The protein in cow’s milks is 80% casein and 20% whey protein. Whey protein powder is extremely popular due to its high digestibility and well-researched benefits for both muscle gain and fat loss.
Whey Protein is most often used for
Whey protein is a collection of proteins found in whey, a byproduct of cheesemaking. When a coagulant (usually renin) is added to milk, the curds (casein) and whey separate; whey protein is the water-soluble part of milk. As a supplement, it’s sold as dry powders with various levels of processing that affect how concentrated a source of protein they are and how fast they’re absorbed.
It’s a high quality, well-absorbed source of protein that’s very useful for hitting targeted daily protein goals. Its benefits extend to the benefits of increased protein intake in general, such as augmenting muscle gain in conjunction with resistance training, limiting muscle loss during low-calorie diets, and modestly limiting fat gain during periods of excessive calorie intake. These effects aren’t exclusive to whey protein but it will likely be more effective than most other protein sources per gram.
Whey does not harm the liver or kidneys, but it can exacerbate pre-existing damage. People with damaged livers or kidneys should exercise caution when increasing protein intake quickly without the guidance of a doctor. See more: can eating too much protein be bad for you?
Eating a high-protein diet doesn't appear to harm the kidneys or liver unless there is pre-existing damage and dysfunction. It's possible that dramatically increasing protein intake in a short timespan can lead to adverse effects on the liver and kidneys, but evidence for this is lacking. Bone health also appears to be either largely unaffected or benefited by eating more protein.
Glutamine supplementation does not affect body composition, but it may accelerate strength recovery from resistance-training sessions and reduce the occurrence of infections in hard-training endurance athletes.
Several scales have been developed to rate proteins according to their respective bioavailabilities and, more recently, amino acid profiles. Those scales can help guide your choice of protein, as long as you understand their premises and limitations.