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Image 1: Still one of the top-
sellers in almost all supplement
shops - l-glutamine; tip: buying
bulk powder will save money |
Although glutamine is one of the
non-essential amino acids, even the fact that
your body continuously 'sacrifices' truly essential amino acids to synthesize glutamine in your muscle tissue, should go to tell you that, after all, glutamine, the
most abundant amino acid in human muscle and plasma, cannot be so non-essential as its classification would suggest.
Under normal conditions it forms 50% of the whole body amino acid pool. In cells, esp. muscles, where glutamine makes up 66% of the amino acid pool. Within the cellular space, the purported cell-volumizer can reach concentrations that are up to 33 times higher than on the outside of the cell.
In times of acute stress, severe burns or surgical trauma, on the other hand, tissue glutamine levels have been observed to decline by up to -50% - an observation, which gave and still gives rise to the hypothesis that glutamine repletion / supplementation could ameliorate or even prevent the catabolic processes which threaten all metabolically active tissues and weaken the immune system whenever the human body is exposed to severe physiological (and even psychological) stress. In that, it is important to understand that
glutamine does not reduce the amount of corticosteroids which are released in those circumstances, but
may reduce the negative effects of increased cortisol and catecholamine levels on the body. In a 1995 study by Hickson et al., for example, intravenous infusion of glutamine reduced muscle mass losses subjects who had previously received a glucocorticoid infusion by -70% and ameliorated the cortisol-induced decline in untra-muscular myosin heavy-chain content by -50% (
Hickson. 1995).
Did you know that 90% of the nitrogen that is derived from BCAA catabolism is released as glutamine, which is formed primarily in your muscles, but also in your lungs, your liver and your brain in a process called glutamine synthase, where glutamate, which has a side-chain hydroxyl instead of the amine group of glutamine, and ammonia are synthesized to form glutamine. During its subsequent hydrolysis, i.e. the catalysis of glutamine to glutamate + ammonia in the intestine, cells of the immune system and the liver, a substantial amount of energy is released. In that, glutamine, the 2nd major interorgan nitrogen carrier, derives a major advantage over alanine, the #1 interorgan nitrogen carrier, from its protein and amino acid derived carbon skeleton, which constitutes an energetically denser substrate for gluconeogensis (esp. in the liver) than that of alanine or aspartate, the third most abundant interorgan nitrogen carrier in the human body.
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Note: This is the detailed transcript of my show notes to "Amino Acids for Super Humans Part IV"
click here to download the podcast if you want to listen before / during / after you read the rest of the notes |
I. Physiological role of glutamine in the human body
Stress-protection aside, glutamine performs a whole host of other important physiological functions. Glutamine...
- ... is required for hepatic ureagenesis and renal ammoniagenesis, is an essential contributor to detoxification processes;
- ... is necessary to maintain and restore an optimal ph-balance;
- ... is a substrate / precursor to peptides and proteins, amino sugars, purines and pyrimidines;
- ... is used as cellular fuel in muscle, intestine, skin and immune system, where it's availability / non-availability directly regulates protein synthesis and degradation;
- ... is intricately involved in the anti-oxidant defense system of the body as a precursor to glutathione (=glutamate + cysteine + glycine) production.
Glutamine and intestinal health & functionYou may be surprised to see that I devote an entire chapter of this write-up to the role of glutamine in gut health; yet with the
increasing public interest in and scientific awareness of pathologies beyond Crohn's, Celiac & Co, I consider the direct effects glutamine and glutamic acid exert on the health of the intestinal system of paramount importance.
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Table 1: Effects of glutamine supple-
mentation on intestinal health
(Stehle & Fürst in ed. Cynober. 1955) |
In their contribution to
Pharmacological nutrition: immune nutrition (ed.
