Public-health researchers in London have come up with a new plan to save the planet: wealthy westerners should all reduce by several inches in height by starving their children. This would not only save food, but make people much lighter, meaning that cars and buses would use less fuel.
The new insight comes from Professor Ian Roberts and Dr Phil Edwards of the London School of Hygiene and Tropical Medicine. According to the two men:
A lean population, such as that seen in Vietnam, will consume almost 20% less food and produce fewer greenhouse gases than a population in which 40% of people are obese (close to that seen in the USA today) ... a lean population of 1 billion people would emit between 0.4 and 1.0 gigatonnes less carbon dioxide equivalents per year compared with a fat one.
Between 1994 and 2004 the average male BMI in England increased from 26 to 27.3, with the average female BMI rising from 25.8 to 26.9 (about 3 kg - or half a stone - heavier). Humankind - be it Australian, Argentinian, Belgian or Canadian - is getting steadily fatter.
Or more accurately, humanity's averaged body mass index (BMI) is increasing. But BMI - a frankly bizarre way of measuring fatness - is calculated using weight divided by the square of height.
It's not hard to show how stupid this is. Take a normal healthy adult male standing 5'10" and weighing 12 stone - BMI 24, "healthy" - and scale him up in all dimensions by 7 per cent. He is a slightly larger, exact copy of his smaller self; an almost identical physical specimen.
But he stands 6'3", and because human beings are three-dimensional rather than two-dimensional as the BMI requires them to be, he weighs nearly 15 stone - for a BMI of 26. Suddenly he is "overweight", though he is an exact scale model of a "healthy" person.
Gains in BMI don't particularly signify that people are getting fatter. Often, they mean that people are getting taller or more muscular. American major-league baseball players over the last century, for instance, have shown BMI increases comparable to those of ordinary Englishmen in recent times: but major-league ballplayers are actually a lot healthier, stronger and fitter than they used to be.
Not that anyone's particularly saying that ordinary Englishmen are fitter and healthier than they used to be: but BMI's a pretty stupid way of measuring what is going on. You would see the same BMI increases if everyone started building more muscle mass, or to a lesser degree if lots of people gave up smoking, as they have. And indeed, while Englishmen may be growing, podging or bulking out, there's reason to think that Englishwomen might not be over the longer run. Consider this comparison of UK women in 1951 versus those of today, carried out for the fashion industry rather than for the medical bureaucracy - which needs the obesity numbers to be scary, and which surveys people at home rather than in shops.
The fashionistas say that Ms 1951 came in at 5'3" and 9 stone 10, for a BMI of 24.13. Ms Today, however, is an inch and a half taller. If her body depth and breadth had simply increased in proportion, she should weigh 10 stone 6 (and would be magically "overweight").
But, in fact, according to the London College of Fashion, Ms Today actually weighs 10 stone 3. Her body is either less dense or more elongated than that of her grandma.