Background
Night shift work is associated with weight gain and an increased risk of developing type 2 diabetes due to disrupted circadian rhythms and lifestyle factors. Intermittent fasting (IF) and continuous energy restriction (CER) are dietary approaches used to promote weight loss and improve metabolic health. However, their effectiveness specifically in night shift workers has been under-investigated.
This study aimed to evaluate the effectiveness of two modified IF protocols compared to CER on weight loss and insulin resistance among overweight or obese night shift workers.
Methods
A three-arm, parallel-group randomised superiority clinical trial was conducted in Melbourne and Adelaide, Australia. Eligible participants were night shift workers aged between 25 and 65 years with overweight or obesity. Participants were randomised in a 1:1:1 ratio to one of three groups: continuous energy restriction (CER), or one of two modified intermittent fasting strategies.
The two IF strategies involved consuming a reduced energy intake of 2100 kJ/day on two designated days per week (modified IF), with the rest of the week following their usual diet. One IF group fasted on days off or day shifts (IF:2D), while the other fasted during night shifts (IF:2N). The intervention lasted 24 weeks.
Primary outcomes were body weight and insulin resistance assessed by the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR) at 24 weeks. Weight assessors and participants were aware of group allocation, while biochemical outcome assessors and the study statistician were blinded. Statistical analysis employed mixed-effects regression models to compare groups.
Findings
Between October 2019 and February 2022, 250 participants were randomised: 85 to CER, 83 to IF:2D, and 82 to IF:2N. The average age was 46.8 years with 53.2% women. A total of 170 participants (68%) completed the study.
No significant differences were found between either IF strategy and CER for body weight change (IF:2D vs CER mean difference [MD] = -0.2 kg, 95% CI -6.4 to 5.9; IF:2N vs CER MD = -0.6 kg, 95% CI -6.8 to 5.6) or insulin resistance (IF:2D vs CER MD = -0.1, 95% CI -1.0 to 0.8; IF:2N vs CER MD = -0.3, 95% CI -0.5 to 1.2).
However, participants in the IF:2D group showed significantly lower total cholesterol and LDL cholesterol compared to CER (MD = -23.2 mg/dL and MD = -19.3 mg/dL respectively).
Completer analysis revealed favorable changes across all groups in body weight, insulin resistance, body composition, blood pressure, and cardiometabolic markers. Importantly, no serious adverse events related to the intervention were reported.
Interpretation
After 24 weeks, no significant differences in weight loss or insulin resistance were observed between the modified intermittent fasting groups and continuous energy restriction. Despite this, clinically meaningful improvements in weight and metabolic health were achieved for most night shift workers who completed the intervention.
These findings suggest that both modified intermittent fasting and continuous energy restriction can be effective dietary strategies for managing weight and metabolic risk factors in night shift workers.
Funding and Registration
This study was funded by the National Health and Medical Research Council (APP1159762) and registered with the Australian New Zealand Clinical Trials Registry (ACTRN-12619001035112).
Reference
Bonham MP, Leung GKW, Rogers M, et al. Intermittent fasting for weight loss in night shift workers: a three-arm, superiority randomised clinical trial. EBioMedicine. 2025 Jul;117:105803. doi:10.1016/j.ebiom.2025.105803 IF: 10.8 Q1 .
