Encyclopedia of Health and Medicine

O
obesity The circumstance of weighing 20 percent
or greater in excess of ideal or healthy weight as a
consequence of excessive body fat. Doctors consider
a BODY MASS INDEX (BMI) of 30 to be the boundary
of obesity. In the 1990s health experts classified
obesity as a clinical diagnosis as well as an independent
risk factor for numerous health conditions,
including DIABETES, GALLBLADDER DISEASE,
HYPERTENSION (high BLOOD PRESSURE), ATHEROSCLERO-
SIS, HEART FAILURE, HORMONE-DRIVEN CANCERS of the
BREAST and PROSTATE GLAND, and CORONARY ARTERY
DISEASE (CAD). Obesity also interferes with INSULIN
sensitivity and with HEALING. Many researchers
believe obesity is as significant a risk factor as cigarette
smoking for CARDIOVASCULAR DISEASE (CVD).
Causes of Obesity
The simple cause of obesity is more intake than
outgo—energy from food consumed exceeds
energy expended through physical activity. However,
the circumstances that establish this imbalance
are complex. Lifestyle factors—EATING HABITS
and physical inactivity—are key causes of obesity.
The extent to which genetic factors influence obesity
remains unknown, though researchers have
identified gene-directed processes that regulate
many of the variables within the body responsible
for how the body uses and stores energy. Social,
cultural, emotional, and psychologic issues further
influence the development of obesity.
Genetic factors Researchers have discovered a
number of genes that regulate body functions
related to APPETITE and METABOLISM. One is the ob
GENE, which regulates the production of the HOR-
MONE leptin. Leptin suppresses the HUNGER,
appetite, and SATIETY centers in the HYPOTHALAMUS
and brainstem. Certain mutations of the ob gene
result in diminished sensitivity of the leptin receptors
to leptin, reducing leptin’s effectiveness.
Other mutations influence the production of leptin.
Leptin also influences the actions of another
protein, neuropeptide Y (NPY), that stimulates
appetite. Researchers believe mutations of the ob
gene predispose individuals to obesity because
appetite control mechanisms within the body do
not function properly. However, these mutations
do not unequivocally cause obesity.
Social and cultural influences Many people
who meet the diagnostic criteria for obesity do not
recognize that their weight has become a health
condition with serious consequences if untreated.
About two thirds of people who have obesity
identify themselves as such; one third perceive
themselves as overweight but not to an extent
that interferes with health or exceeds their ability
to manage by losing weight at will. There is a
social tendency to joke about excessive weight,
diminishing its significance as a health factor with
a corresponding cultural shift toward accommodating
larger body size.
Emotional and psychologic factors The reasons
people eat often have little to do with hunger or
nutritional need. Eating can provide a sense of
comfort during times of emotional stress. Overeating
is an eating disorder that often has complex
psychologic foundations related to issues of selfesteem,
control, or psychologic injury such as may
occur as a consequence of sexual, domestic, or
childhood abuse.
Symptoms and Diagnostic Path
The primary symptom of obesity is significantly
increased body size due to excessive body fat. The
diagnostic markers for obesity include
• BMI of 30 or greater
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