Obesity
Medical Author: Ruchi Mathur, MD
Medical Editor: Dennis Lee, MD
What is obesity?
The definition of obesity varies depending on what one reads, but in general,
it is a chronic condition defined by an excess amount body fat. A certain amount
of body fat is necessary for storing energy, heat insulation, shock absorption,
and other functions. The normal amount of body fat (expressed as percentage of
body fat) is between 25-30% in women and 18-23% in men. Women with over 30% body
fat and men with over 25% body fat are considered obese.
How common is obesity?
Obesity has reached epidemic proportions in the United States. One in three
Americans is obese. Obesity is also increasing rapidly throughout the world, and
the incidence of obesity has nearly doubled form 1991 to 1998.
What are the health risks associated with obesity?
Obesity is not just a cosmetic consideration; it is a dire health dilemma
directly harmful to one's health. In the United States, roughly 300,000 deaths
per year are directly related to obesity, and more than 80% of these deaths are
in patients with a BMI (body mass index, which will be discussed later in this
article) over 30. Obesity also increases the risk of developing a number of
chronic diseases including:
- Insulin Resistance. Insulin is necessary for the transport of blood
glucose (sugar) into the cells of muscle and fat (which is then used for
energy). By transporting glucose into cells, insulin keeps the blood glucose
levels in the normal range. Insulin resistance (IR) is the condition whereby the
effectiveness of insulin in transporting glucose (sugar) into cells is
diminished. Fat cells are more insulin resistant than muscle cells; therefore,
one important cause of IR is obesity. The pancreas initially responds to IR by
producing more insulin. As long as the pancreas can produce enough insulin to
overcome this resistance, blood glucose levels remain normal. This IR state
(characterized by normal blood glucose levels and high insulin levels) can last
years. Once the pancreas can no longer keep up with producing high levels of
insulin, blood glucose levels begin to rise, resulting in type 2 diabetes, thus
IR is a pre-diabetes condition. In fact scientists now believe that the
atherosclerosis (hardening of the arteries) associated with diabetes likely
develops during this IR period.
- Type 2 (adult-onset) diabetes. The risk of type 2 diabetes increases with
the degree and duration of obesity. Type 2 diabetes is associated with central
obesity; a person with central obesity has excess fat around his/her waist, so
that the body is shaped like an apple.
- High blood pressure (hypertension). Hypertension is common among obese
adults. A Norwegian study showed that weight gain tended to increase blood
pressure in women more significantly than in men. The risk of developing high
blood pressure is also higher in obese people who are apple shaped (central
obesity) than in people who are pear shaped (fat distribution mainly in hips and
thighs).
- High cholesterol (hypercholesterolemia)
- Stroke (cerebrovascular accident or CVA)
- Heart attack. The Nurses Health Study found that the risk of developing
coronary artery disease increased 3 to 4 times in women who had a BMI greater
than 29. A Finnish study showed that for every one kilogram (2.2 pounds)
increase in body weight, the risk of death from coronary artery disease
increased by one percent. In patients who have already had a heart attack,
obesity is associated with an increased likelihood of a second heart attack.
- Cancer. While not conclusively proven, some observational studies have
linked obesity to cancer of the colon in men and women, cancer of the rectum and
prostate in men, and cancer of the gallbladder and uterus in women. Obesity may
also be associated with breast cancer, particularly in postmenopausal women. Fat
tissue is important in the production of estrogen, and prolonged exposure to
high levels of estrogen increases the risk of breast cancer.
- Osteoarthritis (degenerative arthritis) of the knees, hips, and the lower
back
- Pickwickian syndrome (obesity, red face, underventilation, and drowsiness)
Next: What causes obesity? »
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Last Editorial Review: 7/22/2003
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