Milk contains many nutrients, including carbohydrates, proteins, fats, vitamins and minerals. Sugar is a specific type of carbohydrate, and lactose is the primary source of sugar in milk. Lactose is a disaccharide, meaning it is composed of two smaller sugars, namely glucose and galactose. It is less soluble than the other types of dietary sugars and has about one-sixth the sweetness of pure glucose.
Lactose in Milk Products
Since lactose is naturally found in milk, it also is referred to as milk sugar. The lactose content of milk and milk products varies. Generally, milk has the most lactose, with about 9 to 14 g for a one-cup serving, although low-fat yogurt contains similar amounts. Ice cream and ice milk typically contain 7 to 10 g for a one-cup serving. Except for cottage cheese, which has 7 to 8 g in a 2 oz. serving, cheeses typically contain very little lactose.
Lactose in Other Foods
Lactose is found predominantly in milk and milk products, but occasionally it is used for brewing beer and also might be added to various foods and beverages. To determine if a particular food contains lactose, read ingredient lists. Other food that might contain lactose include whey, curds, cheese flavors, nonfat milk powder, nonfat milk solids, sweet or sour cream, buttermilk and malted milk.
In most mammals, the production of lactase, the enzyme that digests lactose, declines with age and a lack of dietary intake. Lactose intolerance is caused by a partial or total lack of lactase. Modern Nutrition in Health and Disease estimated that as much as 75 percent of the world's population is lactose intolerant.
Several tests exist for determining lactose tolerance. Direct measures include a small intestine biopsy or intestinal perfusion. Direct methods can be invasive and carry complications, so are seldom used. Indirect methods for assessing lactose tolerance include breath tests, blood tests, urine and fecal tests, and assessment of intolerance symptoms. The breath hydrogen test is most widely utilized. It is based on the assumption that lactose escapes digestion and becomes fermented in the large intestine, producing hydrogen gas.
Improving Lactose Intolerance
According to Dietitians of Canada, lactose tolerance might be improved through eating small amounts of foods with lactose foods daily. This can include eating lactose-containing foods as part of a meal, or drinking lactose-containing beverages, such as milk, with food. As little as 6 g of lactose a day, or one-half cup of milk or yogurt, can help to decrease symptoms. Interestingly, cold milk is frequently better tolerated than warm, and chocolate milk better than white.