A great deal has been written about how losing excess weight is good for you. Two British epidemiologists did some number crunching and found that it's also good for everyone else.

Being overweight means that you cause more carbon dioxide production, which contributes to global warming. Some of this comes from the energy used to produce and process the extra food that you're eating. Some also comes from the fact that it takes more energy to transport a heavy person than it takes to transport a lighter one. More gasoline for car travel, more jet fuel for airplane travel. And possibly, overweight people choose to walk less and drive more.

A thinner population would reduce carbon dioxide emissions by about 440 million tons a year, at a minimum.

There are estimated to be one billion overweight and obese people in the world. It's getting worse year by year. In the UK, it's estimated that 40% of the population will be obese by 2010. The numbers are similar for the US. How much less carbon dioxide would these one billion people produce if they were slimmer?

Phil Edwards and Ian Roberts are epidemiologists at the London School of Hygiene and Tropical Medicine. They also wondered about this question. Then they crunched some numbers. They changed peoples' present weights back to what they were on average in the 1970s UK, when only 3.5% percent of the population was obese. How much less carbon dioxide would these slimmer people produce?

A lot less — a thinner population would reduce carbon dioxide emissions by about 440 million tons a year, at a minimum. That's one big effect a leaner population would have on the environment. And they'd also look a lot better, too.

In addition to their greater carbon dioxide emissions, the obese tend to use their cars more as they find it harder and harder to move their bodies around, thus increasing gas consumption.

The study points out how an individual's actions can still change the world. Unfortunately, right now we're changing the world for the worse. Take the case of the Flying Doctor, an airborne ambulance used to service rural and remote areas of Australia. In January 2009, the Australian government announced that the planes had to be redesigned because they're only capable of transporting patients who weigh up to 308 pounds. Not good enough in modern day Australia.

From this viewpoint, keeping in shape becomes much more than a personal issue. Some might even see it as an obligation. Not only will it improve your quality of life, it will do it for everyone else, too. Winners all around.

The article was published in the April 20, 2009 issue of the International Journal of Epidemiology.