The Physiology of Digestion, Absorption, and Metabolism in the Human Intestine
Victor R. Preedy, Ronald R. Watson in Alcohol and the Gastrointestinal Tract, 2017
This chapter will not describe all of the clinical studies of glutamine supplementation which have been performed. These have been reviewed recently.217 The most significant recent studies concern the effect of glutamine on gut barrier and transport function. In a pig model of infectious cryptosporidiosis and diarrhea,59 it was noted that glutamine stimulated electroneutral and electrogenic Na+ uptake, whereas glucose stimulated only electrogenic uptake via the SGLT-1 system (see above). This was linked to the process of active glutamine metabolism. The animal model which appears to be most sensitive to the effects of glutamine supplementation, the rat, has been used widely. Where barrier function was impaired by intravenous infusion of endotoxin, supplementation of the parenteral nutrition regime with glutamine led to improved nitrogen balance, but more importantly villus architecture was improved and the transmucosal movement of endotoxin into the portal supply was reduced.218 Permeability of the rat intestine in vivo to sugar probes which resulted from parenteral nutrition was also reduced by glutamine supplementation.219 This has been confirmed in the most recent clinical trial of critically ill patients who received intravenous nutrition supplemented with glutamine in dipeptide form.220 It is therefore clear that glutamine is of great significance to intestinal metabolism.
Glutamine
Linda M. Castell, Samantha J. Stear (Nottingham), Louise M. Burke in Nutritional Supplements in Sport, Exercise and Health, 2015
Glutamine, the most abundant amino acid in the body, has in recent years become regarded as conditionally essential rather than non-essential. Glutamine is synthesized, stored and released predominantly by skeletal muscle: it is taken up by organs including the intestine, liver, kidney, and by some key immune cells. From clinical studies, it is known that the plasma concentration of glutamine is decreased in trauma and starvation. There is considerable evidence that glutamine feeding has a beneficial effect on gut function (Castell,2003); it has had a positive effect on morbidity, mortality and some aspects of the immune system; glutamine provision has also shortened the recovery time from surgery and maintained muscle protein mass. The main source of glutamine is meat, poultry and fish.
Management of Obesity-Associated Type 2 Diabetes
Emmanuel Opara in NUTRITION and DIABETES, 2005
Opara et al. also investigated methods of ameliorating diet-induced obesity and diabetes in animal models by analyzing the effects of amino-acid supplementation during high-fat feeding. The authors studied C57BL/6J mice on 4 diets: 1) a low-fat, low-sucrose diet (LL); 2) a high-fat, low-sucrose diet (HL); 3) a high-fat, low-sucrose diet supplemented with L-glutamine (HL + Gl); and 4) a high-fat, low-sucrose diet supplemented with L-alanine (HL + Ala) [7]. For each dietary regimen, 10 age-and weight-matched male mice were maintained on the diet for 5.5 months. As expected, the mice that received a high-fat diet were significantly heavier than those who received a low-fat diet. Yet, at eight weeks, it was noted that the HL + Gln and HL + Ala mice had gained significantly less weight than the HL mice. With regard to glucose metabolism, it was found that HL mice had higher plasma glucose levels than LL mice, as expected, and this difference persisted for more than five months. However, both alanine and glutamine supplementation of the high-fat diet were effective in reducing plasma glucose concentrations for the first three months, and glutamine supplementation helped maintain normoglycemia for more than five months. Hyperinsulinemia was also attenuated by amino-acid supplementation. Thus, the authors concluded that the supplementation of a high-fat diet with glutamine reduces body weight and attenuates hyperglycemia and hyperinsulinemia [7]. These findings in mice are particularly intriguing given the recent interest in high-protein diets in human studies (see the Nutrition Management section – High Protein Diets).
