Lactose intolerance is a clinical condition that results from inadequate amounts of the lactase enzyme being available to break down lactose – the characteristic disaccharide in milk – into its component monosaccharides glucose and galactose. Lactose intolerance is therefore a type of food intolerance.
As a consequence of this relative deficiency in lactase enzyme (hypolactasia), lactose remains undigested, although some will subsequently be broken down by enzymes produced by bacteria lower down in the intestine. However, that process produces end products that include various organic acids and hydrogen. These acids, together with the water that is drawn into the intestine by the increased osmotic pressure of the excess lactose, cause the main symptoms: diarrhea, abdominal pain, bloating and excess flatulence. Perianal excoriation and vomiting may also occur 1-3.
Lactase is produced in the brush border cells of the small intestine. A deficiency of lactase can result from any condition that affects those cells, such as inflammatory bowel disease or gastroenteritis, in which case the deficiency is likely to be transient. Moreover, significant proportions of the world’s population have a genetic disposition to lose lactase activity at some time after infancy, making lactose intolerance much more likely.
What it is not
Although it is a form of food intolerance, this condition is not a food allergy, i.e. it has no immunological component, and therefore none of the laboratory findings (e.g. raised IgE) or allergic symptoms (such as rashes, wheezing, etc) seen in milk allergy 4.
Unfortunately it is all too common for the public to attribute any kind of discomfort (real or imagined) after consuming dairy products to “milk allergy”. This may result in unnecessary dietary restrictions leading to inadequate intake of calcium and other nutrients for which dairy foods make a major contribution in our diet.
People who remove dairy foods from their diet to treat lactose intolerance may be at increased risk of low bone mineral content and development of osteoporosis later in life5&6.
Another common misunderstanding is that low lactase necessarily equates to a clinical condition of lactose intolerance. However it is quite possible to have laboratory-proven low enzyme activity and lactose malabsorption without any clinical symptoms. And even those with some symptoms may be able to tolerate a reasonable amount of dairy food, particularly the lower lactose forms such as cheese and yogurt.
Source: The DairyAustralian
References
1. Joneja JV. Dietary management of food allergies and intolerances. 2nd ed. J.A.Hall Publications, Canada, 1998.
2. Casellas F. et al. Development, validation, and applicability of a symptoms questionnaire for lactose malabsorption screening. Dig Dis Sci. 2009 May;54(5):1059-65.
3. Poskitt EM. Nutritional problems of preschol children. In Sadler MJ et al. (eds.), Encyclopedia of human nutrition, Academic Press, NY, 1999.
4. Wüthrich B. [Food allergy, food intolerance or functional disorder?] Praxis (Bern 1994). 2009 Apr 1;98(7):375-87.
5. Di Stefano M. Lactose malabsorption and intolerance and peak bone mass. Gastroenterology. 2002; 122: 1793-9.
6. Matlik L et al. Perceived milk intolerance is related to bone mineral content in 10-to 13-year-old female adolescents. Pediatrics. 2007; 120(3): e669-77.