I don't think there is a survey, but if there were, it would be no suprise if trim people drove trim cars - larger people drive big vehicles.
Obesity has been on the rise in recent years. Pardon the pun, but my gut feeling is many Americans purchase larger vehicles along with larger clothes as they get bigger. This is probably one of the less spoken reasons for SUV sales. Stadium seating in America has had to allow for larger seats, so it's reasonable to assume that's why Japanese car makers have had to sell larger vehicles in the US.
I don't know if losing 40 pounds over the past year has improved my mpg, but I feel better.
