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.
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.
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%