An average person of 68 kg (150 lbs) with 15 percent body fat stores energy approximately equivalent to 283 jelly doughnuts.
Power, often confused with energy, is the time rate of doing work. Power can be measured in watts (W = kg ⋅ m2/sec3), or joules per second. Table 1 also shows power requirements for some common computing devices. The reader should be aware that in some literature, units of power are combined with units of time to indicate energy. For example, watt seconds, watt hours, and kilowatt hours are often used instead of joule, kilojoule, and megajoule.
https://faculty.cc.gatech.edu/~thad/p/journal/human-powered-wearable-computing.pdf