Glutamine
Destroying the Dogma, Part 1
by David J. Barr
One of the most frequent supplement questions I get as a strength *
coach is whether or not athletes should use the amino acid glutamine *
for either performance enhancement or size gains.
The topic comes up so much that it almost seems as though glutamine *
is a "no brainer" supplement just like creatine. In fact, its *
popularity is such that at least two separate online message boards, *
as well as numerous magazines, have feature articles on the use of *
glutamine as a supplement. The dogma of glutamine supplementation had *
even permeated the SWIS symposium to the extent that the numerous *
conversations about this amino acid were solely about how much to *
take, rather than whether or not to take it.
So, it seems as though everything is pretty cut and dried when it *
comes to glutamine use? or is it? While there was some literature-
supported speculation as to the potential benefits of glutamine *
supplementation, there needs to be an updated review of the *
literature examining the current status of this purported "wonder *
supplement." In fact, there's quite a bit of information that's been *
left out of the popular bodybuilding literature that needs to be *
brought to light.
But before we get on to that, we should review some of the basics of *
glutamine.
Glutamine: The Basics
For those of you who are new to the concept of glutamine *
supplementation, you should know that it's a non-essential amino acid *
created largely by our muscles. It's also noteworthy that glutamine *
is the most abundant free amino acid in our bodies, comprising up to *
2/3 of the muscle free amino acid pool.(13) This fact, coupled with *
the idea that muscle is the largest producer of this amino acid, *
could suggest that supplementation would be beneficial.
One potential problem with this is that glutamine is a non-essential *
amino acid (meaning that we don't have to consume outside sources *
containing this amino acid because our bodies can make it on its *
own), but this is where things get interesting: the use of glutamine *
by many different cells in our bodies is so great that there may be *
times when its use exceeds its availability, therefore glutamine has *
been termed a "conditionally essential" amino acid.(18)
This means that during times of physical stress the body may actually *
need glutamine from the diet to maintain proper cellular function. *
Clearly, activities such as resistance training constitute a physical *
stress on the body, which is one reason that athletes have been *
targeted for glutamine supplementation.
Another interesting fact about our muscles and glutamine is the issue *
of transport. For an amino acid to get into or out of our muscles, it *
has to be transported by specific carriers. Using these carriers, our *
muscle takes up amino acids according to demand from protein *
composition (i.e. what our muscles need the most), BUT amino acid *
release is NOT according to composition.
Alanine and glutamine can account for up to 50% of amino acid release *
from muscle despite accounting for only about 15% of total muscle *
protein.(31) Obviously, this is a huge discrepancy?which is normally *
made up for through glutamine production?but as mentioned earlier, *
during times of physical stress (i.e. exercise), the synthesis of *
glutamine is hindered. Everyone knows that lacking even one amino *
acid can hinder muscle growth, which fortifies the theory of *
glutamine supplementation by athletes.
Now that you're familiar with the basics behind glutamine *
supplementation, it's time to delve into the literature and pull out *
some more specific theories as to the beneficial effects of glutamine *
supplementation.
Glutamine and Muscle Mass
Interest first arose in glutamine as a supplement when it was found *
that glutamine enrichment elevated levels of protein synthesis in *
isolated rat muscles.(21) This isn't surprising since it's also been *
found that muscle protein synthesis levels can be correlated with *
free glutamine levels.(17) It's also been shown in vitro using rat *
skeletal muscle cells that glutamine may decrease protein breakdown.(22)
Additionally, we know that the anabolic/catabolic state of a muscle *
cell is related to it's hydration status?this simply means that *
cellular swelling has an anabolic or an anticatabolic effect on the *
affected cells (including muscle cells). Based on this, it's been *
found that glutamine supplementation may mediate cell swelling and *
therefore an anticatabolic effect through either increasing cell *
swelling or hindering cellular dehydration.(28)
Sure you say, these theories are all well and good in cell cultures *
or animals, but what about the human studies? Well, studies in humans *
indicate that glutamine supplementation may improve nitrogen balance *
in critically ill patients, as well as assist in the prevention of *
protein synthesis decreases following surgery (a HUGE physical *
stress) or following a 14-hour fast.(13, 12,24,13) There have even *
been a couple of studies done on resistance trained subjects (more on *
that a little later)!
Glutamine and Overtraining
We've all felt the scourge of overtraining: the lethargy, the *
sickness, and the lack of desire to train. Aside from the horrible *
feeling associated with overtraining, we also know that the longer *
we're out of the gym, the longer we go without any anabolic stimulus *
to our muscles. Based on this, another theory suggesting glutamine *
supplementation for athletes involves the prevention of overtraining.
