Beneficial Effects Of Glutamine
Glutamine has been one of the most intensively studied nutrients in the field of nutrition support in recent years. Animal studies show that glutamine is effective against catabolic stress (Millward 1989; Castell 1994; Ziegler 1996). Glutamine supplementation was shown to improve organ function, survival, or both in most published studies. These studies also have supported the concept that glutamine is a critical nutrient for the gut mucosa and immune cells (Furst 1989; Castell 1994; Campos 1996; Ziegler 1996).
Molecular and protein chemistry studies define the basic mechanism involved in glutamine action in the gut, liver, other cells and organs (Ziegler 1996). Double-blind prospective clinical investigations suggest that glutamine-enriched diets are generally safe and effective in catabolic patients (Griffiths 1997). Intravenous glutamine has been shown to increase plasma glutamine levels, exert protein anabolic effects, improve gut structure and function, and reduce important indices of disease (e.g., infection rates and length of hospital stay) in selected patient subgroups (Sacks 1999).
Glutamine is the most abundant free amino acid in the human body. In catabolic stress situations, such as after surgical operations or trauma and during sepsis, glutamine is rapidly transported to organs and blood cells. This results in an intracellular depletion of glutamine in the muscles and the ensuing catabolic wasting effect (Balzola 1996). Increasing evidence suggests that glutamine is a crucial substrate for immunocompetent cells. Glutamine depletion decreases the proliferation of lymphocytes, possibly by arresting a critical phase of the growth cycle of the cells (Roth 1996).
Glutamine is a precursor for the synthesis of glutathione and stimulates the formation of heat-shock proteins (Zhou 1997). Moreover, there are suggestions that glutamine plays a crucial role in the stimulation of intracellular protein synthesis (Hankard 1996). Experimental studies revealed that glutamine deficiency causes a necrotizing enterocolitis--an inflammation of the small intestine and colon, leading to cell death--and increases the mortality of animals subjected to bacterial stress (Becker 2000).
A clinical human study involving bone-marrow transplant patients demonstrated, after supplementation with glutamine, a decrease in the incidence of infections and a shortening of hospital stay. In critically ill patients, parenteral glutamine reduced nitrogen loss and caused a reduction of the mortality rate (Roth 1996). In surgical patients, glutamine invoked an improvement of several immunological parameters (Slotwinski 2000). Moreover, glutamine exerted a nutritional (tropic) effect on the intestinal mucosa, decreased the intestinal permeability, and thus may prevent the translocation of bacteria.
Glutamine is an important metabolic substrate of rapidly proliferating cells. It influences cellular hydration (molecular water content) state and has multiple effects on the immune system, intestinal function, and protein metabolism (Sacks 1999). In several disease states, glutamine may become an indispensable nutrient supplement. Catabolic wasting patients should consider supplementing with 2,000mg of glutamine daily.
Scientists have examined the impact of whey protein concentrate on preventing or treating catabolic wasting, immune dysfunction, and cancer. A study involving HIV-positive men fed whey protein concentrate found dramatic increases in glutathione levels, with most men reaching their ideal body weight (Bounous 1993). In another study, when different groups of rats were given a powerful carcinogen, those fed whey protein concentrate showed fewer tumors and reduced tumor masses (McIntosh 1995). Whey appears to inhibit the growth of breast cancer cells at low concentrations. In one clinical study, when cancer patients were fed whey protein concentrate at 30 grams a day, some patients' tumors showed a regression (Kennedy 1995).
The research using whey protein concentrate has led researchers to a discovery regarding the relationships between cancerous cells, whey protein concentrate, and glutathione. Glutathione is an antioxidant that protects the body against harmful compounds. It was found that whey protein concentrate selectively depletes cancer cells of their glutathione, thus making them more susceptible to cancer treatments, such as radiation and chemotherapy (Kennedy 1995; Baruchel 1996). It has been found that cancer cells and normal cells will respond differently to nutrients and drugs that affect glutathione status.
