It is quite permissible for adult Europeans.
Most mammals lose the ability to digest milk sugar (lactose) as they mature. This is due to a decrease in the activity of the gene responsible for the corresponding enzyme. In humans, there is also a mechanism for 'turning off' this gene; however, in Europeans and African pastoralist populations, it has been disrupted by mutations. It is believed that during the development of pastoralism, natural selection favored the spread of these mutations.
Currently, 85–95% of adult Europeans are able to digest lactose.
In East Asia, only 3–5% of the population has this ability. The consumption of fresh milk leads to increased gas production in them, as undigested lactose enters the intestine, where it is processed by bacteria, releasing carbon dioxide. In fermented dairy products, lactose has already been converted into lactic acid.
