Whey protein, often referred to as lactalbumin, is currently the supplemental protein source of choice for many bodybuilders and strength athletes. Whey proteins represent the major proteins in human breast milk, as opposed to bovine milk which is comprised primarily of casein with lesser amounts of whey. Whey is comprised of alpha-lactoglobulin, beta-lactoglobulin, bovine serum albumin (BSA), and immunoglobulins (IgG1, IgG2, Secretory IgA, and IgM). Other components of the lactalbumin fraction include: enzymes, iron binding proteins, calcium, potassium, sodium, phosphorous, and vitamins A, C, B1, B2, B3, B5, B12, folic acid, and biotin. Whey is a balanced source of essential amino acids and peptides with a high protein efficiency ratio. It is considered to be an excellent source of sulfur amino acids (methionine and cysteine), as well as the branched chain amino acids (leucine, isoleucine and valine), and glutamine. (See sections on branched chain amino acids and glutamine for information on their potential benefits).
Whey transits the stomach quickly and is rapidly absorbed from the human intestine. The beta-lactoglobulin component remains soluble in the stomach and empties rapidly as an intact protein needing further hydrolysis by pancreatic enzymes. Casein, on the other hand, transits the stomach slowly.23
Skeletal muscle is the largest repository of metabolically active protein and a major contributor to total body nitrogen balance. Supplying energy alone (i.e., carbohydrate and lipids) cannot prevent negative nitrogen balance (net protein catabolism) in animals or humans; only provision of protein or amino acids allows the attainment of nitrogen balance.
While no studies exist comparing the impact on nitrogen balance, body composition, or performance of different protein sources in trained athletes, whey has been shown to promote growth and enhance nitrogen balance in experimental animals, low birth-weight infants, and burn victims.24-26
Whey protein is rich in substrates for glutathione synthesis,27 containing substantially more cysteine, which is considered to be a rate-limiting step in glutathione synthesis, than does casein. Whey also contains high amounts of glutamine and glycine.
Glutathione is a powerful antioxidant and is involved in metabolic detoxification pathways. The role free radicals play in the development of exercise-induced tissue damage, or the protective role antioxidants might play, remains to be completely elucidated. Research has indicated free radical production and subsequent lipid peroxidation are normal sequelae to the rise in oxygen consumption with exercise.28 However, physical training has been shown to result in an augmented antioxidant system and a reduction in lipid peroxidation. Supplementation with antioxidants appears to further reduce lipid peroxidation but has not been shown to enhance exercise performance. 29
Glutathione levels have been shown to decrease with exercise. 30 Additionally, running a marathon causes a large increase in the tissue content of oxidized glutathione (189%) at the expense of reduced glutathione (-18%).31 While no information is available on the effects of resistance exercise and glutathione levels, it is hypothesized an increased intake of antioxidants might protect the active person against minor muscle injuries.32
Whey protein is more efficient at inducing supernormal glutathione levels than a cysteine-enriched casein diet.33 A whey-rich diet has been shown to increase heart and liver tissue glutathione content in rats. The whey protein diet appeared to also increase longevity when fed at the onset of senescence.33 Whey-based formula enhances cysteine retention and results in greater taurine excretion, thought to be a reflection of greater taurine stores.34 Whey protein fed to three HIV-sero-positive individuals over a period of three months, at doses increasing progressively from 8.4 to 39.2 g per day, resulted in progressive weight gain and increased glutathione levels in all three cases. 35
Experimental studies suggest the whey protein component of milk might exert an inhibitory effect on the development of several types of tumors. It is thought the rich supply of substrates for glutathione synthesis contributes to this inhibitory effect.36 In experimental animals, a diet consisting of 20 g of whey/100 g diet has been shown to be more protective than similar diets utilizing casein, soybean, or red meat against dimethylhydrazine-induced intestinal cancers.37 Peptides from whey protein have also been shown to have antithrombotic38 and immunoenhancing activities.38,39
The primary concerns about supplementing whey protein are the possibility of food allergies, its lactose content, and proposed links to insulin-dependent diabetes mellitus (IDDM). While the possibility of food allergies from whey has to be considered, it is probable it is no more and possibly less antigenic than soy, casein, or egg-based protein supplements. A significant concern might be the method of processing of the whey protein, since high temperatures during heating or drying can generate browning reaction products by covalent interaction of proteins and lactose. Browned proteins have lowered digestibility and are thought to result in more uptake of intact protein through intestinal mucosa. All whey protein available contains some degree of lactose, although many have very low amounts.
The BSA component of whey has been implicated as a possible trigger for IDDM in children. A similarity exists between the amino acid sequence of the beta cell protein, found on the insulin-secreting beta cells of the pancreas, and BSA. Because elevated levels of anti-BSA antibodies have been found in sera from children developing IDDM, it has been proposed that absorption of BSA, or partially digested fragments of BSA, stimulate the immune system which then incorrectly destroys beta cells.40 Pardini et al found the prevalence of anti-BSA antibodies was 52% in children with less than one year of IDDM, 47% in children with greater than one year of IDDM, and 28% in the control group. They concluded the prevalence of anti-BSA antibodies is higher in IDDM subjects than in control subjects; however, because of the large overlap of antibody titers observed in patients and control subjects, anti-BSA antibodies were not sensitive nor specific markers of IDDM. 41 Ivarsson et al found IgG antibodies to BSA were not significantly increased at onset of IDDM.42 Currently, the exact nature of the relationship between BSA and IDDM remains unclear.
The routine use of a post-workout shake might be the most important nutritional supplementation habit for enhancing body composition. It is probably in this manner whey can be best utilized by athletes concerned with maximizing lean body mass and strength.
Amino acid availability following a workout regulates protein synthesis and degradation. Because of the anabolic effects of insulin on protein synthesis and protein degradation, a rapid synergistic response occurs when both amino acids and insulin increase after a protein-containing meal.43 It is thought the body is highly insulin sensitive after exercise and preferentially shuttles carbohydrates and protein into muscle cells rather than fat cells. Experts think this sensitivity gradually declines post-workout for about two hours until it again reaches normal sensitivity.
A carbohydrate-whey protein supplement has been shown to be more effective in generating a plasma insulin response than either a carbohydrate or a protein supplement alone during recovery from prolonged exhaustive exercise. The rate of muscle glycogen storage was also significantly faster during the carbohydrate-protein treatment. The participants in this study ingested 112.0 g carbohydrate and 40.7 g protein immediately after each exercise bout.44
Whey is an excellent choice as a protein source for the post-workout shake because of its rapid transit into the small intestine and because of its high levels of branched chain amino acids and glutamine. Glucose-polymers or maltodextrins are considered to be the best form of carbohydrates to use because of their ability to stimulate an insulin response. Fat should not be added because it might slow transit and decrease the insulin response.
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