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The aim of this study was to investigate the relationship between estrogen and leptin, thyroid (T3), Uncoupling Protein2 (UCP2), sex hormone binding globulin (SHBG), and resting energy expenditure(REE) in obese subjects with normal and low REE, and to investigate the relationship of estrogen with body composition and energy intake.A total 49 subjects (25–50 years old) were selected. Anthropometric measurements, body composition, and resting energy expenditure were measured. Fasted circulating leptin, T3, SHBG and UCP2 levels were also measured. Subjects were divided to three groups: BMI > 30 and low resting energy expenditure (group I, n = 16), BMI > 30 and normal resting energy expenditure (group II, n = 17), and non-obese women as the control group (group III, n = 16).A significant association was observed between estrogen and REE in obese women with normal REE. There was a significant association between estrogen and leptin in groups I (β = 0.98, p < .0001), and II (β = 0.84, P < .0001). However, no significant association was observed between estrogen and T3 and UCP2 protein in the three groups. Regression analyses demonstrated no correlation between fat mass, percent fat mass, and plasma estrogen. Plasma estrogen was not correlated with caloric intake or macronutrients of the diet.Estrogen has been shown to affect metabolism and hemostasis in obesity and increases resting energy expenditure via leptin. Production of UCP2 in PBMC is not affected by estrogen.Estrogen affect metabolism and hemostasis in obesity and increase REE via leptin.Variation in the physiologic range of leptin, T3, and estrogen may contribute to the inter-individual differences in REE.Production of UCP2 in PBMC is not affected by estrogen.Significant association not found between dietary macronutrients or energy intake and level of estrogen.