LONGITUDINAL CHANGES IN BODY COMPOSITION, BONE MASS, AND BASAL METABOLISM DURING RECOVERY FROM HYPERTHYROIDISM: 12-MONTH FOLLOW-UP STUDY USING DXA AND INDIRECT CALORIMETRY

Abstract

Hyperthyroidism is associated with weight loss, altered body composition, and increased resting energy expenditure (REE). This study evaluated the pattern of body weight changes during the first 12 months of anti-thyroid drug (ATD) therapy in treatment-naïve patients with Graves’ disease (GD) and examined their association with thyroid hormone levels, REE, and physical activity (PA). This prospective longitudinal study included 38 treatment-naïve patients with GD who were followed for 12 months. Total body weight (TBW), BMI, pulse rate, and thyroid function tests were assessed at baseline and after 12 months of ATD therapy. Body composition, including lean mass, fat mass, and bone mineral content, was measured using DXA. REE was determined by indirect calorimetry and compared with predicted basal metabolic rate (BMR). Changes between baseline and follow-up were analyzed using paired t-tests. Within- and between-individual correlations were assessed using the Bland–Altman correlation method. Significant increases were observed in TBW, BMI, and lean body mass following treatment. Although absolute REE remained unchanged, the REE/BMR ratio decreased significantly from 111.6% to 101.9% (p = 0.043), indicating normalization of metabolic efficiency. Multivariate analysis identified Baseline FT3 ( p = 0.018) and Age (p = 0.043) as the primary independent predictors of 12-month weight gain Within-individual analysis demonstrated a strong inverse correlation between weight gain and reduction in free triiodothyronine (FT3) levels ( r = −0.742, p < 0.001). Between-individual analysis showed a significant positive correlation between body weight and absolute REE ( r = 0.536, p = 0.002). No significant association was observed between changes in PA and body weight. Our study revealed that treatment of GD over 12 months leads to a significant increase in TBW distributed across both lean and fat tissues. The increase in body weight is correlated with the reduction of FT3 and the normalisation of metabolic efficiency (REE/BMR ratio), but not with changes in PA.