Adaptive thermogenesis is the dissipation of energy via heat production and primarily occurs in brown adipose tissue (BAT). Earlier retrospective studies suggest that BAT activity is greater in women than men. Furthermore, sex and stress steroids regulate thermogenesis in rodents. This study aimed to investigate cold- and meal-induced BAT thermogenesis in healthy men (n=14; age 23.07 ± 0.7 years, BMI 23.22 ± 0.7 kg/m2) and women at 2 stages of the menstrual cycle (luteal, n=9; age 25.22 ± 1.7 years, BMI 21.56 ± 0.4 kg/m2 and follicular, n=11; age 24.64 ± 1.2 years, BMI 22.12 ± 0.9 kg/m2). Cutaneous temperature at the supraclavicular region (human BAT depot) and the manubrium (BAT negative control) were measured at 1min intervals using infra-red thermography. Cold-induced thermogenesis involved the immersion of one hand into cool (15°C) water for 5 mins. Once BAT temperature returned to baseline, a liquid meal (Ensure, 10kcal/ kg body weight) was consumed. Thermogenic responses to both diet and cold were greater in females (P<0.05) than males, and this was effect was greater (P<0.05) during the luteal phase of the menstrual cycle. During cold-exposure, the increase in BAT temperature was abrogated (P<0.05) in females during the follicular phase compared to luteal phase of the menstrual cycle. Regression analyses revealed that serum estradiol concentration was correlated to cold- (P<0.05, R2=0.13) and meal-induced thermogenesis (P=0.07, R2=0.10), whereas meal-induced changes in BAT temperature were inversely correlated with serum testosterone concentration (P<0.05, R2=0.13). There was no correlation between BAT temperature and serum progesterone concentration. On the other hand, serum cortisol concentration was inversely related to baseline BAT temperature (P<0.05, R2=0.17). In summary, women exhibit greater thermogenic responses to both cold and meal stimuli than men. Furthermore, BAT activity in women is influenced by the stage of menstrual cycle, which relates to fluctuating levels of estradiol.