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Growth hormone (GH) is a peptide hormone that sparks growth, cell reproduction, and cell regeneration in humans and other animals. It has many beneficial properties, including lowering fat mass and increasing muscle mass and strength. These properties are clearly evident in livestock, as animals given growth hormone produce more and leaner meat. Results in humans, however, are inconsistent. A greater understanding of the relationship between amino acids and growth hormone may be the key to bringing more consistency to advancements in growth hormone therapy.
Growth hormone is one of the most popular performance-enhancing drugs. The use of growth hormone as a performance enhancer is banned by all anti-doping governing bodies, so we can presume that growth hormone has some beneficial gains, particularly amplifying the training effects of resistance exercise.
Growth hormone therapy is also a sought-after anti-aging treatment. Secretion of growth hormone declines with advancing age. Along with the decline in growth hormone, muscle mass decreases and body fat percentage increases. Although there is no proof that a deficiency in growth hormone causes these changes in body composition, the hope is that growth hormone therapy can reverse these age-related changes.
There are two important reasons why there has been much effort to identify a nutritional approach to stimulating growth hormone release. For one thing, growth hormone is ineffective when taken orally because it is digested. Therapy requires frequent shots that are very expensive. The second reason is relevant to competitive athletes. Nutritional stimulation of growth hormone secretion would achieve the benefits of growth hormone treatment within the regulations of drug enforcement agencies.
And the Winner Is…Amino Acids!
So far…
Amino acids have been the focus of nutritional approaches to stimulating growth hormone release. In fact, the intravenous infusion of arginine is well accepted as a clinical test of the ability to secrete growth hormone. However, the intravenous arginine infusion test results in much higher arginine concentrations in the blood than can be achieve with oral consumption. This is because orally-ingested arginine is rapidly cleared by the liver, which blunts the increase in arginine concentration in the blood.
Coupled with the fact that oral consumption of a large amount of arginine causes diarrhea and other symptoms of GI distress, the doses of oral arginine that have been tested as potential growth hormone boosters don’t measure up to intravenous infusions of arginine. Oral consumption results in much lower concentrations of arginine in the blood than achieved during the intravenous arginine test. Consequently, oral arginine only stimulates growth hormone secretion in certain circumstances.
Oral arginine has been tested both alone and with other amino acids. Trials have been run with combinations of arginine and ornithine, and arginine and lysine. Lysine has been tested alone as well. In addition, glutamine and glycine have each been tested as growth hormone stimulants.
Results have been inconsistent. It appears that regardless of the amino acid combination, some studies report positive results while others fail to find a significant effect. The most consistent result seems to be when oral arginine is used in conjunction with resistance training.
There is no combination that is universally beneficial. In all studies there are people who respond and people who don’t. Further, there is very limited data indicating that stimulation of growth hormone release by one or two individual amino acids translates to an increased rate of protein synthesis in muscle.
It’s a numbers game…
The reason stimulation of growth hormone release with one or two individual amino acids doesn’t motivate the synthesis of new muscle protein is that all the essential amino acids are required to produce a complete muscle protein.
Furthermore, it is not growth hormone, per se, that stimulates muscle protein synthesis. Although growth hormone may have some direct metabolic effects, its main action is to encourage the expression of insulin-like growth factor one (IGF-1). IGF-1 is a potent stimulator of muscle protein synthesis if expressed inside the muscle cell. It is not clear whether individual amino acids increase the expression of IGF-1 in muscle, but studies indicate that essential amino acids can work synergistically to increase IGF-1 function inside muscle cells.
An important study in which older individuals were given a balanced formulation of all the essential amino acids or a placebo for three months showed that muscle mass and muscle protein synthesis benefits were evident in the amino acid group. Participants supplementing with a complete essential amino acid formula had an increase in the expression of IGF-1 in muscle and favorable lean body mass results. Muscle protein synthesis not only increased when essential amino acid levels in the blood shot up after consumption, but also in the basal state between meals. This means that IGF-1 is released continuously into the muscle, where it increases the capacity to make new muscle protein, both day and night.
What we’ve seen thus far is that growth hormone release can be stimulated by resistance exercise and consumption of a variety of individual amino acids (arginine, lysine, ornithine, glutamine, glycine), either alone or in combinations. But this enhanced response doesn’t work for everyone. Responses in sedentary individuals, including older individuals, are much less consistent.
The inability of individual amino acids to stimulate muscle protein synthesis in every circumstance and in every human is likely due to the fact that all essential amino acids are required to make new muscle protein. Dietary supplementation with a balanced mixture of essential amino acids has the advantage over individual amino acids because muscle protein synthesis is directly stimulated by essential aminos, and the increase in IGF-1 in muscle stimulates the synthesis of new muscle protein 24 hours a day.
#DrRobertWolfe
