Lactose-free whey is a a substance derived from milk as a byproduct of the process of making cheese or extracting casein protein that has had its lactose, a type of sugar found in milk, filtered out. Whey is high in protein and is used in the production of many foods, and proteins isolated from whey are common ingredients in dietary supplements. Lactose-free whey is produced for use as an ingredient in products for people who are lactose intolerant, meaning that they cannot properly digest lactose and may suffer adverse reactions to consuming it. Most adult humans are lactose-intolerant to at least some degree, though due to the fact that dairy farming has been practiced much longer and more intensively in some parts of the world than in others, its frequency varies greatly between the native populations of different areas.
Whey is what remains of milk after after the primary protein in milk, called casein, is coagulated into a solid and removed in a process called curdling. This leaves behind another protein that normally makes up about 1/5 of the protein in milk, called whey protein, along with water and other constituents of milk. Lactose-free whey is produced by subjecting this substance to a process known as microfiltration, in which the whey is strained through a filter that separates the whey protein from the whey's carbohydrates, including lactose. It can then be used in the the production of lactose-free products, such as lactose-free whey protein shakes, baked goods, and non-dairy creamer.
Lactose (C12H22O11) is an organic compound that is part of a larger category of compounds called disaccharide sugars. It is part of the milk of all mammal species, including humans. Children, aside from those with certain intestinal injuries or a rare genetic disorder called congenital lactose deficiency, are naturally able to digest lactose because their bodies produce an enzyme called lactose that metabolizes it, but in adulthood lactose production usually diminishes or stops altogether. A lactose-intolerant person who consumes lactose may suffer symptoms such as nausea, cramps, and diarrhea, which vary in severity according to the amount consumed and the person's degree of lactose deficiency. As a result, many people who are lactose intolerant try to avoid lactose or eat an entirely lactose-free diet, so there is a sizable market for lactose-free foods.
Lactose intolerance is very common because the practice of milking cattle or other animals to produce milk for human consumption is only around eight to ten thousand years old, which is very recent relative to the historical time frames in which evolution operates. Thus, for most of human evolutionary history, there would have been no benefit in being able to digest milk in adulthood. The greatly varying frequency of lactose intolerance in different populations also reflects the role of evolutionary adaptation, because the first dairy farming on a significant scale is believed to have started in central Europe. As a result, lactose intolerance in the present day is very rare among people of central or northern European ancestry but tends to become increasingly common with greater separation from Europe, to the point of being almost universal in China, southeast Asia, and much of sub-Saharan Africa, as well as among Native Americans.