FITNESS MYTH: POST EXERCISE ANABOLIC WINDOW
Post-exercise nutrition has become ingrained within the fitness culture. Especially in reference to anabolism (muscle gain). Supplement companies capitalize on these types of products as well as gyms selling over-priced protein shakes so that the client doesn’t miss their “anabolic window.”
For those who are unaware of this myth, the idea is that by timing your nutrition (especially carbohydrate and protein intake) so that you eat a meal immediately after exercise will lead to dramatic increases in muscle gain (Ivy & Portman, 2004). There have even been those that have proposed that the timing of your nutritional intake is more important than total daily intake (Candow & Chilibeck, 2008). As mentioned, these ideas are common amongst gym-goers and athletes alike but are they legitimate?
I can understand the premise of the argument. The aim is to facilitate the repair of damaged muscles and to maximize the adaptations we want from exercise (Ivy & Portman, 2004). Indeed, intense exercise and training can bring about a need for repair and replenishment. Muscle damage is one of the proposed mechanisms by which we create muscle hypertrophy (growth) (Schoenfeld, 2010). It is also true that while we compete or exercise we can deplete a significant amount of our stored glycogen, depending on the intensity and duration. Our bodies respond to this by significantly increasing carbohydrate absorption after exercise due to the increased translocation of GLUT4 (Murray & Rosenbloom, 2018). This means that we can absorb dietary carbohydrate faster into our muscles after exercise, thus replenishing what was lost. A normal absorption rate of glycogen synthesis could be around 2-3 mmol/g wet weight/h (many factors), but after intense exercise and with the help of GLUT4 this rate increases between 12-30 mmol/g wet weight/h (Murray & Rosenbloom, 2018). Given this state that our bodies are in after exercise has led to many research articles trying to not only find the ideal macronutrient quantity and ratio to intake (Pritchett et al., 2009) but also presenting the existence of an “anabolic window of opportunity” (Candow & Chilibeck, 2008).
While there may be some application for carbohydrate timing, the suggestion for immediate protein ingestion is weak. A proposed reasoning is that after exercise our bodies slightly increase the rate by which it breaks down protein from our muscles. In a fasted state and 195 minutes after exercise, it has been shown that this muscle-protein breakdown is significantly increased and can persist up to 24 hours after exercise (Aragon & Schoenfeld, 2013). Insulin is believed to play the key role in preventing our bodies from using muscle protein. Therefore, intaking protein and carbohydrates after exercise will spike insulin and reduce the breakdown of muscle protein. Furthermore, it is purported that this decrease in breakdown will allow for an enhanced accumulation of contractile proteins and greater hypertrophy (Aragon & Schoenfeld, 2013). But, research has shown that a meal containing 75g carbohydrate, 37g protein and 17g fat raised insulin 3x above fasting levels within 30 minutes, 5x above at 1 hour and still 2x above after 5 hours (Capaldo et al., 1999). Other research has shown that 45g of whey protein takes about 50 minutes to spike insulin and remained at a level high enough to show a net muscle protein balance for 2 hours (Aragon & Schoenfeld, 2013). Adding carbohydrates to whey protein would peak higher and stay elevated longer but the timing is already outside of the “window.” Other research has shown that many of the postulated benefits have more to do with muscle protein synthesis (MPS) rather than insulin (Aragon & Schoenfeld, 2013).
Increasing MPS may be the response that gets touted the most. MPS is a driving force for adapting to exercise. But there is no clear evidence that there is an elevated benefit to MPS by immediately intaking protein after exercise. Research has shown no difference in leg net amino acid balance between a group intaking protein 1 hour versus 3 hours post exercise and other research showed that taking in a protein meal before exercise actually produced a more sustained MPS response than the group eating after exercise (Aragon & Schoenfeld, 2013). It should also be noted that short-term spikes in MPS may not always indicate long-term-hypertrophic outcomes.
