Any one can make a claim about amino and hype it.
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.(1
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.(2
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.