Diet & Fitness

 

Glutamine, one of the most abundant amino acids in the body, supports the health of the cells lining the gastrointestinal tract and is important for immune function.¹ Glutamine is depleted when the body is under stress, including the stress of surgery.² Blood levels of glutamine decrease following surgery, and as they return to normal, their increase parallels the increase in immune cells.³ Two controlled trials have shown that the use of glutamine-enriched intravenous formulas, providing approximately 20 grams of glutamine per day, resulted in increased immune cell activity and shorter hospital stays.^4,5 Double-blind studies report that patients receiving intravenous formulas supplemented with glutamine after surgery had better nutritional status and better health outcomes, including fewer infections and other complications, compared with patients receiving regular formulas.^6,7

The amino acid glutamine is important for immune system function. Liquid diets high in glutamine have been reported in controlled studies to be more helpful to critically ill people than other diets.^8,9 Endurance athletes are susceptible to upper respiratory tract infections after heavy exercise, which depletes glutamine levels in blood.¹⁰ Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,^11,12 a double-blind study giving athletes glutamine (2.5 grams after exercise and again two hours later) reported significantly fewer infections with glutamine.¹³

  

The combination of glutamine, arginine, and the amino acid derivative, hydroxymethylbutyrate (HMB), may prevent loss of lean body mass in people with AIDS-associated wasting. In a double-blind trial, AIDS patients who had lost 5% of their body weight in the previous three months received either placebo or a nutrient mixture containing 1.5 grams of HMB, 7 grams of L-glutamine, and 7 grams of L-arginine twice daily for eight weeks.¹⁴ Those supplemented with placebo gained an average of 0.37 pounds, mostly fat, but lost lean body mass. Those taking the nutrient mixture gained an average of 3 pounds, 85% of which was lean body weight.

The amino acidglutamine is needed for the synthesis of glutathione, an important antioxidant within cells that is frequently depleted in people with HIV and AIDS.¹⁵ In well-nourished people, the body usually manufactures enough glutamine to prevent a deficiency. However, people with HIV or AIDS are often malnourished and may be deficient in glutamine.¹⁶ In such people, glutamine supplementation may be needed, along with NAC, to maintain adequate levels of glutathione. It is not known how much glutamine is needed for that purpose; however, in other trials, 4–8 grams of glutamine per day was used.¹⁷ In a double-blind trial, massive amounts of glutamine (40 grams per day) in combination with several antioxidants (27,000 IU per day of beta-carotene; 800 mg per day of vitamin C; 280 mcg per day of selenium; 500 IU per day of vitamin E) were given for 12 weeks to AIDS patients experiencing problems maintaining normal weight.¹⁸ Those who took the glutamine-antioxidant combination experienced significant gains in body weight compared with those taking placebo. Larger trials are needed to determine the possible benefits of this nutrient combination on reducing opportunistic infections and long-term mortality.

 

In a double-blind study of children (ages six months to two years) with acute diarrhea, supplementing with glutamine significantly reduced the duration of diarrhea by 26%.¹⁹ Children were given 136 mg of glutamine per pound of body weight per day for seven days. Glutamine appeared to work by improving the health of the intestinal lining, rather than through any effect on the immune system.

 

Glutamine, an amino acid, is the principal source of energy for cells that line the small intestine and stomach. More than 40 years ago, glutamine was reported to help people with peptic ulcer in a preliminary trial.²⁰ Glutamine has also prevented stress ulcers triggered by severe burns in another preliminary study.²¹ Despite the limited amount of published research, some doctors suggest 500 to 1,000 mg of glutamine taken two to three times per day to help people overcome peptic ulcers.

 

Various amino acids have shown promise for people with gastritis. In a double-blind trial, taking 200 mg of cysteine four times daily provided significant benefit for people with bleeding gastritis caused by NSAIDs (such as aspirin).²² Cysteine is a sulfur-containing amino acid that stimulates healing of gastritis. In a preliminary trial, 1–4 grams per day of NAC (N-acetyl cysteine) given to people with atrophic gastritis for four weeks appeared to increase healing.²³Glutamine, another amino acid is a main energy source for cells in the stomach and supplementation may increase blood flow to this region.²⁴ Patients in surgical intensive care units often develop gastrointestinal problems related to a glutamine deficiency.²⁵ When burn victims were supplemented with glutamine, they did not develop stress ulcers, even after several operations.²⁶ Nevertheless, it remains unclear to what extent glutamine supplementation might prevent or help existing gastritis. Preliminary evidence suggests the amino acid arginine may both protect the stomach and increase its blood flow,²⁷ but research has yet to investigate the effects of arginine supplementation in people with gastritis.

The amino acid glutamine appears to play a role in several aspects of human physiology that might benefit athletes, including their muscle function and immune system.²⁸ Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.²⁹ Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,³⁰ an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,³¹ and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.³² However, glutamine supplementation (30 mg per 2.2 pounds body weight) has not improved performance of short-term, high-intensity exercise such as weightlifting or sprint cycling by trained athletes,^33,34 and no studies on endurance performance or muscle growth have been conducted. Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,^35,36 double-blind trials giving athletes glutamine (5 grams after intense, prolonged exercise, then again two hours later) reported 81% having no subsequent infection compared with 49% in the placebo group.³⁷

The amino acid glutamine appears to play a role in several aspects of human physiology that might benefit athletes, including their muscle function and immune system.³⁸ Intense exercise lowers blood levels of glutamine, which can remain persistently low with overtraining.³⁹ Glutamine supplementation raises levels of growth hormone at an intake of 2 grams per day,⁴⁰ an effect of interest to some athletes because of the role of growth hormone in stimulating muscle growth,⁴¹ and glutamine, given intravenously, was found to be more effective than other amino acids at helping replenish muscle glycogen after exercise.⁴² However, glutamine supplementation (30 mg per 2.2 pounds body weight) has not improved performance of short-term, high-intensity exercise such as weightlifting or sprint cycling by trained athletes,^43,44 and no studies on endurance performance or muscle growth have been conducted. Although the effects of glutamine supplementation on immune function after exercise have been inconsistent,^45,46 double-blind trials giving athletes glutamine (5 grams after intense, prolonged exercise, then again two hours later) reported 81% having no subsequent infection compared with 49% in the placebo group.⁴⁷