Whey is the fluid portion of milk that is obtained by coagulating and removing the curd (casein) during cheese production. After its separation from milk, whey contains almost all of the vitamins and minerals, 50% of the milk solids, and 20-24% of the milk proteins. The main protein fractions of whey are a-lactalbumin and ß-lactalbumin, which comprise between 70-80% of whey Additional protein fractions include glycomacropeptides, bovine serum albumin, lactoferrin, immunoglobulins, phospholipoproteins, and other bioactive factors and enzymes.
Although the nutritional value of this protein was recognized and applied to animal nutrition, its application to human nutrition was delayed. Initially, the major limitation was because whey was available only in a heatdenatured form. Morr et al. reviewed a variety of techniques that were developed to produce undenatured whey in commercial quantities. The results after generations of developing whey separation techniques include a whey protein concentrate (WPC) with a high protein concentration and low levels of minerals, fat, and lactose.
In most protein foods the limiting amino acid is either lysine or methionine plus cystine. Whey proteins are unique in that they contain high levels of essential amino acids (EAAs), which include lysine, methionine, cystine, and the branched-chain amino acids (leucine, isoleucine, and valine). The excellent amino acid profile led to the application of whey protein to medical disorders. WPCs were exposed to different types of hydrolysis (enzymatic and pH) to create whey protein hydrolysates (WPH).
The use of acid and alkali media to hydrolyze whey can cause denaturation of essential amino acids, so enzymatic hydrolysis became the method of choice. However, this method can result in incomplete hydrolysis and bitter-tasting hydrolysates. The use of different enzymatic methods (i. e. , papain) can result in hydrolysates that are far less bitter tasting. The final products are high quality (providing undenatured amino acids and peptides) and have received tremendous attention from not only the scientific community, but life extensionists, athletes, and health! fitness enthusiasts as well.
To understand the mechanism by which whey protein can exert its effects on protein synthesis, several areas must be investigated. These areas include the impact of whey on growth during development and recovery from stress or injury. Studies in vitro and in animals have investigated the effects of whey protein on growth and development recovery from severe burns and repair of gastric mucosa. In general, WPC is better for calf growth and development than dried skim milk (DSM) when supplied as 67% or 100% of the major protein source.
However, if a starter formula is added to both the WPC and DSM diets, then growth rates between the two diets are similar. When studied as a replacement for colostrum in calves, WPC resulted in similar weight gain and a lower immune status for calves. From this brief summary it may be concluded that whey protein concentrate is better than dried skin milk, but not colostrum, in terms of the growth and development of calves.
Poullain et al.compared the effects of different molecular forms of whey such as WPC, WPH, or amino acid mixture (AAM) on growth and nitrogen retention in rats. The male Wistarrats were divided into six groups of eight. Three groups were starved for 72 hours before being refed one of the three forms of whey ad libitum for 96 hours. The other three groups served as controls and were fed one of the three whey diets. Animals that were starved before feeding lost on average about 13% of their body weight. Although no differences were found in the control groups, the WPH-refed group regained weight much faster than the WPC- or AAM-refed groups. Urinary nitrogen excretion was much lower for both the refered and control WPH groups, in comparison to all other groups. This suggests the mechanisms of increased nitrogen intake are not influenced by nutritional status (i. e. , gut atrophy).
The improved protein anabolism of the WPH diets were not associated with an increase in ureagenesis. The diets were identical in energy, nitrogen, amino acids, and nonnitrogenous nutrient content. The intakes of the rats were all the same therefore, it is speculated that the different absorption rates and blood patterns of amino acids may be the cause of the differences in nitrogen balance between the WPH, WPC, and AAM diets. These differences may be related to the effects of blood levels of amino acids on hormone production. Thus, by ingesting a WPH, a sudden surge in blood levels of specific amino acids may induce the release of insulin or some other anabolic hormone, resulting in increased protein synthesis and greater nitrogen uptake.
Data from the previous study, published separately, examined the effects of WPH, WPC, and AAM diets on the jejunal mucosa of controls versus starved then refed rats. During starvation for 72 hours, gut atrophy occurred and villus height decreased. After refeeding, all diets resulted in repair of the fasting-induced gut atrophy. The WPC diet produced the most rapid repair and growth of intestinal villi in the refed rats. The WPH and AAM diets produced better results on villus growth and disaccharidase activity in the control groups. The significance of this work is the demonstration that enteral feedings of different molecular forms of whey can alter jejunal morphology and enzyme activity. Combining the data from the two Poullain studies it is noted that the increased body weight and positive nitrogen balance in the WPH refed rats occurred even though, the mucosal lining had not undergone the same extent of repair as that in the WPC refed rats. This provides further evidence that the mechanisms by which whey protein positively affects nitrogen balance and body weight may be independent of nutritional status.
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