Weight loss maintenance one year after modified intermittent fasting in circadian-disrupted night shift workers: longer-term secondary outcomes from the SWIFt randomised clinical trial

Background: Extended health benefits of a period of intermittent energy restriction in circadian-disrupted night-shift workers are unknown. Methods: We examined secondary 18-month outcomes of the SWIFt trial; a three-arm, parallel-group randomised controlled trial. Night-shift workers ( n = 250) were randomised 1:1:1 to 24 weeks of moderate (20%) energy restriction; daily (continuous energy restriction; CER); or modified intermittent fasting on two days per week, undertaken on days off/day shifts (IF:2D) or during night shifts (IF:2N). The primary endpoint was reported previously. Outcomes of body weight, HOMA-IR and cardiometabolic risk factors were assessed 18 months after study enrolment, which was 12 months after completion of the supported intervention period. Analyses used the intention-to-treat principle. ANZCTR ACTRN-12619001035112 (19/07/2019). Results: Here we show that at 18 months, mean difference in weight and HOMA-IR does not appear to differ between groups: weight, IF:2D versus CER = 2·7 kg [95% CI −3·6 to 9·2] and IF:2N versus CER = 0·9 kg [95% CI −5·6 to 7·3]; HOMA-IR, IF:2D versus CER = 0·7 [95% CI −0·3 to 1·7] and IF:2N versus CER = 0·7 [95% CI −0·2 to 1·7]. Between group differences are not observed in other cardiometabolic measures. Within-group body weight remains lower than baseline: CER: −4.8 kg [95% CI −6.1 to −3.1], IF:2D: −4.5 kg [−6.3 to −2.8], IF:2N: −3.2 kg [−5.1 to −1.04]. Attrition is similar between groups, with 141 participants providing data at 18 months. Conclusions: Findings indicate no apparent difference between strategies at 18 months, although the study may have insufficient power to detect small but clinically meaningful effects.