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GLUTAMINEThis Amino Acid Helps to

Preserve Muscle Mass While BolsteringImmune and Gastrointestinal Health

By Armotid Scipione

"Patients who hadmajor surgery and were

given glutamine didnot lose muscle mass

during the recuperativeperiod, even thoughthey were inactive."

G lutamine is an important aminoacid tiiat may help to maintain

muscle, boost the immune system,support gastrointestinal health,and sustain healthy growth hor-mone levels." Of the 20 aminoacids needed for protein synthesis,glutamine is the most abundant,making up 50% of all amino acidsin the blood and 60% of those inthe body.' It is found in high con-centrations in skeletal muscle,lung, liver, brain, and stomach tis-sue. The best dietary sources ofglutamine include poultry, beef,fish, cabbage, beets, and dairyproducts.

Amino acids are generally divid-ed into two categories: essentialand non-essential. Essential aminoacids cannot be synthesized in thebody and must be obtained fromdietary sources. By contrast, non-essential amino acids are formedin the body. Giutamine, however, isreferred to as a "conditionally"essential amino acid because incertain circumstances, the body isunable to produce enough gluta-mine to meet its needs.'^ Studieshave shown that prolonged exer-cise, surgery, burns, and infectiousdisease can deplete glutamine lev-els by as tnuch as 50%.' Underthese conditions, supplementationwith glutamine becomes crucial.

Glutamine synthetase enzyme computer model.This ligase enzyme forms chemicai bonds betweenmotecules. The different colors show the different

sub-units that comprise the protein.

Maintaining Muscle Mass

Maintaining skeletal muscle isessential to good health and weightmanagement. An increase in musclemass increases the basai metabolicrate, or amount of caiories the bodyburns while at rest. Giutamine mayhelp to maintain healthy muscle tis-sue in people who are susceptible toa loss of muscle mass. One studyfound that patients who had majorsurgery and were given glutaminedid not iose muscle mass during therecuperative period, even thoughthey were inactive.' The researchersconcluded that glutamine supple-mentation counteracts the declinein muscle protein synthesis thatoccurs after surgery, while improv-ing nitrogen retention. This researchmay prove especially useful to thoseon calorie-restricted diets, whooften have difficulty maintainingmuscle mass.

Increasing Growth Hormone

Produced by the pituitary gland,growth hormone supports health ina variety of ways. According toresearchers, growtb hormone ieveisbegin falling around the age of 30and continue to diminish over time,contributing to weight gain, reducedenergy, and muscle loss.

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Unfortunately, growth hormoneinjections require a prescriptionand are seldom covered by healthinsurance. The cost of supple-menting with this revitalizing hor-mone can exceed $1,000 a month.However, in a study published inthe American Journal of ClinicalNutrition, a relatively smallamount of glutamine significantlyincreased growth hormone levels.'The study subjects were giveneither a placebo or 2 grams of glu-tamine to drink. At 30 and 60 min-utes after supplementation, theirblood samples were analyzed forplasma growth hormone levels.Those who consumed glutaminehad markedly increased growthhormone levels, while the placebogroup exhibited no change ingrowth hormone levels.

Another study adds to the evi-dence that that glutamine boostsgrowth hormone levels. In a ran-domized, double-blind, placebo-controlled trial of 42 healthymiddle-aged and elderly adults, thesubjects consumed either a place-bo or 5 grams of a nutritional sup-plement composed mainly ofglutamine, glycine, and niacin. The

•

supplement was ingested twice dai-ly for three weeks. At baseline and atthe study's end, the investigatorsanalyzed the participants' blood.Ingesting the supplement led to a70% increase in serum growth hor-mone levels compared to placebo,leading the researchers to concludethat an oral mixture of glutamine,glycine, and niacin can enhancegrowth hormone secretion inhealthy adults.**

Boosting Immunity,Antioxidant Status

Because glutamine fuels whiteblood cells, it is essential in sup-porting the body's immune systemand immune response. Trauma,surgery, viral infections, andchemotherapy have all been shownto deplete glutamine levels.- It hasbeen suggested that diminishedplasma glutamine levels may leadto suppressed immune function.'

