The function of lactase is to break down milk sugar into two simpler sugars, glucose and galactose, which are then absorbed into the bloodstream. Because the activity of lactase is generally low compared with that of other intestinal enzymes, lactose is digested slowly, which puts people at risk for lactose maldigestion. When insufficient enzymes exist to digest lactose in the diet, various unpleasant symptoms may result.
Intolerance Symptoms
Symptoms of lactose intolerance, including gas and bloating, abdominal cramps, nausea, and diarrhea, usually begin to appear 30 minutes to two hours after eating or drinking foods containing lactose. Their severity depends upon the amount of lactose ingested and the individual's tolerance level.
When undigested lactose enters the colon, it is fermented by bacterial flora, producing carbon dioxide and hydrogen and short chain organic acids. Fluid reabsorption is disrupted and the increased fluid load and products of bacterial fermentation cause the bloating, gas, abdominal cramping, and diarrhea. Watery diarrhea occurs when undigested lactose in the intestinal tract draws large amounts of fluid into the bowel. Not everyone deficient in lactase has these symptoms; however, those who do exhibit such symptoms are considered lactose intolerant. Perhaps as many as three-quarters of the world's population are affected. The good news is that lactose maldigestion does not appear to impair the absorption of any vitamin or mineral.
The Hydrogen Breath Test
Although lactose intolerance is quite common, tests for lactose maldigestion show that not everyone who claims to suffer symptoms of discomfort after drinking milk are true lactose maldigesters. The best way to measure lactose intolerance is to have a physician administer a hydrogen breath test to determine the amount of hydrogen in the breath after the consumption of a lactose-laden beverage. A person able to digest lactose has very little hydrogen in his or her breath. When a person is lactose intolerant, however, undigested lactose in the colon ferments to produce hydrogen, which is absorbed into the bloodstream and exhaled from the lungs. Therefore, the greater the level of hydrogen in an individual's expired air, the greater the level of lactose intolerance.
Milk Allergy is Different
Although the symptoms of lactose intolerance may be similar to those experienced by individuals with an allergy to cow milk protein, differences do exist. With an allergy, symptoms such as rhinitis and atopic dermatitis appear in addition to abdominal distress and gas. Cow milk allergy usually occurs in the first few months of life and may disappear by age three; lactose intolerance usually does not appear until age three or older.
What Causes Lactose Intolerance?
Lactose intolerance may result from one of three different conditions-congenital, primary, or secondary lactase deficiency. When babies are born with a lactase deficiency, they are unable to produce sufficient quantities of lactase from birth. This congenital lactase deficiency is very rare. Primary deficiency occurs when lactase activity declines early in childhood-after the age of two years. Children most likely to develop this condition are African Americans, American Indians, Latin Americans, and people of Asian and Mediterranean descent. Lactose intolerance is less prevalent among Caucasians of Northern European origin.
Among adults in North America, some measure of lactose maldigestion occurs in about one-fifth of whites, one-half of Hispanics, four-fifths of African Americans and Native Americans, and over 80 percent of Asian Americans. This primary lactase deficiency is usually not an absolute deficiency. Symptoms of lactose intolerance may be experienced depending upon certain conditions including the actual level of lactase possessed by a person and the amount of lactose consumed at one time.
Secondary lactase deficiency is a temporary condition caused by various factors that injure the intestinal lining that contains lactase. Infectious diarrhea, parasites, inflammatory bowel disease, celiac disease, allergy to milk protein, and some medications can harm the small intestine and reduce the amount of lactase produced. Because damaged cells can recover, the resulting lactose intolerance is only temporary. Secondary lactase deficiency is reversed when the damaging factor is removed.
Other Lactose Sources
Milk and other dairy products are not the only food sources that contain lactose. It is often added to prepared foods, sometimes in significant amounts. Food products that may contain lactose include: breads and other bakery products; candies and some snacks; processed breakfast cereals; instant potatoes; soups; sauces; breakfast drinks; margarine, mayonnaise, and salad dressings; and pancake mix, biscuits, cakes, and cookies.
Some products such as nondairy creamers and nondairy whipped toppings, which are often made with whey or dry milk solids and other ingredients derived from milk, may also contain lactose. Individuals who are intolerant to even small amounts of lactose must learn to carefully read food labels. Finally, lactose is used as a base for more than twenty percent of prescription drugs, six percent of over-the-counter medicines, and may also be used as a carrier for vitamin pills.
