Protocol for a randomised controlled trial on the feasibility and effects of 10-hour time-restricted eating on cardiometabolic disease risk among career firefighters doing 24-hour shift work: the Healthy Heroes Study

Introduction: Career firefighters experience chronic circadian rhythm disruption, increasing their risk of cardiometabolic disease. The recent discovery that eating patterns regulate circadian rhythmicity in metabolic organs has raised the hypothesis that maintaining a consistent daily cycle of eating and fasting can support circadian rhythms and reduce disease risks. Preclinical animal studies and preliminary clinical trials have shown promising effects of time-restricted eating (TRE) to reduce disease risk without compromising physical performance. However, there is a lack of research on TRE in shift workers including firefighters. This study aims to investigate the feasibility and efficacy of 10-hour TRE on health parameters that contribute to cardiometabolic disease risks among career firefighters who work on a 24-hour shift schedule.

Methods and analyses: The Healthy Heroes Study is a randomised controlled parallel open-label clinical trial with 150 firefighters over 1 year. Firefighters are randomised with a 1:1 ratio to either the control or intervention group. The control group receives Mediterranean diet nutritional counselling (standard of care, 'SOC'). The intervention group receives the same SOC and a self-selected 10-hour TRE window. After the 2-week baseline, participants enter a 3-month monitored intervention, followed by a 9-month self-guided period with follow-up assessments. The impact of TRE on blood glucose, body weight, body composition, biomarkers (neuroendocrine, inflammatory and metabolic), sleep and mood is evaluated. These assessments occur at baseline, at the end of intervention and at 6, 9 and 12-month follow-ups. Temporal calorie intake is monitored with the smartphone application myCircadianClock throughout the study. Continuous glucose monitors, wrist-worn actigraphy device and questionnaires are used to monitor glucose levels, activity, sleep and light exposure.

Ethics and dissemination: The study was approved by the Institutional Review Boards of the University of California San Diego and the Salk Institute for Biological Studies. Results will be disseminated through peer-reviewed manuscripts, reports and presentations.

Trial registration number: NCT03533023; Pre result.