The ability to digest milk in adulthood varies across populations among our species

Many individuals in a relatively small number of human populations can digest milk throughout life

Most humans cannot. How does this biological variation

intersect with policies that promote milk consumption on a daily basis?

Milk contains a unique double sugar (disaccharide), lactose, which is made up of one unit each of glucose and galactose

Lactose requires the enzyme lactase, which is found in the small intestine, to break it down into its two single sugars

These single sugars can then be absorbed and used for energy

© 2011 Taylor and Francis

© 2011 Taylor and Francis

© 2011 Taylor and Francis

© 2011 Taylor and Francis

Some mammals never produce lactase because their milk contains no lactose

Some human populations produce lactase throughout life

Lactase persistence: the production of lactase into adulthood

Lactase impersistence: the cessation of lactase production in childhood; the norm for the human species

Prevalence of lactase persistence in various human populations %

Northern Europeans 85–97 European-Americans 78–94 Central Europeans 77–91 South Asians Northern South Asia 70–80 Southern South Asia 30–40 Hispanics 20–50 African-Americans 20–40 Native Americans 0–20 East and Southeast Asians 0–5Source: Adapted from data in Sahi (1994).

© 2011 Taylor and Francis

All lactase persistent populations keep dairy animals BUT not all dairying populations are lactase persistent

Dairying population who use dairy products with lactose removed (yoghurt, cheese) generally have LOW rates of lactase persistence

DAIRYING populations that consume fresh milk tend to have HIGH rates of lactase persistence

At high latitude lactose may substitute for Vitamin D, which is essential to calcium absorption. Vitamin D is produced during exposure to UVB light.

At low latitudes being able to digest milk may provide advantages in terms of hydration and carbohydrates.

© 2011 Taylor and Francis

Hypolactasia (Sahi, 1994)

Lactose maldigestion (National Dairy Council)

Lactose malabsorption (National Dairy Council)

“a shortage of the enzyme lactase, which is normally produced by the cells that line the small intestine” (American College of Gastroenterology).

“late-onset lactase deficiency is a common disorder…[when there are] abnormal findings on lactose tolerance tests ” (American Academy of Pediatrics)

How do these terms illustrate the concept of “bio-ethnocentrism?”

© 2011 Taylor and Francis

© 2011 Taylor and Francis

What is the purpose of the food pyramid?

What is different about the milk “group”?

Who is responsible for creating dietary guidelines in the United States?

What are some other food programs that encourage milk consumption?

© 2011 Taylor and Francis

PCRM’s notice of their lawsuit against grocery stores promoting milk to minorities (Source: Physicians Committee for Responsible Medicine, used with permission).