A team at the Injury Research Center of the Medical College of Wisconsin in Milwaukee has found that being obese increases male drivers' risk of dying in a car crash, as does being very slim. However, being moderately overweight might help cushion the blow.
The researchers suggest that the unexplained reasons for the gender difference in BMI and motor vehicle fatality might be, in part, the difference in body habitus or body shape between men and women, and should be studied further. Their findings may also lend credence to the theory of a "cushioning effect" for slightly overweight men that might protect them from fatal injury in a crash, according to Dr. Zhu. |link|
(Yes, I heard about this on Car Talk)
1 The other two advantages are that a few extra pounds can supply the human body with valuable energy reserves in case of a minor famine and that your ass is less likely to hurt when riding public transportation.