Cynober, Fürst, Lawin. 1995) Stehle and Fürst compiled a list of immediate effects of glutamine supplementation on gut function (cf. table 1), many of which could be of great importance for athletes, who are not only
particular reliant on optimal nutrient absorption, but also at an extraordinary risk of developing increased gut permeability, which has lately become commonly known and almost hysterically feared as "leaky gut" (syndrome). In this context, Carl V. Gisolfi writes in a review of the importance of optimal intestinal function for athletes (
Gisolfi. 2000):
An increase in gut permeability may be an important link to gut-barrier impairment (Fig. 3). The hypothesis proposes that exercise stress produces biochemical changes that uncouple oxidative phosphorylation, reducing ATP produc ion and increasing Ca2+ efflux from mitochondria and endoplasmic reticulum. These events lead to increased cytosolic Ca2+ concentration, the generation of reactive oxygen species, and loss of tight junction control, producing increased intestinal permeability. [...] When the tight junctions open, their maxi-
mal channel size is too small to permit passage of endotoxin but will allow passage of luminal contents that are chemotactic for neutrophils. These agents (dietary antigens, chemotactic oligopeptides) stimulate intraepithelial lymphocytes to secrete interferon-γ. [...] Interferon-γ opens tight junctions and activates macrophages and neutrophils to release oxygen radicals and immunosuppressive peptides. Thus increasing intestinal permeability by opening tight junctions can initiate immunologic and inflammatory events that can alter gut structure and function.
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Image 2: More than 50% of the
dietary glutamine are used by your
digestive system and do not even
reach systemic circulation. |
Scientifically
documented causative factors for increased gut permeability in athletes are ...
- prolonged exercise (triathlon, marathon, etc.)
- high intensity endurance exercise at 80% of VO2 max
- (co-)ingestion of aspirin with medium intensity exercise at 60-65% of VO2 max
And desite the fact that Coeffier et al., in a recent review on the efficiacy of gutamine supplementation in patients with irritable bowel syndrome, state that previous "clinical studies with oral glutamine in CD [Crohn's disease] are until now disappointing" (
Coeffier. 2010). There is
substantial evidence for glutamine to exert beneficial effects on overall enterocyte health and
accumulating evidence for the ability of glutamates, the carboxylate anions and salts of glutamic acid, to stabilize the gut lining and to reduce intestinal permeability (
Vermeulen. 2011).
Did you know that in a 2010 study by dos Santos et al. (
dos Santos. 2010), administration of glutamine at a dose of 500mg/kg/day (human equivalent ~40mg/kg or
3.2g per day for an adult weighing 80kg) to mice with experimentally induced intestinal obstruction "
decreased intestinal permeability and bacterial translocation to physiologic levels in the treated animals and preserved intestinal barrier integrity".
Thus, even if the following dissertations will entail the conclusion that the ergogenic value of glutamine is largely overrated, the increase in gut permeability that has been observed after strenuous workouts (Davis. 2005) would be an argument in favor of post-workout glutamine / glutamic acid supplementation, you should remember.
II. Glutamine and the athlete
While intravenous glutamine infusions are a longstanding and well-established part of medical treatment strategies used in hospitalized and critically ill patients (
Windle. 2006), the use(-fulness) of glutamine as a dietary supplement for athletes is still questioned by many of the practicing exercise and nutrition scientists. In the following I will try to tackle the two most frequent promises you ill hear and read about in the advertisements for respective products.
"Glutamine supplementation saves athletes from getting sick"
It is unquestionably true that glutamine is of paramount importance for healthy immune function (
Calder. 1999).
It is also non-debatable that intense exercise, and, in that, specifically chronic endurance exercise (cf. figure 1), has been shown to decrease both serum as well as tissue glutamine levels.
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| Figure 1: Serum glutamine and glutamate levels in ultra-marathon runners pre- and at different time-points post exercise (data adapted from Castell. 1997) |
As the data from
figure 1 documents, the exercise induced decline of glutamine levels is yet far from being as dramatic as the -50% drop which has been reported for hospitalized critically ill patients. Nevertheless, the
highly advertisable claims of increased incidences of upper respiratory infects due to weakened immunity secondary to exercise induced glutamine-deficiency are going on forever and I doubt that this will ever change, although the recently published position stand on dietary supplements by Walsh et al. is only the latesst in a line of reviews to conclude, based on contemporarily available evidence, that
glutamine supplementation for athletes is "[n]ot recommended, [because] body stores [generally] exceed exercise-lowering effects" (
Walsh. 2011).
