WALTER WILLETT, MD, DrPH, is a professor of epidemiology and nutrition and chairman of the department of nutrition at Harvard School
MALISSA WOOD, MD, is a clinical cardiologist and staff physician at Massachusetts General Hospital
DAN CHILDS is the managing editor of medical coverage for ABC News
Tackling a weight problem is often viewed as a personal responsibility that requires making healthier choices. The latest research, however, shows that external factors”from family and friendships to advertising and the workplace environment”make an equal, if not greater, contribution. Just look at the stats: A person’s chance of becoming obese increases by 57 percent if a close friend is obese, 40 percent if a sibling is obese, and 37 percent if a spouse is obese.