leucine in the plasma that theoretically should continue to provide the substrate and the trigger for MPS (Atherthon, 2011). However, there are some data that suggest there is no muscle full effect in post-exercise conditions (Churchward-Venne, 2012). Athletes are (or should be) more or less always in post-exercise conditions, as exercise appears to sensitize the muscle to amino acids for at least 24 hours (duration likely depends on training status and exercise volume) (Burd, 2011). In addition, there is no evidence that leucine supplementation could overcome a possible muscle full effect, but protein does not. Simply said, there is very little support for this strategy.
A very popular ”leucine” strategy is the ingestion of branched-chain amino acids (BCAAs). Leucine is one of three BCAAs (isoleucine and valine are the other two). When taken in isolation, BCAA ingestion results in only a relatively small increase in MPS, likely because you need the other amino acids as building blocks for muscle growth (Jackman, 2017). When BCAAs are supplemented on top of some protein, the increase in MPS is smaller compared to simply eating more protein or adding only leucine (Churchward-Venne, 2014). This may sound counter-intuitive. Why would the addition of the two other BCAAs be worse than leucine alone? Isoleucine and valine use the same transporter as leucine for uptake in the gut. Therefore, it is speculated that isoleucine and valine compete for uptake with leucine, resulting in a less rapid plasma leucine peak. Don’t you just love how wonderfully consistent that is with the advanced hypotheses I just laid out?
So, leucine supplementation on its own is better at producing the trigger for maximal MPS, and a complete protein is just better at providing the bricks for muscle growth. A BCAA supplement doesn’t fit anywhere in this picture; it’s worse than only leucine at doing leucine’s job, and it’s worse than a complete protein at its job.
My advanced protein recommendations are an expanded version of my optimal recommendations. Eat at least four meals with at least 40g of protein, spread them out throughout the day (e.g. breakfast, lunch, dinner, and pre-sleep), and get the majority of that protein from animal-based sources. In addition, ingest 5g of supplemental leucine before your meals or during your meal (best and second best option, respectively). If supplemental leucine is no option, a whey protein or hydrolyzed protein shake could be used a replacement (third best option).
- Daily protein intake averaged 1.5 and 1.4g/kg/d in male and female athletes, respectively (likely a bit more due to underreporting). Current recommendations are 1.3-1.8g/kg/d.
- Protein needs do not appear to depend on body weight or amount of lean body mass. Therefore, protein recommendations expressed as g/kg/d may underestimate protein needs for smaller athletes.
- Women tend to eat less protein than men (108 versus 90 g/d), but likely need the same absolute amount.
- Protein intake correlates with energy intake. Make sure your protein intake remains high when dieting.
- Animal-based protein contributed 57% of total protein intake in the athletes we studied, with the remaining 43% originating from plant-based protein.
- Animal-based protein is more anabolic when compared to plant-based protein because of a higher essential amino acid content. This can (largely?) be compensated for by eating more plant-based protein.
- The majority of protein is consumed during the three main meals: breakfast, lunch, and dinner.
- Twenty grams of protein in a meal gives a near-maximal increase in protein MPS. Further increasing protein to 40g gives a relatively small additional 10-20% increase in MPS.
- Protein intake was below the recommended 20g for 58% of athletes at breakfast, 36% at lunch, and 8% at dinner.
- Older adults need more protein than younger adults, and it’s even more important for them to go up to 40g per meal.
- An additional protein meal just before sleep improves total protein intake and protein distribution.
- The plasma leucine peak following protein ingestion is a major determinant of MPS.
- There are no conditions in which branched chain amino acid supplementation appear to be the optimal choice.
- Minimalist recommendation (to get the most results with minimal effort): Eat at least 120g of protein per day.
- Optimal recommendation (almost all results, considerable effort): Four meals of 40g of protein, spaced out evenly throughout the day (breakfast, lunch, dinner, and pre-sleep), with the majority of protein from animal-based protein sources.
- Advanced recommendation (only results matter. Speculative, but there’s some supporting research): In addition to the optimal recommendations, supplement 5g leucine 15-30 minutes before a meal or during a meal.
Jorn Trommelen is a PhD candidate in Muscle Metabolism. Follow him on Facebook where he frequently breaks down the latest research, and read more practical posts like this on his website Nutrition Tactics.
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