What is Whey Protein Isolate?
Whey protein isolate is made from pasteurized fluid whey, a by-product of cheese making. While similarly named, fluid whey is not same as whey protein (to make sense of the difference, read this post). As the name implies, whey protein isolate is almost pure whey protein without other nutrients. Starting with fluid whey, dairy processors remove almost all the water, lactose, fat, and minerals. More condensed than whey protein concentrate, whey protein isolate contains at least 90% whey by weight. Trace amounts of lactose and minerals remain.
Why is Whey Protein Isolate Added to Infant Formulas?
While there is a wide range of proteins in mammalian milks, two classes predominate: caseins and whey. In human milk, the proportion of casein to whey changes as the infant grows. Early milk is 70-80% whey and decreases to 50-60% within a few weeks. Mature cow milk that is used to make dairy ingredients is about 18-20% whey. Thus, manufacturers add whey to balance out the ratio of casein to whey in order to mimic that of human milk. Given that the percentages change as the infant grows, age-specific formulas (e.g. newborn, Stage 1) have higher percentages of whey.
While the proportional differences of whey to casein between human and cow milk have been long known, technical improvements allowing in-depth analysis of specific proteins in each class has renewed the focus on understanding casein and whey in human milk. For example, newer analysis methods suggest that casein levels in human milk may be lower than previously believed. Variation between women may be greater than previously understood. One study found that 37 out of 166 common proteins in human milk differed between women of different ethnicities over the course of lactation. These technological improvements are exciting, as they progress scientific knowledge of infant nutritional needs.
Is Whey “Easier” to Digest?
Higher levels of whey, up to 100%, are promoted by some companies in their solution formulas. Indeed, casein is frequently described as being “harder” to digest, implying that casein is metabolically more difficult or taxing on an infant. However, this portrayal a mental short-cut and isn’t technically correct, especially for healthy infants.
Clinicians have long believed that casein is much slower to leave the stomach than whey, an effect called delayed gastric emptying time. While early research showed this to be the case, more recent work throws a wrench in this assumption for healthy infants.
Regulations and Safety
The US FDA considers whey protein isolate safe. The European Food Safety Authority (ESFA) reviewed whey protein isolate in 2018, finding it safe for use in infant formula.
Dietary Considerations
Whey protein isolate is not appropriate for vegans since it comes from fluid milk. It is acceptable for vegetarians who drink milk (lactovegetarians). The OU (Orthodox Union) Kosher considers many infant formulas as OU-D, kosher-dairy, but not kosher for Passover. Since whey protein isolate is derived from fluid milk, it is not Cholov Yisroel unless specifically certified as such. For reference, see the Orthodox Union Kosher Dairy Primer.