In part one of looking at what part BCAAs play in bodybuilders’ diets, I discussed what BCAAs are, their unique role in protein synthesis, as well as what foods they are contained in and in what percentages. On a gram per gram basis, you would get more than double the amount of BCAAs for your money if you opt for a high quality whey protein isolate than if you were to purchase isolated BCAA; as well as the benefit of all the other essential and non-essential amino acids. As such, I see no use for BCAAs unless they prove to be beneficial despite a sufficient protein intake.
Given the controversy that surrounds their use on top of a sufficient protein intake, I examined the limited human trials on the very matter and came to the conclusion that BCAAs would seem to make little, if any, difference in the presence of sufficient protein. In the absence of sufficient human data looking at body composition endpoints, these conclusions are somewhat speculative. However, my personal observations support my contention that they provide no benefit to those hoping for more muscle and less fat.
As I feel that the available human data doesn’t sufficiently answer the main question behind this article series, I will dig a little deeper and see if more mechanistic and theoretical arguments shed any more light on this matter. I will spend this post looking at the issue of meal frequency and how it pertains to maximising anabolism, as it will lay the foundations for the discussion in the third and final part, in which I will dissect the claims made about between-meal BCAA dosing strategies, and their use whilst dieting.
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Maximising anabolism: the role of leucine in muscle protein synthesis.
To quote myself from my protein requirements article:
“The amount of muscle tissue in the human body remains fairly stable over time. However these tissues are undergoing a continuous process of breakdown and resynthesis; these processes are referred to as protein turnover. The amount of muscle mass a person has depends on the long-term relationship between muscle protein breakdown and synthesis. For example, if muscle protein synthesis exceeds breakdown, there will be an increase in the amount of that protein. Protein turnover is mediated by several factors including hormones (testosterone, growth hormone, thyroid, insulin, glucagon & cortisol), caloric intake, amino acid/protein availability and training. The largest factors that influence skeletal muscle metabolism are eating and training… This may lead one to assume that the simple act of eating a load of protein will lead to gains in muscle mass. However, this isn’t the case due to a process called diurnal cycling, whereby net protein synthesis following a meal is matched by an increased protein breakdown when food is not being consumed… diurnal cycling tends to keep the body at a stable amount of muscle mass. However, when [resistance] exercise is introduced, it basically “forces” the body to store more protein (assuming sufficient protein and overall caloric intake that is).”
As such, it would appear that maximising daily dietary-induced muscle protein synthesis (MPS) would yield the greatest benefit in terms of maximising the potential for muscle gain. Theoretically, it seems that maximising the anabolic response via eating, revolves around the leucine content of a protein containing meal, and the frequency of which such meal is eaten (i.e. meal frequency; technically protein frequency).
Of the three BCAAs, it is leucine that plays the major role in initiating MPS via the stimulation of the biochemical sensor named the ‘mammalian target of rapamycin’ (mTOR). Relating to the ingestion of protein, a threshold amount of leucine of 2-3 g (~ roughly 0.05g/kg body weight) is thought to exist so that changes in plasma leucine concentrations maximally stimulate MPS. Intakes above this threshold (~8 g leucine) do not appear to have any further stimulatory effects on MPS. From table 1 (in part 1), this would translate to 25-37.5 g of leucine-rich protein sources (e.g. whey, eggs and meat). It is worth highlighting that these hypotheses were developed using rodent models based on acute human data by Paddon-Jones et al. and Tipton et al.. However these notions do have some solid grounding, with more recent human data seeming to support them. This would also seem to be where the ‘broscience’ myth of being only able to absorb 30g (or other random amount) of protein came from. If this were the case, then you wouldn’t be reading this today.
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Frequency of meal/protein ingestion
Now that we know roughly how much protein is needed at each meal in order to optimise MPS, the question remains of how frequently you need to eat to maxmimise MPS, with the hope setting yourself up for maximal muscle gains.
Before we get into that, I want to quash the myth that eating more frequently helps someone to stay lean/lose more body fat by “stoking’ the metabolic fire” or whatever other silly reason is given. It makes no difference how many meals are consumed as long as total kcals (and macros) remain the same. Though the digestion of food requires energy (Thermic effect of food; TEF), TEF is directly proportional to the macronutrient content of a meal. For example, it would take twice the amount of energy to digest a 1000 kcal meal than if you were to eat only half of that meal. Therefore, you can see why splitting food intake into more meals will have no impact whatsoever on metabolic rate. As such, strictly speaking of fat loss, the optimal meal frequency is the one that suits an individual most in terms of hunger, routine, practicality etc.
Now that I’ve got that out of the way, meal frequency gets a little more complicated when talking of muscle gain; at least in theory. It would appear that increasing the frequency of which these maxmimal stimulations of MPS occur (i.e. increased meal frequency) is beneficial for those looking to build muscle. Therefore, logic would dictate that one should eat threshold amounts of protein as frequently as possible if the aim were to maximise MPS within a given 24 hour period. Unfortunately, things aren’t that simple.