With reference to the purported beneficial effects of
supplemental glutamine on immunity in the athletic population, Newsholm et al. (
Newsholm. 2011) write in Part 18 of a 2010/11 series on purported ergogenic sport supplements in the
British Journal of Sports Medicine:
Glutamine supplementation after exercise reduced the self-reported incidence of illness in endurance athletes. However, when glutamine was given to athletes to combat exercise-induced depletion of circulating glutamine, no effects were observed on the immune parameters studied, apart from reduced neutrocytosis and increased circulating IL-6.
But if the existing anecdotal evidence is not merely a result of placebo effects (
If you spent 50 bucks on a big pot of l-glutamine you do want that stuff to work, don't you? And if each and every "pro" tells you it does, it should work, shouldn't it?) or an increased awareness of how healthy you have "become", now that you are taking supplemental glutamine (when you have in fact been healthy all along),
dosing issues, the addition of other nutrients and most importantly, training type and intensity would have been taken into consideration to explain the inconsistency of respective trials.
Did you know that moderate training, in contrast to the bodybuilding "go heavy or go home" type of training, leads to "improved glutamine availability due to a positive balance between muscle synthesis and peripheral clearance", while physical inactivity can reduce glutamine synthesis and availability!
In this context, it is noteworthy that declining glutamine levels after / in the course of periods of increased training intensity have only lately been (re-)introduced as a potentially useful indicator of overtraining by Agostini & Biolo (
Agostini. 2010). They point out that "[s]trenuous physical exercise as well as
exhaustive training programs [which] lead to glutamine depletion due to lowered synthesis and enhanced uptake by liver and immune cells". Lower glutamine levels, on the other hand, have been "
associated" (notice we do not have enough evidence for a causal relationship here) with compromised immunity. Immediate / continuous repletion of whole body glutamine stores (serum & tissue) via
adequate dietary or supplemental intake could thus very well help to maintain immunity.
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Image 3: BCAAs are not only way
more ergogenic, they may in fact
also be a more versatile source of
glutamine than l-glutamine, itself. |
Personally, I find it telling that
much of the positive data on glutamine supplementation for immune health comes from studies on endurance athletes from the early and late 1990s. If you consider the poor nutritional advice those athletes were given at that time, many of them were hardly getting enough protein along with the shitloads of carbohydrates they were told to eat. Now,
someone who lacks essential amino acids, and more specificically BCAAs, for glutamine production, is of course at higher risk of 'running out of fuel for his immune system', especially if he exhausts his already compromised tissue stores by chronic endurance exercise.
Conversely,
the group of athletes who consumes the largest amounts of supplemental glutamine, i.e. bodybuilders, is probably the one who will benefit least of all from additional l-glutamine in their diet. No wonder that Candow et al. who studied the effect of a standardized strength training protocol with or without a
0.9g/kg lean tissue mass glutamine supplement on strength, body composition and protein turnover in young athletes found "that
glutamine supplementation during resistance training has no significant effect on muscle performance, body composition or muscle protein degradation in young healthy adults" (
Candow. 2001). While this obviously does not say anything about immunity you may safely assume that the latter was not compromised in the first place and thus evidently would not have benefited from the roughly 50-60g of l-glutamine (certainly a "sufficient" dose ;-) the subjects in the Candow study consumed.
"Glutamine increases regeneration and improves muscle and strength gains"My preceding remarks on the useful- respectively -lessness of glutamine supplementation in marathon runners and bodybuilders have already touched on one of the recurring themes of the
Amino Acids for Super Humans series: What is essential and beneficial for athlete A in situation B may be ineffective for athlete B in situation B or even athlete A in situation A. The data (table 2) from studies, which evaluated the effects of
oral glutamine supplementation on exercise-related parameters
in humans ("+" indicates improvement; "#" indicates no effect; "-" indicates detrimental effect), substantiates this observation.
