Q and A

Carbs and Protein synthesis


I’ve heard a few people say that consuming carbohydrates post workout doesn’t actually help with increasing muscle protein synthesis. Is this true? And if it is do I still need to consume them?

This is where a little bit of knowledge can kind of get you into trouble.

While it is true that consuming carbohydrate with protein in the post workout period does not lead to muscle protein synthesis rates higher than those seen after consuming protein alone that does not mean that there is no benefit from doing so.

Muscle protein synthesis is only one reason that we consume nutrients post training (or at any time for that matter) and there is so much more to the story and fate of carbohydrates when ingested post training.

Carbohydrates are essential for replenishing muscle glycogen stores as well as enhancing recovery after exercise. This includes potentially helping to reduce the continued catabolic effects of hormones like cortisol.

Glycogen stores have a direct effect on exercise intensity. The greater the glycogen stores, the more intensely one may exercise. Incomplete glycogen replenishment will have a negative effect on the quality and quantity of exercise one is able to perform. The higher the intensity, the more the body has to rely on the fuels already stored in the muscles.

Carbohydrate (specifically glucose) is also essential for maintaining immune system function. Along with water, protein, and electrolytes, it is an important fuel substrate for the cells that make up our immune system- lymphocytes, neutrophils, and macrophages.

Having low levels of blood glucose is a trigger for increased levels of cortisol, epinephrine, and growth hormone. This is a necessary to mobilize fuels to allow continued exercise to take place. That in-and-of itself is not the problem; the problem arises when this response is allowed to go unchecked.

Prolonged low blood glucose, and subsequent low levels of glycogen, encouraged continued elevation of cortisol in order to mobilize fuels from various sources, like adipose tissue, liver glycogen, etc. It has been well established that chronically high levels of cortisol contribute to immunosuppression.

Training on low levels of carbohydrate has been suggested to increase the immuno- suppressive effect of exercise. In fact, it causes greater disruption to immune cells.

Maintaining optimal glycogen stores as well as stable blood sugar is key to avoiding the immune system depression as well as increasing peak performance.

While the research may not be clear regarding the immune system response to immediate post training ingestion of carbohydrates, one thing is certain- training in a glycogen depleted state does increase immunosuppression.

The fastest way to replenish glycogen stores is to consume them shortly after exercise when you can take advantage of muscle-induced uptake of glycogen as well as the insulin spike that goes along with the carbs. Restoring glycogen post-exercise is also critical for your next bout of activity.

So while post exercise carbohydrate ingestion may not directly increase muscle protein synthesis above that seen from ingestion of protein or amino acids, it is crucial in replenishing glycogen stores.

These glycogen stores are essential to mediating the immunosupression seen post training.

Without carbohydrate to help with recovery, cortisol levels often remain elevated, the immune system is suppressed, and we are at increased risk for overtraining, injury, and illness. None of those things will increase our muscle protein synthesis either.

Gunzer W. Konrad M. Pail E. Exercise-induced immunodepression in endurance athletes and nutritional intervention with carbohydrate, protein, and fat- what os possible, what is not? Nutrients. Sept 2012; 4(9): 1187-1212.

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