Milk

In many cultures, especially in the West, humans continue to consume milk beyond infancy, using the milk of other mammals (especially cattle, goats and sheep) as a food product. Initially, the ability to digest milk was limited to children as adults did not produce lactase, an enzyme necessary for digesting the lactose in milk. People therefore converted milk to curd, cheese and other products to reduce the levels of lactose. Thousands of years ago, a chance mutation spread in human populations in Europe that enabled the production of lactase in adulthood. This mutation allowed milk to be used as a new source of nutrition which could sustain populations when other food sources failed.[16] People process milk into a variety of products such as cream, butter, yogurt, kefir, ice cream, and cheese. Modern industrial processes use milk to produce casein, whey protein, lactose, condensed milk, powdered milk, and many other food-additives and industrial products.

Whole milk, butter and cream have high levels of saturated fat.[17][18] The sugar lactose is found only in milk, forsythia flowers, and a few tropical shrubs. The enzyme needed to digest lactose, lactase, reaches its highest levels in the human small intestine after birth and then begins a slow decline unless milk is consumed regularly.[19] Those groups who do continue to tolerate milk, however, often have exercised great creativity in using the milk of domesticated ungulates, not only of cattle, but also sheep, goats, yaks, water buffalo, horses, reindeer and camels. India is the largest producer and consumer of cattle