Background: There is now overwhelming scientific evidence that central obesity, as opposed to total obesity assessed by body mass index (BMI), is associated with the most health risks and that the waist-to-height ratio (WHtR) is a simple proxy for this central fat distribution. This Opinion reviews the evidence for the use of WHtR to predict mortality and for its association with morbidity. A boundary value of WHtR of 0.5 has been proposed and become widely used. This translates into the simple screening message 'Keep your waist to less than half your height'. Not only does this message appear to be suitable for all ethnic groups, it also works well with children.
Discussion: Ignoring this simple message and continuing to use BMI as a sole indicator of risk would mean that 10% of the whole UK population, and more than 25% of the UK population who are judged to be normal weight using BMI, are misclassified and might not be alerted to the need to take care or to take action.
Summary: Accepting that a boundary value whereby WHtR should be less than 0.5 not only lends itself to the simple message 'Keep your waist to less than half your height' but it also provides a very cheap primary screening method for increased health risks: A piece of string, measuring exactly half a person's height should fit around that person's waist.