Abstract: 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". Keywords: Shape chart, body mass index, waist-to-height ratio, anthropometry, body weights and measures. The public health approach to communicating the risks of obesity was, for a long time, firmly rooted in the use of appropriate body weights for height. Tables of appropriate weight for height for men and women, originally derived from Insurance Company data [1], were used until the mid 1980s. The Metropolitan Life Insurance Company's sexspecific tables were the standard; they used minimum and maximum weights associated with the lowest mortality among men and women between 25 and 59 years old, hence they were not suitable for children. The table creators attempted to use "frame size" as a way to compensate for the differences between people with different skeletal muscle mass. But in practice, the definition of frame size was too difficult for people to use, so virtually nobody used it as intended. Instead, people subjectively chose their own categories. Those tables survived well into the 1970s and 80s when the Quetelet index (QI), later to be called the 'Body Mass Index' (BMI), provided the option of displaying optimal weights for men and women on the same chart. QI is a formula which is used to estimate a healthy body weight based on a person's height. It is defined as the individual's body weight divided by the square of his or her height; the unit of measure is invariably expressed as kg/m 2 . *Address correspondence to this author at the Ashwell Associates (Europe) Ltd, Ashwell Street, Ashwell, Herts, SG7 5PZ, UK; Tel: +44(0)1462742166; E-mail: margaret@ashwell.uk.com While the Quetelet formula dates back to the 19th century [2], the term 'body mass index' for the same ratio and its popularity date back to a 1972 paper by Ancel Keys who found the BMI to be the best proxy for body fat percentage among ratios of weight and height [3] . BMI was explicitly cited by Keys as being appropriate for population studies, and inappropriate for individual diagnosis. Nevertheless, due to its simplicity, it came to be widely used for individual diagnosis. George Bray began to advocate for the use of BMI about 1973 at the time of the Fogarty Center Conference in Washington when he wrote about methods for assessing obesity [4] . Later, Bray prepared a nomogram for BMI with recommended levels based on the upper and lower limits of BMI for men and women (medium frame) in the 1959 Metropolitan Life Insurance Tables [5] . These BMI levels were close to 19-24 kg/m 2 for women and 20-25 kg/m 2 for men. The first BMI chart, which displayed BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colours for different BMI categories, first appeared in 1981 in John Garrow's book "Treat obesity seriously" [6] . Garrow used the term Quetelet index, rather then BMI, and made it clear that the grades of obesity had arbitrary boundaries at 25, 30 and 40 kg/m 2 , since different treatments are needed for different severities. Minimal risk was denoted between the boundary values of BMI between 20 to 25 kg/m 2 since mortality was lowest here in the U-shaped relationship. Risk therefore increased from BMI 25 onwards and since the increased risk was linear, BMI=30 was designated to be the next boundary value for risk, probably because it was five
WCHR cut-off values for healthy, overweight, and obese categories proposed by Ashwell REF are 0.4, 0.5, and 0.6, respectively.
Charts Based on Body Mass Index and Waist-to-Height Ratio to Assess the Health Risks of Obesity: A Review
The Open Obesity Journal
Medicine