Charts Based on Body Mass Index and Waist-to-Height Ratio to Assess the Health Risks of Obesity: A Review

This review focuses on the rationale behind the charts that have been used as public health tools to assess the health risks of obesity, with special emphasis on where the boundary values are placed. A chart based on body mass index (BMI) was introduced in the 1980s to replace Tables of best weights for heights and this BMI chart (based on adult weight for height) is still very much in use today. Although the importance of the distribution of body fat, as opposed to the total amount of body fat, in determining health risks of obesity was first suggested in the 1940s, it was not until the mid 1990s that a chart based on Shape was suggested. The Ashwell Shape Chart was based on the use of waist-to-height ratio (WHtR) as a proxy for abdominal obesity. The chart contains three boundary values for WHtR: 0.4, 0.5 and 0.6; originally set on pragmatic decisions. Substantial evidence from a recent systematic review now supports the global boundary value WHtR of 0.5 for Consider Action. WHtR of 0.6 has been proposed for Take Action. An exciting prospect is that the same Shape Chart might be used to assess risk for adults and children in several ethnic groups. Use of the Shape Chart could also improve the efficiency for screening for cardiometabolic risk and could provide substantial cost savings in terms of obesity treatment. The public health message could not be simpler: "Keep your waist circumference to less than half your height".