The classic nutritional approach of personal trainers is to prescribe a protein or carbohydrate-rich meal or supplement immediately following exercise. But, where does this recommendation stem from? Evidence-based fitness helps us understand the reasoning behind this recommendation.
Alan Aragon – “The Nutrition Specialist”
Alan Aragon was another one of the four speakers presenting at the PTC conference. Aragon is well respected in the field of evidenced-based fitness and is specifically recognised as a leader in the area of applied nutrition. Aragon holds a Bachelor and Master of Science in Nutrition and maintains a position as continuing education provider for the Commission on Dietetic Registration and National Strength and Conditioning Association. He has authored and co-authored on a number of professionally published journals in addition to acting as a contributing editor to popular publications like Men’s Health Magazine.
On the Saturday, Day 1, Aragon addressed the issue of nutrient timing and the proposed “anabolic window” theory. This theory was first introduced by John Ivy and Robert Portman in 2004 and proposes that muscular adaptations are significantly compromised if key nutrients are not consumed within 45 minutes following exercise . In their book “Nutrient Timing – The Future of Sports Nutrition,” Ivy & Portman explain that immediate, post-exercise co-ingestion of fast-absorbing protein and carbohydrates are critical for optimising muscular recovery and growth via reducing muscle protein breakdown and maximising net muscle protein synthesis . In other words, nutrients from either solid food or supplements must be consumed immediately following exercise to optimise muscle building or strength. This theory was enlarged and popularised by supplement companies for financial gain and still remains a driver for post-workout nutritional prescription by the great majority of personal trainers.
However, there are some important imitations in Ivy & Portman’s guidelines for nutrient timing. Specifically, the authors fail to indicate population specificity or who the guidelines are targeted towards. Also, the authors focus on the acute effects rather than the chronic effects of research to inform their guidelines on nutrient timing. Finally, the authors rely upon research using overnight-fasted subjects put through endurance/depletion protocols, which we will learn is different when compared to the response of non-fasted subjects.
The Origins of the “Anabolic Window”
In 1988, Ivy and Colleagues published a research study in the Journal of Applied Physiology that set out to examine the effect of carbohydrate timing on muscle glycogen storage following exercise .
The authors placed 12 male cyclists on a cycle ergometer for 70 continuous minutes at 68% VO2 max, interjected by six 2-minute cycle sprints at 88% VO2 max, on two separate occasions . The subjects were either given a 25% carbohydrate solution (2g/kg) immediately following exercise or delayed consumption of this solution by 2 hours post-exercise. Blood samples were obtained during exercise and at specific times following exercise .
During the first 2-hours following exercise, glycogen storage for the group administered carbohydrates immediately post-exercise was 3 times greater (7.7 mumol.g) than the 2-hour delayed group (2.5 mumol.g) . During the second 2-hour time period following exercise, glycogen was still roughly twice as fast in the immediate group compared to delayed group . At the 4-hour mark, the immediate group had 34.7% greater glycogen storage compared to the delayed group .
Delaying the ingestion of a carbohydrate supplement post-exercise will result in a reduction in muscle glycogen storage .
The Fallacy of “Spiking” Insulin Levels Post-Exercise
Following a workout, it is proposed that insulin has anti-catabolic effects that reduce the breakdown of muscle protein . A common strategy among personal trainers is prescribing high-glycemic (glucose or blood sugar), fast-absorbing proteins/amino acids or carbohydrates immediately following exercise to maximise insulin response and mitigate muscle protein breakdown and accelerate recovery. This is often prescribed by personal trainers in the form of sugar-rich foods like juice or supplements.
However, this post-exercise nutritional prescription is based on the assumption that exercise is performed under a fasted state (abstinence of food or drink). Under a fasted state, there is compelling evidence indicating muscle protein breakdown is elevated following a workout . Muscle protein breakdown is found to significantly increase 3-hours post exercise, up to 50% in some instances, then can persists further for up to 24-hours post-exercise under these conditions .
But, what if exercise is not performed under fasted conditions? The research shows that a pre-workout meal (solid or supplemental) of either protein or mixed (protein, carbohydrate and fat) is more than sufficient to elevate insulin levels during and following a workout . If this is the case, then the addition of insulin immediately post-workout would be redundant for reducing muscle protein breakdown or accelerating recovery.
In support of this argument, there is evidence showing that no greater elevation in net muscle protein balance, which is muscle protein synthesis (gaining) minus protein breakdown (losing), has been found beyond insulin elevation of 15-30 mU/L, which is approximately 3-5 times fasting levels . This means that there is a “ceiling” on insulin intake and anything above these levels will not yield any additional benefit in the context of post-workout recovery.
