Nutrient Timing and the Anabolic Window: An Update

Confusion often surrounds the need to consume protein immediately post training – Conflicting research data, anecdotal evidence and personal beliefs lead to many misconceptions and assumptions with regards to nutrient timing and it’s hierarchy of importance for inducing muscle hypertrophy.

This update is in light of a new study that aimed to identify whether protein timing is in fact as importance as we are led to believe. But first, you’ll need to have a basic understanding of how muscle is built and modulated through dietary protein.


The Essentials

Once you’ve applied a stimulus or stress on the worked muscles through weight training, an adaptation occurs in order to cope with the demands for the next session – This adaptation occurs in the form of muscle hypertrophy (muscle growth). Whilst lifting weights, your working muscles undergo a process known as muscle protein breakdown (MPB). MPB is a catabolic process where the muscle ‘breaks down’ as a result of your training session. Once you’ve completed your training session, another process called muscle protein synthesis (MPS) occurs. MPS is the adaptation phase that rebuilds the muscle that you’ve broken down in the gym – bigger and stronger.

Since the goal is to build muscle, get stronger, and recovery quicker – Muscle protein synthesis must exceed the rates of muscle protein breakdown. In other words, you’re trying to rebuild the wall quicker than it’ being torn down.

MPS is switched on by consuming adequate amount of protein in a meal. Leucine is an amino acid found within protein (whey, dairy, poultry, beef, eggs etc) and is an essential amino acid for muscle growth. Leucine is known as an anabolic trigger which stimulates MPS. The trick is that you have to consume sufficient leucine per serving in order to trigger MPS. if you don’t consume sufficient leucine per serving, MPS will not be stimulated, therefore muscle growth may not occur at a higher rate- in other words it has a dose dependant response.

The leucine dose is roughly 3 grams, which equates to approximately 25g of whey protein, or 30-40g of protein (under most circumstances) found within eggs, beef, poultry etc. It can therefore be said that if you don’t consume a sufficient dose, then the protein within that meal is almost worthless regarding muscle hypertrophy; it’ll only help keep you full and add as an ingredient to a recipe…

Pre Vs Post Exercise Protein Intake

Early research indicated that an anabolic window of 45-60 minutes post exercise did exist, where consuming protein within that period would maximise the MPS response and enhance muscle hypertrophy. Consuming protein outside of this anabolic window was thought to be detrimental to hypertrophic gains – Hence the urgency to consume protein immediately post exercise.

Since then, findings would suggest that the muscle is sensitised to protein for 24-48 hours post resistance exercise. Therefore, this would suggest that the anabolic window is more of an anabolic barn door.

Recent work by Schoenfeld et al (2017) investigated whether 25g of whey protein either pre or post resistance exercise would yield different results. The research design would have participants consume an equal amount of dietary protein and calories to ensure that any noticeable differences are likely down to the timing of protein ingestion. The participants were well trained, and followed a three day per week whole body training programme for 10 weeks. Furthermore, the nutrition guidance provided to the participants required them to be in a 500 calorie surplus which will allow for a more favourable environment for muscle gain.

To reduce any ‘splash’ with the results, the group that consumed 25g of whey protein PRE training were not allowed to consume any protein post training for three hours, where the POST training group were not allowed to consume any protein for three hours pre training – this essentially negates any possibility of the one hour anabolic window interfering with the outcome.

After 10 weeks of resistance exercise, and to confirm the researchers hypothesis; no significant difference were noted between consuming 25g of whey protein PRE or POST exercise with regards to muscle mass, fat mass and strength when total daily intake of protein is adequate.

A major limitation to the study was the participant’s compliance to the caloric intake – The advice provided was to consume 500 additional calories per day, however participants for one reason or another followed a calorie restricted diet to induce fat loss. Therefore, under the ‘well trained’ population that they fall into, muscle hypertrophy under these conditions is very difficult to achieve as seen in the study; +0.3kg (PRE protein group) and +04kg (POST protein group). Furthermore, preliminary data would suggest that well trained individuals performing whole body resistance training sessions may benefit from a greater amount of protein post exercise; therefore implying that the whey protein dose used may not have been suited for the type of exercise performed.


