GABA supplementation could enhance muscle recovery, encourage strength gains and aid in fat loss

The naturally occurring amino acid known as GABA is popular as an ‘anti-anxiety’ supplement. However, exciting new research suggests that it may also stimulate the natural release of a growth hormone, which could yield benefits such as enhanced muscle recovery, strength gains and fat loss.

Back in the 90s, the use of creatine as a strength-building supplement revolutionised sports nutrition, because unlike most other supplements out there, it actually did what it claimed on the tin! Since then, a number of would-be pretenders to the throne have appeared on the market, but none has matched creatine for its sheer efficacy.

Creatine is able to produce strength gains because it enhances the short-term, high-intensity energy pathway in muscles known as the ‘phospho-creatine (PC) system’. An enhanced PC energy pathway allows muscle fibres to contract vigorously for longer, thus producing more intense loading and fatigue. This in turn produces a greater repair and growth stimulus, and in the longer term, with adequate rest and nutrition, greater strength gains.

The role of growth hormone

One of the key players in muscle repair and growth following exercise is a substance called ‘growth hormone’ or GH for short. GH is a large protein molecule that is synthesised, stored, and secreted by specialised cells within anterior pituitary gland in the brain (see box 1 overleaf).

In the body, GH has a number of biological functions, but of particular interest to athletes is the fact that it increases protein synthesis and promotes fat burning(1), increases calcium retention and therefore strengthens and increases bone mineralisation, and it also stimulates the immune system.

In adults, GH is not secreted steadily, but instead in discrete bursts resulting in about five large pulses or peaks of GH release each day. These peaks last from about 10-30 minutes and the most predictable of these peaks occurs roughly an hour after the onset of sleep(2). However, another extremely powerful GH release stimulus is exercise, particularly high-intensity exercise such as resistance training or high-intensity anaerobic training (see PP issue 222 for more information)(3-6).

Given that GH promotes muscular growth and repair, and also stimulates fat burning, it’s not surprising that some athletes have been tempted to resort to GH abuse in order to accelerate recovery from training, increase strength and maintain low body fat levels. However, not only is this illegal, GH abuse is a potentially risky business, leading to potential health complications such as high blood pressure and heart damage(7).

The GABA-GH connection

If you want to maximise natural GH release and create an anabolic environment, intense exercise and adequate sleep are vital. But are there any nutritional tricks you can use to further enhance GH secretion? Given that GH is secreted from the brain, the obvious question to then ask is whether there are any nutrients that could in some way influence brain function.

As it happens, there are a large number of biologically active compounds that are involved in regulating brain chemistry and the central nervous system (CNS), and which are synthesised from simple constituents of foods. These compounds are collectively known as neurotransmitters, which control and regulate brain and CNS activity by acting on specific receptors within those regions (see box 2).

The neurotransmitter/diet link

Many key neurotransmitters are actually simple amino acids (AA) or metabolites of amino acids. Examples include the AAs glycine and gamma amino butyric acid (GABA), which regulate spinal reflexes/motor behaviour and inhibition of motor neurons respectively, and serotonin, which is synthesised from the AA tryptophan in the body(8).

At this point eagle-eyed readers may be wondering whether and how protein in the diet (which is built of AA building blocks) can influence neurotransmitter synthesis and subsequent brain function. The answer is that ingesting AAs can affect neurotransmitter levels and/or synthesis, but not as a result of normal dietary protein consumption – an AA neurotransmitter will only be significantly boosted via diet in the brain when large amounts of that AA enter the brain relative to others.

Box 1: GH in the body – irGH and ifGH

The problem is that virtually all dietary protein contains 20 or more AAs; in order to enter the brain after digestion, these AAs have to compete with each other to cross the ‘blood-brain barrier’. The net result is that no one single AA can dominate over the others, meaning that there’s no large increase in the brain levels of any single AA over the others. And while it’s true that some sources of protein contain a relative abundance of one particular AA compared to others (eg cottage cheese, which is very rich in tyrosine), the presence of other, competing AAs means that even eating these foods in isolation has a minimal impact on subsequent brain levels of that AA.

However, things are very different with single AA supplements taken away from food. With no other AAs around to compete for absorption across the blood brain barrier, even small doses of a single AA can have a significant effect. A good example of this is the increasingly popular use of the AA supplement tryptophan, which is a precursor to serotonin, low levels of which are strongly associated with depression and other disorders of brain chemistry. Studies show that taking tyrptophan away from other proteins produces a significant rise in brain serotonin(9).

The role of GABA in brain chemistry

Gamma amino butyric acid (more commonly known as GABA) is a naturally occurring AA present in small amounts in the body. Although it’s not present in muscle tissue or in food (unlike most other AAs), it can be synthesised in the body from the AA L-glutamine(10) and is found in the CNS, pancreatic islet cells and kidney.

In the CNS, GABA is the chief inhibitory neurotransmitter, tending to decrease the electrochemical activity and therefore excitability of nerve cells. This explains why the administration of GABA can produce anti-anxiety and anti-convulsant effects and why much research into anxiolytic and anticonvulsant medication has focused around slowing down the breakdown of GABA in the CNS.

All well and good, but what can GABA offer to athletes? Well, it just so happens that GABA supplementation while at rest seems to directly stimulate GH secretion in the brain via centrally mediated mechanisms(11,12). However, until recently, there was no research available to show whether this effect is significant; ie does supplementation boost ifGH (the active form) and how relevant is this compared to the effect of GH release as a result of exercise?

More importantly, what is the effect of combining both resistance exercise and supplemented GABA on irGH and ifGH?

GABA and resistance training for GH release

Until recently the answers to the questions above were unknown, but a fascinating recent study carried out by US scientists at the University of Florida makes for truly intriguing reading(13).

