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Obesity
Obesity is the most common and most expensive nutritional
problem in the United States. A convenient and reliable indicator
of body fat is the
body weight (in kilograms) divided by the square of height (in
meters). Values above 25 are abnormal. Individuals with values
of 25–30 are overweight, and those with values > 30 are
obese. In the United States, 55% of the population are overweight
and 22% are obese. The incidence of obesity is also increasing
in other countries. Indeed, the Worldwatch Institute
has estimated that although starvation continues to be a
problem in many parts of the world, the number of overweight
people in the world is now as great as the number of
underfed. Obesity is a problem because of its complications.
It is associated with accelerated atherosclerosis and an increased
incidence of gallbladder and other diseases. Its association
with type 2 diabetes is especially striking. As weight
increases, insulin resistance increases and frank diabetes appears.
At least in some cases, glucose tolerance is restored
when weight is lost. In addition, the mortality rates from
many kinds of cancer are increased in obese individuals. The
causes of the high incidence of obesity in the general population
are probably multiple. Studies of twins raised apart show
a definite genetic component. It has been pointed out that
through much of human evolution, famines were common,
and mechanisms that permitted increased energy storage as
fat had survival value. Now, however, food is plentiful in many
countries, and the ability to gain and retain fat has become a
liability. As noted above, the fundamental cause of obesity is
still an excess of energy intake in food over energy expenditure.
If human volunteers are fed a fixed high-calorie diet,
some gain weight more rapidly than others, but the slower
weight gain is due to increased energy expenditure in the
form of small, fidgety movements
thermogenesis; NEAT).
slow but steady rate throughout adult life. Decreased physical
activity is undoubtedly a factor in this increase, but decreased
sensitivity to leptin may also play a role.
body mass index (BMI), which is(nonexercise activityBody weight generally increases at aDisorders of Iron Uptake
Iron deficiency causes anemia. Conversely, iron overload
causes hemosiderin to accumulate in the tissues, producing
hemosiderosis.
damage tissues, causing hemochromatosis. This syndrome
is characterized by pigmentation of the skin, pancreatic
damage with diabetes (“bronze diabetes"), cirrhosis of the
liver, a high incidence of hepatic carcinoma, and gonadal
atrophy. Hemochromatosis may be hereditary or acquired.
The most common cause of the hereditary forms is a mutated
Large amounts of hemosiderin canHFE
It is located on the short arm of chromosome 6 and is
closely linked to the human leukocyte antigen-A (HLA-A)
locus. It is still unknown precisely how mutations in
gene that is common in the Caucasian population.HFEcause hemochromatosis, but individuals who are homogenous
for
HFE mutations absorb excess amounts of iron becauseHFE
transporters that participate in iron uptake. If the abnormality
is diagnosed before excessive amounts of iron accumulate
in the tissues, life expectancy can be prolonged by
repeated withdrawal of blood. Acquired hemochromatosis
occurs when the iron-regulating system is overwhelmed by
excess iron loads due to chronic destruction of red blood
cells, liver disease, or repeated transfusions in diseases such
as intractable anemia.
normally inhibits expression of the duodenal