obesity, also called corpulence or fatness,
excessive accumulation of body fat, usually caused by the consumption of more calories than the body can use.
The excess calories are then stored as fat, or adipose tissue. Overweight, if moderate, is not necessarily obesity, particularly in muscular or large-boned individuals.
Causes of obesity
In European and other Caucasian populations, genome-wide association studies have identified genetic variations in small numbers of persons with childhood-onset morbid obesity or adult morbid obesity. In one study, a chromosomal deletion involving 30 geneswas identified in a subset of severely obese individuals whose condition manifested in childhood. Although the deleted segment was found in less than 1 percent of the morbidly obese study population, its loss was believed to contribute to aberrant hormone signaling, namely of leptin and insulin, which regulate appetiteand glucose metabolism, respectively. Dysregulation of these hormones is associated with overeating (or hyperphagy) and with tissue resistance to insulin, increasing the risk of type II diabetes. The identification of genomic defects in persons affected by morbid obesity has indicated that, at least for some individuals, the condition arises from a genetic cause.
For most persons affected by obesity, however, the causes of their condition are more complex, involving the interaction of multiple factors. Indeed, the rapid rise in obesity worldwide is likely due to major shifts in environmental factors and changes in behaviour rather than a significant change in human genetics. For example, early feeding patterns imposed by an obese mother upon her offspring may play a major role in a cultural, rather than genetic, transmission of obesity from one generation to the next. Likewise, correlations between childhood obesity and practices such as infant birth by cesarean section, which has risen substantially in incidence worldwide, indicate that environment and behaviour may have a much larger influence on the early onset of obesity than previously thought. More generally, the distinctive way of life of a nation and the individual’s behavioral and emotional reaction to it may contribute significantly to widespread obesity. Among affluent populations, an abundant supply of readily available high-calorie foods and beverages, coupled with increasingly sedentary living habits that markedly reduce caloric needs, can easily lead to overeating. The stresses and tensions of modern living also cause some individuals to turn to foods and alcoholic drinks for “relief.” Indeed, researchers have found that the cause of obesity in all countries shares distinct similarities—diets rich in sweeteners and saturated fats, lack of exercise, and the availability of inexpensive processed foods.
The root causes of childhood obesity are complex and are not fully understood, but it is clear that children become obese when they eat too much and exercise too little. In addition, many children make poor food decisions, choosing to eat unhealthy, sugary snacks instead of healthy fruits and vegetables. Lack of calorie-burning exercise has also played a major role in contributing to childhood obesity. In 2005 a survey found that American children age 8 to 18 spent an average of about six hours a day watching television and videos, playing video games, and using computers.
Furthermore, maternal consumption of excessive amounts of fat during pregnancyprograms overeating behaviour in children. For example, children have an increased preference for fatty foods if their mothers ate a high-fat diet during pregnancy. The physiological basis for this appears to be associated with fat-induced changes in the fetal brain. For example, when pregnant rats consume high-fat diets, brain cells in the developing fetuses produce large quantities of appetite-stimulating proteinscalled orexigenic peptides. These peptides continue to be produced at high levels following birth and throughout the lifetime of the offspring.
As a result, these rats eat more, weigh more, and mature sexually earlier in life compared with rats whose mothers consumed normal levels of fats during pregnancy.
Treatment of obesity
The treatment of obesity has two main objectives: removal of the causative factors, which may be difficult if the causes are of emotional or psychological origin, and removal of surplus fat by reducing food intake. Return to normal body weight by reducing calorie intake is best done under medical supervision.
Dietary fads and reducing dietsthat produce quick results without effort are of doubtful effectiveness in reducing body weight and keeping it down, and most are actually deleterious to health. (See dieting.) Weight loss is best achieved through increased physical activity and basic dietary changes, such as lowering total calorie intake by substituting fruits and vegetables for refined carbohydrates.
The development of drugs for the treatment of obesity has been controversial, primarily because the syndrome is viewed as stemming largely from behavioral influences that cannot be corrected by drugs alone. Two agents,rimonabant andtaranabant, both of which belong to a class of drugs known asselective cannabinoid receptor type 1 (CB1) blockers, have shown some promise in suppressing calorie consumption and reducing body weight. However, because rimonabant can cause severe psychological side effects such as depression, anxiety, and nervousness, it has not been approved in most countries. Taranabant appears to have less-serious side effects than rimonabant, although it is still in clinical trials in the United States. Another agent being tested for obesity is SRT1720, a compound derived from resveratrol that promotes the metabolism of stored fat.
In 2012 the U.S. Food and Drug Administration(FDA) approved two antiobesity agents,Belviq (lorcaserin hydrochloride) andQysmia (phentermine andtopiramate). Belviq decreases obese individuals’ cravings for carbohydrate-rich foods by stimulating the release of serotonin, which normally is triggered by carbohydrate intake. Qysmia leverages the weight-loss side effects of topiramate, an antiepileptic drug, and the stimulant properties of phentermine, an existing short-term treatment for obesity.
Phentermine previously had been part of fen-phen (fenfluramine-phentermine), an antiobesity combination that was removed from the U.S. market in 1997 because of the high risk for heart valve damage associated with fenfluramine.
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