You’ve probably heard that around two–thirds of your bodyweight is comprised of fluid, principally water. But did you know that half of the remaining third (ie about 17% of your total body mass) is made of protein. And this is not just your muscles, important though they are. Protein also forms your skin, hair and nails; the collagen that literally holds your cells together is a protein, as are many of the countless enzymes that govern your body’s vital biochemical reactions, and the antibodies that you need to fight disease. In fact it’s not too much to say that these many thousands of different proteins are the very building blocks of your body; perhaps even of life itself. And all of these proteins are themselves formed of building blocks known as amino acids, of which more than twenty have been identified and isolated.

Phenylalanine is one of the 10 amino acids which are known as essential because they cannot be manufactured within the body, and must therefore be obtained from the protein consumed in the diet. Dietary proteins are in turn divided into two groups. Those known as first class, or complete, which contain all of these essential amino acids, are principally those from the animal sources – meat, fish, eggs and milk etc. Second class proteins, typically obtained from vegetables, grains, nuts and beans, contain some but not all of the essential amino acids. Vegetarians therefore need to be careful to combine these foods to ensure they obtain an adequate intake of complete protein.

So important is dietary protein to the body that an average adult is reckoned to need at least 56 g of a day to keep the body in repair. This amount increases in proportion to lean bodyweight and the stresses placed on the body. So athletes in training may need as much as 1.5 g of protein per kilogram of bodyweight. But weightlifters and other strength and power athletes looking for rapid gains in muscle mass may need considerably more; perhaps even twice as much as this.

Dietary protein obtained through foods consumed is broken down by the digestive process to release individual amino acids into the blood stream, but there is some evidence that taking these individual amino acids directly, in the form of dietary supplements, may be beneficial in some circumstances. These are often consumed by sports people in training; weightlifters, bodybuilders and field athletes in particular; and phenylalanine is one of the individual amino acids most commonly used in this way.

In general terms phenylalanine is known to be required for the manufacture of certain chemicals in the brain, and research suggests it may help improve sex drive and mental alertness, and even act as a natural anti-depressant. The downside of these effects, however, can be an over-stimulation of the brain which may lead to insomnia and undue agitation during the day if an excess is consumed for too long.

More specifically, phenylalanine is also known to be involved in the body’s production of the chemical, norepinephrine, which has pain relieving, sedative and tranquilising effects. Phenylalanine has therefore been widely adopted by athletes as a way of relieving the pain of injuries, particularly muscular strains sustained in competition or training; and as a way of minimising the necessary recovery time following such setbacks. The usual recommended dose of phenylalanine is between 500 and 1,000 mg a day as capsule or powder for a period of three weeks; taken on an empty stomach for maximum absorption and optimum effect. Such supplements should not be taken indefinitely, however, unless in conjunction with a multi-amino acid supplement, because of the risk of creating imbalances.

But those training with the intention of developing increased muscular bulk and power will not wish to use phenylalanine in this way in any event, because there is also evidence that it has a role to play in the regulation of the appetite, and may in fact be an appetite suppressant. So it will be a matter of fine judgement in each individual case as to the optimum length of time that phenylalanine supplementation should be continued.

But as always, in any case, the body functions holistically, and all nutritional supplements will function best in the presence of optimum levels of all the nutrients required by the body.

So if supplementing with phenylalanine for any of the purposes described above, you should ensure you’re also getting a rich supply of good quality dietary protein, as well as taking comprehensive multi-vitamin and multi-mineral preparations. Plentiful supplies of vitamins C and B6, however, appear to be particularly important to get the best results from any program of phenylalanine supplementation.