Original URL: http://www.theregister.co.uk/2009/04/20/more_bmi_foolery/

Profs: Human race must become Hobbits to save planet

British men 3'3" tall would meet UK carbon pledges

By Lewis Page

Posted in Science, 20th April 2009 14:32 GMT

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.

British people must become Hobbits to meet the government's carbon pledge

So no, we're not necessarily "getting fatter". But no doubt about it, we in the UK - as Messrs Roberts and Edwards suggest - are getting heavier. Or anyway, those of us who are to be found in the house with time on our hands when the government health surveyors come calling (methodology pdf) are getting heavier. ("Response varied by region ... Household response was highest in the North East and East Midlands regions and was lowest in the London region", apparently. But "weighting should reduce non-response bias". In 2003, the government's adjustment for the fact that on the whole it would be the fatties who were found at home in the daytime was just 300 grams.)

And we fat/heavy Brits eat more food than people do in Vietnam, that's true. But we aren't just fatter and heavier than Vietnamese people - we're taller too. Le Nguyen Bao Khanh of the Vietnamese School and Work Nutrition Department says that Vietnamese youngsters tend to stop growing early due to malnutrition, and "many are dwarfish". The Vietnamese government, indeed, are embarking on a national programme intended to raise the average male height to 5'5" from its current 5'4".

Average UK men, by contrast, stand four inches taller than Vietnamese ones do. If they were as lean as their Far Eastern counterparts - were simply enlarged scale copies of them, with the same physique - one would still expect Brits to weigh 25 per cent more, consume extra food on similar lines, and burn more transport fuel to move their larger (but still lean) bodies about.

Getting slimmer, then, isn't going to cut our food consumption by 20 per cent to Vietnamese levels. Nor is it going to reduce our use of transport fuel in any serious way. We'll also have to get shorter by four or five inches if the profs' recommendations are to be followed. But that will be achievable, as a Vietnamese diet means widespread, severe child malnutrition and stunted growth.

But hey - we'd reduce our greenhouse gas emissions by a tonne/CO2 per head! That's worth doing!

Well, maybe. Us Brits emit almost ten tonnes per head a year, though. In order to meet the government's stated goals, much more serious efforts would be required: we'd have to halve the British population and shrink the average UK male to a height of 3'3" to achieve Mr Miliband's 80 per cent pledge, according to our calculations*. That's about the average height of a Hobbit, if we've recalled our Tolkien correctly.

If the entire developing world agrees merely to stay malnourished on the less radical Vietnam plan (and we Westerners join them) but in other respects everyone gets to live a western-style life, with mobility and industry and babies and stuff, greenhouse gas emissions are still going through the roof.

Merely shrinking ourselves, it seems, isn't going to save the planet. And volunteers to starve their babies into carbon righteousness are probably going to be scarce anyway.

Perhaps some other plan might be in order.

Subscribers to the International Journal of Epidemiology can read the research here. ®

Bootnotes

*The UK population needs to achieve 8 times the carbon savings suggested in the study to meet current government targets: thus they must lose 8 times as much weight, which would require vanishing altogether and then some. If numbers are cut by half, however, each person needs to lose only 80 per cent of their body volume. This equates to reducing all physical dimensions by 40 per cent, eg average UK men should become approximately 3'3". Alternatively, you might say that each remaining person needs to lose 60 per cent of volume, so that men would come out at 4'2" - more in the dwarf league.

Full Disclosure: Lewis Page is 6'3" and weighs 16 stone (BMI = "overweight"). It only gets worse the more phys he does. This whole article is basically an attempt to deal with his terrible body-image problem.