Lactose intolerance varies among ethnic groups. It is less common in people of Northern and Eastern European descent and more common in people from South America, Africa and Asia.

If a person catches a stomach virus that causes vomiting and diarrhea, he may become lactose-intolerant temporarily. This is why doctors commonly recommend a milk-free diet for a few days after someone gets the “stomach flu.”

The amount of lactose in milk products varies, which is why some foods cause upset while others do not:

• 8 ounces low-fat milk: 11 grams

• 4 ounces ice cream: 6 grams

• 8 ounces yogurt: 5 grams

• 4 ounces sour cream: 4 grams

• 4 ounces cottage cheese: 3 grams

• 4 ounces whipping cream: 3 grams

• 1 ounce American cheese: 1 gram

• 1 ounce cream cheese: 1 gram

• 1 teaspoon butter: trace

Lactose intolerance can be diagnosed with a procedure called the hydrogen breath test. This test usually requires a visit to a gastroenterologist’s office, so most pediatricians and family doctors make the diagnosis by determining if a patient’s symptoms resolve when lactose is removed from the diet. This could take a week or more, because the symptoms of lactose intolerance can be intermittent and do not always occur immediately after someone ingests milk products.

Howard Bennett