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An excess of subcutaneous fat in proportion to lean body mass. Excess fat accumulation is associated with increase in the size (hypertrophy) as well as the number (hyperplasia) of adipose tissue cells. O. is variously defined in terms of absolute weight, weight-height ratio, distribution of subcutaneous fat, and societal and esthetic norms. Measures of weight in proportion to height include relative weight (RW, body weight divided by median desirable weight for a person of the same height and medium frame according to actuarial tables), body mass index (BMI, kg/m2) and ponderal index (kg/m3). These do not differentiate between excess adiposity and increased lean body mass. In contrast, subscapular and triceps skinfold measurements and determination of the waist-to-hip ratio help define the regional deposition of fat and differentiate the more medically significant central o. from peripheral o. in adults. No single cause can explain all cases of o.. Ultimately it results from an imbalance between energy intake and energy expenditure. While faulty eating habits related to failure of normal satiety feedback mechanisms may be responsible for some cases, many obese persons neither consume more calories nor eat different proportions of foodstuffs than nonobese persons. Contrary to popular belief, o. is not caused by disorders of pituitary, thyroid, or adrenal gland metabolism. However, it is often associated with hyperinsulinism and relative insulin resistance. Studies of obese twins strongly suggest the presence of genetic influences on resting metabolic rate, feeding behavior, changes in energy expenditures in response to overfeeding, lipoprotein lipase activity, and basal rate of lipolysis. Environmental factors associated with o. include socioeconomic status, race, region of residence, season, urban living, and being part of a smaller family. The prevalence of o. is greater when weight is measured during winter rather than summer. O. is much commoner in the northeastern and midwestern U.S. than in the south and west, a phenomenon independent of race, population density, and season. SYN: adiposity (1), corpulence, corpulency. [L. obesus, pp. of obedo, to eat up, + -ity] O. is a major public health problem and the leading nutritional disorder in the U.S. A widely accepted definition of o. is body weight that is 20% or more in excess of ideal weight-for-height according to actuarial tables. By this definition, 34% of adults in the U.S. are obese, and there is evidence that the prevalence of o. is increasing in both children and adults. The National Institutes of Health have defined o. as a BMI of 30 kg/m2 or more, and overweight as a BMI between 25–30 kg/m2. By these criteria, 55% of adults are either overweight or obese. O. is an independent risk factor for hypertension, hypercholesterolemia, type 2 diabetes mellitus, myocardial infarction, certain malignancies (cancer of the colon, rectum, and prostate in men and of the breast, cervix, endometrium, and ovary in women), obstructive sleep apnea, hypoventilation syndrome, osteoarthritis and other orthopedic disorders, infertility, lower extremity venous stasis disease, gastroesophageal reflux disease, and urinary stress incontinence. Lesser degrees of o. can constitute a significant health hazard in the presence of diabetes mellitus, hypertension, heart disease, or their associated risk factors. Body fat distribution in central (abdominal or male pattern, with an increased waist-to-hip ratio) versus peripheral (gluteal or female pattern) adipose tissue deposit is associated with higher risks of many of these disorders. Obese persons are more liable to injury, more difficult to examine by palpation and imaging techniques, and more likely to have unsuccessful outcomes and complications from surgical operations. Not least among the adverse effects of o. are social stigmatization, poor self-image, and psychological stress. Weight reduction is associated with improvement in most of the health risks of o.. All treatments for o. (other than cosmetic surgical procedures in which subcutaneous fat is mechanically removed) require creation of an energy deficit by reducing caloric intake, increasing physical exercise, or both. Basic weight-reduction programs involve consumption of a restricted-calorie, low-fat diet and performance of at least 30 minutes of endurance-type physical activity of at least moderate intensity on most and preferably all days of the week. Behavior modification therapy, hypnosis, anorexiant drugs, and surgical procedures to reduce gastric capacity or intestinal absorption of nutrients are useful in selected cases, but the emphasis should be on establishing permanent changes in lifestyle. Weight reduction is not recommended during pregnancy or in patients with osteoporosis, cholelithiasis, severe mental illness including anorexia nervosa, or terminal illness.
- android o. central o. (apple shape) with fat excess primarily in abdominal wall and visceral mesentery; associated with glucose intolerance, diabetes, decreased sex hormone–binding globulin, increased levels of free testosterone, and increased cardiovascular risk.
- hypothalamic o. o. caused by disease of the hypothalamus.
- hypothalamic o. with hypogonadism SYN: adiposogenital dystrophy.
- morbid o. o. sufficient to prevent normal activity or physiologic function, or to cause the onset of a pathologic condition.
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obe·si·ty ō-'bē-sət-ē n, pl -ties a condition that is characterized by excessive accumulation and storage of fat in the body and that in an adult is typically indicated by a body mass index of 30 or greater
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n.
the condition in which excess fat has accumulated in the body, mostly in the subcutaneous tissues. Clinical obesity is considered to be present when a person has a body mass index of 30 or over. The accumulation of fat is usually caused by the consumption of more food than is required for producing enough energy for daily activities. However, recent evidence indicates that a genetic element is involved. Hunger and satiety appear to be controlled by peptide messengers, encoded by specific genes and acting on the brain; an example is leptin. Obesity is the most common nutritional disorder of recent years in Western societies: some patients may require surgical treatment to attain worthwhile weight reduction; drug treatments also exist (see orlistat, sibutramine).
• obese adj.
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obes·i·ty (o-bēsґĭ-te) [L. obesus fat] an increase in body weight beyond the limitation of skeletal and physical requirement, as the result of an excessive accumulation of fat in the body. Called also adiposity, adiposis, and corpulency.Medical dictionary. 2011.