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Saturday, November 24, 2007

Is Reducing Global Warming the Key to Preventing Obesity?

The link between two major problems of our times, global warming and the obesity epidemic, may be closer than we think. 

The following are a few random thoughts on why I believe solving one will go a long way to solving the other.

If we accept that a major contribution to the rising incidence of obesity is (energy) overconsumption and lack of physical activity, then reducing consumption and increasing physical activity will be important. 

But reducing consumption and increasing physical activity will also help reduce global warming - here is why:

Over the past century, fossil fuels have increasingly displaced food as the energy source for human movement. Both occupational and domestic physical activity has been replaced by automation and labor-saving devices, all of which consume energy from fossil fuels.  But not just automation, also the physical effort to move from one place to another is today largely dependent on fossil fuels.

As people get larger the fuels consumed to move the extra weight around only adds to the problem. It was estimated that in 2000,  US airlines spent $275 million to burn 350 million more gallons of fuel just to carry the additional weight of Americans. Obviously, it also takes more fuel to move heavier people around on the ground whether this is in cars or on elevators, escalators or amusement park rides. 

But increased use of fossil fuels is not just part of the activity equation. The use of fossil fuels is also intimately linked to our food. World-wide, agricultural activity, especially livestock production (including ruminant methane production, transport and feed), accounts for about one fifth of total greenhouse-gas emissions.

In most industrialised countries today the total energy put into food production vastly exceeds the food energy yield [see McMichael et al. for in depth discussion of this topic].

As energy inputs, mainly in the form of fossil fuels, have gradually increased, the energy ratio (energy out/energy in) in agriculture has decreased from being close to 100 for traditional pre-industrial societies to less than 1 in the present food system. Each calorie of food you eat may have consumed 10 to 50 calories in fossil fuels (the exact number depends on how you calculate this relationship - but no matter how you do it, the numbers are scary). 

Processing 1 pound of coffee requires more than 8,000 calories of fossil fuel, the equivalent of one quart of crude oil, 30 cubic feet of natural gas or 2 1/2 lbs of coal.  It has been estimated that the CO2 emissions attributable to producing, processing, packaging and distributing the food consumed by a family of four is about 8 tonnes a year. (For more on this click here).

Not surprisingly, many environmental organisations are now targeting built environments, transportation as well as food production and supply as major culprits in global warming. How do some of these issues relate to obesity prevention?

Rebuilding our cities to allow shorter trip distances will also allow changes in travel mode (e.g. walking or bicycling instead of driving). When it comes to both  the environment and to obesity, urban sprawl is a killer! 

Compact densely populated neighbourhoods where the majority of trips can be done by active transport paired with efficient urban public-transport systems powered by renewable energy would not only reduce local air pollution and greenhouse emissions but would also reduce traffic injuries and improve the safety of neighbourhoods (more people on the street!). 

Creation of human-scale, mixed-use urban "villages" with unique identities, improved local services, neighbourhood events and activities, accessible public transport including high-quality pavements, cycle paths, lighting and public art will get people out and moving - thereby reducing both greenhouse gases and increasing physical activity. (for an in-depth analysis of these issues refer to Woodcock et al. in the Lancet series on Energy and Health). 

Perhaps the key to both global warming and the obesity epidemic may be in living, working and eating local. 

Is this utopia? To some perhaps, but the alternative is scary!


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