Americans are increasingly overweight, with the number of obese adults and overweight children doubling between the late 1970s and early 2000s. Several studies of the health consequences of Americans’ weight gain indicate that health care costs and the number of premature deaths associated with obesity and overweight are high. A recent (lower) estimate of the number of premature deaths published in the Journal of the American Medical Association reveals the uncertainty researchers face in associating weight status with mortality. Of course, scientific uncertainty does not mute demands for public action.