Obesity

Obesity, body condition characterized by storage of excessive amounts of fat in adipose tissue beneath the skin and within other organs, including muscles. All mammals store body fat; in women the normal amount of body weight stored as fat is 25 per cent, in men 15 per cent. Obesity is a result of taking in more energy in food than one uses in activity. Besides excess eating, obesity can also be caused by drastically reduced activity, and this often occurs in those who are sedentary or bedridden. Although intake of food has declined in recent years, this has been accompanied by a substantial decline in physical activity: for example, people in developed countries are more likely to work in sedentary jobs; use domestic labour-saving devices; and travel by car. However, it is now thought that obesity may be caused by a number of factors other than overeating or inactivity. It is still not known why some thin people eat a lot and exercise little, and why some overweight people eat moderate amounts or reduce food intake, often through repeated attempts at dieting, with no appreciable or sustainable weight loss.

Deposition of fat, which has twice the potential energy of carbohydrate or protein, is a way of storing energy for times of future need. Storage of greatly increased amounts of fat, however, is associated with impairment of health. It has been shown that people who are 30 per cent or more overweight run measurably increased risks of disease, notably diabetes mellitus, cardiovascular and gall-bladder disease, and arthritis, and may encounter complications if undergoing surgery. A person’s level of obesity can be assessed through the body mass index (BMI), which is measured by the following equation:

An alternative method of measuring obesity is waist-hip ratio (WHR), which some researchers regard as a better indicator of central adiposity, which has been linked to some obesity-related diseases. WHRs for women of 0.8 and for men of 1.0 were seen as cut-off points; “ideal” waist measurements were seen as less than 94 cm (37 in) for women and less than 102 cm (40 in) for men.

Research is looking into disturbances of the endocrine system as a possible cause—particularly the effect of chemicals produced in the body, such as leptin, which acts on the hypothalamus in the brain to control food intake. It is as yet not proven that it could be inherited, although a family tendency towards obesity is very common; the causes of this are usually family eating habits, but research is continuing to examine possible genetic susceptibility. Overweight babies do not, however, necessarily grow up to be overweight adults. It has also been suggested that the AD-36 virus, which causes cold-like symptoms, affects food-energy absorption and more than doubles the normal level of body fat, although as yet this is far from proven. In addition, the suggestion that obese people may have more bacteria in their digestive systems that are especially efficient at extracting calories from food is likewise unproven.

Many approaches to weight loss, including a multiplicity of diets, have been tried in obese people, with only limited success. Slimming pills, containing the stimulant drug dextroamphetamine or one of its derivatives, became popular in the 1950s, but it is believed that they did not work and could be habit-forming, and thus they are no longer prescribed. Many complex diets have been promoted for weight loss, but there is no scientific evidence that they are effective. Surgical procedures used to aid weight loss include intestinal bypass and gastric bypass. In the former operation, a length of intestine is removed to reduce absorption of nutrients. This operation has been largely abandoned because it produced severe side effects, such as liver damage and chronic diarrhoea, and caused several deaths. In the gastric-bypass procedure, which is only performed on extremely obese people, most of the stomach is closed off with surgical staples. Only a small pouch remains to receive food, thereby greatly reducing the person’s eating capacity.