Background

Definition Obesity is a chronic condition characterised by an excess of body fat. It is most often defined by the body mass index, a mathematical formula that is highly correlated with body fat. Body mass index is weight in kilograms divided by height in metres squared (kg/m²). In the United States and the United Kingdom, people with a body mass index between 25 and 30 are categorised as overweight, and those with an index above 30 are categorised as obese.1

Incidence/prevalence The prevalence of obesity has increased steadily in many countries since 1900. In England, in 1994, it was estimated that 13% of men and 16% of women were obese. 1 2 In the past decade alone, the prevalence of obesity in the United States has increased from 12.0% in 1991 to 17.9% in 1998.3

Aetiology The aetiology of obesity includes both genetic and environmental factors. Obesity may also be induced by drugs (high dose glucocorticoids, for example) or be secondary to a variety of neuroendocrine disorders such as Cushing's syndrome and polycystic ovary syndrome.4

Prognosis Obesity is a risk factor for several chronic diseases, including hypertension, dyslipidaemia, diabetes, cardiovascular disease, sleep apnoea, osteoarthritis, and some cancers.1 The relation between increasing body weight and mortality is curvilinear, with mortality increasing in people with low body weight. Whether this is caused by increased mortality risk at low body weights or by unintentional weight loss is not clear.5 Results from five prospective cohort studies and national statistics for 1991 show that in US adults about 280 000 deaths a year are attributable to obesity.6

Aims To achieve realistic gradual weight …