Lactose intolerance is an intolerance to milk due to an inability to digest the sugar lactose. This is caused by inadequate production of the digestive enzyme lactase, and commonly results in severe abdominal pain, gas, and diarrhea.

Lactose is found in most types of milk, especially cow and human milk. Most infants and small children have higher levels of lactase than adults to aid in digesting their primary food, breast milk, and therefore lactose intolerance (LI) is most likely after a child reaches four to five years of age, although it may appear much later in life. Most adults have some degree of LI: Asian, native Australian, and many African populations tend to become intolerant as they get older, while European, Arabian, and East African populations are less likely to be LI*. (This is an excellent example of microevolution in humans; those populations that relied heavily on milk for centuries have slowly developed to retain the lactase into adulthood.)

Symptoms of LI may include abdominal bloating, excessive intestinal gas, nausea, weight loss, diarrhea, and abdominal cramping. LI may result in intestinal diseases such as celiac sprue and gastroenteritis. There is no cure, except to stop drinking cow milk and eating milk byproducts such as cheese and ice cream.

LI can be managed without eliminating milk entirely. There are dairy products that have been treated to 'pre-digest' the lactase; lactose free milk is commonly available in most grocery stores. Many LI individuals can handle lactase at low levels, particularly when eaten with other foods. Some dairy products, such as yogurt and kefir are naturally low in lactose, as the bacteria that work to curdle them feed on the lactase. Other types of milk, such as goat milk, are also naturally low in lactase.

Africans (as a whole): 10-30% retain lactase into adulthood.
Orientals: 0-30% retain lactase into adulthood.
Northern Europeans: 80% retain lactase into adulthood.
Haviland, 1994, Anthropology

This is almost certainly due to centuries of Europeans drinking fresh milk. Other cultures that traditionally sour their milk (or did not raise cattle) did not need to evolve to extend their lactase production into adulthood, as the souring process reduces lactose.

Lactose intolerance is the norm for almost all adult mammals. There is no "cure", because there's really nothing wrong with you to begin with. Lactose intolerance is the inability to cleave a lactose molecule into galactose and glucose. This causes all sorts of problems, from getting diarrhea to extreme bloating and abdominal pain after drinking milk or eating dairy products containing lactose. This is because when the sugar lactose is not digested properly, it lines the colon and ferments via all your little large intestine bacteria buddies. The assertation stated a few writeups below that the initial discomfort experienced after lactose ingestion is due to the displacement of water into your gut would account for diarrhea, but not the massive amounts of gas I seem to get about 20 minutes after eating anything with cream or butter in it.

Mammals usually begin losing their ability to process lactose at or near puberty. OR EARLIER! Baby mammals do need the ability to process lactose when they are young and breast-feeding. Personally I didn't feel the effects of being lactose intolerant til around age 13-14. It's not a big deal in my culture to be lactose intolerant because adults don't usually drink milk, eat cheese (our mice don't even eat cheese :P), cream or yogurt. But here in America, cheese and friends are everywhere.

Some people adjust to this inability to produce lactase, the enzyme that cleaves lactose, by taking lactase pills. From personal experience, this didn't work very well. I spent Christmas over at my very mid-western American in-laws place... and I had massive gas attacks from their food day and night for my entire stay. I was chewing those lactase pills maybe 6-8 pills (that's over a gram's worth of pills) per meal. Maybe there's something else in the food that I couldn't digest either... or I hadn't taken the stoichiometric equivilent of the lactose I was ingesting.

Others opt for drinking soymilk rather than regular ole cow milk. (I am not insinuating that soymilk is milk. Soymilk is pressed/ground soaked soy bean liquid, and if you actually thought soymilk is milk from soy cows, you oughtta go whack yourself good on the head. I suggest soymilk as a substitute because I for one don't enjoy eating cereal with water, prune juice, punch, etc. It's just not the same to dip my cookies in something like, say, lemonade rather than milk. Soymilk at least *looks* somewhat like milk and does contain some calcium (~10mg/cup).) Cow milk, after all, is for baby cows, is it not? On the other hand, yogurt is safe because it comes predigested. The bacteria in yogurt take over for the missing enzyme and digest much of the milk sugar for you. The yogurt has to have live bacterial cultures; killed bacteria do not work. Buttermilk, although fermented, still cause as much distress in most people as plain milk. Also beware of frozen yogurt. When yogurt is commercially frozen, it is sometimes re-pasteurized, and this kills the bacteria that are helping you digest lactose.

