Obesity can be defined as a disease in which excess fat has accumulated such that health may be adversely affected (Kopelman, 2000) and mortality increased. Obesity is a serious public health threat. After smoking it is the second leading cause of preventable premature death in the U.S.A.(1998). Obesity causes and exacerbates many health problems. It is an independent risk factor for coronary heart disease (Hubert et al, 1983) and associated with hypertension, dyslipidaemia and impaired glucose metabolism, which are also independent risk factors for coronary artery disease. Increasing levels overweight and obesity are positively associated with reduced life expectancy (Katzmarzyk et al, 2001; Lew, 1985). The Framingham study found that any weight gain after the age of 30 years, regardless of the initial weight, was associated with increased risk of death (Hubert et al, 1983).
The World Health Organization (WHO) has recognized an epidemic of obesity throughout most of the developed and developing world (2000). The prevalence of obesity has at least doubled in the majority of developed countries over the last 2 decades. In Australia, obesity (BMI > 30 kg/m2) in adult Australians over 20 years of age has increased from 8% in 1980 to 15% by 1995 (Australian Institute of Health and Welfare, 1998) and is currently estimated to be 20.5% (Dunstan et al, 2001). Similarly in the USA the prevalence of obesity is currently 28% and in some regions and among specific ethnic groups, much higher (National Institute of Health, 2001). There is no evidence that this epidemic in Australia or elsewhere has reached its peak. The increase in overweight and obesity is not confined to wealthy countries. The WHO consultation on obesity clearly demonstrates that developing countries experiencing improved socioeconomic conditions undergo a rapid population transition from underweight to overweight (2000). In addition the increasing prevalence of obesity in children is alarming (Bundred et al, 2001) and heralds a life long disorder with great risk of obesity related disease (Dietz, 1994; Dietz, 1998).
The direct cost of obesity is 2-5% of most developed countries, including Australia (Levy et al, 1995). In 1995 the total cost of obesity in the U.S.A. was estimated to be US$ 99 billion with US$ 52 billion representing direct health costs, 5.7% of total health cost (Wolf and Colditz, 1998). If the direct cost of physical inactivity is combined with that of obesity, in the USA, the estimated cost is 9.4% of the national health budget (Colditz, 1999). The most costly elements are those of managing the obesity comorbidies of hypertension, type 2 diabetes and coronary artery disease (Birmingham et al, 1999; Swinburn et al, 1997; Wolf, 1998). It is estimated that obesity accounts for 85% of the total cost of treating type 2 diabetes and 45% for hypertension (Oster et al, 2000). The burden of obesity not only includes the direct health cost, but indirect cost through lost output due to reduction in or cessation of productivity (Levy et al, 1995). In addition there are intangible costs. The individual burden of obesity comprises reduced quality of life, increased morbidity and premature mortality and these will be discussed in detail later. There is also society's stigmatization of the obese resulting in decreased opportunities in education, housing and employment (Hutton, 1994).