Comment A famous mad professor who has previously called for Britons to starve their children into dwarfism so as to ease strains on the planetary ecosystem has reiterated his arguments, this time insisting that the amount of surplus flab carried by the human race will soon be equivalent to having another half-a-billion people on Earth.

Regular readers will be familiar with Professor Ian Roberts of the London School of Hygiene and Tropical Medicine already: he and his colleague Dr Phil Edwards wrote a paper in 2009 in which they suggested that it would be a good idea for Britons and Americans to model their diet and physique on that of the "lean" Vietnamese, as this would assist in such things as meeting British government carbon pledges. Lightweight Vietnamese people, according to the two scientists, not only need less food but use less energy to move themselves around.

Unfortunately, as we pointed out at the time, this would not merely have been a matter of Britons shedding some flab. In order to match the Vietnamese on weight, Brits would also have to lose four inches or so of height. Extrapolating from Roberts' and Edwards' figures, in fact, the people of the UK would need to shrink to a Hobbit-like stature barely over three feet to meet the more ambitious governmental carbon goals.

Even relatively hefty Vietnamese heights and weights are achieved only by means of serious child malnutrition, so it was clear that Roberts' and Edwards' ideas were not going to be taken seriously (though it was perhaps a little alarming to hear such things from official government-funded experts on public health).

Nothing daunted, however, the two men are back again this week - along with some colleagues - with a new effusion in which they make the flab-equivalent-to-half-a-billion-people assertion.

Accompanying press releases state:

North America has only 6% of the world's population but 34% of the world's biomass mass due to obesity. In contrast Asia has 61% of the world's population but only 13% of the world's biomass due to obesity.

"Our results emphasize the importance of looking at biomass rather than just population numbers when considering the ecological impact of a species, especially humans," says trainee doctor Sarah Walpole, who also worked on the document.

"Everyone accepts that population growth threatens global environmental sustainability – our study shows that population fatness is also a major threat," adds Roberts. "Unless we tackle both population and fatness - our chances are slim."

Unfortunately the entire edifice of their argument is based on the long-discredited Body Mass Index (BMI), a frankly bizarre method of assessing how fat people are which was developed by an obscure Belgian social scientist without any medical qualifications in the early 19th century. The BMI assumes that healthy human mass goes up in proportion to the square of height, a patently absurd suggestion given that human bodies are three-dimensional rather than flat 2D shapes. All other things being equal a human's weight should go up related to the cube of height - and indeed they aren't equal. Any engineer will point out that cross-sectional area in support structures (feet, leg bones etc) needs to go up in direct proportion to weight carried, adding still more heft than a cube law would as height goes up. This is why elephants are not simply scaled-up dogs, and dogs are not simply scaled-up insects - they have proportionally thicker legs and other supporting structures and come out much heavier.

As one would expect, then, it has been confirmed by several recent studies among the taller populations of the modern-day developed nations that a BMI assessment of "overweight" should really be assessed as normal or healthy, while the previous "normal" range ought in fact to be dubbed "underweight", as it has negative health consequences similar to being "obese".

By suggesting that the human race - including the taller peoples - needs to shift into the outmoded BMI "normal" range, Roberts and his fellow public-health experts are advocating a course which would cause more health problems: scarcely what they are paid to do.

Furthermore even by the researchers' ridiculous BMI-based numbers it's apparent that fatness just isn't a big deal:

Using data from the United Nations and World Health Organization, researchers from the London School of Hygiene and Tropical Medicine estimated that the adult human population weights in at 287 million tonnes. 15 millions of which is due to the overweight and 3.5 million due to obesity.

Or in other words, even in their crazy BMI cuckoo world just 6 per cent of the total body weight of the human race is surplus. Not a big issue when you reflect that human numbers are projected to increase by almost 30 per cent in the next few decades, and that most of humanity's carbon emissions have nothing to do with body mass (see below).

And in the real world, where a BMI reading of "overweight" in a tall population actually means "healthy", barely a single percentage point of the human race's mass can be assessed as surplus flab - this is not even worth talking about.

But the allied profs and docs, not content with advocating shortened lifespans due to unhealthily low body weights, go further:

If all countries had the same age-sex BMI distribution as Japan, total biomass would fall by 14.6 million tonnes, a 5% reduction in global biomass or the mass equivalent of 235 million people of world average body mass in 2005. This reduction in biomass would decrease energy requirements by an average of 59 kcal/day per adult living on the planet, which is equivalent to the energy requirement of 107 million adults.

Again, however, Americans or Brits would need to shed not just fat but several inches of height to achieve Japanese-style BMIs. The only way for us to do that would be to starve and malnourish our children, preventing them gowing as tall as their parents.