| Author(s) | Protocol | +/#/- | Main Result(s) |
| Castell. 1997 | exhaustive exercise in middle-distance, marathon and ultra-marathon runners, and elite rowers, in training and competition
2x5g glutamine vs. maltodextrin 0, 2h post exercise | + immunity | "[...] provision of oral glutamine after exercise appeared to have a beneficial effect on the level of subsequent infections [...] the ratio of T-helper/T-suppressor cells appeared to be increased in samples from those who received glutamine" |
| Bishop. 2000 | review of intra-workout / -competition supplementation | #cortisol
#immune | Consuming "carbohydrate [...] but not glutamine [...] during exercise attenuates rises in stress hormones, such as cortisol, and appears to limit the degree of exercise-induced immunosuppression" |
| Krzywkowski. 2001 | bicycle exercise for 2 h at 75% of maximum O(2)
5x 3.5g glutamine vs. 3.5g maltodextrin at 0, 45, 90, 135, 170min post cycling | #immune | "no effect on lymphocyte trafficking, NK and lymphokine-activated killer cell activities, T cell proliferation, catecholamines, growth hormone, insulin, or glucose [...] Neutrocytosis was less pronounced in the glutamine-supplemented group, but it is unlikely that this finding is of any clinical significance" |
| Wilkinson. 2006 | 90 min cycling at 65% VO2max
post-exercise oral CHO 1g/kg/h + 9.25g EAA + glutamine 0.3g/kg BW vs isoenergetic CHO-EAA w/out glutamine | #anabolism,
+long-term recovery | Consuming "addition of glutamine to a CHO + EAA beverage had no effect on post-exercise muscle glycogen resynthesis or muscle protein synthesis, but may suppress a rise in whole-body proteolysis during the later stages of recovery" |
| Carvalho-Peixoto. 2007 | 15 athletes, 120 min (approximately 34 km) outdoor running
3 groups CHO g/kg/d + Gln 70 mg/kg/d; only CHO or only Gln in addition normal diet | +ammonia detox | "ammonia was not different for the first 60 min, but for the second hour [ammonia] was lower than in the control" |
| Wilkinson. 2006 | 90 min cycling at 65% VO2max
post-exercise oral CHO 1g/kg/h + 9.25g EAA + glutamine 0.3g/kg BW vs isoenergetic CHO-EAA w/out glutamine | #anabolism,
+long-term recovery | Consuming "addition of glutamine to a CHO + EAA beverage had no effect on post- exercise muscle glycogen resynthesis or muscle protein synthesis, but may suppress a rise in whole-body proteolysis during the later stages of recovery" |
| Favano. 2008 | 9 soccer players, cardiopulmonary exercise test + simulated soccer match, peptide glutamine (Gln) = 50 g of maltodextrin + 3.5 g of peptide glutamine or CHO alone 50 g of maltodextrin 30 min before test | +performance | "Total distance covered was 12750 [CHO] and 15571 [Gln]", i.e. +22% distance; "total duration of tolerance was 73 +/- 23 min when using CARBO and 88 +/- 24 min when using [Gln] (p<0.01)", i.e. +20% duration of tolerance" |
| Bassini-Cameron. 2008 | prof. football players, Gln Alanine 100mg/kg, either short-term or long-term, immediately before exercise;
intervals (n = 18) and continuous intensity (n = 12) exercise tests | #anabolism,
+long-term recovery | "[...] results suggest that chronically supplemented Gln protects against exercise-induced hyperammonemia depending on exercise intensity and supplementation duration |
| Table 2: Some scientific data from human studies on oral glutamine supplementation from the last years ("+" indicates improvement; "#" indicates no effect; "-" indicates detrimental effect) |
Despite the fact that the existing human data does not support the idea that athletes in general and weight trainers or fitness fanatics in particular would benefit from the tons of glutamine supplements that are sold year by year,
some of the advertisment claims are in fact based on observations in petri dishes or animal models:
- In the petri dish, glutamine actually is the potent "cell volumizer" the advertisments would have it and its administration to isolated hepatocytes (liver cells) does in fact stimulates anabolic processes within the cells, which involve an increased synthesis of DNA, RNA, and proteins.
- It has also been found in cell studies that glutamine-induced cell swelling activates extracellular signal-regulated kinases and p38 (mitogen-activated protein kinase, MAPK), which are involved in stress response + adaptation and could thus facilitate muscle growth.
- Two grams of glutamine taken on an empty stomach have furthermore been shown to evoke an immediate growth hormone response, which - and this is the major caveat - is not only so minuscule that it is physiologically irrelevant; it also reduces the amount of growth hormone that is released after the sudden burst occurred, so that the overall AUC, the area under the 24h GH curve or, in other words, the overall 24h growth hormone production remains unaltered (similar effects have been observed for acetyl-l-carnitine (more on ALCAR in Part IV (2/3) of the AA for SH Series) and combinations of l-lysine and l-ornithine).
