The long term health outcomes for young people with different amounts of total body fat are unknown as most large scale studies examining the effects of childhood obesity have not used measures of body fat, but proxies such as body mass index (BMI). However, BMI may not indicate the level of central adiposity which is also associated with clustering of cardiovascular disease risk factors including dyslipidaemia, hypertension and insulin resistance. Clusters of risk factors are fairly stable characteristics that tend to track from adolescence to adulthood, hence the early identification of children who are likely to develop an elevated risk profile is of interest.1

Waist circumference has been recommended as a means of identifying young people at metabolic risk.2 Yet, there are several studies that indicate that waist circumference measurements have a similar performance to BMI in identifying dyslipidaemia and screening for the metabolic syndrome.3,4,5 These results are not unexpected, BMI and waist circumference are highly correlated.6

However, the waist to height ratio has been shown to more readily identify young people with adverse cardiovascular risk factors (cross-sectionally) when compared to BMI7 and may be an accurate indicator of change over time in fat distribution as it accounts for both waist circumference and height.8

Anecdotally there has been much interest expressed in the waist to height ratio by clinicians. Recent evidence suggests that the waist to height ratio, unlike BMI and waist circumference, does not require specification of sex or age and a ratio cut-point of 0.5 has been proposed as a simple means of indicating whether the amount of central adiposity is excessive in both children8 and adults.9 The concept of an increased waist girth relative to height may be easier to understand by patients and families compared to BMI percentiles, particularly if the message is 'keep your waist circumference to less than half your height'.8 However, to our knowledge use of the 0.5 ratio has not been validated at predicting metabolic risk in young people.

Aim: Examine the effectiveness of the waist to height ratio in identifying young people at risk of metabolic risk clustering.