Lactose is the primary carbohydrate in milk. Cow's milk contains 4-5% lactose, whereas human milk contains almost twice that amount. Lactose provides 30-50% of the energy in milk, depending on the fat content (skim vs. homogenized). A number of individuals are affected by lactose in the diet, but there is a difference between intolerance and maldigestion.

Lactose maldigestion is "a disorder characterized by reduced digestion of lactose due to the low availability of the enzyme lactase." Lactose intolerance is "the term for gastointestinal symptoms (flatulence, bloating, abdominal pain, diarrhea, and 'rumbling in the bowel') resulting from the consumption of more lactose than can be digested with available lactase." In other words, intolerance refers to the symptoms of the maldigestive disorder caused by an insufficient enzyme required to hydrolyze lactose to galactose and glucose.

Genetic defects often cause a deficiency of lactase, as well as injuries to the mucosa lining of the intestines or with age (as we age our enzyme levels decrease). When lactose molecules remain in the intestine undigested, they absorb water and this can cause bloating, discomfort, cramping, diarrhea, and nausea. Bacterial fermentation along the intestinal tract that produces lactic acid and gas is also a characteristic of lactose intolerance.

It is estimated that one in three adults suffer from lactose maldigestion and it appears to be inherited in about 80% of the world's population, including most Greeks, Asians, and Africans.

Those who suffer from any discomfort after eating or drinking milk products can consume foods labeled lactose free or take an enzyme preparation such as Lact-Aid to aid digestion. Do note, however, that lactose intolerance varies and the amount of lactose allowed in a diet depends on an individual's tolerance. Some people cannot tolerate milk, ice cream, or creamed foods, but they can eat aged cheeses and yogurt (some brands are better tolerated than others) without difficulty. Lactose products include:

Grain Products: Breads and muffins made with milk, pancakes, and waffles; cake or cookie mixes, pie crusts made from butter or margarine, French toast, some dry cereals, and biscuits.

Fruits and Vegetables: Canned and frozen fruits or vegetables processed with lactose, buttered, creamed, or breaded vegetables.

Milk and Milk Products: Milk (dried, evaporated, nonfat, and whole), yogurt, ice cream, sherbet, cheese, custard, puddings, and whey and casein proteins manufactured with lactobacillus/acidophilus culture.

Meat and Meat Alternatives: Meats, fish, or poultry creamed or breaded, sausage and other cold cuts containing nonfat-milk solids, some peanut butter, and omelets and souffl?s containing milk.

Other: Instant coffees, margarine, dressings, sugar substitutes containing lactose, toffee, chocolate, creamed soups, butter, cream, some cocoas, caramels, chewing gum, some vitamin-mineral supplements, some drugs, peppermint, and butterscotch.

Since calcium is a major component of many lactose-containing foods, it is vital that individuals who are lactose-intolerant receive adequate calcium from other foods (in fact, milk is not an ideal source of calcium, as will be discussed in Chapter Seven). These include almonds, brazil nuts, caviar, kelp, canned salmon, canned sardines, shrimp, soybeans, and turnip greens, broccoli, strawberries, and leafy greens. Leafy greens are currently under suspicion as a viable calcium source since greens are now believed to contain certain calcium binding agents that prevent calcium absorption.

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Brian D. Johnston is the Director of Education and President of the I.A.R.T. fitness certification and education institute. He has written over 12 books and is a contributing author to the Merck Medical Manual. An international lecturer, Mr. Johnston wears many hats in the fitness and health industries, and can be reached at info@ExerciseCertification.com. Visit his site at http://www.ExerciseCertification.com for more free articles.