Susan couldn't help it. She and her friends began lunch with cheese. Then they ate cheeseburgers and drank milk. Things seemed fine, but then suddenly Susan's stomach started making noise. Her stomach hurt, and, racing to the restroom, she had terrible gas! She was so ashamed. She had been so excited to go to lunch with her friends that she totally forgot to watch how many dairy products (奶制品) she ate! Susan is lactose intolerant (乳糖不耐受的), and eating too many dairy foods can make her feel really sick.

    Lactose intolerance means that the body can't easily digest (消化) a special sugar called lactose. Unfortunately for Susan and millions of other people with this problem, lactose is found in almost all dairy products — cheese, milk and ice cream.

    Our body uses lactase (乳糖酵素) to break lactose into a simpler form of sugar. Once lactose is broken down, it's easy to digest and it provides great energy for the body. But people like Susan don't have enough lactase to break down all the lactose they take in. So, about half an hour to two hours after eating dairy­rich foods, their stomachs begin to hurt and they have gas, making their stomachs get bigger. Sometimes they even get diarrhea (腹泻) when they eat too many dairy foods.

    So how can someone living with this problem still eat out with his or her friends? Here are some tips. If you're going to eat a dairy­rich food like ice cream, eat something that doesn't have any dairy with it, like a salad or a sandwich without cheese. This will help slow digestion, and your body will have time to create more lactase.