Glutamine – Supplement Profile
Anybody who has been bodybuilding during the last ten years or so is certainly familiar with glutamine. Even if you have only bought a tub of protein lately you have probably heard about glutamine. Everybody seems to be claiming that it is the bell or whistle that makes their protein so “special”. Go to any bodybuilding contest and you will hear several competitors swear by it. So what does it do? Why does everybody give it so much credit? Well, the answer might surprise you.
Glutamine is the most abundant free amino acid in the body. Most free amino acids are quickly incorporated into body proteins as they become available. Glutamine however, due to its unique functions, is kept in pools, mostly in muscle tissue. Skeletal muscle comprises approximately 60% of total body glutamine stores. The second major location for glutamine is the lungs. Glutamine also accounts for about 35% of amino acid nitrogen in plasma where it is the major vehicle for nitrogen transfer between tissues.
Not all amino acids are necessary in the diet because they can be made within the body from other amino acids. If the body can’t make an amino acid however, it must be present in the diet and is labeled “essential”. Those that your body can manufacture are called “non-essential”. Glutamine is generally considered a non-essential amino acid because the body can make it from other amino acids with the help of glutamine synthase (clever name huh?). Glutamine synthase is found in high concentrations in skeletal muscle.
People with average protein intakes generally consume about 5 to 10 grams of glutamine per day. Although glutamine is officially a non-essential amino acid because it can be made in the body from other amino acids, if the demand for glutamine exceeds the body’s ability to make it, bad things start to happen, especially in skeletal muscle and the immune system. In such cases, glutamine becomes essential, and is now widely labeled a conditionally essential amino acid.
During stress, glutamine is released primarily buy skeletal muscles where it is then shuttled to tissues that need it. The lungs are the second largest contributor of free glutamine during stress. When faced with chronically high levels of stress, muscle and the lungs must bare the brunt of supplying the rest of the body with glutamine. This is in part responsible for the wasting associated with illness.
Glutamine plays a crucial role in maintaining function in rapidly dividing cells such as lymphocytes and mucosal enterocytes, of the immune system and digestive tract respectively. Cells of the immune system like lymphocytes rely on glutamine as a metabolic fuel. Enterocytes of the small intestine have a high rate of turnover and are the largest “consumer” of glutamine in the body. Glutamine supplementation increases the height of microvilli, as well as increasing the robustness of the mucosal lining in the GI tract. This serves to ensure optimal nutrient absorption as well as protect you from foreign bacteria you inadvertently put in your mouth.
Glutamine also buffers the body from high levels of ammonia by binding to it. Glutamine can then release ammonia when needed to form other amino acids, amino sugars, nucleotides, or to be excreted as urea.
Glutamine can be used for gluconeogenesis, and it contributes to nucleotide, amino sugar, and protein biosynthesis. Glutamine, along with cysteine, and glycine, plays a key role in glutathione synthesis. Glutathione is a coenzyme and is an important intracellular antioxidant.
There is a strong positive relationship between intracellular glutamine levels and protein synthesis. During muscle-protein wasting associated with injury or disease the levels of free glutamine in muscle tissue falls. In order to find out the consequences of this, MacLennan et al. looked at the relationship between the rate of muscle protein synthesis and intramuscular glutamine concentration (1). These investigators used in-vitro methods in order to acutely view changes in protein synthetic rates. Increasing intramuscular glutamine levels by 200% led to a 66% increase in protein synthesis in the absence of insulin. When they added insulin to the mix, a 30% increase in intramuscular glutamine was accompanied by an 80% increase in protein synthesis. Clearly, increasing the amount of free glutamine inside your muscles increases protein synthesis. Anyone reading this should have one question in mind however, is it possible to increase intramuscular glutamine levels by 200% by using a supplement?? More on that in a minute.
Some in vitro evidence exists that shows glutamine to have a direct effect on protein synthesis, however, this effect may be conditional (2). Zhou and colleagues found that glutamine has a stimulatory effect on the rate of protein synthesis in stressed myotubes but not in normal-cultured myotubes. Myotubes are muscle fibers in their early stages of development. Now, they found that the protective effect of glutamine on skeletal muscle protein might be associated with “heat shock proteins” or HSP. One common HSP in skeletal muscle is HSP70. They found that the level of HSP70 correlated with the levels of glutamine. What does this mean to you? It?s hard to say. It?s too early really at this point to make any conclusive remarks.
