Encyclopedia of Health and Medicine

L–M
lactose intolerance The inability to digest lactose,
a disaccharide sugar in milk and other dairy
products. Lactose intolerance occurs because of a
deficiency of the enzyme lactase, which is necessary
to break down lactose into simpler sugar molecules.
It is the most common form of
CARBOHYDRATE INTOLERANCE, affecting an estimated
50 million Americans. Lactose intolerance may be
congenital (present at birth), occur as a consequence
of a disease process that affects the cells
that produce lactase (such as CELIAC DISEASE), or
develop with aging as the number of lactase-producing
cells naturally declines.
Congenital lactose intolerance becomes apparent
when a young child begins drinking cow’s
milk, which is high in lactose. The doctor can usually
confirm the diagnosis with a lactose challenge
test in which the child drinks a solution that contains
lactose. Breath samples taken at certain
intervals allow measurement of hydrogen, which
increases when lactose remains undigested in the
gastrointestinal tract.
Switching to a fortified SOY formula nearly
always eliminates symptoms when the child is
young. As the child grows older, trial and error
will tell whether he or she can eat small amounts
of other dairy products such as cheese and ice
cream. Many people who have lactose intolerance
produce enough lactase to digest small amounts of
lactose. Lactase enzymes are available without a
doctor’s prescription; added to milk, they act on
the lactose to split it into its composite sugars.
Within 24 hours the milk will be 70 to 90 percent
lactose-free. This approach allows the child to
benefit from the numerous NUTRIENTS milk and
dairy products provide. Lactose intolerance generally
does not affect an individual’s overall general
health, as long as the person acquires necessary
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nutrients through alternative foods or via supplements.
See also AGING, NUTRITION AND DIETARY CHANGES
THAT OCCUR WITH.
malnutrition A state of multiple nutrient depletion
that alters body functions. Infants, the elderly,
and people who have active cancer, ALCOHOLISM,
OBESITY, or chronic health conditions are most susceptible
to malnutrition. Malnutrition may
develop when a person does not eat enough food,
eats a very narrow selection of foods, or eats too
much food. Malnutrition is possible with extended
adherence to fad diets that limit food types and
when the diet primarily contains foods that have
low NUTRIENT DENSITY such as “junk” foods. The
most severe presentations of malnutrition are the
polar extremes of STARVATION and obesity.
In the United States malnutrition resulting
from inadequate food or nutrient consumption
occurs most often in the chronically ill, the very
young, and the very old. Most people who have
significant obesity have some degree of nutrient
imbalance, not only among the energy NUTRIENTS
but also of vitamins, minerals, and other micronutrients.
People who have alcoholism, serious
chronic health conditions such as HIV/AIDS, or gastrointestinal
MALABSORPTION disorders including
INFLAMMATORY BOWEL DISEASE (IBD) and CELIAC DIS-
EASE or are also vulnerable to malnutrition.
Symptoms and Diagnostic Path
Early malnutrition can be difficult to detect
though initial indications may include dry SKIN,
pallor, swollen or bleeding gums, PETECHIAE (pinpoint
hemorrhages under the skin), MUSCLE weakness
and atrophy, and disturbances of sensory
perception (PARESTHESIA) in both inadequate and