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 con-
sider a BODY MASS INDEX(BMI) of 30 to be the bound-
ary of obesity. In the 1990s health experts classified
obesity as a clinical diagnosis as well as an inde-
pendent risk factor for numerous health condi-
tions, including DIABETES, GALLBLADDER DISEASE,
HYPERTENSION(high BLOOD PRESSURE), ATHEROSCLERO-
SIS, HEART FAILURE, HORMONE-DRIVEN CANCERSof the
BREASTand 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 ciga-
rette 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. How-
ever, the circumstances that establish this imbal-
ance are complex. Lifestyle factors—EATING HABITS
and physical inactivity—are key causes of obesity.
The extent to which genetic factors influence obe-
sity 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 APPETITEand METABOLISM. One is the ob
GENE, which regulates the production of the HOR-
MONE leptin. Leptin suppresses the HUNGER,
appetite, and SATIETYcenters in the HYPOTHALAMUS
and brainstem. Certain mutations of the obgene
result in diminished sensitivity of the leptin recep-

tors to leptin, reducing leptin’s effectiveness.

Other mutations influence the production of lep-

tin. 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 accommo-

dating 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. Overeat-

ing is an eating disorder that often has complex

psychologic foundations related to issues of self-

esteem, 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

299