What is lactose intolerance, and why can some people tolerate milk products?
Lactose is milk sugar that cannot enter the bloodstream directly from the digestive tract. It must be broken down in the small intestine by an enzyme called lactase to form glucose and galactose before it can enter the bloodstream. If you don’t have enough lactase and thus the lactose is not digested properly, the undigested milk sugar moves into the large intestine, where it is consumed by bacteria that live in your digestive tract. There, the lactose can cause your gastrointestinal tract a lot of problems. It can pull water from the bloodstream into the gut and cause diarrhea. As the bacteria digest the lactose, they produce acids and gas that can cause bloating, cramping and flatulence. Because of heredity, about 75% of adults in the world have trouble digesting lactose. The exceptions are northern and some central Europeans, several people from Africa and some people from India. The remainder of the world’s population has difficulty digesting lactose. The National Institutes of Hea