Alleviating Symptoms
Since symptoms can be controlled through diet, lactose intolerance is fairly easy to treat. Children and adults should reduce or try to completely avoid consumption of lactose-containing foods (see Lactose Levels sidebar, page 90). Individuals' tolerance levels differ and each person can learn by trial and error how much lactose they can handle.
Take Care to Avoid Deficiencies
Those who eliminate dairy products from their diet as a result of lactose intolerance may risk nutritional deficiency. For those on a plant-based diet, milk is a significant source of calcium, riboflavin, vitamin D, and vitamin B12. While yogurt, lowfat cheeses, and lactose-reduced milk can provide the calcium and vitamins supplied by milk, regular use of a soy beverage, fortified with calcium and the vitamins mentioned above, can protect against possible nutritional deficiencies and provide a safe nutritional alternative without any offending lactose.
Symptoms Vary According to Tolerance
Several factors can influence a person's tolerance to dairy foods:
The amount of lactose ingested at any given time
Many lactose intolerant individuals are able to consume small amounts of dairy products over the course of the day without suffering any pain. Lactose intolerant individuals can usually handle 3 to 6 ounces of milk without symptoms.
The type of dairy food consumed
Whole milk is better tolerated than skim milk, since the fat delays gastric emptying. Chocolate milk produces less symptoms than plain milk. Cheese and ice cream have less lactose than milk, and therefore cause fewer symptoms. Lactose intolerant individuals are often better able to handle aged cheeses-such as Swiss and cheddar-since they contain less lactose than softer cheeses. Cultured buttermilk appears no easier to tolerate than regular milk.
The presence of other food
If lactose-containing foods are eaten in conjunction with other foods, the chances of developing symptoms are diminished. For example, milk is better tolerated when consumed with a meal. The delayed gastric emptying that results from eating the meal allows more time for the lactase to digest the milk sugar.
Fermentation or presence of active cultures can help
Even though it can contain fairly large levels of lactose, yogurt with active cultures can be tolerated by many persons with lactose intolerance; plain yogurt seems to be better tolerated than fruit-flavored yogurt. The bacterial cultures in yogurt, Lactobacillus bulgaricus or Streptococcus thermophilus, appear to survive the enzymes of the stomach and intestinal tract and facilitate lactose digestion in humans by making their own ß-galactosidase, the enzyme needed to digest lactose.
The same does not hold true for frozen yogurt since the product is normally pasteurized before freezing, during which time it loses its ß-galactosidase activity. Manifestations of lactose intolerance are similar for ice cream and ice milk. Sweet acidophilus milk is normally not tolerated any better than regular milk. If they contain high concentrations of yogurt cultures, yogurt milk and sweet acidophilus milk are better tolerated than regular milk.
Help from lactose-digesting enzymes
Milk is better tolerated with less maldigestion when pretreated with LactAid, an enzyme that causes the lactose in the milk to be substantially "predigested" before consumption. The lactose is broken down to glucose and galactose before it reaches the body; this change makes for a sweeter product since the resulting sugars are sweeter than the original lactose. Lactose-reduced dairy products are available from regular supermarkets. Another alternative is an oral enzyme tablet, which can be swallowed before a meal containing dairy products.
Choose nondairy products
A large number of nondairy products are currently available as alternatives to dairy foods. Frozen desserts made from rice or soy milk can substitute for ice cream. Fortified soy and rice beverages, available in health food stores, can take the place of milk. Soy yogurt, nondairy toppings and cheese alternatives based upon soy protein or tofu are lactose-free, low in saturated fat, and have no cholesterol.
| Lactose Levels in Dairy Products | |
|---|---|
| (grams) | |
| 8 ozs. skim milk | 11-14 |
| 8 ozs. milk (whole, lowfat, or buttermilk) | 9-13 |
| 8 ozs. chocolate milk | 10-12 |
| 6 ozs. plain yogurt | 3-13 |
| 1/2 c. ice cream | 2-6 |
| 1/2 c. ice milk | 5 |
| 8 ozs. lactose-reduced, lowfat milk | 3 |
| 1/2 c. cottage cheese | 0.7-4 |
| 1 oz. processed cheese(Swiss, American, cheddar) | 0.5-4 |
| 1 tbsp. sour cream | 0.5 |
| 1 tbsp. whipping cream | 0.5 |
| 1 pat butter | 0.05 |
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