A regular diet of complete protein (ie, containing all essential amino acids in good proportions) is necessary because surplus amino acids are not stored in the body. Adequate Nutrition for protein can be achieved with lesser amounts of high quality protein than with greater amounts of low quality protein (quality being a function of completeness and essential amino acid proportions).
Egg white (albumin) is often given as a standard for high-quality protein. Whey protein, however, is not only more complete than egg albumin, it may offer additional benefits. It is high in branch-chained amino acids (leucine, isoleucine and valine), which means it is good for preventing muscle-wasting during weight-loss programs.
Whey protein (also known as "lactalbumin") constitutes 18% of cow milk and 67%of human milk protein (which are 82% & 33% casein, respectively). Cow and human lactalbumin (whey) can be broken-down into constituents as follows:
|alpha-lactalbumin||21 %||42 %|
|immunoglobulin G||11 %||1 %|
|serum albumin||7 %||9 %|
|immunoglobulin A||2 %||15 %|
Lactoferrin is an iron-binding protein which has been shown to reduce uptake of LDL cholesterol by macrophages — and hence reduce the foam-cell formation of atherosclerosis. [BIOCHEMICA ET BIOPHYSICA ACTA 1213:82-90 (1994)]. Rats fed high levels of whey protein showed reduced plasma VLDL cholesterol & liver cholesterol in contrast to diets of casein & soya-bean protein. Lower levels of whey only reduced liver cholesterol. The effect of whey protein was explained by reduced whey-protein binding of bile acids. Interestingly (to a person attempting CRAN), the whey-fed rates ate less than the casein-fed rats. [BRITISH JOURNAL OF NUTRITION 70:139-146 (1993)]
A 6-month study on mature mice showed a 30% increase in mean survival time of whey-fed mice, in contrast to those fed "nutritionally-equivalent Purina mouse chow" [CLINICAL AND INVESTIGATIVE MEDICINE 12:343-349 (1989)]. Full-lifespan studies on Syrian hamsters showed a dramatic increase in lifespan with animals on varying levels of lactalbumin, in contrast to a commercial diet:
|10 % lactalbumin (whey)||43 %||54 %|
|20 % lactalbumin (whey)||52 %||46 %|
|40 % lactalbumin (whey)||39 %||62 %|
Although protein-calorie restriction experiments extended the life of animals kept in highly sterile conditions, resistance to infection was depressed in these animals. The humoral immune response of a 20-gram (protein)/100-gram (dietary total) whey-protein diet was demonstrated to be significantly higher than that of a 20-gram/100-gram portion of protein from either of casein, soy, wheat, corn, egg-white, fish, beef, Spirulina maxima, Scenedesmus algae or Purina mouse chow [noted in CLINICAL AND INVESTIGATIVE MEDICINE 11(3):213-217 (1988)]. The clonal expansion & antibody production required for the humoral immune response demands availability of amino acids for protein synthesis.
Whey protein contains 8 times more of the amino-acid cysteine than casein. Cysteine administered directly into cells increases the synthesis of the tripeptide glutathione — which, in turn, enhances lymphocyte DNA synthesis. But the humoral response of mice fed a whey protein diet was found to be 5 times greater than for a diet of either pure casein or casein enriched with cysteine [CELLULAR IMMUNOLOGY 97:155-163 (1986) and CLINICAL AND INVESTIGATIVE MEDICINE 11(4):271-278 (1988)].
Glutathione (GSH) is a tripeptide composed of the amino acids cysteine, glycine and glutamic acid (gamma-glutamyl-cysteinyl-glycine). Cysteine is toxic outside of cells, and is not readily transported into cells. Inside cells, cysteine alone does not increase synthesis of glutathione as much as the dipeptide glutamyl-cysteine. Dietary glutamyl-cysteine is also believed to increase cellular cysteine much more than dietary cysteine. The whey proteins beta-lactoglobulin, serum albumin and lactoferrin are especially rich in glutamyl-cysteine. Liver glutathione concentrations have been shown to be more than twice as high in whey & casein-fed rats than in soyabean-protein fed rats. [JOURNAL OF NUTRITION 125:809-816 (1995)].
Reduced glutathione is often written as GSH to indicate the importance of the thiol (-SH, sulfhydryl) group. GSH accounts for 90% of total non-protein sulfhydryl in cells. GSH represents one of the most powerful celluar defenses against DNA damage from hydroxyl radicals (HO*) by the transformation:
GSH + HO* —> GS* + H2O
The thiyl radical (RS*) is not reactive enough to damage DNA. Glutathione can even react with DNA peroxyl radicals (DNA*) before they lead to DNA damage:
GSH + DNA* —> GS* + DNA
[PHARMACOLOGY & THERAPEUTICS 39:101-108 (1988)]
Glutathione concentration in liver, kidney, heart and brain are 30%, 34%, 20% and 30% lower (respectively) in elderly mice than in mature mice [CLINICAL AND INVESTIGATIVE MEDICINE 14(4):296-309 (1991)]. Glutathione concentrations in the eye are normally very high, and the lens even possesses a transport mechanism to facilitate GSH uptake. Decreasing glutathione levels in the lens due to aging is associated with cataract formation [CURRENT EYE RESEARCH 3(1):83-87 (1984)]. In an experiment on the induction of colon cancers in mice, all animals fed whey protein were still alive at the end of the experiment, in contrast to only 66% still living of those who had been fed casein or Purina diet [TUMOR BIOLOGY 11:129-136 (1990)].
Thus, by providing high quality protein, whey boosts the immume system,
prevents muscle wasting, and maintains adequate protein nutrition. Moreover,
the antioxidant effects of increased glutathione may be the basis for
the increased lifespan seen with whey protein in some animal studies.