Intakes of dairy produce show enormous diversity between regions, cultures, and individuals around the world. At the geographic level, intake maps closely onto the distribution of lactase persistence (LP), a genetic trait that allows milk to be consumed beyond the weaning period without gastrointestinal side effects. The LP trait has been independently selected at least 4 times and is under rapid positive selection, which shows that dairy consumption has positive survival benefits. For people lacking the LP trait, the fermentation of milk into yogurt and related products (a process known for ≥8500 y) aids milk digestion through the breakdown of some lactose and the provision of β-galactosidase, which remains active in the gastrointestinal tract. In global ecologic comparisons, milk and dairy intakes are strongly associated with adult height, and many international advisory bodies recommend the consumption of 400–500 mL milk equivalents/d. There are very few countries where such high intakes are met, and in populations in whom intakes are much lower there is evidence of adaptations that help to maintain bone health with surprisingly low intakes. Despite concerns that the high-saturated-fat content of full-fat dairy products would promote heart disease, recent meta-analyses show that dairy consumption is neutral or beneficial for weight control, coronary disease, diabetes, hypertension, and most cancers.
Alex's Notes: This article is a great brief review of dairy in relation to global health. I figure its easiest if I just pick out some notable quotes for those who can't access the full-text.
"it can safely be concluded that the ability and proclivity to consume dairy products have been highly beneficial to human populations on an evolutionary basis."
"Currently, industrialized nations consume ∼5 times the milk per capita as do developing nations."
"the consensus is that the consumption of dairy products has many benefits, and prior concerns that the fat and saturated-fat content of full-fat milk products would contribute to heart disease are not supported by the literature (see below). Indeed, the evidence is mixed on the question of whether low-fat dairy products have superior health benefits to their full-fat counterparts."
"evolutionary evidence shows clearly that the consumption of milk and milk products into later childhood and adulthood has conferred significant advantages in terms of survival and/or reproductive success among our forebears. This ability to consume high lactose loads without unpleasant side effects has been achieved through evolution of the LP trait and through domestication of lactic acid bacteria to create fermented milk products... it is clear that the consumption of dairy products, and especially of fermented dairy products, has numerous benefits and is not associated with clear evidence of any detrimental health effects."