A brief summary of current research.
Tagliaferri, F, Compagnone, C, Yoganandan, N, Gennarelli, TA. The Journal of Trauma: Injury, Infection, and Critical Care Vol. 66 (3) March 2009 pp 727-729.
This study found that clinically obese people (Body Mass Index >30) experienced a significant increase in death and injury severity after a frontal collision when compared to those not obese. Also, obese passengers are more likely to suffer a more severe head trauma after a frontal collision in a vehicle crash.