Are these scientists really trying to improve public health?

No, they are trying to cut energy usage and thus carbon emissions - for all that this is not their job nor their field of expertise. We can be sure that they don't know much about energy, in fact, as their saving of 59 kcal/day per adult is tiny: this is 0.07 of a single, measly kilowatt-hour. A human being, for these purposes, can be considered as a mobile space heater using about 3 kilowatt-hours of food energy per day, so the saving on human food energy we could achieve by stunting our kids is just 2.3 per cent.

And it gets worse. Food energy is not a big deal in terms of human energy consumption, except among primitive savages. Citizens of developed nations use far more energy for heating and cooling, for instance (a lot of this is heating water to provide the modern hygiene so critical to our high standards of health - and cooling to keep food safe and healthy to eat). This is true even though our highly productive farming is relatively energy intensive, so that it takes 15 kilowatt-hours per day per Briton to produce our 3 kWh-worth of food and a bit more to bring it to us: but that 15 kWh is only a small proportion of the 195 kWh per day it takes to keep each Brit ticking over.

In other words, the energy savings we would make by starving and malnourishing ourselves to Japanese heights and weights would be utterly, totally insignificant: 2.3 per cent of that 15 kWh comes to about 0.35 kWh/day, or 0.18 of one per cent of the energy we now use, with roughly corresponding carbon reductions.

What an astonishingly silly thing to suggest. It really does tend to lower the status of science and peer-reviewed publishing - not to mention that of the medical profession - that this sort of twaddle (pdf) is considered to be serious, publishable research worthy of debate (blame the open-access journal BMC Public Health in this case).

Needless to say, once freed even from the lax editorial controls of peer review, Prof Roberts goes further still. He has also written a book called Energy Glut. Among other things the prof feels that the roads should be largely cleared of motor vehicles so as to cut emissions, get rid of the scourge of flab and eliminate danger to cyclists.

Some selected passages:

Under a system of carbon rationing, there would be a strong incentive to reclaim the streets from motor vehicles ... Legislation could be passed to give pedestrians legal right of way ... physical fitness would start to improve ... Market forces would eventually ensure that those access needs that are not met within a cycle ride soon would be.

Sedentary home-based activities like watching television, playing computer games or surfing the net, might become less popular as people become reluctant to use up carbon credits on home heating and electricity Use. People would begin by insulating their homes and wearing warmer clothes. The street space would become a public space, and public activities would replace sedentary solitary indoor pastimes ... processed foods would become more expensive than locally grown seasonal fruit and vegetables.

And then, fruitcake mode at full power:

They blame you for being killed on the roads, they blame you for getting fat, and they will blame you when the planet fries.

The media are gagged due to their financial dependence on advertising income from motor vehicle manufacturers, air travel and distant holidays and are understandably reluctant to bite the hand that feeds them. So it remains a secret ...

Currently, because it reserves the interests of the businesses that make up the petro-nutritional complex, all roads lead to the shopping mall and all the malls look the same.

Damn that sinister petro-nutritional complex, anyway.

The prof evidently doesn't know or care that without motor vehicles the government would not be able to afford any roads for cyclists and pedestrians to use - indeed it would also not be able to afford various other things, as it makes a lot more from the vehicle and fuel taxes than it spends on roads.

As for the idea that cycling is dangerous, this really doesn't hold water. You have to cycle more than 20 million miles in the UK, spending hundreds of years in the saddle, before it's likely that you'll be killed. There's a lot of foolish fear of motor vehicles among UK cyclists or potential UK cyclists, but it's largely unjustified.

Rather than demanding an end to motoring and some kind of hellish 19th-century-slumdweller street-based lifestyle without telly or video games or heating (and complete with malnourished, dwarfish children) it might be nice if Professor Roberts and his crew got back to work on actually improving public health. If they are truly concerned about carbon emissions, they would do well to learn something about the subject - but not on the taxpayers' time. ®

Full Disclosure: Lewis Page stands 6'3" and weighs a tad over 16 stone (BMI = "Overweight"). In former days when properly fit he weighed over 17 stone ("Obese"). He is fortunate enough to live close enough to his place of work that he can reach it by cycle in (much) less time than it takes to use public transport - driving is not an option due to parking - and as such he commutes by cycle come rain or shine through the not-so-scary London rush hour traffic, spending a bit over an hour a day in the saddle. At that rate he can expect to be killed in around 6000 years.

The Register gains only negligible and intermittent revenue from motor vehicle advertising and none at all from the aviation or travel sectors, more's the pity. And we are quite happy to bite the hand that feeds us anyway.