The main advantage of whey protein is that it is enriched in human milk. It is thought that the high whey composition of human milk is what makes it more satisfying for infants.
One possible reason for this is because whey leaves the stomach efficiently to be well absorbed . This is called gastric emptying (GE). In one study in children, GE of whey protein was almost 50% faster than casein , with lower levels of digestive discomfort.
Another advantage is that whey protein from cow’s milk is higher in calcium than human whey protein, and this is true of cow’s milk in general. Combined with the naturally occurring BCAAs, whey protein, especially when fortified with a complete source of micronutrients, would support tissue building during growth and development.
In one very early study, infants with lower weights at birth were fed either a formula containing 40% whey, or one with 15% whey . Infants in the 40% group grew larger and showed better absorption of nitrogen (a part of amino acids).
Whey protein may also be more beneficial to the infant gut microbiome. In one study, whey protein formulas resulted in a bacterial composition that was closer to breastfed infants than those fed a casein-based formula .