Shift workers are a growing population. It is well established that these workers face an increased risk of developing chronic diseases, but the underlying mechanisms remain debated. Various factors such as internal circadian desynchronization, unhealthy lifestyle behaviours, and lack of sleep interact in complex ways. Recently, it has been suggested that the gut microbiota (GM) may play an important role in this increased risk.

The goal of this study is to describe the variations of the GM composition in shift workers across three different rotating weekly shifts (morning, afternoon, night) and to measure the impact of a 3- week walnuts supplementation intervention consisting in a controlled experimental study.

Therefore, we propose a 6-weeks study including an observational and an experimental part. First, in the observational part, we will compare the gut microbiota of shift workers across three shifts (morning, afternoon and night). In the second part of the study, participants will add to their usual intakes a daily serving of nuts (30g). Again, we will compare the gut microbiota composition across the three types of shifts. During the study, participants will record their food intake, sleep and defecation time. We will also monitor their blood glucose levels continuously during the 4 first weeks of the study.

Inclusion Criteria:

• Working 3x8 shifts (weekly rotations between AM, PM and N shifts) for at least 3 months prior to the study
• No anticipated changes in shift work planning
• No prebiotics or probiotics supplements.

Exclusion Criteria:

• Antibiotic and/or immunomodulator use in the last 3 months or during the study
• Change in medication during the last month or during study
• Inflammatory bowel disease or important gut surgery
• Nuts allergy
• Major digestive tract surgery.

De-identified individual participant data for all primary and secondary outcome measure will be made available.

Data will be available within 12 months of study completion

At the end of the project the data will be deposited in the Yareta repository developed by the University of Geneva OR in an institutional repository. This choice will ensure that data is archived and shared in accordance with FAIR principles.