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Do you need post-workout carbs?

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Aaron Deere is a sports nutritionist, functional medicine consultant and advanced personal trainer. He is based in London.

If you take on carbs as soon as your workout finishes in the belief that you need to replenish energy levels as quickly as possible, you may be taking on unnecessary calories, especially if getting lean in your primary training objective. That’s because replacing the glycogen you’ve just burned isn’t as crucial to recovery as some have claimed. Indeed, unless you are training very intensively and multiple times per day – like a pro athlete – it’s likely that your current diet is already providing enough energy to keep your body operating optimally. Here’s what we know from the latest research.

Stored carbs
Glycogen is a multibranched polysaccharide of glucose and is the form in which carbohydrates are stored in mammals. In humans the majority of glycogen is stored in muscles (around 500g) and the liver (around 100g). Each gram of stored glycogen is bound to approximately 3-4g of water[1], which is why cutting carbs is a popular decision when trying to look as lean as possible, because a reduction in glycogen levels results in this water being expelled from the body to give a harder, more defined physique.

The main functions of glycogen are to maintain stable blood glucose concentrations and provide energy. The liver is predominantly responsible for releasing glycogen into the blood, as skeletal muscles are only able to release glycogen through an energy expensive process of conversion to lactate. Muscle glycogen is therefore predominantly used as a local energy source for exercise[2]. Glycogen is the main energy substrate used during exercise with intensity above 70% of VO2max, and decreasing muscles glycogen levels is what causes fatigue.

Glycogen depletion rates
Resistance training, where 70% of the VO2max is rarely reached, initially uses phosphocreatine as fuel, although there is a significant reliance on muscle glycogen as the session progresses. Through muscle biopsies, multiple studies have shown glycogen depletion rates of between 25% to 40% for strength and hypertrophy protocols[3]. The rate of glycogen depletion was directly related to the intensity of the lift, total work performed and main fibre type used, with type II fibres and higher-intensity sessions shown to use glycogen more rapidly.

For serious trainers or athletes who often complete multiple sessions in a day, it is a completely different matter. Consumption of carbohydrates (250g) after the first workout has been shown to dramatically increase workout volume, intensity and duration versus controls in repeated same day bouts of resistance exercise[4].

The case for supplementation
If you are training several times per week and not doing multiple daily sessions, then glycogen status for workouts is unlikely to be a concern, unless you are following a low-carbohydrate diet, which will have a direct effect on glycogen levels. If this is you then you should be able to easily maintain muscle glycogen stores with a well-balanced and calorie-sufficient diet. It has been shown that because there is only between a 25-40% reduction in glycogen levels following resistance exercise, the need for specific glucose supplementation post-workout is likely not necessary.

The two-hour window post-workout has the highest potential for glycogen re-synthesis, so a mixed meal within the timeframe of completing exercise will likely be sufficient to restore optimal glycogen levels after resistance training[5]. If the goal is to rapidly replenish glycogen stores post workout, high GI carbohydrates have been shown to raise glycogen synthesis rates post workout by up to 40% when compared to low GI carbohydrates, making them a preferential option.

1. Olsson, Karl-Erik, and Bengt Saltin. “Variation in total body water with muscle glycogen changes in man.” Acta Physiologica Scandinavica 80.1 (1970): 11-18.
2. Jensen, Jørgen, et al. “The role of skeletal muscle glycogen breakdown for regulation of insulin sensitivity by exercise.” Frontiers in physiology 2 (2011).
3. Tesch, Per A., Erland B. Colliander, and Peter Kaiser. “Muscle metabolism during intense, heavy-resistance exercise.” European journal of applied physiology and occupational physiology 55.4 (1986): 362-366.
Robergs, R. A., Pearson, D. R., Costil, D. L., Fink, D. D., Pascoe, M. A., Benedict, C. P., Lambert, C. P., and Zachweija, J. J. (1991). Muscle glycogenolysis during differing intensities of weight-resistance exercise. Journal of Applied Physiology, 70, 1700-1706.
4. Haff, G. G., et al. 1999. The effect of carbohydrate supplementation on
multiple sessions and bouts of resistance exercise. Journal of Strength and Conditioning Research, 13, (2), 111-7.
5. Betts, James A., and Clyde Williams. “Carbohydrate ingestion during recovery from prolonged exercise.” Agro FOOD Industry Hi-Tech 18.2 (2007): 50-53.

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