Lactose intolerance stems from a deficiency of the enzyme lactase, which is needed to help digest lactose, a sugar in milk.
乳糖不耐症的病因是缺乏乳糖酶，这些乳糖酶是消化乳糖的必需物质，牛奶中的糖就属于此类。
2
Some people have trouble digesting lactose, a carbohydrate in milk and milk products, because of the deficiency of enzyme lactase in the body.
有些人无法消化乳糖，一种在牛奶和奶制品中的碳水化合物，这是因为在他们的身体中缺少乳糖消化酶。
3
What you're supposed to know: Milk (cow, goat, sheep, human . . .) contains a sugar called lactose, which is normally broken down by the enzyme lactase.