If the effect of glutamine on protein synthesis weren’t enough, it appears glutamine may also be anticatabolic. Research has shown that glutamine may exert anticatabolic effects similar to insulin. (3) MacLennan et al. was able to show that, glutamine was just as anti-catabolic as insulin. The anti-catabolic effects of glutamine were not enhanced when combined with insulin, indicating a similar mode of action. This type of anticatabolic effect results in the preservation of soluble or non-contractile proteins with no protective effect on myofibrillar proteins. This would make sense considering glutamines effects on protein breakdown were through a similar mechanism to insulin. This study shows that glutamine is indeed anti-catabolic, but it won’t help you hold on to those muscle proteins that really count.
You may have seen glutamine advertised as a “cell-volumizer”. Well, this is true in a way. Glutamine itself doesn’t actually cause cells to swell. It is the sodium that must be co-transported with glutamine that causes the cell to swell. Either way it is a good thing. A consequence of the sodium-dependent entry of glutamine, is an osmotic, or “swelling” of the cell with water. Glutamine has been given a number of anabolic properties such as the stimulation of both protein and glycogen synthesis. The mechanism through which glutamine activates key enzymes in these metabolic pathways may involve this glutamine/sodium-induced cell swelling.(4)
Keep in mind that all of the studies we have looked at have used in-vitro techniques. This is a far cry from in-vivo conditions.
Glutamine may play a role in glycogen repletion after exercise.(5) In a study by Varnier et al. subjects cycled for 90 min at 70-140% VO2max to deplete muscle glycogen; then constant infusions of glutamine or a mixture of alanine and glycine or saline were administered. Muscle glutamine remained constant during saline infusion, decreased 18% during alanine+glycine infusion, but rose 16% during glutamine infusion. By 2 hrs. after exercise, muscle glycogen concentration had increased more in the glutamine-infused group than in the saline or alanine+glycine groups. The rate that blood glucose was incorporated into glycogen was not increased; suggesting that glutamine itself was serving as a substrate for glycogen synthesis rather than increasing glycogen storage from dietary carbs. What this means is that glutamine was being used for gluconeogenesis. This would not be the most practical use of a glutamine supplement. Besides, it would be difficult to mimic the effects of glutamine infusion with an oral glutamine supplement.
So what if you combine glutamine with a glucose polymer? The positive effect of oral glutamine combined with glucose on post exercise glycogen storage was shown to only occur outside of muscle, most likely in the liver.(6) Glutamine does not enhance glycogen synthesis in skeletal muscle beyond what glucose polymers do alone.
The authors of the study combining glutamine with glucose polymers commented that, from their data, only 47-50% of orally administered glutamine can be expected to make it past the liver and other organs, into the blood stream. And only about 10% can be expected to reach extracellular spaces.(6) Now, this is the main argument against glutamine. 90% of the glutamine you take orally never even makes it to your muscles. This isn’t to say it is wasted. Your GI tract loves glutamine from reasons explained earlier. If you are having intestinal problems nothing is better. If you are trying to increase protein synthesis by loading glutamine, it isn’t going to work.
So, is glutamine a “must have” supplement for any aspiring bodybuilder? No, probably not. Is it helpful under situations where overtraining is rearing its ugly head? You bet. Everything considered, glutamine is one of those supplements that probably will benefit anybody preparing for a show, but if you are an off-season, well-fed bodybuilder getting plenty of recovery and using a whey protein supplement, there are more important supplements to spend your money on.
1: MacLennan PA, Brown RA, Rennie MJ. A positive relationship between protein synthetic rate and intracellular glutamine concentration in perfused rat skeletal muscle. FEBS Lett 1987 May 4;215(1):187-91
2: Zhou X, Thompson JR. Regulation of protein turnover by glutamine in heat-shocked skeletal myotubes. Biochim Biophys Acta 1997 Jun 27;1357(2):234-42