Brown adipose tissue (BAT) is able to rapidly generate heat and metabolise macronutrients such as glucose and lipids through activation of mitochondrial uncoupling protein 1 (UCP1). Diet can modulate BAT function1 but the capacity of individual nutrients to promote the abundance and actvity of BAT is not well established. Caffeine consumption has been associated with loss of body weight and increased energy expenditure in rodents2, but whether it can activate BAT in humans is unknown. We therefore aimed to determine whether caffeine could promote BAT thermogenesis in healthy adults. Methods The study was conducted according to the standards of Declaration of Helsinki following approval of the University of Nottingham Medical School Ethics Committee and with informed participant consent. Eleven healthy volunteers, aged 29 (SD 5) years, who had a normal body mass index (mean 23 (SD 3) kg/m2), were studied in a temperature-controlled room maintained at 22°C. Participants acclimated for 30 minutes prior to imaging. Infrared thermography (IRT) was undertaken using the FLIR T540 camera (FLIR Systems AB, Danderyd, Sweden). A baseline assessment of temperature within the exposed supraclavicular region was undertaken (20mins). Participants where then requested to consume either a caffeinated beverage or water (Nescafe© Original 1.8g sachet ~65mg caffeine dissolved in 200ml water at 22°C; n=9 or water alone 22°C n=9). After a 30 minute ingestion period, participants then underwent a second session of thermal imaging over a 20-minute period. Thermal images were analysed by identifying the hottest 10% of the points and then taking the median of those points for each subject (equivalent to the 95th percentile). The primary outcome being the change in temperature from pre- to post-stimulation. Results Drinking coffee significantly (P<0.01 Student’s T test) increased the temperature of the supraclavicular region co-locating with BAT in humans, reflecting increasing supraclavicular temperature (TSCV) relative to reference body surface temperature (Trel) (All data presented as mean ± SEM TSCV: before caffeine ingestion: 33.81 ± 0.16oC; after caffeine ingestion: 34.19 ± 0.13oC; ΔTrel with caffeine ingestion: 0.41 ± 0.25oC; n=9). The same effect was not seen with consuming water alone (TSCV: before water ingestion: 34.55 ± 0.16oC; after water ingestion: 34.55 ± 0.17oC; ΔTrel with water ingestion: 0.13 ± 0.12oC; n=9). Conclusion Drinking coffee stimulated the temperature of the supraclavicular region that is indicative of enhanced thermogenesis in BAT.