Effect of Low-calorie Diets With Different Macronutrient Composition and Macronutrient Distribution in Shift Workers With Prediabetes or Type 2 Diabetes and Overweight or Obesity.

Background and Aims: Shift work, particularly involving night shifts, is associated with increased risk of metabolic disturbances such as type 2 diabetes mellitus (T2DM). Thus, it is important to explore mechanisms underlying this deleteroius effect and strategies that could prevent or mitigate it. The aim of the study is to investigate the effect of three low-calorie diets with different macronutrients composition and distribution along day on glucose metabolism and other health outcomes in overweight or obese shift workers with prediabetes or T2DM.

Methods: In this randomized controlled trial, 120 shift workers with a BMI \> 27.5 kg/m2 and diagnosed with prediabetes or T2DM will be recruited. The trial assesses three low-calorie diets effects on glucose metabolism, body composition, and health outcomes over 12 weeks. These diets include: A) high-protein dinner (60% of total daily protein), B) low-protein dinner (15% of total daily protein), and C) normoproteic diet.


Eligibility Criteria:
Inclusion Criteria:

* Body mass index (BMI) ranging between 27.5 and 40 kg/m2.
* Presence of prediabetes (fasting glucose between 100-125 mg/dL and/or glycated hemoglobin between 5.7 and 6.4%) or type 2 diabetes mellitus (fasting glucose ≥ 126 mg/dL and/or glycated hemoglobin ≥ 6.5% and/or currently taking metformin), based on the criteria of the American Diabetes Association.
* Engaged in shift work, including night shifts, for at least 1 year and intending to maintain this schedule in the upcoming months.
* Provide written informed consent for voluntary participation in the study after reviewing the participant information sheet and addressing any resulting queries.

Exclusion Criteria:

* Treatment with antidiabetic medications (oral or subcutaneous) or insulin in the last 2 months, except for stable use of metformin or Dipeptidyl peptidase 4 (DPP-4) inhibitors for a minimum of 6 months.
* Treatment with lipid-lowering agents in an unstable manner for at least 6 months prior to study entry.
* Regular consumption of functional foods such as phytosterols or red yeast rice, which have a significant effect on lipid or glucose metabolism, in an unstable manner for at least 6 months prior to study entry.
* Presence of other chronic conditions that are not well-controlled and could interfere with study outcomes, such as cardiovascular disease, renal disease, or liver disease.
* Presence of uncontrolled endocrine disorders, including hypothyroidism.
* Use of medications that could interfere with lipid and/or glucose metabolism, unless taken stably throughout the study.
* Consumption of sleep supplements, except for stable use for 6 months with the intention to continue stable use throughout the study.
* Presence of any laboratory abnormalities that could affect study results.
* Weight gain or loss of ≥ 5% in the last 3 months.
* Use of vitamin supplements in an unstable manner for at least 6 months prior to study entry.
* High intake of alcohol (\> 30 g of ethanol) on a regular basis.
* Pregnancy or intention to become pregnant during the study.
* Severe illness of any kind with a life expectancy of less than 1 year or that, in the investigators' judgment, limits uniform dietary intake throughout the study.
* Any other circumstance that, in the investigators' judgment, would impede adequate adherence to the proposed nutritional intervention (e.g., frequent travel during the study, inability to attend visits due to personal or work-related circumstances, etc.).