No changes in dietary intake after quitting smoking; a prospective study in Switzerland

BACKGROUND: After quitting smoking, quitters frequently increase their weight and change their dietary intake. Still, most studies on the topic are over 20 years old and focused on few dietary markers. We analysed the changes in weight and dietary intake after quitting smoking using a large panel of dietary markers. METHODS: Prospective study including 5064 participants, 169 of whom (3.3%) quitted during a median follow-up of 5 years. Dietary intake was assessed using a food frequency questionnaire. Participants were excluded if they lacked dietary data or reported extreme total energy intakes (TEI) < 850 or > 4000 kcal/day. RESULTS: Data from 128 participants (43.8% women, aged 56.0 ± 10.0 years) were used. After quitting smoking, mean weight increased 2.1 ± 0.7 kg; the majority (58%) of the participants gained over 1 kg, and only 7.1% were on a diet to reduce their weight. Total protein intake increased from (median [interquartile range]) 14.4 [12.9–16.4] to 15.1 [13.4–17.9] % of total energy intake (TEI), p = 0.008, while animal protein intake increased from 9.7 [8.0–12.1] to 10.8 [8.5–13.5] %TEI, p = 0.011. Fish intake increased from 27 [17–45] to 37 [19–55] g/day, p = 0.016 and dairy intake decreased from 177 [94–288] to 150 [77–243] g/day, p = 0.009. No other changes were found. Among the 68 (53%) participants who reported time since quitting, quitting for <=1 year led to a decreased consumption of fruits, while the opposite was found for participants who quit for longer than one year. No associations were found between weight or dietary changes and time since quitting. CONCLUSIONS: People who quit smoking tend to gain weight, do not significantly change their dietary intake, and seem to make little effort to prevent weight gain. Systematic dietary support should be provided to all smokers wishing to quit. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40795-021-00440-4.