Body composition, resting energy expenditure and metabolic changes in women diagnosed with differentiated thyroid carcinoma.

BACKGROUND: Thyroid hormones heavily impact energy expenditure, body mass, and body composition. Their role in the state of exogenous subclinical hyperthyroidism in differentiated thyroid carcinoma (DTC) patients, however, is less well-defined. The first aim of this study was to assess changes in body weight, body composition, resting energy expenditure (REE), respiratory quotient (RQ), and metabolic parameters in female DTC patients, starting from the phase of a euthyroid state prior to total thyroidectomy through the subsequent year following thyroid-stimulating hormone (TSH) suppression. The second aim was to assess the relationship between these variables and thyroid function parameters.

METHODS: This observational case series analyzed changes in body composition, calorimetric and metabolic parameters of 15 DTC female patients at five time points: (1) at initial DTC diagnosis (euthyroid state), (2) at 2-3 weeks after thyroidectomy (hypothyroid state), (3) at 2-3 months of levothyroxine (LT4) treatment (exogenous euthyroid state), (4) after 6-9 months, and (5) after one year of TSH suppressive LT4 therapy (exogenous subclinical hyperthyroid state). A generalized estimating equation (GEE) analysis was performed to estimate the longitudinal correlations of TT3/FT4 ratio (as an independent variable) with body composition, metabolic and calorimetric parameters changes (as dependent variables).

RESULTS: REE, REE per kilogram of lean body mass (REE/LBM), pulse, and systolic and diastolic blood pressure were significantly higher after TSH suppressive LT4 therapy. The GEE analysis revealed longitudinal negative correlations between the TT3/FT4 ratio and systolic blood pressure, fasting blood glucose, body mass index, android (abdominal wall and visceral mesentery) fat distribution, trunk, and arm fat distribution, REE and REE/LBM. There was a positive correlation with RQ.

CONCLUSIONS: REE, REE/LBM, pulse, and systolic and diastolic blood pressure were significantly higher after thyroidectomy, radioiodine and TSH suppressive therapy in female DTC patients, while no changes were observed in body weight or body composition. A lower TT3/FT4 ratio longitudinally correlated with increases in REE, REE/LBM, abdominal fat distribution, systolic blood pressure and fasting blood glucose, as well as with decreased RQ. These findings highlight the importance of judicial balancing of the benefits and detriments of TSH suppression with subsequent decreased TT3/FT4 ratios for female DTC patients.