Dietary Macronutrients and Metabolic Markers

This prospective, single-group, 12-week dietary intervention study investigated the effects of a ketogenic diet on thyroid function and glucose-insulin metabolism in premenopausal women aged 30-50 years. Participants were classified according to baseline BMI into normal-weight, overweight, and obesity categories for analytical purposes. All participants received the same ketogenic dietary intervention; BMI categories did not represent separate intervention arms.

The ketogenic diet was individually prescribed and characterized by very low carbohydrate intake, moderate protein intake, and a high proportion of dietary fat. Participants received individualized dietary plans and nutritional counseling throughout the intervention. Nutritional ketosis was monitored during the study.

Assessments were performed at baseline and after 12 weeks. Thyroid function was evaluated using serum TSH, FT3, and FT4 concentrations. Glucose-insulin metabolism was assessed using fasting glucose, fasting insulin, HbA1c, and HOMA-IR. Body mass and anthropometric measurements were also obtained to evaluate changes in adiposity-related parameters.

A total of 150 women were screened for eligibility, 120 entered the intervention, and 100 completed the 12-week study. The study was conducted at the Jerzy Kukuczka Academy of Physical Education in Katowice, Poland. The primary objective was to determine whether the metabolic and thyroid responses to a ketogenic diet differed according to baseline adiposity.

Inclusion criteria

Premenopausal status, defined by ongoing menstrual cycles and no history of menopause.

No use of a specific diet, calorie-restricted diet, or food-elimination regimen during the preceding 12 months.

Low-to-moderate habitual physical activity. Willingness to follow the prescribed ketogenic diet for 12 weeks. Willingness to participate in all study assessments. 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.

Pharmacological treatment for insulin resistance. Pharmacological treatment for dyslipidemia.