The Dairy Dilemma: Lactose Intolerance and Tolerance: How the Domestication of Cattle Changed Human Genetics and Culture

Humans first domesticated the wild ancestors of cattle about 10,000 years ago. Soon after, they discovered that cow's milk (as well as milk from goats, sheep, and water buffalo) could be a valuable source of nutrition. However, adult milk drinkers soon encountered a new problem, lactose intolerance.Virtually all infants and young children are able to digest lactose, the sugar in milk. This is because their intestines produce the enzyme lactase, which breaks milk sugar into smaller nutrients that can be absorbed. However, all children in these early farm and dairy cultures naturally lost this ability to make lactase as they grew older, and they became lactose intolerant adults.Within a few thousand years after the first domestications of cattle, rare mutations appeared in some people that caused lactase production to continue in adulthood. These people were lactose tolerant, and as adults they could consume large amounts of milk and dairy products without ill-effect. This new trait had a powerful selective advantage, and it spread rapidly in many dairying populations. Today in some regions the great majority carry the trait; for example, 90% of the Irish population is lactose tolerant. In contrast, most of the world's population lacks this trait, and about 70% of the global adult population may suffer from lactose intolerance. The actual severity of lactose intolerance varies widely, and is affected by the amount and type of dairy consumption, the types of bacteria present in the colon, and even the mood and hormone state of the individual. This 70% often faces difficult eating decisions, given the sometimes embarrassing and distressing effects of lactose intolerance, and the widespread presence of dairy in many diets.Building on decades of research experience in this area, Dr. Sox tells this complex story of cattle domestication and the subsequent appearance on three continents of various mutations that led to adult lactase production.With this foundation, he explores the diagnostic tests and treatment strategies for lactose malabsorption and intolerance. This is done in the context of the history of the recognition of lactose intolerance as a medical condition, and the research that has led to our current treatment options. This book is more than a simple self-help book for the lactose intolerant. Instead, it critically evaluates all available treatments, and points out there shortcomings. This unique work is a complete resource for those who suffer from lactose intolerance, and readers with a broad interest in human biology.