The prevalence of obesity is increasing worldwide. Among 25-64 year-old Finns, 19.8% of men and 19.4% of women had a BMI ?30 kg/m in 1997 (Lahti-Koski et al. 2000a). The most alarming trend is the increasing prevalence of abdominal obesity (Lahti-Koski et al. 2000b), which is strongly associated with the metabolic syndrome and type 2 diabetes. Obesity is also associated with several other chronic conditions, such as coronary heart disease, obstructive sleep apnoea, asthma and other pulmonary syndromes, degenerative joint disease, and certain types of cancer. On a societal level the health risks associated with obesity pose a serious and costly public health hazard. On an individual level obesity not only shortens life expectancy but also reduces the number of healthy and functional life-years (WHO 2000).
Quality of life is a broad concept including physical, mental, and social well-being. Health-related quality of life is a narrower concept including attempts to define the impact of diseases and their treatments on functional status and well-being (Testa and Simonson 1996). The basic principle of measuring quality of life is that the patient is asked what he/she can do (functioning) and how he/she feels (well-being). Information on HRQL may influence the development of clinical pathways, service provision, health care expenditures, and public health policy.