We identify a target for treating obesity and type 2 diabetes, the consumption of calories by an increase in the metabolic rate of resting skeletal muscle. The metabolic rate of skeletal muscle can be increased by shifting myosin heads from the super-relaxed state (SRX), with a low ATPase activity, to a disordered relaxed state (DRX), with a higher ATPase activity. The shift of myosin heads was detected by a change in fluorescent intensity of a probe attached to the myosin regulatory light chain in skinned skeletal fibers, allowing us to perform a highthroughput screen of 2,128 compounds. The screen identified one compound, which destabilized the super-relaxed state, piperine (the main alkaloid component of black pepper). Destabilization of the SRX by piperine was confirmed by single-nucleotide turnover measurements. The effect was only observed in fast twitch skeletal fibers and not in slow twitch fibers or cardiac tissues. Piperine increased ATPase activity of skinned relaxed fibers by 66 ± 15%. The K d was ∼2 μM. Piperine had little effect on the mechanics of either fully active or resting muscle fibers. Previous work has shown that piperine can mitigate both obesity and type 2 diabetes in rodent models of these conditions. We propose that the increase in resting muscle metabolism contributes to these positive effects. The results described here show that up-regulation of resting muscle metabolism could treat obesity and type 2 diabetes and that piperine would provide a useful lead compound for the development of these therapies.myosin | fluorescence | skeletal muscle | super-relaxed state | obesity A n epidemic of obesity and type 2 diabetes is currently affecting a large fraction of the world population (1, 2). This is primarily due to an overconsumption of food coupled with a reduction in physical activity. A natural antidote to both obesity and type 2 diabetes is to choose a healthy lifestyle, including a low-calorie diet and increased physical activity. However, many do not choose this option, and for some advanced patients, increased physical activity is not possible. The response to overfeeding in humans is diverse: some store the excess calories almost entirely, whereas others metabolize most of them (3). The variation is strongly dependent on both lifestyle and genetics. As strenuous activity was limited in some of these protocols, the diversity of weight gain was attributed to light activities, such as fidgeting (3, 4). Alternatively, the diversity may be due to variation in the metabolic rate of resting muscle and to how this responds to activity (5).A pharmacological approach to combating obesity has been of limited value, of the order of 5-10% weight loss when combined with lifestyle changes (for review, see refs. 6 and 7). Therapies for type 2 diabetes produce little effect, with the exception of metformin (for review, see ref. 8). Lifestyle changes, including better diets and increased activity levels, have a larger effect than pharmaceuticals. Here we suggest a target for combating obesity and...