With this in mind, it’s probably not a good idea to feed your pet cat any more milk unless you want to stink up the house!
Like kamalian writes, this is a problem for cats.

But ! Whiskas, the famous cat food manufacturer, has identified this problem, and therefore produce and $ell "Whiskas Cat Milk" in small expensive tetra pak containers.

A better alternative to this would of course be

  • Low lactose cow milk - which is available in most stores
  • Water with a little cream in it
The latter is what I give my kitty, and he thinks it's gRRRReat!

There are so many misconceptions about lactose intolerance. This node is partially in response to errors in the previous nodes.

"Lactose is found in cow milk". Well, yes it is, it is also found in varying amounts in all other milks from all other mammals. We are just used to drinking cows' milk so we tend to limit our thinking to the familiar.

"LI may result in intestinal diseases such as celiac sprue". Celiac Sprue may co-exist with lactose intolerance but doesn't result from it. They are both malabsorption syndromes but a celiac individual can't tolerate gluten (the protein in wheat and rye and to a lesser degree in oats and barley) while the lactose intolerant individual can't tolerate lactose (the sugar found in milk).

"This is because when the sugar lactose is not digested properly, it lines the colon and ferments." Well, again, yes - sort of... The immediate distress is because of osmosis. When lactose remains intact in the gut, water moves across the membranes to dilute it, causing the sudden distress the lactose intolerant individual feels. Fermentation also happens, but more slowly.

"Mammals usually begin losing their ability to process lactose at or near puberty." OR EARLIER

Soy milk is not really a milk (product of the secretion of a mammary gland of a mammal) and does not contain lactose. In fact, lactose is not found in any other substance other than mammalian milk.

In reference to kittens becoming lactose intolerant as adult cats, yes they do. But the suggestion that they be fed "Low lactose human milk - which is available in most stores" is amusing. Of course the author meant cows' milk with lactase added to it that many humans drink and not human milk which is breastmilk and not yet available in most stores.

Human milk has more lactose than any other mammalian milk. Human infants use lactose to great advantage and are almost never lactose intolerant. Lactose intolerance is something that happens past the natural age of weaning not in infancy. A baby whose parent is lactose intolerant may become lactose intolerant as a young child, adolescent or adult but will not be lactose intolerant as an infant. The infants who are lactose intolerant are very rare and consist of very early premature babies as well as any gestational age infant who has had a bout of gastroenteritis and may have sustained injury to the brush border of the bowel where lactase is produced. Even in these cases the intolerance is often just partial and almost always is outgrown in a matter or weeks. Infants who are lactose intolerant without cause are so rare as to be almost non-existent. True primary lactose intolerance in infancy would not have been compatible with life (outside of the modern world) when lactose free alternatives to breastfeeding did not exist.

Formula companies have recently begun marketing an infant formula based on cows' milk that has no lactose. It is directed at the almost non existent "lactose intolerant infant". This is simply a marketing ploy. It should be used only rarely in the situations mentioned above but I see many parents requesting it for their normal infants because they, the parents, are lactose intolerant. This is silly and probably dangerous. Anything that we evolved to expect should not be removed arbitrarily from an infant's diet.

Growing on lactose is normal for human infants.

Darn, the earlier reference to "Low lactose human milk - which is available in most stores" was changed. It is now more accurate but I enjoyed the giggle. I also find it illuminating that well intentioned folks think of cows' milk in this way...but then I'm odd in my obsessive observation of all things related to lactation.

I've figured out ways to drink or eat dairy without getting sick. Regular milk tears me up but chocolate milk doesn't. If I have a glass of milk with breakfast I have to finish my milk before I finish my meal. As for cheese, the longer its aged the less lactose it has in it. I can't drink milk even the day before it goes bad or ill be sick. A milkshake will give me gas for 2 days but a scoop of ice cream with my cake is fine. There's ways to get around it. It just takes a while to figure them all out.

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