There are many notable flaws in much of the research purporting benefits and supporting the existence of the “anabolic window.” One is that they use subjects who are under-fed in their total daily intake to begin with, thus leading to a greater response. Many also fail to equate total daily intake when comparing groups. Untrained individuals are often used even though they have been shown to react differently than well-training persons (Aragon & Schoenfeld, 2013). Finally, a lack of long-term interventions exist leading to inferred conclusions from singular responses. A study that accounted for many of these factors found that 33 trained males split into groups eating within the “window” and others who only ate morning and night presented no differences in lean mass gain over a 10 week exercise prescription (Hoffman et al., 2009).
Another glaring negligence is the assumption that exercisers are entering the session in a fasted state, as seen by the participants in many studies. This may be the case for some athletes and gym-goers, but not always. In a practical application, athletes will likely not be fasting before exercise. Our food does not instantly disappear when we eat it. The process of digestion and utilization takes time and can vary depending on the source. An egg protein meal, for example can take as long as 5-6 hours to fully digest (Schoenfeld & Aragon, 2018). This creates a wider window before we need to eat another protein meal. Hence, other researchers have rather pushed the importance of total daily intake being more important than a temporal allotment of macronutrients around training (Jentjens & Jeukendrup, 2003).
There may be instances when athletes have to play in multiple games, or practice session in one day. In these instances it would be recommended to intake a high carbohydrate meal accompanied with protein immediately after the session in order to be as replenished as possible before the next session. Other instances include my powerlifting athletes who will have long breaks in between different lifts. Eating after their attempts for the squat could help them to be replenished before performing the bench press.
Given the current state of research I would fall back on the recommendations of Schoenfeld and Aragon (2018) that athletes looking to maximize their performance and lean mass intake between 1.6-2.3 grams of protein/kg of bodyweight per day. Additionally, this total daily intake should be spread over 3-4 meals that are equally spaced out throughout the day, which has been shown to be an added benefit to muscle gain, even when total daily intake is equated (Yasuda et al., 2020). Given the nature of digestion, this will prevent any major loss of muscle protein throughout any given day, despite the timing of exercise.
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, 10(5).
Candow, D. G., & Chilibeck, P. D. (2008). Timing of creatine or protein supplementation and resistance training in the elderly. Applied Physiology, Nutrition, and Metabolism, 33(1), 184-190.
Capaldo, B., Gastaldelli, A., Antoniello, S., Auletta, M., Pardo, F., Ciociaro, D., Ferrannini, E., & Sacca, L. (1999). Splanchnic and leg substrate exchange after ingestion of a natural mixed meal in humams. Diabetes, 48(5), 958-966.
Hoffman, J. R., Ratamess, N. A., Tranchina, C. P., Rashti, S. L., Kang, J., & Faigenbaum, A. D. (2009). Effect of protein supplement timing on strength, power, and body-composition changes in resistance-trained men. International Journal of Sports Nutrition and Exercise Metabolism, 19(2), 172-185.
Ivy J., & Portman R. (2004). Nutrient timing: The future of sports nutrition. North Bergen, NJ: Basic Health Publications.
Jentjens, R., & Jeukendrup, A. E. (2003). Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine, 33(2), 117-144.
Murray, B., & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews, 76(4), 243-259.
Pritchett, K., Bishop, P., Pritchett, R., Green, M., & Katica, C. (2009). Acute effects of chocolate milk and a commercial recovery beverage on postexercise recovery indices and endurance cycling performance. Applied Physiology, Nutrition, and Metabolism, 34(6), 1017-1022.
Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. The Journal of Strength and Conditioning Research, 24(10), 2857-2872.
Schoenfeld, B. J., & Aragon, A. A. (2018). How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. Journal of the International Society of Sports Nutrition, 15(10).
Yasuda, J., Tomita, T., Arimitsu, T., & Fujita, S. (2020). Evenly distributed protein intake over 3 meals augments resistance exercise-induced muscle hypertrophy in healthy young men. The Journal of Nutrition, 150(7), 1845-01851. https://doi.org/10.1093/jn/nxaa101