Whey proteins can differ dramatically from one another 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) 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 micro-filtration can remove different components of the total whey protein, resulting in end products with different taste, texture and functional properties. Whey proteins processed using the ion exchange methodology appear to retain the majority of the functional benefits associated with immune system maintenance. Enhanced resistance to infection and elevated glutathione levels (an antioxidant enzyme containing cysteine) have been noted in subjects consuming concentrated whey protein. 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, where it has shown benefits in promoting weight gain, elevating glutathione levels (an antioxidant), and preventing metabolic acidosis (although the same 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 in humans (their primary claim) has never been demonstrated.

There are no adverse side effects associated with whey protein.