Lactose and Lactase, although they’re spelled almost the same, differ completely. But the interaction between them is very important. What are they? The last three letters of each word identifies for us what we need to know about the difference in these substances.
“ose,” the suffix in lactose, means sugar, eg. gluc-ose, sucr-ose, fruct-ose
“ase,” the suffix in lactase, means enzyme, eg. amyl-ase, polymer-ase, cholinester-ase
“lact” is the prefix that means milk, or dairy.
So, “lactose” is the sugar (a disaccharide) found in many dairy products and breast milk, and “lactase” is the enzyme produced by the cells lining the small intestine, whose function is to digest lactose. Lactose is the “main carbohydrate of mammalian milk.” Human breast milk is 7% lactose while cow’s milk is about 4.6%. “Lactose is often added to prepared foods,” such as bread, baked goods, breakfast cereals, pancakes, biscuits, cookies, lunch meats, salad dressings, candies, and other snacks.
“Lactose Intolerance,” then, is not a problem caused by lactose, itself, but instead is caused by an inadequate amount of lactase, the enzyme that digests lactose. Lactose intolerance should instead be called lactase deficiency, or insufficiency, because that term more aptly describes the abnormality present.
Lactase enzyme is produced by the cells of the “brush border,” or microvilli (microscopic finger-like projections), of the small intestinal lining. When milk, or other dairy products, are ingested, they pass through the stomach and duodenum into the jejunum, the second section of the small intestine. In the jejunum, the cells on the surface release lactase and it splits lactose into glucose and galactose, two monosaccharide sugars. If lactase enzymes are absent, lactose remains undigested and is not absorbed. In fact, if undigested, 75% of dietary lactose passes into the colon. Unabsorbed lactose attracts liquid in the intestine preventing it from being absorbed into the bloodstream. The intestine normally reabsorbs liquid, but when it doesn’t, the result is loose, watery bowel movements plus bloating, excessive gas, and abdominal pain.
Unabsorbed, undigested lactose then enters the colon and is “fermented” by bacteria, producing more gas. Bacteria further degrade lactose disaccharides into monosaccharides (simple sugars). Monosaccharides are not absorbed by the colon lining, either, so more loose watery stools and gas are produced. So if your GI tract is intolerant of dairy products, you’re really “lactase deficient” and not truly lactose intolerant. To confirm the diagnosis several tests are available to provide proof.
Most cases of lactose intolerance are diagnosed from the history provided by the patient and changes in their diet they make to prevent symptoms. A history of symptoms after ingesting dairy products only results in a presumptive diagnosis. That is accurate about 60% of the time. There are tests that will accurately detect lactase deficiency; the most reliable of these is the hydrogen breath test which is positive in 90% of patients with lactose intolerance.
The symptoms of lactose intolerance are similar to those of irritable bowel syndrome so the two are often confused. Also, lactose intolerance does not mean the patient is allergic to milk. “Milk allergy is related to the proteins in milk and not to lactose.” There is no medication specifically produced for treating lactose intolerance. The mainstay of treatment is the avoidance of ingesting lactose-containing foods, but abstinence works at the expense of reduced intake of calcium, vitamins A and D, riboflavin, and phosphorous. Thus, total avoidance of dairy products is not recommended. “Most people with lactose intolerance can tolerate up to 12 to 15 grams of lactose per day.” A patient, then, should only avoid foods that have a high rate of causing symptoms, and not avoid dairy products altogether. Supplemental calcium, vitamin D, and vitamins are recommended. “Patients with mild lactose intolerance may benefit from enzyme supplements containing lactase,” but this is not a substitute for dietary restriction.
Lactose intolerance/lactase deficiency is a troubling problem. It is limiting in that it determines what a patient can eat and sometimes where. Although it is largely genetically inherited, it can be the result of any external source that damages the microvilli in the lining of the jejunum. It “is present in up to 15% of persons of Northern European descent, up to 80% of blacks and Latinos, and up to 100% of American Indians and Asians.” Because they are symptomatic with dairy products, “a sizable number of adults believe they are lactose intolerant, but do not actually have lactase deficiency.” Diagnostic testing should be done for confirmation.
In researching this problem I looked into the lactose-free milk called Lactaid. Nowhere in the references that I used was Lactaid mentioned as milk alternative for lactase-deficient adults. It is, however, an option as long as it doesn’t cause symptoms itself.
Lactose intolerance/lactase deficiency is a fairly common problem, and it should be fairly easy to control as long as the patient is aware of foods containing lactose and is adherent to avoiding foods he/she knows will cause symptoms. I think a person suspected of lactose intolerance should have diagnostic testing to confirm the diagnosis, thus avoiding uncertainty. It is “academic,” but also good medicine to know you have it rather than just think you do.
References: Swagerty DL, Walling AD, Klein RM. Lactose Intolerance. Am Fam Phys 2002;65(9):1845-1851.
Szilagyi A, Ishayek N. Lactose Intolerance, Dairy Avoidance, and Treatment Options. Nutrients 2018;10:1994. www.mdpi.com/journal/nutrients
