Most mammals normally cease to produce lactase, becoming lactose intolerant, after weaning, but some human populations have developed lactase persistence, in which lactase production continues into adulthood. It is estimated that
- 75% of adults worldwide show some decrease in lactase activity during adulthood.
- 5% in northern Europe
- 71% for Sicily
- 90% in some African and Asian countries.
Lactose intolerance means the body cannot easily digest lactose, a type of natural sugar found in milk and dairy products. This is not the same thing as a food allergy to milk.
When lactose moves through the large intestine (colon) without being properly digested, it can cause uncomfortable symptoms such as gas, belly pain, and bloating. Some people who have lactose intolerance cannot digest any milk products. Others can eat or drink small amounts of milk products or certain types of milk products without problems.
Lactose intolerance is common in adults. It occurs more often in Native Americans and people of Asian, African, and South American descent than among people of European descent.
Lactose intolerance occurs when the small intestine does not make enough of an enzyme called lactase. Your body needs lactase to break down, or digest, lactose.
Lactose intolerance most commonly runs in families, and symptoms usually develop during the teen or adult years. Most people with this type of lactose intolerance can eat some milk or dairy products without problems.
Sometimes the small intestine stops making lactase after a short-term illness such as the stomach flu or as part of a lifelong disease such as cystic fibrosis. Or the small intestine sometimes stops making lactase after surgery to remove a part of the small intestine. In these cases, the problem can be either permanent or temporary.
Lactose intolerance, also called lactase deficiency and hypolactasia, is the inability to digest lactose, a sugar found in milk and to a lesser extent milk-derived dairy products. It is not a disorder as such, but a genetically-determined characteristic.
Lactose intolerant individuals have insufficient levels of lactase, an enzyme that catalyzes hydrolysis of lactose into glucose and galactose, in their digestive system.
In most cases this causes symptoms which may include
- abdominal bloating and cramps,
- borborygmi (rumbling stomach),
- vomiting after consuming significant amounts of lactose.
- Some studies have produced evidence that milk consumption by lactose intolerant individuals may be a significant cause of inflammatory bowel disease.
The severity of symptoms typically increases with the amount of lactose consumed; most lactose-intolerant people can tolerate a certain level of lactose in their diet without ill-effects.
Lactose is a water-soluble substance. Fat content and the curdling process affect tolerance of foods. After the curdling process, lactose is found in the water-based portion (along with whey and casein), but not in the fat-based portion. Dairy products that are “reduced-fat” or “fat-free” generally have slightly higher lactose content.
Low-fat dairy foods also often have various dairy derivatives, such as milk solids, added, increasing the lactose content.
typical lactose levels found in various foods.
Dairy product Serving size Lactose content Percentage Milk, regular 250 ml 12 g 4.80% Milk, reduced fat 250 ml 13 g 5.20% Yogurt, plain, regular 200 g 9 g 4.50% Yogurt, plain, low-fat 200 g 12 g 6.00% Cheddar cheese 30 g 0.02 g 0.07% Cottage cheese 30 g 0.1 g 0.33% Butter 1 tsp (5.9ml) 0.03 g 0.51% Ice cream 50 g 3 g 6.00%