Effect of Glutamine on Short-term Surgical Outcomes in Rectal Cancer Patients Receiving Neoadjuvant Therapy: A Propensity Score Matching Study
Published in Nutrition and Cancer, 2023
Gang Tang, Feng Pi, Zhengqiang Wei, Xiangshu Li
Glutamine is an important energy source for normal and tumor cells (33). Studies have shown that human tumor tissue consumes glutamine at 5–10 times the rate of normal tissue, and there is growing concern that glutamine may stimulate tumor growth and thus affect the efficacy of anti-tumor therapy (34). Several studies have shown that glutamine supplementation is able to increase glutamine stores in muscle without stimulating tumor growth (34–36). Li et al. (37) found that oral administration of glutamine (1 or 2 g/kg/day) inhibited tumor growth in mice by improving the body’s immune function and activating the apoptotic pathway. In addition, none of the clinical studies (34, 38) found any adverse effects of glutamine supplementation on tumor control and survival in patients with non-small cell lung cancer. Our study found a short-term benefit of glutamine supplementation in patients undergoing colorectal cancer surgery. However, the relevant data on the effect of glutamine on the survival of colorectal cancer patients are currently lacking. Future studies may explore the effect of glutamine supplementation on the long-term cancer prognosis of patients with colorectal cancer.
The impact of glutamine supplementation on the short-term mortality of COVID-19 diseased patients admitted to the ICU: A single-blind randomized clinical trial
Published in Egyptian Journal of Anaesthesia, 2022
Omar M. Soliman, Amr M. A. Thabet, Gamal Mohamed Abudahab, Emad Zarief Kamel
There is currently no specific treatment available. The main focus is on improving respiratory functioning, especially in patients with lower respiratory tract involvement. In the early stages of the condition, supportive care appears to be the most successful therapeutic method. The condition has a greater morbidity and mortality rate, particularly in elderly patients with weakened immune systems, those with dietary deficits, and those with chronic illnesses. [3,4] Normal protein intake is insufficient to sustain recovery in COVID-19, as it is in other acute disorders, because the catabolic process is still going on. Increasing the amounts of particular amino acids that reduce acute stress, such as cysteine, arginine, and glutamine, enhances immunity in such patients [5]. These highlighted amino acids are known to influence various functions in the cell and aid recovery by acting as signal molecules and mediators on a cellular level [6]. Glutamine is a non-essential amino acid found in large quantities in the human body. It is mostly produced by skeletal muscle and makes up 30% of plasma free amino acids [7]. In times of high stress, endogenous glutamine production may not be enough to meet patients’ needs [8]. Exogenous glutamine supplementation is therefore essential in this situation to maintain normal plasma glutamine concentrations [7].
Role of Glutamine in the Management of Oral Mucositis in Patients with Cancer: A Meta-Analysis of Randomized Controlled Trials
Published in Nutrition and Cancer, 2022
Gang Tang, Wang Huang, Linyu Zhang, Zhengqiang Wei
Safety is important for the clinical application of drugs. Glutamine, the most abundant amino acid in the human body, is safe for human consumption (56). It is mainly metabolized through the liver or kidney. As chemotherapy is often accompanied by hepatotoxicity and nephrotoxicity, hyperammonemia should be considered when glutamine is supplemented at high doses (57). In a study that investigated tolerable doses of glutamine, Ward et al. (57) showed that an oral dose of 0.65 g/kg is safe in pediatric patients with cancer receiving chemotherapy. In adult patients with cancer, the recommended dose of glutamine is 20–30 g/day (58). However, several studies have shown that high-dose glutamine (30–40 g/day) supplementation is well tolerated in patients with cancer (58–60), and this is consistent with the results of this study. Among the studies that we included, three (28, 30, 34) showed that no adverse reactions occur with glutamine supplementation, even in the study in which high doses, up to 30 g/day, were used. Furthermore, Peterson et al. (32) showed that glutamine supplementation is as safe as a placebo. Thus, we believe that high-dose glutamine is safe in patients with cancer. However, owing to the potential risk, glutamine supplementation is not recommended for patients with hyperammonemia or hepatic encephalopathy.