Obesity, with its almost inevitable secondary consequences such as high blood pressure, diabetes, heart attack and arthrosis, is a chronic disease with restricted quality of life and a high morbidity and mortality risk.  Obesity affects all age groups and does not differ with regard to ethnic origin and sex. Obesity is defined as an increase in body fat above the normal extent.
In accordance with the guidelines of the Deutschen Adipositasgesellschaft weight classification is evaluated on the basis of the Body Mass Index (BMI). The BMI is the ratio of weight to body height squared (kg/m2). Overweight is defined as BMI > 25 kg/m2, obesity as BMI > 30/m2 (Table 1).
The wide range of causes of overweight and obesity are summarised in Table 2. Obesity has developed into a serious health problem in Germany. The prevalence of obesity (BMI > 30) has continually grown for many years. At present between 20 and 25% of all adult Germans are obese. Large prospective studies have shown that as BMI increases, life expectancy is shortened. 

1. family disposition, genetic causes
2. modern lifestyle  (lack of physical activity, poor diet e.g. frequent snacks, high consumption of high energy food, Fast Food, soft drinks containing sugar, alcoholic drinks)
3. chronic stress
4. eating disorders (e.g. binge eating disorder, bulimia, night-eating disorder)
5. endocrine diseases (e.g. hyperthyroidism, Cushing’s syndrome)
6. medications (e.g. some antidepressants, neuroleptica, antidiabetica
7. glucocorticoids, Beta-blocker)
8. other causes (e.g. immobilisation, pregnancy, operations in the hypothalamus region, stopping smoking)