Total parenteral nutrition is theintravenous administration ofnutrients to critically ill patients.Until recently, however, commer-cial total parenteral nutrition solu-tions did not contain glutamine.This can result in atrophy of the gutmucosa and compromised integri-ty of the gastrointestinal tract.'' Inone study, glutamine was added tothe total parenteral nutrition ofpatients following bone marrowtransplantation. The results indi-cated lower incidence of infectionand shorter hospital stays com-

pared to patients who received glu-tamine-free parenteral nutrition.'

Endurance athletes also havedecreased plasma glutamine con-centrations after prolonged, stren-uous exercise.^'" Post-exerciseglutamine depletion and associat-ed immunosuppression may ren-der the athlete more susceptible toinfection. In one study, a group of151 elite runners and rowers weregiven two drinks containing eitherglutamine or a placebo immediate-ly after and two hours after exercise.Over the following seven days, thepercentage of infection-freepatients was significantly higher inthe giutamine group (81%) than inthe placebo group (49%).'"

Glutamine also plays animportant role in the body'santioxidant systems. In combina-tion with L-cysteine and glycine,glutamine promotes glutathionesynthesis in the liver. Glutathioneneutralizes damaging free radi-cals and recharges oxidized vita-min G." Optimal amounts ofglutathione are also necessary tosupport the immune system andliver function.'^

Aiding Digestive Health

A healthy gastrointestinal tract isa vital component of overall well-being. In fact, the gastrointestinaltract lining serves as a first line ofdefense against disease-causingmicroorganisms. Enterocytes,which are epithelial cells lining the

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small intestine, use glutamine astheir primary metabolic fuel."Glutamine is thus essential inmaintaining the structural integri-ty of the intestinal lining. Insuffi-cient glutamine may lead to a lossof gut mucosal integrity, which canallow toxins and infectious agentsto be absorbed.'"^ This condition,known as increased intestinal per-meability, may be associated withhealth problems such as allergies,skin disorders, and Crohn's dis-ease.-"'"' By helping guard againstincreased intestinal permeability,glutamine may have applicationsin the management of these andother conditions.''

Insufficient levels of glutaminecan also lead to atrophy of the villiin the small intestine. Resemblingsmall fingers, the villi serve toincrease the gastrointestinal tract'sabsorptive surface area. Supple-menting with glutamine can helpincrease villous height, thus help-ing to maximize the surface areaavailable for nutrient absorption.-

Gehac disease, which is causedby the body's abnormal immuneresponse to gluten protein fromwheat, barley, or rye, is associatedwith villous atrophy. While avoid-ing gluten protein is essential to

managing celiac disease, gluta-mine's ability to support the intes-tinal lining and increase villousheight suggests that it may helpspeed the recovery of the mucosallining.-""

Grohn's disease is a chronicinflammatory condition that canaffect the small and large intes-tines, as well as other tissues of thebody. A study comparing Grohn'sdisease patients with healthy con-trol subjects found that Grohn'ssufferers have an abnormally high-er incidence of intestinal hyper-permeability. The investigatorsspeculated that increased intestin-al permeability could play a role inthe genesis of Grohn's disease. Fur-ther research is needed to clarifythe relationship between Grohn'sand intestinal hyperpermeability,and whether glutamine may be aneffective therapeutic tool in man-aging the condition.'"

Altered intestinal permeabilitymay also be involved in the causa-tion of skin conditions and foodallergies. In one study, individualswith intestinal hyperpermeabilitywere more susceptible to experi-mentally induced chronicurticaria (an allergic skin condi-tion marked hy itching and hives)

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compared to healthy control sub-jects. " Intestinal hyperpermeabili-ty has also been associated withmultiple food intolerance andatopic dermatitis in infants andyoung children."

By supporting the structuralintegrity of the gastrointestinal lin-ing, glutamine may offer relief for anumber of gastroimestinal condi-tions, as well as support for certainskin and allergic conditions.

Summary

Because glutamine can be syn-thesized in the human body, its useas a nutritional supplement haslong been overlooked. However,factors as varied as viral infections,surgery, burns, infectious disease,and even prolonged exercise cansignificantly deplete levels of thismultifunctional amino acid.' Inthese instances in which the body isunder marked stress, supplementa-tion with glutamine becomesessential. An impressive body ofresearch supports glutamine's effi-cacy in helping to maintain musclemass, revitalize the immune sys-tem, promote gastrointestinalhealth, and support healthy antiox-idant levels.

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References

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