Box 2: Neurotransmitters

The researchers hypothesised that GABA ingestion would increase circulating irGH and ifGH concentrations at rest, and that oral GABA administration would augment the irGH/ifGH response to resistance exercise (ie result in a larger release of GH) – ideal for athletes for all the reasons given earlier.

The study was designed as a randomised, double-blind, placebo-controlled, crossover study – ie to be as rigorous and as accurate as possible. In the study, 11 healthy, resistance-trained males (average age 23.6yrs, average weight 87.5kgs) were investigated to see what effects 3 grams of GABA supplementation had on subsequent irGH and ifGH release followed by either a period of rest, or a session of resistance training.

The study consisted of four trials, each separated by a week; in trial 1, the subjects were given either 3 grams of GABA or capsules containing inert sucrose (table sugar) of the same calorific value. After taking GABA or placebo they then rested and measurements were made. In trial 2, exactly the same protocol was followed but those who had taken placebo now took GABA and vice-versa. Trials 3 and 4 mirrored trials 1 and 2, except that now, after taking the GABA/placebo supplements, the subjects performed an intense 15-minute resistance routine, which included the following exercises: chest press, lat pulldown, chest fly, seated row, shoulder press, biceps curl, triceps extension, leg press, leg curl, leg extension, and calf raise. Figure 1 shows a schematic representation of the overall experimental design.

Before each trial, blood was collected and then again afterwards at 15, 30, 45, 60, 75, and 90 minutes in the ‘rest’ trials and after 1, 15, 30, 45, 60, 75 minutes in the ‘exercise’ trials. These blood samples were analysed for subsequent irGH and ifGH concentrations. The researchers also timed the trials and blood collections so that they all took place between 07.00h and 09.00h in order to minimise any circadian variability (GH secretion tends to rise and fall naturally at different times of the day).

Figure 1: Experimental design of GABA/resistance training study

Results of GABA supplementation

The results obtained by the team were as follows:

Exercise performance – there was no difference in exercise performance between those subjects taking GABA and those taking placebo (as expected – GABA would not be expected to exert a direct effect at the muscular level);

irGH and ifGH secretion – as might be expected, compared to the equivalent resting trials, those with resistance training resulted in significantly higher levels (up to 18-fold) of irGH and ifGH (we already know that exercise is a powerful stimulator of GH release);

GH release at rest – GABA ingestion produced significantly elevated levels of both irGH and ifGH regardless of whether exercise was performed – up to 15-fold!

Effects of GABA plus exercise – the fact that GABA can enhance GH release is encouraging enough, but even more impressive was that GABA plus exercise produced significantly higher levels of irGH and ifGH than exercise plus placebo, both at various time points after administration and in terms of total amounts secreted (area under curve – AUC). For example, the irGH response after exercise-GABA was approximately 200% greater than exercise-placebo at 30 minutes after exercise cessation. Likewise, the ifGH response after exercise-GABA was 175% greater than exercise-placebo at 30 minutes after exercise. The same trends were noted for peak concentrations of both irGH and ifGH.

Figures 2, 3 and 4 (below) illustrate these results.

What does this mean for athletes?

The two key findings from this study are that, firstly, GABA supplementation at rest dramatically enhances the release of ifGH. This is important because it’s the first study that shows GABA supplementation at rest increases ifGH – the portion of GH that’s known to be biologically active. This increase is significant; compared to rest-placebo, ingestion of GABA produced three to four times as much total secretion. Similarly, GABA ingestion combined with rest produced peak concentrations of ifGH that were over four times higher than without GABA.

However, even more interesting is the combined GABA-exercise effects on GH; looking at the figures given above, you can see how, compared to exercise alone (ie plus placebo), taking GABA boosted the GH response significantly: 200% more irGH and 175% more of the biologically active ifGH at 30 minutes after exercise following GABA ingestion is not to be sneezed at! Moreover, compared to placebo-GABA, the same trends were observed for total units of irGH and ifGH released (AUC) when GABA and exercise were combined.

For athletes seeking to gain strength, lose fat and recover rapidly, this seems like a win-win situation; for the same degree of exercise intensity (remember the GABA in itself does not directly improve exercise performance), the magnitude of the subsequent GH release is nearly doubled. Even GABA taken on its own raised levels of both irGH and ifGH, which opens up the intriguing possibility that it could also be used to augment the natural peak of GH production that occurs during the early hours of sleep.

However, before we get too excited, there are important caveats to add. The first is that there’s still little understanding of how ingested GABA is able to produce this GH-boosting effect. As any exercise biochemist will tell you, when mechanisms are poorly understood, caution is the by-word.

The second is that despite everything we know about GH, exactly how the administration of GABA to boost exercise-induced GH might affect subsequent growth and recovery in athletes has yet to be determined. Until long-term studies have been conducted to investigate this, we can’t be sure if these theoretical benefits will actually translate into improved performance. As the researchers themselves put it, ‘Although GABA-induced irGH/ifGH secretion may alter substrate metabolism and/or enhance the skeletal muscle responses to resistance training, this still remains to be determined.’

Despite these caveats, GABA is considered a safe supplement with low toxicity and is relatively cheap: for example, 200g (66 servings) typically costs around $20-30 in the US and £15-20 in the UK. Those who wish to experiment with it as an adjunct to resistance training therefore, may have little to lose. However, this of course presupposes that the emphasis remains firmly intelligent training and good general nutrition – no supplement can ever be a magic bullet. That said, while the jury’s still out, the research on GABA to date is promising and it remains an area to watch. 

Andrew Hamilton BSc Hons, MRSC, ACSM is a member of the Royal Society of Chemistry, the American College of Sports Medicine and a consultant to the fitness industry, specialising in sport and performance nutrition

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