The timing of nutrient intake is important to consider whether it is before, during, or after a bout of exercise. Depending on what nutrients are consumed and when, they may be able to enhance athletic performance (Ivy et al., 2014). However, research shows conflicting results based on limitations of studies to be able to come to definitive conclusions to state exactly what should be consumed and when in order to improve performance. When glycogen is depleted following intense and/or long durations of exercise, it is best to replenish the glycogen stores with a high-glycemic index carbohydrate source. However, some studies have found that when carbohydrate and protein sources are combined post exercise, muscle glycogen levels may be replenished quicker compared to carbohydrate intake alone (McGuire et al., 2018). So, when is the best time to consume carbohydrate-only supplements, when is the best time to consume a combination of carbohydrate and protein supplements, and which activities may be most positively impacted by either method?           

In the article, “Nutrient Timing: The Means to Improved Exercise Performance, Recovery, and Training Adaptation”, researchers discuss three phases of exercise: the energy phase, the anabolic phase, and the adaptation phase. The energy phase is up to four hours before exercise as well as the time during exercise. Finding a balance between consuming an adequate amount of carbohydrate prior to exercise to sustain longer durations or intense sessions, but also not too much too quickly to create a hypoglycemic response in the form of a sugar crash was originally thought to be a challenge. However, it is generally agreed upon that pre-exercise and during exercise carbohydrate consumption is beneficial to athletic performance as this helps sustain blood glucose levels since the supply is limited (Ivy et al., 2014). Furthermore, during higher intensities of exercise (70-75% VO2max), carbohydrate supplementation has been shown to delay fatigue, and during lower intensities of exercise, carbohydrate supplementation has been shown to spare muscle glycogen and improve endurance performance (Ivy et al., 2014). Finally, adding protein to carbohydrate supplements has been shown to be effective for both endurance and resistance trained athletes as this method reduces muscle damage that occurs following either form of exercise (Ivy et al., 2014).   

Next is the anabolic phase. This is the time immediately following exercise when the body is in a catabolic state. After a bout of intense exercise, insulin levels are low, cortisol is elevated due to the stress of the exercise, glycogen stores are depleted, and muscle protein catabolism may be occurring because substrate availability is low. The body remains in this state until nutrients are consumed (Ivy et al., 2014). Research has found that replenishing with a carbohydrate and protein supplement within 45 minutes after exercise helps to reverse this catabolic state and gets the body into an anabolic state where glycogen stores may be replenished and muscle damage is reduced (Ivy et al., 2014). Furthermore, the addition of protein (especially in the form of whey) to the carbohydrate supplement has been found to increase muscle protein synthesis when given immediately after exercise compared to delaying the supplement (Ivy et al., 2014). Finally, since the consumption of whey protein may speed protein synthesis, this is what is thought to lead to a faster recovery from muscle damage attributed to exercise (McGuire et al., 2018).       

Last is the adaptation phase. This phase is when the body is responding and adapting to stressors experienced from the bout of exercise. Adapting to a new or more intense exercise level allows the body to handle an increased load next time. However, it is important to ensure that adequate recovery methods have been taken to allow the body to properly adapt. Part of this recovery process is nutrition. Carbohydrate and protein supplementation 4-6 hours after the supplements taken during the anabolic phase have been digested, result in continuous muscle protein synthesis. In addition, ingesting small amounts of the carbohydrate and protein supplement, at regular 2 to 3 hour intervals, keeps a steady stream of blood glucose to replenish the glycogen stores and allows for continuous muscle protein synthesis (Ivy et al., 2014).      

Based on these findings, when is the best time to consume carbohydrate and protein supplements and which activities may be most positively impacted by either method? Personally, I believe it is a matter of determining when and how one is going to be exercising that makes the biggest difference on timing nutrient intakes. Supplementing with carbohydrate and protein prior to and during exercise has been shown to help enhance efforts and allow one to exercise longer due to additional circulating glucose - especially at higher intensities. Furthermore, if one participates in early morning exercise in a completely fasted state, they would likely benefit from consuming a carbohydrate and protein supplement soon after exercise to replenish glycogen stores, enhance protein synthesis, and reduce muscle soreness (Ivy et al., 2014). Also, if weight loss is one of the goals of exercise, it may be best to consume dairy to help with these efforts (Ivy et al., 2014). On the other hand, if one is going to be exercising in a fed state, consuming a carbohydrate and protein supplement immediately after exercising isn’t going to be as important or effective since the body is still digesting and utilizing the nutrients that were consumed just hours before (Aragon, et al., 2013). As far as which activities are most impacted from a carbohydrate and protein supplement before, during, and after exercise, benefits have been shown in both endurance as well as two-a-day resistance training activities exercising the same muscles. Not as significantly impacted by supplementing with this method are resistance training activities at a high intensity but moderate volume as this doesn't deplete the glycogen stores as much (Aragon et al., 2013). Finally, it is important to keep in mind that not one single method will always work for every single person. Finding out which method works best on an individual level as well as maintaining an overall healthy diet that consists of adequate amounts of carbohydrate, protein, and fat is necessary to enhance athletic performance.                

References

Aragon, A., Schoenfeld, B. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10(5), 1-11. https://doi.org/10.1186/1550-2783-10-5 

Ivy, J., & Ferguson-Stegall, L. (2014). Nutrient Timing: The Means to Improved Exercise Performance, Recovery, and Training Adaptation. American Journal of Lifestyle Medicine, 8(4), 246–259. https://doi.org/10.1177/1559827613502444 

McGuire, M., & Beerman, K., (2018). Nutritional Sciences: From Fundamentals to Food (3rd ed.). Boston, MA: Cengage Learning