Amino acids are typically categorized by their nutritional role as essential or nonessential. Essential amino acids are not produced in the body and therefore must be obtained from dietary sources. Nonessential amino acids can be either manufactured directly by the body or obtained by conversion from another amino acid. It is important to keep in mind that nonessential does not mean that these amino acids are not important. Rather, it simply means that under ideal circumstances, there are routes other than the diet through which these amino acids can be obtained. Several of the nonessential amino acids are considered "conditionally essential," meaning that under certain conditions, such as injury, disease, increased stress, or intense physical activity, the body's metabolic machinery is unable to generate adequate levels, and supplemental dietary sources are required.|
A growing body of evidence suggests that specialized amino acid mixtures based on essential or semiessential amino acids can be especially beneficial for promoting postexercise recovery (Volek et al., 2002 2 g of carnitine for 3 weeks); increasing collagen deposition and wound healing (Williams et al., 2002 14 g of arginine, 3 g of HMB, and 14 g of glutamine for 7-14 days); and stimulating muscle growth (Ras-mussen et al., 2000; Tipton et al., 2001 6 g of essential amino acids plus 35 g of sucrose). Considerable debate on this issue continues, however, because not all studies support a benefit of amino acid supplementation for enhancing muscle metabolism or exercise performance (Lambert et al., 1993 single 4.2-g dose of arginine, lysine, ornithine, and tyrosine; Vukovich et al., 1997 2.9 g of leucine, isoleucine, valine, glutamine, and carnitine for 7 days).
Whey is one of two proteins found in milk (the other is casein). Whey protein accounts for only about 20% of the total protein found in milk, while casein makes up about 80% of milk protein. Long considered a useless byproduct of dairy (cheese) manufacturing, whey protein is enjoying an increased interest as a protein supplement. Because whey protein includes a variety of immunoglobulin compounds (a lactalbumin; K, lactoglobulin; lactoferrin; albumin; and immunoglobulins A, G, and M), whey supplements are often touted as effective in boosting immune protection and enhancing post exercise recovery. It is important to note that commercial products vary widely in their content of immunoglobulins and other immune-active protein fractions, and much of the difference among products is related to different manufacturing processes.
Whey protein also contains approximate 20-30% of its amino acid content as BCAAs (leucine, isoleucine, and valine), which can be readily oxidized by the muscle as energy and may be associated with a delay in fatigue during long-duration exercise, especially in the heat.
In addition to its high content of immunoglobulins and BCAAs, whey protein is a rich source of cysteine, an important amino acid constituent of the cellular antioxidant glutathione. Intense exercise is known to reduce cellular glutathione levels; thus, high cysteine whey protein supplementation may be an effective approach to restoring glutathione levels in the body.
It is important to note that commercial whey proteins can differ dramatically depending on the processing method and the total protein content. For example, whey protein can exist as simple whey powder (30% or less total protein content), whey protein concentrate (30-85% protein content) or whey protein isolate (90% or higher protein content). In the case of whey protein isolates (the most expensive type), two key processing methods ion exchange filtration and cross-flow microfiltration can remove different components of the total whey protein, resulting in end products with different tastes, textures, and functional properties. Whey proteins processed using the ion exchange methodology appear to retain most of the functional benefits associated with immune system maintenance. Enhanced resistance to infection and a 25-44% increase in glutathione levels (an antioxidant enzyme containing cysteine) have been noted in HIV-positive subjects consuming concentrated whey protein (Micke et al., 2001). Whey protein also contains lactoferrin, a protein that has been shown to possess bacteriostatic and bactericidal activity against microorganisms that can cause gastroenteric infections and food poisoning.
Whey protein has been used in a number of animal and human feeding studies that have shown its benefits in promoting weight gain, elevating glutathione levels, and preventing metabolic acidosis (although this effect can be claimed for virtually any high-quality protein source). Whether or not the minor content differences between various whey proteins actually result in any appreciable differences in muscle gain or exercise performance in humans has never been convincingly demonstrated.
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Article Added on Sunday, July 10, 2011
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