Protein alone versus protein plus carbs?
Optimizing anabolic response in muscle
by Newsletter Editor
The rate limiting step in stimulating growth of muscle mass is the availability of amino acids. Thus, the most efficient way to stimulate muscle protein synthesis is to consume protein. Specifically, research points to 10 grams of essential amino acids as the optimal amount to consume. That’s only 40 calories. Adding carbohydrate to protein would stimulate insulin secretion, and insulin is thought to decrease protein breakdown and possibly promote greater protein synthesis.
In order to test this idea, researchers recently had a group of healthy adults ingest 10 grams of essential amino acids. Measures of muscle protein synthesis and breakdown were made over the next 3 hours. Another group consumed the same 10 grams of essential amino acids plus an additional 30 grams of sugar. Yet another group consumed 10 grams of essential amino acids pus 30 grams of alanine, a non-essential amino acid.
As expected, the addition of sugar to the essential amino acid drink caused greater increases in blood glucose and insulin levels than essential amino acids alone. However, there was no significant difference in the rate of muscle protein breakdown or synthesis between groups. Thus, when looking at muscle protein balance, the addition of sugar or extra alanine to an essential amino acid mixture had no additional effect.
What does this mean? These results emphasize that the most important factor for optimizing the anabolic response in muscle is the availability of essential amino acids. Adding extra calories in the form of carbohydrates that spike insulin levels has no additional benefit on protein balance. However, if you have goals other than weight loss such as replenishing glycogen stores for endurance sports, then consuming carbohydrates may be appropriate.
Reference: Glynn EL, Fry CS, Timmerman KL, Drummond MJ, Volpi E, Rasmussen BB. Addition of carbohydrate or alanine to an essential amino Acid mixture does not enhance human skeletal muscle protein anabolism. J Nutr. 2013 Mar;143(3):307-14.