Hormone Series Part 3: Growth Hormone.

Growth Hormone (GH) is a peptide hormone containing a chain of 181 amino acids. GH is an unusual hormone in the sense that it plays a role in anabolism of many of the body’s tissues, including muscle and bone growth whilst also being involved in catabolic process such as the breakdown of stored body fat for use as a fuel. GH is released form the pituitary gland in the brain and is then circulated through the blood stream. It is important to note that several different ‘isoforms’ of GH exist (by several I mean over 100!) These functionally similar but differently structured proteins that fall under the umbrella of ‘GH’ have different effects on the tissues of the body and play a role in the turnover, growth and remodelling of many tissues including bone, skin, muscle, nerves and also interacts with the male and female reproductive system, foetal development and is in a large part responsible for growth and maturation from infancy into adulthood with the sex specific steroid hormones.

GH generally works in opposition to insulin, at least in regard to glucose and fatty acid metabolism, but shares a pathway through the release of insulin-like growth factor 1 (IGF-1) to promote muscle protein anabolism, although this is a modest anabolic effect in comparison. Therefore, like insulin, many of growth hormones’ actions are mediated by the nutritional state we are in. In a fasted state, GH levels are increased, allowing fatty acids from the body fat to be released (a process called lipolysis) to be used as energy. This enables the body to help preserve its other fuel reserves such as glycogen. In this situation, insulin levels are also low which facilitates lipolysis to take place. Although GH does not appear to have a profound effect on glucose metabolism directly (such as glucose uptake into cells and the creation of new glycogen), its indirect action of preserving glycogen is an important function in total body glucose/glycogen regulation and it is during the fasted state where GH plays an important role in preventing loss of amino acids from the muscle by preventing muscle protein breakdown.

In the fed state, insulin levels rise and this becomes the dominant hormone in this relationship. It acts in a comparable way in some of the same protein anabolism pathways as GH, but as blood glucose levels rise this need to be taken up into the body’s cells to be stored as glycogen or used as fuel, with a trade-off of fatty acids no longer being released. Despite the release of these hormones being governed by different endocrine organs (pituitary for GH, and pancreas for insulin), there is still feedback mechanisms which exist that indirectly link the release of insulin with a decrease in GH.

GH also interacts with thyroid hormones. Thyroid hormone helps to enable the anabolic and metabolic effects of GH in the body’s tissues and also increases its production in the pituitary gland. High levels of GH reduce the release of thyroid stimulating hormones from the pituitary gland in the brain, but increases conversion of thyroxine (T4) to triiodothyronine (T3) in other tissues in the body. Ghrelin which is commonly referred to as the hunger hormone also has an apparent role in signalling the release of GH, and this may impact on appetite control and feeding behaviour.

So what can we do to increase GH levels? Well, training protocols that include using more muscle mass (compound movements), higher volume of reps, shorter rest periods, and eccentric contractions increase in GH levels and this appears to be strongly associated with lactate accumulation in the muscles. Unfortunately, despite these acute elevations in GH post-exercise, the links between GH and muscle growth are poor. This could mean a couple of things: firstly, that GH is not a fundamental anabolic agent, but instead plays a role in preventing protein breakdown i.e. takes a more backseat role, or secondly, that these elevations are more to do with the need to provide increased fatty acid and energy provision as fuel reserves are lowered during a training session. Some supplements such as GABA and arginine have also been associated with elevations in some types of GH isoforms; however, their impact on overall daily GH release and muscle growth does not appear to be significant, although they may have some other benefits, but that’s for a different article!

In summary, GH is not something that we cannot control overly through diet, assuming we are providing the raw materials with which to produce GH. GH’s effects in terms of muscle growth are outweighed by insulin and other reproductive hormones. Despite many nutritional and supplement strategies being focused on increasing GH, in practical terms, preferentially targeting elevations of GH at the cost of other more potent hormones is unwise. A classic example is avoiding carbohydrates before bed as (at least for males), as our GH response is mostly delivered in a large pulse in our sleep. It is suggested that having carbohydrate ‘might’ interfere with this release due to an increase in insulin. This is also true for women who produce more frequent pulses of GH throughout the day. If GH was as anabolic (compared to insulin and testosterone) as some would suggest, then women would naturally carry more muscle than men. This demonstrates the limited anabolic potential for GH as a muscle building agent. So my advice is that if you need carbohydrates before bed or throughout the day to fuel recovery and growth, then any concerns about GH release should come secondary to this need when looking at the bigger, muscle building picture.