Data from rodent and human amino acid infusion studies have demonstrated that MPS lasts for approximately two hours before returning to baseline, despite elevated amino acid levels in the blood. More recently, data from Layne Norton’s lab has shown that consuming a complete meal delays and extends its effects on MPS to roughly three hours, peaking at 45-90 minutes. It therefore appears that there is a refractory response to protein synthesis (i.e. MPS decreases despite the presence of the initiating stimulus, amino acids) and that once MPS is maximally stimulated following a protein containing meal, further stimulation will not occur by simply ingesting more protein.
An explanation for this resistance to further stimulation of MPS comes from the ‘protein stat hypothesis’, which suggests that an extracellular (outside of the muscle cell) membrane-bound sensor is influenced by relative changes in amino acid concentrations as opposed to absolute concentrations. Specifically, the change from a lower concentration of AAs to a higher one is what seems to drive MPS, meaning that this whole process needs time to “reset” before MPS can be triggered again with the next meal. It therefore seems that spacing meals and allowing blood AA levels to drop, would maximise MPS in subsequent feedings.
Based on this refractory phenomenon, in his aptly titled The Protein Book, Lyle McDonald poses two questions in the attempt to negotiate an ideal meal/protein frequency:
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Is it possible to eat too frequently?
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How long will a typical meal maintain the body in an anabolic state?
The first question is getting at how long it takes for the processes discussed above to “reset”, before a subsequent meal will max out MPS. The second question refers primarily to digestion rates (i.e. how long after a meal are nutrients (e.g. amino acids) being released into the blood stream?).
Looking at the first question, based on the available data, it would seem that 3-4 hours would theoretically be the minimum time that should pass between meals if you wish to maximise MPS in the second meal. With regards to the second question, there are plenty of data points to determine roughly how long it takes for proteins to be digested. It has been shown that even a modest meal (37g PRO, 75g CHO, 17g FAT) is still releasing nutrients in to the blood stream five hours later. Slowly digesting proteins such as casein (touted as the good old “pre-bed” source to stop you waking up with no muscles) may still be releasing AAs into the blood 7-8 hours, or more, after ingestion!
However, meals consumed by most people looking to gain muscle, often contain more protein and total nutrients than in the aforementioned studies. Therefore, taken together, a VERY conservative time limit of six hours passing between meals, during waking hours, would seem reasonable. Incidentally, these recommendations of eating every 3/4-6 hours are similar to those of Layne Norton, who advocates consuming threshold doses of protein containing meals 4-6 hours apart, interspersed with a BCAA/CHO solution with the aim of circumventing this refractory phenomenon associated with MPS (more on this in the next article!). So, eating every 3-6 hours while awake (assuming eight hours of sleep) would yield a meal frequency of roughly 3-6 meals per day.
Since I previously recommended an intake of between 2.5-3 g/kg of bodyweight for bodybuilders/strength athletes, using my body mass as an example (77 kg), this equates to a protein intake of between 192.5-231 g per day. Using the higher end as an example, at a fairly standard frequency of 3-6 meals, daily protein intake would equate to roughly 38.5-77g per meal on average. At the bottom end of this intake, 38.5 g of any high quality protein would adequately cover the upper-end of the 2-3 g leucine threshold for maximising the anabolic response to a given meal (see table 1). In theory, it would seem that splitting the intake over six meals rather than three would lead to better gains in muscle mass due to 6 vs. 3 stimulations in MPS per day. In reality things aren’t that straight forward. If it were, using this example, six stimulations of MPS per day SHOULD lead to double the rates of muscle growth than three.
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This is where things get confusing
For example, 25g of a whey protein isolate (WPI) (see part 1) would provide roughly 3g of leucine (the maximum amount likely to maximally stimulate MPS in anyone). If someone were to ingest 25g of WPI every three hours (six ingestions per day), then MPS should theoretically be maxed out in a day, with an intake of only 150g of protein. If we take a 100kg rugby player, this would provide an intake of 1.5g/kg per day of protein. This is half of the upper end of what I advocate for strength/power athletes, and is also on the low side of the already conservative values cited in research. What’s going on?
Though I’ve used somewhat of an extreme example to illustrate my point, it seems that there is more to building muscle than just hitting these leucine thresholds on a meal per meal basis. In my opinion, total protein intake is the more important variable in terms of muscle mass accrual, compared with how it is split up throughout the day; at least in terms of a typical meal frequency encountered by those who have more to worry about than prepping half a dozen Tupperware boxes per day.
To quote Lyle McDonald from The Protein Book on the matter,
“Optimizing the function of other important pathways [besides MPS] of AA metabolism would very likely raise protein requirements even further.”
Indeed, as alluded to in my article on protein requirements, increased levels of AA oxidation (likely due to intakes in excess of these leucine thresholds), may be involved in the overall “anabolic drive”, meaning there are likely to be “hidden” signaling pathways that contribute to muscle anabolism that we are not yet aware of. As such, increased AA oxidation may actually provide benefit as opposed to its traditional view as being a wasteful process. Essentially, we know that more protein is better (hence my recommendations), but science hasn't figured out the whys yet.
