What Is Lactose Intolerance?
Lactose intolerance is inability to digest lactose (milk sugar) because of lactase deficiency. Lactase is an enzyme that breaks down lactose to glucose and galactose, which are normally completely absorbed from the small intestine into the blood. In lactose deficiency, undigested lactose causes bloating and diarrhea, mainly after dairy meals.
Types of Lactose Intolerance
a) The amount of enzyme lactase in some individuals tends to lower through the years from an unknown reason; symptoms of lactose intolerance typically appear in adolescence or early adulthood, but often not until old age. This is called primary lactose intolerance. Lactose intolerance in small children, especially under one year of age, is not common.
b) Inherited (recessive autosomal) lack of lactase is rare; in this case a baby has a diarrhea from birth.
c) In extensive intestinal inflammation (in infection, Crohn’s disease, celiac disease), production of lactase in the small intestine may be reduced so temporary lactose intolerance may occur. This is secondary lactose intolerance.
d) Surgical removal of a long part of the small intestine may cause permanent secondary lactose intolerance.
Symptoms of Lactose Intolerance
In individuals with lactase deficiency, ingested lactose, undigested in small intestine, reaches the colon where it is broken down by normal colonic bacteria, which produce gas, thus causing bloating and flatulence. Lactose also drags water into the bowel (by osmotic effect) thus causing diarrhea; symptoms appear in 30 minutes to 2 hours after the meal. Some lactose intolerant people can digest small amount of dairy products while others may not even try them without experiencing symptoms. Amount of lactose that affected person can digest decreases with his/her age.
Tests for Lactose Intolerance
a) Lactose-free diet trial. Complete cessation of symptoms after 2-3 days of lactose-free diet speaks for lactose intolerance.
b) Hydrogen breath test with lactosedetects an amount of hydrogen in expired air few hours after a lactose-rich meal. In lactase deficiency, undigested lactose travels toward the colon where normal colonic bacteria break it down and produce hydrogen – this is then absorbed into the blood and appears in exhaled air.
c) In lactose intolerance test, blood glucose level is checked after a lactose-rich meal. Normally (in the presence of enzyme lactase), lactose is broken into glucose and galactose, which both are absorbed into the blood, and increased level of glucose in the blood can be detected. In lactase deficiency, lactose is not broken down and glucose level in the blood doesn’t rise. This test is rarely performed today, though.
d) In infants, a stool acidity test reveals acidic stool when lactose is present in it.
Prevention and Treatment of Lactose Intolerance
Lactose intolerance, as a disorder, currently can be neither prevented nor treated.
Main lactose-containing foods are: all sorts of milk (cow’s, goat’s, sheep milk, breast milk, except non-real milk like soy milk, and lactose-free milk from which lactose was removed), yogurts, soft cheese (they are only traces of lactose in most hard cheeses), butter, ice-cream and products where milk is an ingredient: puddings, chocolates, pastries, cookies, etc.
Small amounts of milk in one meal may be tolerated and milk ingested together with other foods may be digested easier. Lactose-free milk also exists. Soy formula may be appropriate for infants, since it contains a lot of calcium. Other calcium reach foods include broccoli, okra, kale, collards, turnip greens, canned fish, almonds, calcium fortified soy milk, tofu or soybeans. People who are intolerant to even small amount of milk, should be aware that lactose may be found in some breads, cereals, instant foods, pre-prepared food mixes, margarine, salad dressings, candies, coffee creamers (even if labeled as non-diary), beers, cream liquors and products labeled as: “Dry milk solids”, “Whey”, “Curds”, “Milk by-products”, “Non-fat dry milk powder”, etc. Lactose in traces may be found in some drugs, supplements, over the counter products or contraceptive pills.
Enzyme lactase in capsules is available; capsules should be taken before the lactose-containing meal. Dairy food can be digested this way but this doesn’t seems to be an optimal solution.
Some probiotic yogurts or other probiotic products contain bacteria that synthesize lactase (should be denoted on the product label), which digests lactose in the product.
Some lactose intolerant individuals, especially children, may need calcium supplements since they may not get enough calcium from other foods.
- Fructose Malabsorption
- Small Intestinal Bacerial Overgrowth
- Tests in Food Allergies and Intolerances
- Low-FODMAP Diet – Foods to Avoid in IBS
- Lactose intolerance (aafp.org)
Article reviewed by Dr. Greg. Last updated on August 3, 2013