American Fitness Professionals & Associates

INTRODUCTION:

Just like the multi-talented decathlete, glutamine is the multi-faceted supplement.  Glutamine helps regulate muscle mass, is involved in the immune system, affects the synthesis of glucose and may even improve insulin metabolism.  Glutamine seems to be involved in a little bit of everything and is in my opinion, the most important amino acid for bodybuilders.

QUESTION:  WHAT IS GLUTAMINE?

We know that the building blocks of proteins are amino acids.  And that the best sources of proteins contain the highest percentage of essential amino acids.  Remember that essential amino acids are those that you need to get from your diet.  Glutamine however is considered a “conditionally essential amino acid.”  You’re thinking, what the hell does that mean?

Interestingly, glutamine (not carbohydrates or fat) is the preferred fuel source for rapidly dividing cells such as enterocytes {intestinal cells} and lymphocytes {a type of white blood cell}.  Furthermore, this jack-of-all trades amino acid has a role in acid-base balance, as a nitrogen carrier, and as a precursor for important macromolecules {ex. proteins, nucleic acids}.  Under certain conditions {ex. catabolic stress}, glutamine may be needed as part of one’s diet; hence, the term “conditionally essential.”

Glutamine makes up roughly 61% of the amino acid pool in skeletal muscle.  The loss of muscle glutamine may be a signal for muscle catabolism.  So it is essential that intramuscular glutamine stores are maintained.

QUESTION:  DOES GLUTAMINE AFFECT THE IMMUNE SYSTEM?

This is one area concerning glutamine that has garnered a huge chunk of research dollars but seems to be one wrought with confusion.  Strenous exercise has been shown to cause a drop in blood levels of glutamine.  Remember that it is glutamine which is used preferentially by cells of the immune system.  Theoretically, it would make sense that low levels of glutamine would have a negative impact on the immune response.  Yet, a recent study has shown that glutamine supplementation has no effect on lymphocyte (a type of white blood cell) metabolism in exercise-trained rats.

In spite of the equivocal evidence on glutamine, here’s why I think its valuable to supplement with glutamine to help your immune system.  Its true that supplementing with glutamine does not seem to impact the immune system per se.  This is due to the fact that the immune system is probably “borrowing” glutamine from of all places, your skeletal muscles!  I mean think about it, which is more important for the survival of your body, having nice large muscles or a healthy immune system.  I know this sounds blasphemous to fellow bodybuilders, but it should be obvious that the preservation of immune function is more important.  I mean how many people have died from having little muscles?  So the reason you need to feed yourself glutamine is really to preserve muscle and to prevent your immune system from utilizing your muscle’s glutamine stores.

QUESTION:  HOW DOES GLUTAMINE INCREASE MUSCLE MASS?

Glutamine’s ability to preserve skeletal muscle mass in times of stress is perhaps its best known quality.  For instance, after the surgical trauma of a total hip replacement, glutamine supplemented as part of total parenteral nutrition (intravenous feeding) attenuates the loss of free amino acids from skeletal muscle.  Also, glutamine supplementation helps prevent the loss of nitrogen (i.e. protein) from patients who have undergone elective abdominal surgery.  Overall, there is strong evidence that demonstrates that the maintenance of high levels of intramuscular glutamine is essential for the prevention of muscle wasting.

At the molecular level, glutamine seems to exert its effect by preventing the loss of a specific protein called myosin heavy chain (MHC).  The MHC protein is the important protein of skeletal muscle in that it determines it’s contractile properties.  That is, if you have what scientists refer to as fast-twitch muscle, its because you have the fast form of the MHC; conversely, if you have slow-twitch muscle, its because you have the slow form of the MHC.  So you definitely do not want to loss any of this precious protein.

Now granted, the stress that your body undergoes after major surgery is tremendous.  But heavy resistance training is also a tremendous stress that your body can be subjected.  So even though surgery and weight-lifting are on the surface quite different in their stimuli, it would seem plausible and likely that the same physiological principles should apply when dealing with these physical perturbations.  So in both cases, it would be wise to supplement with glutamine in order to prevent the potential loss of muscle protein.

QUESTION:  DOES GLUTAMINE AFFECT THE METABOLISM OF SUGAR?

The effect of glutamine on glucose (sugar) metabolism is one effect of glutamine which has not received much press in the bodybuilding world.  In fact, a very recent study from the University of Rochester demonstrated the importance of glutamine as a regulator of gluconeogenesis (formation of glucose).  Using human subjects, they found that the infusion of glutamine resulted in a conversion of glutamine to glucose.  This occurred without any changes in either insulin or glucagon, the two major glucoregulatory hormones.  The conversion of glutamine to glucose likely occurs in the kidney as opposed to the liver which the primary regulator of glucose production.

