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The mechanism for excessive weight gain is clear-more
calories are consumed than the body burns, and the excess calories
are stored as fat (adipose) tissue. However, the exact cause is not
as clear and likely arises from a complex combination of factors.
Genetic factors significantly influence how the body regulates the
appetite and the rate at which it turns food into energy (metabolic
rate). Studies of adoptees confirm this relationship-the majority of
adoptees followed a pattern of weight gain that more closely
resembled that of their birth parents than their adoptive parents. A
genetic predisposition to weight gain, however, does not
automatically mean that a person will be obese. Eating habits and
patterns of physical activity also play a significant role in the
amount of weight a person gains. Recent studies have indicated that
the amount of fat in a person's diet may have a greater impact on
weight than the number of calories it contains. Carbohydrates like
cereals, breads, fruits, and vegetables and protein (fish, lean meat,
turkey breast, skim milk) are converted to fuel almost as soon as
they are consumed. Most fat calories are immediately stored in fat
cells, which add to the body's weight and girth as they expand and
multiply. A sedentary lifestyle, particularly prevalent in affluent
societies, such as in the United States, can contribute to weight
gain. Psychological factors, such as depression and low self-esteem
may, in some cases, also play a role in weight gain.
At what stage of life a person becomes obese can
effect his or her ability to lose weight. In childhood, excess
calories are converted into new fat cells (hyperplastic obesity),
while excess calories consumed in adulthood only serve to expand
existing fat cells (hypertrophic obesity). Since dieting and
exercise can only reduce the size of fat cells, not eliminate them,
persons who were obese as children can have great difficulty losing
weight, since they may have up to five times as many fat cells as
someone who became overweight as an adult.
Obesity can also be a side-effect of certain
disorders and conditions, including:
- Cushing's syndrome, a disorder involving the excessive release
of the hormone cortisol
- hypothyroidism, a condition caused by an underactive thyroid
gland
- neurologic disturbances, such as damage to the hypothalamus, a
structure located deep within the brain that helps regulate
appetite
- consumption of certain drugs, such as steroids or
antidepressants
The major symptoms of obesity are excessive
weight gain and the presence of large amounts of fatty tissue.
Obesity can also give rise to several secondary conditions,
including:
- arthritis and other orthopedic problems, such as lower back
pain.
- hernias
- heartburn
- adult-onset asthma.
- gum disease
- high cholesterol levels.
- gallstones
- high blood pressure
- menstrual irregularities or cessation of menstruation (amenorhhea)
- decreased fertility, and pregnancy complications
- shortness of breath that can be incapacitating
- sleep apnea and sleeping disorders
- skin disorders, arising from the bacterial breakdown of sweat
and cellular material in thick folds of skin or from increased
friction between folds
- emotional and social problems
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