Dr Mark Porter puts the BMI, or bodymass index, to the test. BMI calculates whether someone is too fat, too thin or just right but how accurate is it?

As a man of a certain age Mark's aware that his waistband is getting tighter but assumes it is only a statistical aberration - probably. He compares his results with other measures of body fat and discovers hidden risks.

(Photo: Overweight man measuring his waist. Credit: Science Photo Library)