The branched-chain amino acids, so named because of their branched structures, are essential amino acids'meaning that they must be supplied in the diet because they can't be synthesized in the body from other amino acids and nutrients. The three BCAAs are leucine, isoleucine and valine and make up 20 percent of total protein intake. Other amino acids are primarily metabolized in the liver. BCAAs are metabolized mainly in muscle because the liver lacks the aminotransference enzyme that initiates BCAA metabolism.

In muscle BCAAs constitute about 30 percent of essential amino acid content. Among other functions they provide amino groups in muscle that are used in the synthesis of other amino acids, such as alanine and glutamine. Those, in turn, are vital because they\'re primary substrates for the process of gluconeogenesis, the production of glucose in the liver. That's where the anticatabolic effect of BCAAs comes from'the fact that they spare amino acid degradation for energy purposes.

Leucine is the most potent amino acid for promoting protein synthesis. It activates a number of biochemical pathways that result in upgraded protein synthesis. Some nutrition researchers believe that the lean-tissue-sparing action of high-protein diets is due mainly to the increased leucine intake that occurs. The suggested amount of leucine needed to spare protein is seven to 12 grams a day. That\'s considerably more than the generally recommended intake of one to three grams.

Research shows that the anabolic effect provided by a high-protein meal lasts five to six hours, which suggests that you shouldn't wait longer than that if you want to maintain the positive nitrogen state conducive to greater anabolic activity and muscle protein synthesis. Since muscle protein synthesis is lowest after an overnight fast, a high-protein breakfast is critical for starting the anabolic process.

Studies also show that age may determine how the body handles amino acids. In both younger adults (aged 30 and under) and older adults (aged 60 and over), giving them essential amino acids creates an anabolic effect leading to increased muscle protein synthesis. When younger people add carbohydrates, they get additional protein synthesis. In older people, however, adding carbs totally blocks the anabolic effects of amino acid supplements.

It stands to reason that if BCAAs have anabolic properties, they\'re an effective supplement for those engaged in weight training. A study presented at the 2004 National Strength and Conditioning Association\'s annual conference examined the relationship of BCAA intake to muscle gains. Six healthy, untrained men took either BCAA supplements or a placebo. Both groups took the supplements for three weeks, followed by another week of supplement use combined with intense weight-training sessions.

The men using BCAA supplements had lower levels of the enzyme creatine kinase, which is associated with muscle damage during exercise, and lower levels of cortisol, the body's primary catabolic hormone. They also had consistently higher testosterone levels than those in the placebo group. The authors suggest that heavier people need to take greater amounts of BCAAs to get benefits.

BCAA oxidation in muscle is activated by fatty acid oxidation. So when you do exercise that uses fat as an energy source, the fat released promotes the burning of BCAAs. That implies that BCAAs taken before you do aerobics will exert a sparing action on muscle protein, something that would be particularly helpful during periods of calorie restriction. The precise dosage of BCAAs for that purpose isn't established, but good results have been obtained with five grams taken prior to exercise.

One thing to keep in mind when supplementing is that you must maintain a certain ratio of the three BCAAs. Research shows that it's best to replicate the ratio of leucine, isoleucine and valine found naturally in animal protein sources'2-to-1-to-1. Taking excessive amounts of a single BCAA, such as leucine, activates enzymes that degrade the other BCAAs, leading to a possible amino acid imbalance. [Note: An amino imbalance may be the reason the study discussed on page 68 showed increased cortisol levels with hyrolyzed-protein-only meals.] IM