Nutrition Science and Everyday Application - beta v 0.1

162 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
Figure 3.17. Taking a lactase enzyme supplement allows many people with lactose intolerance
to eat dairy products without suffering symptoms.
The vast majority of humans are born with the ability to digest lactose. All mammalian
milk, including human milk, contains lactose, so historically, infants with lactose intolerance
wouldn’t have survived. (Today, infants with lactose intolerance can consume soy-based
infant formula.) Beyond infancy, lactose intolerance depends on your genes. In much of
the world, it’s common for the activity of the lactase gene to decline with age, resulting
in less lactase production and more lactose intolerance. Worldwide, 65% of the human
population has some degree of lactose intolerance in adulthood. On the other hand, lactose
tolerance is common in cultures where early domestication of dairy animals provided an
important source of nutrition. In the U.S., adults of European descent can often tolerate
lactose, whereas lactose intolerance is common among Asian Americans, African Americans,
Mexican Americans, and Native Americans. 3