Lactose Intolerance (cont.)
What are the symptoms of lactose intolerance?
The common symptoms of lactose intolerance are gastrointestinal, primarily,
abdominal pain, diarrhea ,
flatulence (passing
gas), and, less commonly, abdominal bloating, abdominal distention, and nausea. Unfortunately, these symptoms can be caused
by other gastrointestinal conditions or diseases, so the presence of these
symptoms is not very good at predicting whether a person has lactase deficiency or
lactose intolerance.
Symptoms occur because the unabsorbed lactose passes through the small
intestine and into the colon. In the colon, one type of normal bacterium contains
lactase and is able to split the lactose and use the resulting glucose and
galactose for its own purposes. Unfortunately, when they split the lactose into
glucose and galactose, these bacteria also release hydrogen gas. Some of the gas
is absorbed from the colon and into the body and is then expelled by the lungs
in the breath. Most of the hydrogen, however, is used up in the colon by
other types of bacteria. A small proportion of the hydrogen gas is expelled and
is responsible for the increased flatus (passing gas). Some people have an
additional type of bacterium in their colons that changes the hydrogen gas into
methane gas, and these people will excrete only methane or both hydrogen and
methane gas in their breath and flatus.
Not all of the lactose that reaches the colon is split
and used by colonic
bacteria. The unsplit lactose in the colon draws water into the colon (by
osmosis). This leads to loose, diarrheal stools.
The severity of the symptoms of lactose intolerance vary greatly from person
to person. One reason for this variability is that people have different amounts
of lactose in their diet; the more lactose in the diet, the more likely and
severe the symptoms. Another reason for the variability is that people have
differing severities of lactase deficiency, that is, they may have mildly,
moderately, or severely reduced amounts of lactase in their intestines. Thus,
small amounts of lactose will cause major symptoms in severely lactase deficient
people but only mild or no symptoms in mildly lactase deficient people. Finally,
people may have different responses to the same amount of lactose reaching the
colon. Whereas some may have mild or no symptoms, others may have moderate
symptoms. The reason for this is not clear but may relate to differences in
their intestinal bacteria.
Next: How are lactase deficiency and lactose intolerance diagnosed? »
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