Subclinical hypothyroidism in obese patients: Relation to resting energy expenditure, serum leptin, body composition, and lipid profile

Objective: To evaluate whether subclinical hypothyroidism (SH) affects rest ing energy expenditure (REE) as well as body composition, lipid profile, an d serum leptin in obese patients. Research Methods and Procedures: A total of 108 obese patients with SH defi ned as normal free thyroxine levels and thyroid-stimulating hormone (TSH) v alues of >4.38 muU/ml (mean +/- 2 SD of the values of our reference group o f obese patients with normal thyroid function) were compared with a group o f 131 obese patients matched for age, sex, and body mass index (BMI) but wi th normal TSH levels. We assessed estimated daily caloric intake by 7-day r ecall, REE by indirect calorimetry, body composition by bioelectrical imped ance analysis, serum leptin by radioimmunoassay, and lipid profile (i.e., t otal cholesterol, high-density lipoprotein cholesterol, low-density lipopro tein cholesterol, and triglycerides). Results: All of the variables measured were not different between the euthy roid obese patients and those with SH. In a multiple regression model with REE expressed for kilo-grams of fat free: mass (REE/kgFFM) as a dependent v ariable and percentage of fat mass, BMI, waist-to-hip ratio, age, TSH, free thyroxine, serum leptin, and caloric intake as independent variables, only percentage of fat mass was significantly correlated with REE/kgFFM in both groups. Tn the SH group only, BMI, waist-to-hip ratio, age, and TSH were r elated to REE/kgFFM and explained 69.5% of its variability. After dividing the patients with SH using a cutoff TSH value of 5.7 muU/ml, which represen ts 3 SD above the mean of TSH levels of the group of obese patients with no rmal thyroid function, only REE/kgFFM was significantly different and lower in the group of more severely hypothyroid patients. Discussion: In patients with obesity, SH affects energy expenditure only wh en TSH: is clearly above the normal range; it does not change body composit ion and lipid profile. We suggest that, at least in obese patients, evaluat ion of TSH levels may be useful to rule out a possible impairment of restin g energy expenditure due to a reduced peripheral effect of thyroid hormones .