I'm not a doctor, nor am I a nutritionist (I'm also not a ballet dancer or a bookbinder, just for clarification).

So any of the following comes with a – *klaxon sounding* – health warning. Like most of my columns, it is based on gut feeling, not comprehensive research.

There, disclaimers done – not that it'll stop the letters from people who know what they're talking about.

Anyway, here goes: BMI is a load of damaging nonsense.

Body mass index is used as a way to identify whether someone is overweight. It is your weight in kilogrammes divided by your height in metres squared.

It's a blunt instrument. And, like lots of blunt instruments, it can do damage.

I recently went for a medication review. While it was happening, I was weighed and measured. On the basis of these two simple things, I was told that I'm 11lb overweight.

It might be true. But it might not.

I'm 6ft 1in and 15st 2lb, which was enough to effectively label me fat. The equation did not take into account that I have broad shoulders, 24-inch thighs, a solid frame and – of course – 'big bones'.

I have a friend who is the same height as me and five stone lighter. He admits that he is terribly unfit, and doesn't run and play football as I do. BMI loves him, though.

England rugby union star Manu Tuilagi is an inch shorter than me and 16kg heavier. He might be a remarkable athlete, but the BMI calculator makes him obese.

His teammate, Billy Vunipola, who was such a slob that he was England's player of the tournament during the recent Six Nations grand slam, is 6ft 2in and 19st 12lb. What a chubster. Don't tell him I said that, though.

It beggars belief that such a scattergun approach is used in an age where science and analytics can ensure far greater subtlety and accuracy.

What worries me is the damage it could do to vulnerable people who have issues about their weight.

When I walked out of the surgery after being told I was 11lb the wrong side of the fat line, I felt pretty low. But I was able to talk some sense into myself.

Not everybody can, though.

My own BMI is Be More Intuitive about your body, rather than guided by unhelpful formulae.

We know when our belt has got a bit too tight, or our shirt buttons are threatening to burst.

We know when we are not in good shape. That is not the challenge, it's actually doing something about it.