I’ve had an increasing number of people ask me about glutamine supplementation recently. I also noticed that on the protein powder that I use “L-glutamine” is listed. To be honest, I didn’t know much about the research behind glutamine supplementation and athletic performance. During my dietetic internship, glutamine supplements were sometimes given to critically ill patients in the hospital setting. I wondered if there was any evidence to suggest that athletes should also be taking glutamine supplements. I’ll be sharing the results of my research in this blog!
The structure of the amino acid glutamine
Glutamine is one of the amino acids that make up proteins. Amino acids are classified as either essential or nonessential. Glutamine is a nonessential amino acid. This means that the body can make glutamine and that it does not have to be included in the diet like the essential amino acids. Most people eat about 3-6 grams of glutamine each day through foods containing protein. Glutamine can also be found as a supplement in tablet or powder form and is sometimes added to protein powders. Manufacturers of glutamine supplements claim numerous benefits such as nutritional support of the immune system, prevention of infection and stimulation of glycogen and muscle protein synthesis.
To see if there is any evidence to support these claims, first a brief physiology lesson: As mentioned, glutamine is a nonessential amino acid, so the body makes it. Muscle is the major tissue that makes glutamine and releases it into the blood. Glutamine is very important for the immune cells called lymphocytes. Lymphocytes can’t make glutamine, so they are dependent on muscle for their glutamine needs. Exercise is associated with decreased glutamine levels in the blood. As you may have personally experienced after hard exercise, we also have impaired immune system. There is a hypothesis that this decrease in glutamine levels is what causes the impaired immune function seen post exercise. Muscle levels of glutamine are also related to muscle protein and glycogen synthesis.
Studies show that high intensity exercise that is less than an hour actually causes glutamine levels to rise. On the other hand, studies do consistently show that during prolonged exercise, such as after a marathon or other endurance events, glutamine levels fall. The blood concentrations of glutamine also tend to be lower in athletes who over-train. However, the glutamine immune boosting hypothesis mentioned above does not hold true when tested on athletes. Despite the fall in glutamine that is seen with prolonged exercise, the majority of studies have found no beneficial effect on immune response from maintaining blood glutamine levels through supplements. Overall, the evidence does not support the idea that decreased blood glutamine is the cause of exercise induced immune depression. As usual, more research is needed.
How about glutamine ingestion and muscle growth and glycogen synthesis? After resistance exercise, eating essential amino acids are required for muscle growth. If the protein consumed post-exercise contains the essential amino acids, then the addition of glutamine (a nonessential amino acid) is unlikely to help with muscle growth. Similarly, while glutamine supplementation might help with glycogen synthesis if you are consuming a suboptimal amount of carbohydrates post-exercise, the best way to promote glycogen synthesis is by a post exercise meal that is predominately carbohydrates with some protein.
In conclusion, the evidence is not strong enough to recommend glutamine supplementation in athletes. However, while glutamine supplementation is not recommended for those with kidney disorder, it is safe and tolerated by most people. In other words, while the studies found no beneficial effect of glutamine, there was also no detrimental effect.
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