A recent study led by Dr. Katherine M. Flegal at the Centers for Disease Control and Prevention made headlines by suggesting that overweight people may live longer than their normal-weight friends. Which made those of us who’ve been trying to lose 10 or 20 pounds put down our crullers and jump for joy. Which we then realized was a form of exercise, so we stopped.

But Flegal’s study was careful to point out that “overweight” and “obese” are not the same thing. “Normal-weight” people have body-mass indices of 18.5 to 24.9, while “overweight” includes BMIs of 25 to 29.9. Obesity begins at a BMI of 30. Flegal’s study showed that mortality rates didn’t become markedly higher until individuals hit a BMI of 35.

Now, a new study led by Dr. Thomas M. Rice at the University of California, Berkeley suggests something very similar — except Rice’s study is focused on drivers.

Rice and his colleagues studied 6,806 motorists in the U.S. who had been involved in 3,403 collisions. Of those studied, 46% were of “normal weight”, 33% were “overweight”, and 18% were “obese”. Here are the major takeaways:

• Among those who had a BMI of at least 40, there was an 80% greater likelihood of dying in an accident compared to drivers who were classed as “normal weight”. 
• The situation was particularly bad for women: women with BMIs of at least 35 were twice as likely to die in automobile accidents than those with BMIs between 18.5 and 24.9.
• The findings aren’t so great for “underweight” drivers, either: those with BMIs below 18.5 had a fatality rate 19% above those of “normal weight”.
• The lowest fatality rates were among drivers with BMIs ranging from 18.5 to 30. 

We might assume that these fatality rates were affected by factors like cardiovascular disease, which is often a side-effect of excessive weight. However, the study suggests that a major reason for the spike in deaths is, in fact, the trusty seat belt. As Rice and his colleagues point out, seat belts respond slower to soft tissue (i.e. fat). Thus, when heavy drivers are involved in collisions, their seat belts have less opportunity to lessen the impact.

If this study isn’t enough to make us all dust off our gym cards, perhaps we should remember that extra weight affects our wallet, too. In fact, obesity costs Americans roughly $4 billion each year at the pump. (Our penchant for eating and driving doesn’t help matters.)

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This article originally appeared at The Car Connection.