I am 5ft 41.2in tall. I weigh eight stone. This gives me a body-mass index of 18.6, which is just on the cusp of underweight. It is an indication of quite how screwed up I am about food that this never fails to give me a small frisson of delight. Because I know that BMI is a load of - and I'm being polite - meaningless twaddle.
Based on weight and height measurements, BMI purports to determine whether someone is a healthy weight for their proportions.
It is the reason that, since 2005, all reception and Year 6 pupils have been weighed and measured in school. And it is the reason that, this week, government advisers called for all pupils to be measured from pre-school onwards. BMI, they say, is a cheap and easy way of checking for obesity.
But that's not what BMI is at all. It was pioneered in the 1830s by a Belgian astronomer who wanted to define "average man". He believed that those who deviated from the average physically were more likely to be social deviants. The obese, he reasoned, had criminal or sociopathic tendencies: weight was an indicator of moral laxity.
Yes. This is the same measure we are using on schoolchildren.
It gets worse. Most of the scientists responsible for popularising BMI had connections with the diet industry. They stood to gain, significantly, from a population terrified of being two chocolate biscuits away from obesity.
More importantly, BMI is not an appropriate measurement for bodies that are still growing. A child who is overweight in January might be six inches taller, and significantly thinner, come June, rendering any BMI calculations meaningless.
At a conference this week, Will Cavendish, of the Department of Health, reported that one in four reception children is overweight: cause for collective terror.
OK. Let's look at that again. One in four reception children is overweight. One in four five-year-olds. For heaven's sake. They're supposed to be overweight. There's even a term - baby fat - specifically for it.
Childhood should be a time for carefree gambolling, followed by equally carefree eating. Children need fat in their diets to develop healthily.
BMI's defenders say it is a measure of population trends: individuals should not take an "overweight" classification to heart. To which I say: yeah, right. That's not how people work. If a teacher sees that a quarter of her class is "overweight", she is going to teach dieting-is-good lessons, dressed up as "healthy eating". Parents, similarly, are going to start monitoring their children's eating habits.
But suggest to five-year-olds that they should be watching their diets, watching their weight, and you condition them to be scared of food. You raise a generation who equate dessert with self-indulgence, with being bad. It is a short step from this to skipping meals to make yourself feel worthwhile.
I know that feeling. As I said, I'm quite screwed up about food. Every time I eat a cake, a biscuit, a small square of chocolate, I descend into do-I-deserve-it excoriations. It's not fun. I wouldn't wish it on a whole generation of children. But apparently the Government does.
Adi Bloom, TES social affairs correspondent.