Top Ineffective Supplements for Muscle Building - The Glutamine Fad (Protein synthesis, Growth Hormone, Resistance Training and Sex Differences)

Glutamine and protein synthesis

Changes in muscle glutamine concentrations may not have a major regulatory role on muscle protein metabolism (1). Glutamine fails to affect muscle protein kinetics (2). There is no effect of glutamine supplementation on muscle protein synthesis; after glutamine depletion there is minimal responsiveness to changes in plasma glutamine availability (2).

Using isotopic tracers it was demonstrated that a decrease in plasma and muscle glutamine levels had no effect on muscle protein kinetics (1), and that in healthy volunteers (3) and in burned children (4) there was no effect of increasing glutamine availability in plasma on the rate of muscle protein synthesis. Another study also failed to observe any affect from glutamine supplementation on the rate of muscle protein synthesis (5).

Glutamine and Growth Hormone

Glutamine might increase plasma arginine and glutamate concentrations. Arginine and glutamate have the potential to increase growth hormone secretion (6). In a single study (n=9) 2g of oral glutamine increased 4-fold the mean value of plasma growth hormone 90min after ingestion, however sharp increases were only seen in 4 subjects with the results were not statistically significant (7). This seems irrelevant given the fact that 1 h of moderate to high intensity exercise can result in a 20-fold increase in plasma growth hormone concentration (8), so taking glutamine with such goal in mind is simply a waste of money.

Glutamine and Resistance Training

Muscle mass and performance 

Supplementation 0.9g/kg lean mass tissue of glutamine during 6 weeks of strength training added nothing: Gains in lean muscle mass and strength were the same between placebo and glutamine (9). Strength, torque, lean tissue mass and 3-methylhistidine increased with training with no significant difference between groups. Lean mass increased 2% for the glutamine group and 1.7% for the placebo group. This study concluded that glutamine supplementation during resistance training has no significant effect on muscle performance, body composition or muscle protein degradation in young healthy adults (9).

Another study indicated that short-term ingestion of glutamine does not enhance weightlifting performance in resistance-trained men (10). There were no differences in the average number of maximal repetitions performed in the leg press or bench press exercises among the 3 groups tested.

An oral glutamine dose of 0.3g/kg post-exercise was shown to attenuate short-term (i.e., within 1 hour) strength loss following an acute bout of eccentric-based exercise (11). Participants performed 100 drop jumps from 0.6m and muscle soreness was significantly lower over 96 hours with L-glutamine supplementation, and resulted in a greater preservation of peak torque over the 96-hour measurement period. This would suggest that L-glutamine supplementation during periods of intense exercise could accelerate the recovery of muscle strength (10,12).

No ergogenic effect was also found when consuming an acute dose of 0.03g/kg of body mass 90 minutes before 5 bouts of 60 second cycle ergometer tests at 100% VO2 max (13).

However, another study tested a glutamine dose of 0.1g/kg for 4 weeks and observed no effect on perceived muscle soreness and strength loss 24 and 48 hours post-eccentric exercise (14). The dose was smaller than the previous study (0.1 vs 0.3g/kg), the exercise protocol was different with eccentrics leg extensions at 75%RM vs. drop jumps, and this study supplemented pre-and-post exercise vs. post-exercise only. These factors that could explain the different outcomes.

Another study also reported reduced muscle soreness after supplementation pre-and-post exercise, but the participants received a 3.6 gram supplement containing 12 amino acids (including L-glutamine) and not glutamine alone (15).

Glutamine and Sex Differences

The benefits of oral L-glutamine supplement in women is currently unknown. The previous studies (11,14) used male participants only. Another study using both men and women observed increased plasma concentration and decreased post-exercise plasma ammonia concentrations in woman only after three 30s Wingate bouts (16).

Authors suggested that “the lower plasma ammonia after sprint exercise in females seems to be explained by a lower accumulation of ammonia in skeletal muscle and by a buffering of ammonia in the form of glutamine in females. The greater reduction in plasma leucine in males seems to be related to their greater increase in muscle ammonia after sprint exercise” (16). This indicate that women may not experience the same degree of benefit from oral glutamine supplementation as men.

Another study also supplemented with 0.3g/kg of glutamine plus 0.3g/kg of maltodextrin once per day over a period of 72h. Exercise consisted of 8 sets of 10 repetitions of eccentric unilateral knee extension (125% concentric RM) with 2 minute rest intervals. The L-glutamine supplementation resulted in faster recovery of peak torque and diminished muscle soreness following eccentric exercise. In addition results also indicated that the effect of L-glutamine on muscle force recovery may be greater in men than women (17).

Take-home points:

1. The aminoacid pool (130g) is tightly regulated by metabolism (18), measurements under a variety of conditions result in similar results (19,20).
2. Adding a few extra grams of glutamine to increase glutamine levels in the muscle compartment is futile.
3. The concentration of each individual aminoacid inside a cell is tightly regulated by biophysical and biochemical mechanisms (19).
5. We usually do not take glutamine via the parenteral route.
6. Could be useful for endurance athletes when they show depressed levels (21), and catabolic hormones can influence muscle glutamine concentrations (19). In this case glutamine supplementation can prevent a decline but won’t increase levels below normal.
7. Glutamine is classified as “apparently ineffective” (22).
8. There is no evidence for muscle mass increase, better body composition and protein synthesis (11).

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