Thyroid hormones influence metabolic function, but it is unclear whether variations in thyroid-stimulating hormone (TSH) within the normal range affect metabolism. This cross-sectional study examined associations between normal-range TSH and body composition, energy expenditure, and macronutrient oxidation in 65 healthy women (euthyroid controls and L-T4 treated). Participants were grouped into low-normal (0.34–2.49 mU/L) and high-normal (2.50–5.60 mU/L) TSH categories. Measurements included total energy expenditure (doubly labeled water), resting energy expenditure (indirect calorimetry), and body composition (DEXA). Weight and BMI were significantly lower in the low-normal group (p=0.05), but no other differences or continuous associations were observed. Findings suggest TSH variation within the normal range does not meaningfully influence metabolic parameters.