- And even the beneficial effects of parenterally administered alanyl-l-glutamine, an alanine + glutamine dipeptide, on (unfortunately) whole body insulin sensitivity are well established (Bakalar. 2006).
The
reproduction or transfer of these effects from the respective model into real world results that would be relevant for the athletic practice have yet failed time and again and a mechanism which would explain the anecdotal evidence on the performance enhancing or muscle building effect of glutamine, which has repeatedly been confirmed by members of the bodybuilding and fitness world, could well be encapsulated within a fundamental physiological process that has acquired sort of a bad reputation lately:
gluconeogenesis.
Did you know that in a 2010 study by van Hall et al. (
Hall. 2010) a
glutamine/carbohydrate mixture (0.8 g x kg(-1) body weight of glucose + 0.3 g x kg(-1) glutamine) failed to increase the rate of glycogen resynthesis in muscle over glucose alone. On the other hand, an isocaloric whey hydrosolate and even a wheat hydrosolate did (whey +20%; wheat +21%). What the study by Hall et al. confirms with respect to the regenerative effects of glutamine, is confirmed in terms of its effects on immune function, muscle protein breakdown and athletic performance by findings from Basset et al. (
Basset. 2000), Hole (
Hole. 2001) and Lehmkuhl et al. (
Lehmkuhl. 2003), where
the actual immuno-modulators, anti-catabolics and ergogenics were BCAAs and creatine, and the BCAA induced elevation of glutamine levels were corollary and not causative, and the addition of supplemental glutamine to creatine monohydrate without any effect on exercise performance.
In view of the current scare of everything carbohydrate-, god-forbid, insulin-related I hardly dare telling you that no other amino acid is so readily (ab-)used by your liver for glycogen production (=glyconeogenesis) as glutamine. This is especially true for doses that exceed the 2-5g range. They do not only provoke an accelerated glutamine clearance which is consistent with the activation of hepatic glutamine removal, but have also been shown to
increase glucose formation in humans up to 7-fold (28g of glutamine infused in 4h time window;
Perriello. 1997)
at rest and to
keep blood glucose levels up, glucose formation elevated (+24%) and glucose utilization increased (+16%) in a study, where dogs had received 12 micromol/kg/min glutamine intravenously during and after exercise (
Iwashita. 2005).
Now, even if you are a carbophobic insulin-hater, this does not mean that you should flush your glutamine supply down the toilette. In view of the fact that even the marked increase in gluconeogenesis that was observed by Perriollo et al. was
not accompanied by an increase in insulin or glucogon levels, glutamine may in fact turn out to be the ideal supplement for endurance athletes or dieting body builders or figure competitors who want to maintain healthy blood glucose levels on a low carb diet. For a sedentary person on a no-carb diet, or example, even 20–40g glutamine per day would probably be enough to fuel their glycogen demands.
Conclusion  |
Image 4: You do not always need supplements.
Oftentimes a nutritionally dense diet with a high
amount of protein will work at least just as well
as the latest and greatest amino acids supplement
you read about in your favorite fitness magazine. |
The latter creative application of glutamine as a carbohydrate replacement aside, I am, based on the available data on the ergogenic effects of
supplemental glutamine, inclined to subscribe to the conclusion of the authors of the
BJSM Supplement Review (
Newsholm. 2011) on glutamine who point out that
[...] there is no consensus or unifying concept to explain the efficacy of exogenous provision of glutamine alone on performance in athletes, although in combination with carbohydrate or other amino acids, significant improvements have been reported.
Thus, notwithstanding its importance in many performance related physiological processes, an
appropriately nourished human body is well able to synthesize more than enough glutamine from essential amino acids (and BCAAs in particular) to satisfy both everyday, as well as athletic demands. Consequently, athletes who wish to take advantage of the undeniably beneficial effects of adequately filled glutamine pools should
give priority to the provision of adequate amounts of essential amino acids (EAAs), in general, and BCAAs, in particular. And despite the fact that the supplement industry would have you believe otherwise, most recreational athletes can easily satisfy their EAA demands by consuming a nutritionally dense high protein diet and an optional whey protein supplement.
