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Digestive Disorders

From the Current Issue

Living With Lactose Intolerance
Difficulty digesting dairy products is a surprisingly common problem that can be addressed with careful attention to one’s diet.

Although dairy products are ubiquitous in the Western diet (and a common source of calcium), a large portion of the population has at least some difficulty digesting milk and foods made with milk. In fact, this condition—called lactose intolerance—affects up to 50 million Americans. But its extent varies widely by race and ethnicity. People of Northern European descent are affected less frequently than blacks, American Indians, and Asian-Americans.

Lactose intolerance comes in degrees, and many people who have difficulty digesting lactose can still consume small amounts of dairy products—such as milk, yogurt, and cheese—without experiencing undue symptoms. However, some people are severely lactose intolerant and need to eliminate dairy completely from their diet.

What Is Lactose Intolerance?

Lactose intolerance is a deficiency of the enzyme lactase, which is responsible for the digestion of lactose, the major sugar in milk. (Milk and all products made from milk contain lactose.) Normally lactase, which is produced in the lining of the small intestine, breaks down lactose into the simpler sugars glucose and galactose. The liver then converts galactose into glucose, which enters the bloodstream and is used by cells as an energy source. Most people with lactose intolerance do not have enough lactase to digest lactose properly.

In many people, the ability to digest lactose declines with age. They begin to produce less lactase after age two but usually experience no symptoms. As some people age, however, the inability of the small intestine to produce a sufficient amount of lactase to break down lactose can start to cause symptoms: As lactose enters the colon, bacteria use it to form gases and other products that can result in the classic manifestations of lactose intolerance—gas, bloating, crampy abdominal pain, and diarrhea.

Diagnosing Lactose Intolerance

Lactose intolerance usually develops slowly, and the symptoms associated with it can have other causes. If you think you are lactose intolerant, you can first check for it on your own. Try excluding all dairy products from your diet for about three days; if drinking a glass of milk after this period causes symptoms, you may be lactose intolerant.

Your doctor can confirm a diagnosis of lactose intolerance by taking a medical history and discussing with you the results of your dietary manipulations. If necessary, the doctor can run a blood or breath test to confirm the diagnosis.

Dealing With Lactose Intolerance

The amount of lactose that lactose-intolerant people can handle varies widely; some experimentation should help you determine what you can eat. In most cases, dairy products don’t have to be avoided. Yogurt and aged cheeses, for example, may be well tolerated because they contain lactase-producing bacteria that lower their lactose content. A cup of milk per day, particularly when consumed with other foods, may be possible for many people who are lactose intolerant. And recent studies have suggested that gradually increasing the amount of lactose in your diet may help improve your tolerance.

In addition, various digestive aids are available to help people consume lactose better. For example, the addition of lactase-containing drops to milk can convert 75% to 90% of the lactose to glucose and galactose after overnight refrigeration. Specialty milks are also available that have lactase added during the manufacturing process to reduce significantly the amount of lactose in them. And tablet forms of lactase can also be taken with dairy products, but be aware that these products vary in their ability to reduce symptoms and may not entirely relieve the effects of lactose intolerance. Your doctor can advise you on which ones to use.

People with severe lactose intolerance should try to remove not only obvious sources of lactose—such as milk, yogurt, and cheese—but also “hidden” sources from their diet. These sources include some baked goods, processed breakfast cereals, salad dressings, mashed potatoes, candies, soups, and even medications and vitamins. The ingredients “milk,” “whey,” or “curds” on a product label indicate that the product contains lactose.

Getting Enough Calcium

Because they tend to eat less dairy than others, people with lactose intolerance often have low calcium intakes, which can lead to weakened bones and osteoporosis. Therefore, they often need to get their calcium from other sources. Nondairy foods that are high in calcium include green vegetables (including broccoli, collard greens, turnip greens, and kale) and fish with soft, edible bones (such as sardines and salmon). Calcium-fortified foods and drinks such as cereal, tofu, oatmeal, orange juice, and soy milk are also excellent sources. People who restrict their dairy intake will probably need to take a calcium supplement. The recommended daily intake for calcium is 1,000 mg (1,200 mg for people over age 50). Because the body cannot absorb more than 600 mg of calcium at one time, divide any amount larger than that into two doses. It’s also best to take calcium supplements with food; stomach acid, as well as other nutrients, enhances the absorption of calcium.


 


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2005
WHITE PAPERS
Digestive Disorders

The Digestive Disorders White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.

 

 

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