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Dr Mark Porter is a family doctor in the UK and in his 50s. He’s tall and slim and thinks he’s fit and healthy – after all he goes to the gym several times a week. Mark meets experts who measure his weight, height and body fat to find out if he is as healthy as he seems.

He begins by finding out his BMI, or body mass index, a term more and more people are using all over the world. It’s an indicator of whether he is too fat, too thin or just right. It’s relatively easy to work out with a calculator – he divides his weight in kilograms by the square of his height in metres.

Mark compares his BMI against two other ways of measuring body fat, the true test of whether he is overweight or not. Is his BMI as accurate as the results of body fat calculations derived by measuring skin folds and an ultra accurate DEXA scan?

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