What is lactose intolerance?

Lactose intolerance, also known as lactose malabsorption, is a disorder that makes people unable to completely digest lactose—the sugar that is naturally present in all mammalian milk. Because of this, eating or drinking dairy products causes those who have lactose intolerance to have gas, bloating, nausea, and diarrhea.

Up to 65% of all humans have a reduced ability to digest lactose after infancy. It’s estimated that 30 to 50 million Americans have lactose intolerance—but it doesn’t affect all ethnic groups equally. The incidence of lactose intolerance is lowest in populations that have a long history of consuming milk products as a main food source. People of Northern European ancestry are least likely to suffer from it—with only 5% of the population being lactose intolerant—while up to 75% of Native Americans and 90% of East Asian have it. Lactose intolerance is also very common among those of Arab, Jewish, Greek, Italian, and West African descent.

Fermented dairy products are easier to digest, and many cultures that have high rates of lactose intolerance have long histories of consuming only fermented dairy products like yogurt—which are easier for the body to digest from a lactose perspective. As well, goat and sheep’s milk dairy products are often better tolerated by those with lactose intolerance than milk and cheese made from cow’s milk. Why? Goat and sheep’s milk both have shorter amino acid protein chains than cow’s milk, which may be easier to digest.

Awareness of the condition is on the rise, partly due to sufferers making adjustments to avoid the uncomfortable effects of this condition. According to TellTheChef, a service that facilitates pre-orders and group bookings for dining establishments, pre-orders of lactose-free restaurant meals rose by more than 7% in 2014.

There are three major types of lactose intolerance:

Primary lactose intolerance is the most common; it happens when people who had adequate amounts of lactase (a lactose-digesting enzyme produced by cells in the small intestine) in childhood begin producing less of it as they grow up. By the time they reach adulthood, they have trouble digesting milk products.

Secondary lactose intolerance happens when your small intestine cuts back on its lactase production due to surgery, an illness, or an injury. Treating the underlying cause may gradually reverse this.

Lastly, there’s a rare form called Congenital or developmental lactose intolerance—it’s when babies are born with no lactase at all, due to a genetic defect or to prematurity.