The concentration of glutathione in tumor cells is higher than that in normal cells surrounding the tumor. This difference in glutathione status between normal cells and cancer cells is believed to be an important factor in the resistance of cancer cells to chemotherapy. Research has shown that cancer cells subjected to whey proteins were depleted of their glutathione and their growth was inhibited, although normal cells had an increase in glutathione and increased cellular growth. These effects were not seen with other proteins.
The researchers concluded, "Selective depletion of tumor glutathione may, in fact, render cancer cells more vulnerable to the action of chemotherapy and eventually protect normal tissue against the deleterious effects of chemotherapy."
Whey protein also appears to play a direct role in bone growth. Researchers found that rats fed whey protein concentrate showed increases in bone strength and bone protein (e.g., collagen). Whey protein was found to stimulate total protein synthesis, DNA content, and increased hydroxyproline content of bone cells in a dose-dependent manner.
It should be noted that not all whey protein concentrates are created equal. Processing whey protein to remove the lactose and fats, but without losing its biological activity, takes special care by the manufacturer. The protein must be processed under low-temperature and low-acid conditions so as not to denature it. Maintaining the natural state of the protein is essential to its biological activity.
Whey protein has the highest biological value rating of any protein. When the biological value is high, that means protein is absorbed, used, and retained better in the body. High biological values also are associated with tissue sparing. Thus, whey protein concentrate can be beneficial for people with catabolic wasting diseases.
For vegetarians or those limiting their animal protein intake, plant-based protein is a viable option. Plant-based protein contains more glutamine than whey or egg protein, with comparable branched chain amino acid (BCAA) values to whey, egg, and casein. It also contains more arginine than these 'gold standard' animal proteins. Arginine is essential for nitric oxide synthesis, which promotes healthy endothelial function and blood vessel dilation and relaxation (Zhou 2001).
The muscle atrophy commonly seen in older adults comes mainly from a loss of fast-twitch (type II) muscle fibers recruited during high-intensity movements (e.g., weight lifting and sprinting). These are the fibers most profoundly affected by the dietary supplement creatine. Various studies have found that creatine helps increase strength and lean body mass in older adults participating in resistance exercise training (Brose 2003; Gotshalk 2002; Chrusch 2001). According to one research group, creatine supplementation in older adults may help attenuate age-related loss of muscle strength as well as improve one's ability to perform functional living tasks (Gotshalk 2002).
While scientists have long known that vitamin D plays an important role in bone health, recent studies suggest that it is also essential for maintaining muscle mass in aging people. Vitamin D helps preserve the Type II muscle fibers that are prone to atrophy in the elderly. Scientists recently noted that vitamin D helps support both muscle and bone tissue. Also, that low levels of vitamin D seen in older adults may be associated with poor bone formation and muscle function. Thus, ensuring adequate vitamin D intake may help reduce the incidence of both osteoporosis and sarcopenia (age-related loss of lean muscle mass, strength, and functionality) in aging people (Montero-Odasso 2005).
Other Nutritional Supplementation
Conjugated linoleic acid (CLA), a fatty acid, has anti-catabolic properties. This has been demonstrated in laboratory mice injected with endotoxin to produce a catabolic response. Seventy-two hours after feeding with linoleic acid, the mice presented body weights similar to controls. The researchers concluded that conjugated linoleic acid prevented anorexia in endotoxin-injected test subjects (Miller 1994). The suggested dose of CLA for a person in a catabolic state is two 1,000mg capsules taken two times a day.
The amino acid arginine, in combination with hydroxyl-methybutyrate (HMB) and glutamine, increased fat-free mass in patients with stage-IV cancer when given at a dose of 14 grams per day (May 2002). Additional amino acid supplementation should include 2,400mg of L-carnitine and at least 1,200mg of leucine, isoleucine, and valine.
Warning: Some nutritionists are concerned about the use of high doses of glutamine or arginine in cancer patients. Because glutamine and arginine promote cellular growth, the concern is that these amino acids could cause cancer cells to grow faster. Scientific studies, however, show that glutamine and arginine provide beneficial effects to cancer patients. Only one study on breast cancer patients hinted at a risk for arginine supplementation.