Smoking cessation and long-term weight gain in the Framingham Heart Study: an application of the parametric g-formula for a continuous outcome.

Weight gain after smoking cessation can lessen the health benefits of, and reduce the incentives for, quitting smoking. Randomized clinical trials of smoking cessation have estimated this weight gain only over short periods of follow-up. We provide an estimate of long-term post-cessation weight gain in the Framingham Heart Study, a prospective observational study. We identified 2001 smokers free of diabetes, cancer, and cardiovascular disease in 1952. Using the parametric g-formula we estimated mean weight in 1972 if all smokers had quit at baseline versus if all had continued smoking. Our estimates were adjusted for demographic, socio-economic, and clinical factors at baseline and during follow-up. The estimated mean weight (95 % CI) at 20 years if all smokers had quit smoking was 75.2 kg (73.5, 76.6), compared with 70.2 kg (68.7, 71.8) if they had smoked 20 cigarettes/day and 73.4 kg (71.9, 74.6) if they had smoked 5 cigarettes/day (i.e., an estimated mean weight gain of 5.1 kg (3.1, 6.6) and 1.8 kg (0.8, 2.8), respectively). Smokers who were overweight or obese at baseline had a greater post-cessation weight gain on average. Our estimates suggest that smoking cessation can result in increases in body weight over 20 years. While the benefits of smoking cessation outweigh the risks due to post-cessation weight gain, our results highlight the need for long-term weight management interventions in combination with smoking cessation.