All subjects received 5:2 IF. They followed a normal diet for 5 days each week and practiced IF for 2 days discontinuously. On normal eating days, women consumed 1200 to 1500 kcal/day and men consumed 1500 to 1800 kcal/day, with macro-nutrient distribution of 45% to 50% carbohydrate, 20% protein, and 30% to 35% fat. They consumed 500 kcal and at least 50 g of protein on a light fasting day. Noncaloric beverages like water and unsweetened tea were allowed without restriction. A nutritionist provided diet guidance and documented any discomfort symptoms throughout the study.

All subjects received 5:2 IF. They followed a normal diet for 5 days each week and practiced IF for 2 days discontinuously. On normal eating days, women consumed 1200 to 1500 kcal/day and men consumed 1500 to 1800 kcal/day, with macro-nutrient distribution of 45% to 50% carbohydrate, 20% protein, and 30% to 35% fat. They consumed 500 kcal and at least 50 g of protein on a light fasting day. Noncaloric beverages like water and unsweetened tea were allowed without restriction. A nutritionist provided diet guidance and documented any discomfort symptoms throughout the study.

BMI will be calculated as weight (kg) divided by height squared (m²). Weight will be measured on a calibrated digital scale and height using a stadiometer. Measurements will be taken at baseline and after the 8-week intermittent fasting intervention.

Fasting venous blood samples will be collected at baseline and after the 8-week intermittent fasting intervention. Serum TSH and FT4 concentrations will be determined using a standardized automated immunoassay. TSH Index will be calculated according to published formulas.

Fasting blood samples will be collected at baseline and after the 8-week intermittent fasting intervention. Serum TSH and FT4 concentrations will be measured using a standardized automated immunoassay. TTSI will be calculated according to published formulas.

Fasting venous blood samples will be collected at baseline and after the 8-week intermittent fasting intervention. Serum FT3 and FT4 concentrations will be measured using a standardized automated immunoassay, and the FT3/FT4 ratio will be calculated as an index of peripheral thyroid hormone conversion efficiency.

Lipid profile: Total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), and high-density lipoprotein cholesterol (HDL-C) will be measured from fasting blood samples.

Glycated hemoglobin (HbA1c, %) will be measured using high-performance liquid chromatography (HPLC). Fasting glucose (mg/dL or mmol/L) will be measured using an enzymatic glucose oxidase method. Fasting insulin (μIU/mL) will be measured using an electrochemiluminescence immunoassay. All blood samples will be collected after an overnight fast at baseline and after the 8-week IF intervention.