BODY-COMPOSITION AND ENERGY-EXPENDITURE IN THYROIDECTOMIZED PATIENTS DURING SHORT-TERM HYPOTHYROIDISM AND THYROTROPIN-SUPPRESSIVE THYROXINETHERAPY

Thyroid hormone levels are a major determinant of energy balance and a re thought to modify body composition by their effects on metabolism o f lipids, carbohydrate and protein. The present study evaluates change s of body composition and basal energy expenditure (BEE) in thyroidect omized short-term profound hypothyroidism while off all thyroid hormon e before diagnostic whole-body I-131-imaging and while on thyrotrophin -suppressive thyroxine therapy, Basal energy expenditure was assessed by indirect calorimetry, and four-point body impedance analysis was us ed to estimate body composition. Patients were compared with healthy c ontrols matched with respect to sex, age, height and weight, Compared to healthy controls the percentages of body water and body cell mass w ere significantly lower while the percentage of fat was significantly higher in patients during shore-term hypothyroidism. Weight did not ch ange significantly when patients were put on thyroxine treatment, but body fat (-0.95 +/- 2.25 kg, p < 0.01) decreased while body water (+0. 94 +/- 1.31kg, p < 0.01) and body cell mass (+0.9 +/- 2.5 kg, p < 0.05 ) increased, With thyroxine replacement, body composition was not sign ificantly different between patients and controls. Compared to healthy controls, BEE was significantly lower in patients without thyroxine r eplacement (5265 +/- 766 kJ/24 h vs 6362 +/- 992 kJ/24 h; p < 0.001), With thyroxine treatment, BEE increased (6492 +/- 967kJ/24 h) but was not significantly different from the controls (p > 0.05). Neither body composition nor BEE was significantly different in a subgroup of thyr oxine-treated patients with free triiodothyronine or thyroxine values above the normal range. In conclusion, both body composition and energ y expenditure showed significant changes when patients were deprived o f thyroid hormone. However, no evidence of excess metabolic effects of thyroid hormone during thyrotrophin-suppressive thyroxine therapy was found.