Double Scoop

The issue with many exercise research protocols is that they don’t necessarily replicate actual training sessions. In other words, they would have a participant perform a few sets of leg or triceps extensions to voluntary muscular failure then assess how protein intake would affect the recovery period. Due to the nature of exercise and amount of muscle being used during the exercise protocol, it suggested that you need a smaller dose of ~20g of protein to maximise the recovery response. When this same protocol has been repeated with a larger dose of 40g, it appeared that 40g of whey protein elicits the same recovery response as 20g.

However, findings by Hamilton et al (2016) would suggest that under different exercise settings; 40g of whey protein consumed post training appears to be more beneficial than 20g. The greater amount of muscle worked in a given session requires a greater amount of protein. Since this study looked at the response of protein intake from FULL BODY sessions, it would suggest that having 2 scoops of whey protein is better than one scoop. Therefore, it can be postulated that if the PRE Vs POST study increased protein intake per serving, then the results may have been different. Since this is the first study to highlight this, more data is required to confirm whether more does in fact equal better when it comes to protein intake.

Therefore; two conclusions can be made from this;

  • IF protein is consumed in close proximity to the training session, then protein intake post training isn’t crucially important.
  • IF protein intake isn’t consumed in close proximity to the training session, then protein post training is important. For example, fasted state training.

Since gaps in the literature exist, it would be prudent to consume protein PRE and POST exercise to cover all potential uncertainties.


Forgetting about the bigger picture

It’s been established, both in the literature and anecdotally that your calorie intake can determine the rate at which you build muscle and strength. This is why ‘off-seasons’ or bulking phases exist. As mentioned previously, it is possible to build muscle whilst in a calorie deficit, but perhaps not optimal. In the short term, catabolic processes are dominant during periods of calorie restriction. Therefore higher rates of protein turnover are observed, thus a reduced capacity to increase muscle size. However as you move from a calorie restricted diet to a calorie surplus diet, these signalling molecules change and the mTOR/anabolic pathway is no longer blunted. Therefore calorie restriction favours catabolism/muscle breakdown, and calorie surplus favours anabolism/muscle growth. The question is, how many calories is above maintenance intake is required. Two studies provide an insight to the answer, and appears to be very much dependant on your training status.
1) Rozeneck et al (2002) placed untrained individuals on a 2,000 calorie surplus diet for 8 weeks. When this calorie surplus was combined with a resistance training programme and adequate protein, it was reported that almost all the weight added (3kg) was through increasing muscle mass (not fat mass), where the control group who consumed a maintenance intake didn’t significantly increase muscle mass. 2) In contrast Garthe et al (2013), placed elite athletes either on a 500kcal surplus diet, or an ‘ad libitum’ diet (maintenance/eat whatever you want) in conjunction with a four day per week hypertrophy focused training programme for 8-12 weeks. As expected, the athletes who consumed a higher calorie intake, gained the most muscle mass (1.7kg Vs 1.2kg), however most interestingly gained the most body fat (1.1kg Vs 0.2kg).
NOTE FOR ATHLETES – This study did performance measures on 1 rep max strength etc. One of the tests was to measure their 40m sprint time. Not surprising, the 500kcal surplus group who gained the most weight also had a decrease in sprint performance. For athletes, power to weight ratio is hugely important! Therefore, this does highlight the importance of calorie intake dependant on your training status. I.e. the more trained you are, the less calories you need to build muscle as the additional calorie intake does not favour increased muscle mass, and is stored as body fat instead. AND vice versa. This has been postulated to be a result of untrained individuals having a greater ability to build muscle, and at a higher rate (newbie gains) when compared to their trained/elite athlete counterparts. Therefore requiring more energy to facilitate muscle growth at a higher rate. If you have the appetite, a 2,000 calorie shake on top of what you normally consume appears to work well (Rozeneck et al 2002)!

Application

The research findings would suggest that personal preference, schedule, convenience and availability for protein timing are a major determinant. As a confined anabolic window doesn’t exist, a pragmatic approach would be to consume protein around your training sessions with an emphasis on consuming an adequate dose based on the type of training session performed. Furthermore, in order to enhance hypertrophic gains, it would not be advisable to restrict calories as this may impair your results. In hindsight, the elevated calories required to maximise muscle growth is very much determined by your training status.  Therefore, a one size fits all approach may not be the best possible practice when looking to maximise muscle hypertrophy though nutrition – Individual circumstances and settings will direct what approach would be most advantageous.

Whilst considering these findings, it would be worthwhile acknowledging other factors attributing to muscle hypertrophy such as; exercise programming, training age, meal frequency, pre-sleep protein, external stressors, sleep quality and genetics.


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