Glutamine is used as a fuel source by many cells of our body, *
including many cells of our immune system. Now if you recall that *
there are times of stress where the body's production fails to meet *
its needs for glutamine, you can see that this could negatively *
affect the immune system. In fact, you may not be surprised to find *
that blood glutamine levels may be compromised following exercise *
induced overtraining.(1)
Surveys of endurance athletes supplementing with glutamine following *
a marathon race showed lower rates of infection than those who didn't *
supplement.(8,9) As for the applicability to bodybuilding, one study *
showed that resistance exercise may induce a small transient (ie *
short-term) negative effect on some cells of the immune system, *
although plasma glutamine levels weren't examined.(6)
So now we have theories for glutamine supplementation to increase *
protein synthesis/inhibit protein breakdown, as well as boost *
immunity following intense exercise. This sounds great, but we have *
yet to look at glutamine's potential effect to stimulate glycogen *
replenishment following exercise. Glutamine infusion has been shown *
to enhance glycogen stores following cycling exercise twice as much *
as compared to subjects who infused saline or other amino acids.(27) *
If this happened after weight training, it could even help with our *
cellular swelling and have the aforementioned postive effect on *
protein accretion.
Another study supports the use of glutamine for enhancing muscle *
glycogen. Bowtell et al. found that glutamine supplementation *
following exercise enhanced glycogen resynthesis in muscle just as *
well as the ingestion of a glucose polymer.(4)
Sadly at this point, many readers have already gone out and bought *
their kilos of glutamine, and are now reading only to find out how to *
use the stuff. You may argue, why not? There's plenty of evidence to *
support the theories presented! This was exactly the thinking when *
glutamine was introduced to bodybuilders several years ago. In fact, *
the journal articles reviewed above are the same research papers that *
can be found time and again, in any outdated article that's trying to *
sell you on glutamine. But things have recently changed; new studies *
have been done on animals, and people involved in resistance *
training, but the results are less than positive.
What the Glutamine Salespeople Don't Want You To Know:
Glutamine and Protein Synthesis ? The other side of the coin
We've seen the theory that glutamine levels in the blood and muscle *
may decrease during or following exercise, and that this decrease *
correlates with reduced levels of protein synthesis. Several studies *
have addressed whether this relationship between glutamine and *
protein synthesis was a coincidental or a causal (meaning that one *
caused the other) relationship.
The first study compared the abilities of glutamine and the amino *
acid alanine to stimulate protein synthesis in rats with artificially *
reduced blood and muscle glutamine levels.(23) As expected, glutamine *
infusion increased intramuscular glutamine levels, while alanine *
didn't. Surprisingly, even depleting muscle glutamine levels by 60% *
had no effect on protein synthesis. What may also surprise you is *
that restoring blood and muscle glutamine levels to normal had no *
effect on protein synthesis compared to rats receiving no glutamine *
treatment! Additionally, even though whole body protein turnover *
didn't change, alanine stimulated protein synthesis!
In support of this contention, researchers studied the effect of *
glutamine supplementation on septic rats. Sepsis is a severely *
catabolic condition, during which glutamine levels (and protein *
synthesis) fall. Again, this study showed that despite increasing ***
muscle glutamine levels to even higher than normal, it had no effect *
on protein synthesis or the catabolic state of the rats.(11)
Cumulatively, these studies show that decreased or increased levels *
of glutamine in the muscle has no effect on protein synthesis.
Another study, performed on people, examined the effect of adding *
glutamine to an amino acid mixture on muscle protein synthesis .(30) *
Ultimately, infusion of the original amino acid mixture increased *
protein synthesis by nearly 50%, but adding glutamine to this mix had *
no additional effect. This study is particularly relevant because *
most consumers of glutamine do so following a workout, along with *
other amino acids (or a whole protein).
Finally, Wusteman et al., used a drug to reduce muscle protein *
synthesis, along with muscle glutamine levels, in rats.(29) Much like *
the Olde Damink et al. study, restoring muscle glutamine levels to *
normal had no effect on protein synthesis. This study further *
supports the concept that blood and muscle glutamine levels have no *
bearing on protein synthesis and protein turnover.
Editor's note: Part 2, which pretty much presents a case for *
relegating glutamine to the Retired Supplements shelf (except for *
very specific circumstances) will be posted next week.
David J. Barr, CSCS, MSc. Candidate, is a Varsity Strength and *
Conditioning Coach at the University of Waterloo.
He did not say it directly but he presented evidence to back his *
statement up that supplementing with glutamine is a waste of money..
