The effects of dietary instruction on cardiovascular risk markers after smoking cessation: study protocol for a multicenter randomized controlled trial in Japan

BACKGROUND: Weight gain frequently occurs after smoking cessation (SC); the risk of new-onset diabetes mellitus increases for several years after SC. However, no large-scale, randomized controlled trials have examined the effects of nutritional guidance on post-SC cardiovascular risk. The current trial will enroll individuals who successfully quit smoking with the help of a SC clinic and who gain weight, to determine the effects of nutritional guidance on cardiovascular, glucose, and lipid metabolism biomarkers. METHODS/DESIGN: This is a multicenter, prospective, parallel-group, randomized controlled trial. Some 250 individuals who successfully quit smoking with the help of a SC clinic and who gain weight (an increase of ≥ 1.25% Body Mass Index (BMI) between the first and the fifth visit to the SC clinic) will be enrolled within 1 month of the final (fifth) visit to the SC clinic. These participants will be randomly assigned to an intervention group (125 individuals receiving nutritional guidance) or a control group (125 individuals not receiving nutritional guidance). A registered dietitian will provide nutritional guidance once every 3 months for a total of three sessions. The primary endpoint for this trial will be the level of adiponectin, a predictor of cardiovascular risk that reflects weight and smoking status. Secondary endpoints will be levels of cardiovascular, glucose, and lipid metabolism biomarkers, BMI, abdominal circumference, and the percentage of individuals who quit smoking for a prolonged period. DISCUSSION: This trial will determine the benefits of nutritional guidance with respect to post-SC weight gain. The findings should provide useful information for devising a quality protocol for SC education to prevent cardiovascular disease. TRIAL REGISTRATION: The study is registered at the University Hospital Medical Information Network Clinical Trials Registry (UMIN000030282). Registered on 6 December 2017. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13063-018-2919-6) contains supplementary material, which is available to authorized users.