Moderate Weight Loss Is Sufficient to Affect Thyroid Hormone Homeostasis and Inhibit Its Peripheral Conversion

Background: Thyroid hormones are important determinants of energy expenditure, and in rodents, adipose tissue affects thyroid hormone homeostasis via leptin signaling. The relationship between thyroid hormones and nutritional status in humans has been assessed primarily in drastic dietary or bariatric surgery interventions, while limited information is available on serial assessment of this axis during moderate, prolonged dietary restriction. Methods: To evaluate the effects of moderate dietary restriction on thyroid hormone homeostasis, 47 subjects with a body mass index (BMI) of 25–45 kg/m2 were enrolled in a longitudinal intervention study; 30 nonoverweight volunteers were also enrolled as controls. Overweight and obese subjects underwent a 12-month individualized dietary intervention aimed at achieving a 5–10% weight loss. Results: The intervention resulted in a 6.3±0.9 kg (6.5±1.0%) weight loss. At baseline, thyrotropin (TSH) and T3 concentrations correlated significantly with fat mass (R=0.257, p=0....