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Hello and welcome to more or less on the BBC World Service.

I'm Ruth Alexander, tipping the scales in favour of numbers that make sense.

This week we're looking at the body mass index,

the internationally agreed measure which, according to the Centre for Disease Control

in the United States, is a reliable indicator of body fatness for most people.

And, according to the National Health Service in the UK,

is a good way to check if you're a healthy weight.

Now, I must declare an interest right at the top,

because I personally have never found the BMI to be reliable.

My BMI has always put me as underweight, and yet I think I'm fit and healthy.

Now the last time I was told this by my doctor was more than ten years ago,

so I'm going to calculate it again with Wesley Stevens and helping me.

Hi Ruth, yes, so what I need you to do is to step on the scales.

Oh, okay.

Yeah, both feet, please.

I'm going to give you a weight out on the radio, is that okay?

Go on then.

It's 54 kilograms, and I also need your height.

BMI, as it's known, is calculated by dividing your weight by your height squared.

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