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Searching for the optimal meal frequency
Since most people tend to eat their total daily protein across 3-4 meals, an important question is whether splitting an existing protein intake across an additional 2-3 meals, will provide any benefit in terms of muscular hypertrophy. In the May 2012 issue of his monthly research review, Alan Aragon (I’d abbreviate to AA but then you may mistake him for an amino acid) attempted to answer this question with a combination of limited available data as well as his own observations in the field. In this article, he states:
“Given a diet with an abundance of high-quality protein from varying sources, frequency and proportional distribution of protein doses within day are not likely to make any meaningful impact unless extremes are pushed. It’s rare for anyone with the primary goal of muscle growth to eat twice a day (or less)… It’s reasonable to hypothesize that consuming a solid, mixed, protein-rich meal every 4-6 hours while dosing BCAA between meals could result in a higher rate of muscle growth than getting all of your protein in a single meal each day. However, I see quite a grey area when [Layne] Norton’s protocol is compared with 2-3 meals containing a matched total of high-quality protein (minus the BCAA or leucine threshold dosing between meals).”
Aragon then goes out on a limb and states that:
“even in the case of an IF-type [intermittent fasting] of scenario where only one or two meals per day are consumed, I would still challenge that any meaningful compromise in muscular growth is speculative in the absence of data."
Though seemingly counter-intuitive, there is actually nothing incorrect about Aragon's claims, despite the criticisms of IF from many experts; the scientific data just isn’t there (yet).
Despite some of its questionable conclusions, according to the ISSN position stand on meal frequency, a reduced meal frequency doesn’t appear to compromise lean body mass (LBM) under hypocaloric conditions in the presence of a sufficient protein intake. That is, eating 10 times per day as opposed to once or twice per day doesn’t seem to make a difference with regards to the sparing of LBM on a diet (assuming you're getting sufficient protein that is). If it were true that maximising MPS following the protocols outlined above (i.e. total protein spread evenly across six meals per day) would result in maximal rates of muscle mass accrual, then it raises the question, ‘why doesn’t reducing meal frequency appear to have a negative effect on LBM whilst dieting?’
It is my contention that as long as sufficient amounts of high quality protein are consumed, then spreading protein intake from 3-4 meals to 6 meals is a waste of time and effort for the vast majority of people. This increase in protein frequency may be of benefit to the elite physique athlete, but I’m yet to see how this could result in more than trivial amounts of muscle mass; quantities of which are unlikely to be detected in research (especially with modern-day assessments of body composition). On a related note, I’m not certain that the concern of eating too frequently is a valid one either. The majority of bodybuilding champions eat upwards of six, sometimes 10, meals per day, and they don’t seem to be held back by it. By the same token, there are many proponents of IF who have achieved excellent improvements in body composition despite a meal frequency of perhaps 1-3 protein feeding per day. With respect to my last point, there is at least some data suggesting that going below 2 protein feedings per day might hinder muscle gains.
So, with all things considered, I think that a minimum of three protein feedings per day would be ideal and easily achievable for >99.9% of people looking to optimally gain muscle mass.
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Summary
To briefly summarise:
- The amount of muscle mass a person has depends on the long-term relationship between muscle protein breakdown and synthesis.
- A threshold amount of leucine of 2-3 g (~ roughly 0.05g/kg body weight) is thought to exist, with no apparent further stimulation of MPS with higher intakes.
- This would translate to 25-37.5 g of leucine-rich protein sources.
- Yes, you can absorb more than 30g of protein in one sitting!
- Due to the apparent refractory nature of MPS, it would seem that eating meals spaced every 3/4-6 hours apart would optimise MPS within a 24-hour period.
- However, it appears that there is more to muscle gain than frequently stimulating MPS; the reasons being as follows:
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A recommendation for higher daily amounts of protein than is likely to ‘max’ out MPS.
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Concept of the anabolic drive and hidden signaling pathways involved in protein turnover and AA oxidation.
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Real-world observations of excellent improvements in muscle mass despite theoretically ‘too high/too low’ meal frequencies.
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Apparent lack of effects on LBM whilst dieting with reduced meal frequencies (i.e. 1-2 meals per day).
- It therefore seems that total protein intake is the most important variable, and how this intake is distributed, impacts body composition to a lesser degree.
- For this reason, I don’t see any reason for meal frequency to be higher than the typical 3-4 meals per day for most people seeking optimal rates of muscle gain.
- Though it is unknown whether moving to the ‘optimal frequency’ would be of benefit, it seems unlikely in the real world; and if so, it may only benefit the elite physique athlete looking for that 1-2% over their competition. Likewise, eating less than twice per day may compromise rates of muscle gain, however, no solid data exist to be make definitive conclusions.
I will get straight in to things in part three and discuss the issue of dosing BCAAs between meals as well as their use whilst dieting. If you’ve been paying attention in this article, you can already see where things are going…
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This month's post is another video. This time, it's one of me delivering a presentation rather than interviewing a fitness industry professional.
