Dietary Macronutrients and Metabolic Markers

This prospective 12-week dietary intervention study evaluated the effects of a ketogenic diet on thyroid function and glucose-insulin metabolism in premenopausal women aged 30-50 years across different adiposity categories. Participants followed an individualized low-carbohydrate ketogenic diet designed to induce and maintain nutritional ketosis. Thyroid-related outcomes included thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), and free thyroxine (FT4). Glucose-insulin metabolism was assessed using fasting glucose, fasting insulin, glycated hemoglobin (HbA1c), and the homeostatic model assessment of insulin resistance (HOMA-IR). Changes in body mass and anthropometric parameters were also evaluated. Outcomes were assessed before and after the 12-week intervention and compared according to baseline BMI categories.

Inclusion Criteria: * Premenopausal status * No use of a specific diet, calorie-restricted diet, or food-elimination regimen during the preceding 12 months * Willingness to follow the prescribed ketogenic diet for 12 weeks * Provision of written informed consent Exclusion Criteria: * Postmenopausal status * Pregnancy or breastfeeding * Previously diagnosed thyroid disease * Thyroid hormone replacement therapy * Use of antithyroid medication * Use of other pharmacological treatments known to substantially affect thyroid function * Use of dietary supplements known to substantially affect glucose or lipid metabolism before enrollment * Use of pharmacological treatment for insulin resistance * Use of pharmacological treatment for dyslipidemia