Tackling Obesity in England - National Audit Office

TACKLING OBESITY IN ENGLANDAppendix2 Themeasurement of obesity1 Obesity is normally measured by clinicians in terms ofthe body mass index (kg/m 2 ). Figure 27 shows thedifferent classifications of body mass index (BMI) usedin England by the Department of Health. This shows thatthere are different degrees of excess weight, and ofassociated risk, above the range considered healthy(BMIs over 20 to 25). Obesity is defined by a BMI over30. People with a BMI over 40 are described as severelyor morbidly obese. At this level it is expected that someclinical complications associated with the obesity willbe present. Data produced by the Health Survey forEngland on the proportion of the population that isoverweight and obese use these definitions.27This table shows the way different BMIs are classified andthe relationship between BMI and risk of associated diseasesBody Mass Index Classification Risk of disease associated(kg/m2)with excess weightLess than 20 Underweight Low (but increased riskof other clinical problems)2 There is a range of other measures used to record bodyshape. Because the health risks of obesity arecompounded by the influence of fat which is distributedaround the waist, the waist circumference or waist:hipratio are sometimes used. In general, men are atincreased risk of obesity-related diseases when the waistcircumference reaches 94cm (37 inches), and womenwhen it reaches 80 cm (32 inches). This risk becomessubstantially increased at 102cm (40 inches) for men,and 88cm (35 inches) for women 10 .3 Classifying obesity in children is more complicated, andthere is no international consensus on the appropriatecut-off point for classifying a child as obese. In children,BMI changes substantially with age, rising steeply ininfancy, falling during the pre-school years, and thenrising again into adulthood. For this reason, child BMIneeds to be assessed against standards which makeallowance for age 10 . Proposed cut-off points have beenpublished based on an international survey of six largenationally representative cross-sectional growthstudies 42 .Over 20 to 25 Desirable or Averagehealthy rangeOver 25 to 30 Overweight IncreasedOver 30 to 35 Obese (Class I) ModerateOver 35 to 40 Obese (Class II) SevereSource:Over 40 Morbidly or Very severeseverely obese (Class III)BMI classifications from the Health Survey for England 1 with additionaldata on associated risk from the World Health Organisation 10appendix two50