Also, the reality is that insulin elevations of 15-30 mU/L are easily attainable and even surpassed with normal-sized mixed meals. Depending on the size of a meal, it takes approximately 1-2 hours for circulating nutrient levels to peak and another 3-6 hours (or more) for these levels to drop back down to baseline. To demonstrate this metabolic response following a meal, Power and colleagues (2009) examined the effect of protein hydrolysis on the insulin response to the ingestion of whey protein supplement . The authors showed that a 45 g dose of whey protein isolate takes approximately 50 minutes to cause blood amino acids to peak . Insulin levels peaked at 40 minutes following ingestion of protein supplement . Importantly, peaked insulin levels remained at elevated levels known to max-out net muscle protein balance (15-30 mU/L, or 104-2018 pmol/L) for about 2-hours . The inclusion of carbohydrates to this protein dose would cause even greater elevations in peak insulin levels and sustain these levels even longer.
A study by Capaldo and colleagues (1999) measured the metabolic effects of ingesting a solid, mixed meal containing 75 g carbohydrate, 37 g protein, and 17 g fat . The study showed that ingestion of this mixed meal raised insulin levels 3 times above fasting levels within 30 minutes, and 5 times greater than fasting at 60 minutes . At the 5-hour mark, insulin levels still remained double that of fasting . Therefore, recommendations from personal trainers to spike insulin levels of their clients post-exercise to promote muscle recovery and growth fail to stand up against the evidence.
Only in the case of an overnight fast would immediate post-workout ingestion of nutrients be advocated to prevent muscle protein breakdown and enhance protein synthesis . Instead, personal trainers should focus closely on the pre-workout meal and timing. If increasing strength and lean muscle mass is the objective, effort should made to consume a solid meal 1-2 hours prior to a workout to maximise performance and post-workout response . A meal consisting of a protein drink supplement can be taken immediately prior to a workout as this form is metabolised more rapidly.
When considering nutrient intake following a workout, it is recommended that the duration between pre- and post-workout meals fall between 3 – 4 hours, depending on the size of the pre-workout meal and based on a workout lasting 45 – 90 minutes . For example, if an individual trains at 5pm, a pre-workout meal at 3:30pm and post-workout meal at 7pm would be optimal for enhancing muscle protein synthesis and preventing muscle breakdown.
If a pre-workout meal is larger, which would increase its anti-catabolic effects, it is reasonable to suggest that the time period between pre- and post-workout meals would increase (5 – 6 hours) . If a workout is performed more than 3 – 4 hours from a pre-workout meal, it is advisable that a protein or carbohydrate-protein mixed meal or supplement be taken immediately following the workout to enhance recovery and prevent a catabolic response .
What Did I Learn? – Practical Application For Our Clients
Nutrition within and surrounding a workout is typically an area that personal trainers advise upon for their clients. When examining the classical recommendation of a protein supplement drink or sugar food immediately following a workout, this recommendation holds little justification.
Only under a fasted state, or in the event of repeated bouts of intense exercise (i.e. cycling, running or weightlifting multiple times a day), would immediate, post-exercise nutrition be warranted. Instead, personal trainers should focus on the timing of a pre-workout meal, advising clients to consume a protein or protein-carbohydrate rich meal within 1-2 hours of initiating training. This time period would allow circulating nutrient levels to peak and remain elevated (depending on meal size) for 1-2 hours (or longer) following a workout. In the event of fasted exercise, which is often the case among those that exercise first thing in the morning, immediate, post-exercise nutrients are recommended. This would also be advised with a pre-workout meal consumed more than 3 – 4 hours from the workout.
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1. Aragon, A. A. & Schoenfeld, B. J. 2013. Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition. January. Vol. 10, No. 1:5, pp.186/1550-2783-10-5.
2. Capaldo, B. et al. 1999. Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humans. Diabetes. May. Vol. 48, No. 5, pp. 958-966.
3. Ivy, J. L., et al. 1988. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. Journal of Applied Physiology. April. Vol. 64, No. 4, pp. 1480-1485.
4. Ivy, J. L. & Portman, R. Nutrient Timing: The Future of Sports Nutrition. 2004. North Bergen, NJ: Basic Health Publications.
5. Power et al. 2009. Human insulinotropic response to oral ingestion of native and hydrolysed whey protein. Amino Acids. July. Vol. 37, No. 2, pp. 333-339.
6. Sensi, S. & Capanni, F. Chronobiological aspects of weight loss in obesity: effects of different meal timing regimens. Chronobiology International. Vol. 4, No. 2, pp. 251-261.