So how does this affect bodybuilders?  Glutamine could affect for instance the amount of fat loss that a pre-contest bodybuilder can attain.  See if you can follow this reasoning.  Part of the difficulty in dieting down to low body fat levels is related to the precise regulation of the glucoregulatory hormones, insuline and glucagon.  Typically, we would like to minimize the level of insulin secreted in order to inhibit the deposition of fat into our adipose tissue.  Of course, the problem with that is that low glucose or carb intake itself may result in muscle proteolysis since it is well known that glucose has a protein-sparing effect.  So in comes glutamine.  Glutamine can itself be converted to glucose.  This is good in that glucose can serve as brain fuel (so you won’t feel to irritable) and it can help spare some of that precious muscle mass you’ve attained.  But also, since the conversion of glutamine to glucose does NOT result in an increase in insulin levels, then you will not get the lipogenic effect that insulin produces.

So if you’re dieting down to the very low levels of body fat seen in competitive bodybuilder, it may be wise to invest in a good dose of glutamine!

QUESTION:  DOES GLUTAMINE HELP REGULATE BODY WEIGHT?

Yes!  In a study in which mice were fed a high fat diet, it was shown that glutamine supplementation impacted how much fat these furry little guys put on.

In this study, both glutamine and alanine supplementation to the high fat diets resulted in a lower body weight gain than the high fat diet alone.  These high fat diets were approximately 45% fat and 36% carbs with the remainder protein.  That percentage of fat is comparable to the diets consumed by many overweight Americans.  Also, glutamine by itself lowered levels of blood glucose and insulin in these fat consuming mice!

These findings may be important for humans who may be predisposed to obesity or diabetes.  It would be useful to test glutamine on diabetics to determine if blood glucose regulation is enhanced and to examine if this versatile amino acid can impact body weight in overfat individuals.

Because high doses of glutamine have been shown to be safe in humans, future studies may lend more support for the use of glutamine as an anti-obesity and anti-diabetic agent.

REFERENCES

Blomqvist, B.I. et al.  Glutamine and alpha-ketoglutarate prevent the decrease in muscle free glutamine concentration and influence protein synthesis after total hip replacement.  Metabolism. 44:1215-1222, 1995.

Castell, L.M. et al.  Some aspects of the acute phase response after a marathon race, and the effects of glutamine supplementation.  European Journal of Applied Physiology.  75:47-53, 1997.

Hammarqvist, F. et al.  Addition of glutamine to total parenteral nutrition after elective abdominal surgery spares free glutamine in muscle, counteracts the fall in muscle protein synthesis, and improves nitrogen balance.  Annals Surgery.  209:455-461, 1989.

Hickson, R.C., S.M. Czerwinski, and L.E. Wegrzyn.  Glutamine prevents the downregulation of myosin heavy chain synthesis and muscle atrophy from glucocorticoids.  American Journal of Physiology.  268:E730-E734, 1995.

Keast, D. et al.  Depression of plasma glutamine concentration after exercise stress and its possible influence on the immune system.  Medical Journal of Australia.  162:15-18, 1995.

Kinscherf, R.  et al.  Low plasma glutamine in combination with high glutamate levels indicate risk for loss of body cell mass in healthy individuals:  the effect of N-acetyl-cysteine.  Journal of Molecular Medicine.  74:393-400, 1996.

Lacey, J.M. and D.W. Wilmore.  Is glutamine a conditionally essential amino acid?  Nutrition Reviews.  48:297-309, 1990.

Opara, E.C. et al.  L-glutamine supplementation of a high fat diet reduces body weight and attenuates hyperglycemia and hyperinsulinemia in C57BL/6J mice.  Journal of Nutrition.  126:273-279, 1996.

Perriello, G. et al.  Regulation of gluconeogenesis by glutamine in normal postabsorptive humans.  American Journal of Physiology.  272:E437-E445, 1997.

Rohde, T. et al.  The immune system and serum glutamine during a triathlon.  European Journal of Applied Physiology.  74:428-434, 1996.

Rowbottom, D.G. et al.  The haematological, biochemical and immunological profile of athletes suffering from the overtraining syndrome.  European Journal of Applied Physiology.  70:502-509, 1995.

Rowbottom, D.G. et al.  The emerging role of glutamine as an indicator of exercise stress and overtraining.  Sports Medicine.  21:80-97, 1996.

Shewchuk, L.D. et al.  Dietary L-glutamine does not improve lymphocyte metabolism or function in exercise-trained rats.  Medicine and Science in Sports and Exercise.  29:474-481, 1997.