Lactose intolerance is the name given to the condition in which lactase, an enzyme needed for proper metabolization of lactose, is not produced in adulthood.
Symptoms and signs
Without lactase, the lactose in milk remains uncleaved and unabsorbed,
and instead gut bacteria metabolize it, producing copious amounts of
gas by fermentation. This causes a range of unpleasant abdominal
symptoms, including stomach cramps, flatulence and diarrhea. Like
other unabsorbed sugars, e.g. mannitol, the lactose raises the osmotic
pressure of the colon contents, preventing the colon from resorbing
water and hence causing a laxative effect to add to the excessive gas
One solution to this problem (other than avoiding milk) is
lactose-free milk, which is produced by passing milk over lactase
enzyme bound to an inert carrier: once the molecule is cleaved, there
are no lactose ill-effects, whatever the milk drinker's ancestry. The
milk sold for pet cats is another example of lactose reduced milk.
Cats have a very short generation time compared to humans, and have
been around people since animal husbandry began, so it would not be
surprising if at least some cats have made a similar adaptation to
dietary lactose, but not every cat has European ancestry - some of the
oriental breeds are particularly sensitive to lactose.
In recent years (1990-2000) there has been an increase in the number
of lactose-reduced and lactose-free dairy products. Some of these
products are cottage cheese, American cheese and ice cream. These
products are made using milk-substitutes such as soy milk, almond
milk, or rice milk. Another recent solution has been a pill which
artificially provides the missing enzyme, allowing a person to
tolerate milk products for a period of a few hours after taking the
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