Overweight and obesity are increasing problems that lead to significant health and social difficulties for people. Commonly defined by a measurement of Body Mass Index (BMI - calculated by dividing body weight (kilograms) by height (metres) squared), the prevalence of overweight (adult BMI of between 25 and 29.9) and obesity (BMI of 30 or over) is increasing. For children, these BMI standards require adjustments for age and gender. Overweight and obesity are global problems and the World Health Organization (WHO) predicts that by 2015 approximately 2.3 billion adults worldwide will be overweight and more than 700 million obese. In the UK, obesity rates have nearly doubled in the past 18 years from 13% of men and 16% of women in 1993, to 24% of men and 26% of women in 2011. In the same year, about 3 in 10 children aged 2–15 years were found to be overweight or obese. Ethnic differences exist in the prevalence of obesity and the related risk of ill health. For example, compared with the general population, the prevalence of obesity is lower in men of Bangladeshi and Chinese family origin, whereas it is higher for women of African, Caribbean and Pakistani family origin as reported by the National Obesity Observatory in 2011.