Shift work is associated with a higher risk of the development of cardiometabolic syndrome (CMtS) than in people working only during the day. One of the factors predisposing to the development of the CMtS in shift workers is an inappropriate composition of their diet. It was observed that the shift workers diet is characterized by a higher intake of saturated fatty acids (SFA) and a lower consumption of unsaturated fatty acids. One potential way to reduce the risk of CMtS in this study group seems to be a modification of their everyday diet by excluding the products of animal origin (e.g. butter) with simultaneously including vegetable oils (i.e. canola oil). The aim of the study is to evaluate the effect of replacement in the everyday diet of saturated fats (butter) with unsaturated fats (canola oil-based spread and canola oil added to main meals) in centrally obese shift workers on changes in body weight and body composition parameters as well as on changes in CMtS markers.

The study was designed as a randomized clinical trial to investigate the effects of the dietary intervention with moderate in fat content (~35% energy as fat) for 12 weeks on the improvement of cardiometabolic risk factors in centrally obese shift workers. Forty centrally obese shift workers (waist circumference ≥94 cm) were randomized (1:1) to the experimental group (n = 20) or the control group (n = 20). Eligibility criteria included: aged between 30-60 years, working rotating shifts for at least 5 years and working night shifts minimum five times a month. Excluded criteria was described in the point "Eligibility". Written informed consent was obtained from all of the participants, and the local ethic committee approved the study. The dietary intervention was mainly based on the simple rearrangement of shift workers' diets by replacing food items including SFA (e.g. butter) with those being sources of unsaturated fatty acids (UFA), mainly canola oil (given to the diet as spread or this oil was added separately to main meals)

Inclusion Criteria:

• centrally obese (≥ 94cm) male
• aged between 30-60 years,
• working rotating shifts for at least 5 years and working night shifts minimum five times a month,

Exclusion Criteria:

• diabetes, familial hypercholesterolemia, thyroid and parathyroid diseases, non-specific intestinal diseases, celiac disease, phenylketonuria,
• taking medication for lowering blood lipids such as statins,
• weight loss therapy for 3 months before the intervention,
• allergies and intolerances
• consuming high-proof alcoholic beverages (>2 portions/week)