Smoking and obesity or overweight are risk factors for many diseases, making them among the world’s greatest health problems. Tobacco is the main cause of premature death worldwide, being responsible for 5.1 million deaths each year.1 Obesity, together with overweight, causes 2.8 million deaths.1 Smoking and obesity are moving in opposite directions, with the prevalence of smoking declining and that of obesity increasing in lower middle income countries and deprived population groups in high income countries.2 It has long been known that smokers weigh less than former smokers or people who have never smoked.2 Weight gain is a widely anticipated consequence of quitting, and many smokers—particularly women3—avoid quitting for fear of gaining weight.4 A common question that …