Encyclopedia of Diets - A Guide to Health and Nutrition

lactase. In a few people, they do not make any at all.

When people do not make enough lactase, they cannot

digest some portion of the lactose they have eaten.

Lactose that is not broken down cannot be absorbed

into the blood. Instead, it remains in the large intestine

(colon) where bacteria convert it into lactic acid. Lactic

acid is a laxative and an irritant to the colon.

Symptoms of lactose intolerance include nausea,

bloating, abdominal pain or cramps, abundant gas,

and diarrhea. These symptoms usually begin any-

where from 30 minutes to 2 hours after eating a food

that contains lactose. Symptoms of lactose intolerance

can be uncomfortable enough to temporarily interfere

with daily activities, however, they do not harm the

digestive system and lactose intolerance does not prog-

ress to any other disease or disorder.

Lactose intolerance is an extremely common con-

dition. It rarely develops before age six, and is due to a

genetically programmed decline in lactase. This

decline begins around age two, the age when most

infants have finished the transition from breast milk

to solid food. In some people this decline continues to

the point where in late childhood or early adulthood

they develop lactose intolerance symptoms. Lactose

intolerance is strongly linked to race and ethnicity.

People of Northern European ancestry have the low-

est rate of lactose intolerance, about 5% In Hispanic,

Jewish, and Southern European populations, the rate

is about 70%, and it reaches 90% or more in Asian

and African populations. Worldwide, in adults the

inability to digest lactose is much more common

than the ability to digest it. Although the symptoms

are similar, lactose intolerance is not the same as cow’s

milk intolerance. Cow’s milk intolerance is a food

allergy and causes an allergic reaction. Only about

3.4% of Americans have cow’s milk intolerance.

The degree to which people are lactose intolerant

varies widely. Some people can drink a glass of milk

daily without developing unpleasant symptoms.

Others can drink only small amounts of milk at a

time, and have fewer symptoms if milk is mixed with

food. Some people can eat cheese, ice cream, or

yogurt, but cannot drink milk. A few people are

100% lactose intolerant and even the smallest amount

of lactose will produce unpleasant symptoms.

Although the greatest quantities of lactose are

found in milk and dairy products, milk is used in the

preparation of many processed foods such as choco-

late bars, puddings, and soups. Food labels must list

all the ingredients in processed foods. Lactose intoler-

ant individuals should look for these words on the

label that indicate the presence of lactose: milk, con-

densed milk, whey, curds, milk-by-products, dry milk

solids.

Lactose is found in other unlikely places such as:

bread and baked goods and biscuit, pancake, and

cookie mixes

processed breakfast cereals and breakfast drinks

instant mashed potatoes

lunch meats (except kosher meats which are lac-

tose-free)

salad dressings

all chocolate candies, caramels, butterscotch, and

many others

as filler in medications. As many as 6% of prescrip-

tion and over-the-counter drugs contain lactose.

The amount of lactose found in these hidden sour-

ces is not enough to affect most people, but for the

severely lactose intolerant, it can be enough to cause

symptoms and make meal planning a necessity and

eating out difficult.

Many individuals diagnose themselves as lactose

intolerant using an elimination diet. However people

Calcium and lactose in common foods

Calcium Lactose

Foods content (mg) content(g)

Soymilk, fortified, 1 cup

Sardines, with edible bones, 3 oz.

Salmon, canned, with edible bones, 3 oz.

Broccoli, raw, 1 cup

Orange, 1 medium

Pinto beans, ½ cup

Tuna, canned, 3 oz.

Lettuce greens, ½ cup

Dairy products

Yogurt, plain, low-fat, 1 cup

Milk, reduced fat, 1 cup

Swiss cheese, 1 oz.

Ice cream, ½ cup

Cottage cheese, ½ cup

200–300

270

205

90

50

40

10

10

415

295

270

85

75

0 0 0 0 0 0 0 0 5

11

1

6

2–3

SOURCE: National Institute of Diabetes and Digestive and Kidney

Diseases, National Institutes of Health, U.S. Department of

Health and Human Services

(Illustration by GGS Information Services/Thomson Gale.)

KEY TERMS

Enzyme—a protein that change the rate of a chem-

ical reaction within the body without themselves

being used up in the reaction

Lactose intolerance diet