Obesity,the primary health threat in the 21st century,affects the quality of life physiologically,economically and psychologically,irrespective of cultural,financial or ethnic background.Prevalence of obesity has been increasing steadily during the past 30 years worldwide,especially in developed countries.In America,almost one-third of adult population are obese (BMI ≥30 kg/m2)[1] and healthcare expenditure for obesity had reached nearly 75 billion USD in 2003[2].A similar picture has been seen in developing countries as well where incidence of obesity is rising at an alarming speed.In China,according to one report,12.1％ and 2.6％ of the urban population are either overweight (25 kg/m2 ≤ BMI ≤30 kg/m2) or clinically obese (BMI ≥30 kg/m2)[3].The situation in children is more disturbing:a 2005 study conducted in northe coastal large cities of China shows that the combined prevalence of obesity had reached 32.5％ in boys and 17.6％ in girls,respectively[4].Possible contributing factors may include steady economic growth,lifestyle changes and significantly reduced family size since the late 1970s.