Milk: White elixir or white poison? An examination of the associations between dairy consumption and disease in human subjects

摘要

Animals were probably first kept for meat, but domestication gave our ancestors access to limited, but continuing supplies of milk. Although the quantity was probably small, it is likely that milk was a more sustained supply of nutrition than meat, and so animals were selectively bred from earliest times. From the study of food residues on pottery fragments found in Turkey, it seems that animals may have been milked as early as the seventh millennium BC, and evidence from other sources indicates thata wide range of animals were kept for their milk, including sheep, goats, cows, water buffalo, reindeer, camels, horses, and even asses.The fact that milk and dairy products have made an important contribution to the diet of humans throughout history is somewhat surprising. Most mammals stop drinking milk soon after weaning, and humans are the only species that consumes milk throughout life. In mammals generally, and in some human races, the gene for the enzyme lactase gets switched off in most individuals, and thus the ability to digest lactose is lost, severely limiting the quantity of milk that can be consumed. In Northern Europeans,however, the gene remains active in most people and well over 90% can digest lactose throughout life and consequently consume relatively high quantities of milk (Sahi, 1994).