Scientists studying obesity have had great interest in brown fat, adipose tissue that actually helps burn fat (for example, to generate body heat in the cold). Studies suggest that higher levels of brown fat correlate with lowered risks for obesity and diabetes, and scientists are studying whether activating brown fat might help in the fight against obesity. Nature recently published a paper showing that the signaling molecule adenosine activates the energy-burning function of brown fat by binding to A2A receptors on the brown fat cells. Here's the abstract for the paper: (Gnad et al. 2014. Adenosine activates brown adipose tissue and recruits beige adipocytes via A2A receptors. Nature. Published online 15 October 2014. http://dx.doi.org/10.1038/nature13816 [Broken]). These results are important because they suggest that drugs targeting the A2A receptor (or some of the downstream signalling pathways) could help fight obesity. Indeed, obese mice treated with drugs that activate the A2A receptor showed weight loss and improved glucose toleance. The study, however, has potentially troubling implications. Caffeine is an A2A antagonist, meaning that it prevents activation of the A2A receptor. The results of the paper would then suggest that caffeine should inhibit energy metabolism by brown fat, negating its beneficial effects. Although the paper shows that A2A antagonist do indeed block energy expenditure by brown fat, it does not look at caffeine specifically. Given the widespread consumption of caffeine, this seems like an issue warranting further study. A quick web searched turned up this news article linking coffee consumption and obesity, but it suggests that the polyphenols in coffee are to blame, not caffeine. Does anyone else know of any studies looking at the relationship between caffeine consumption and obesity?