1. Very, very small energy potential. 2. Infection concerns. 3. Much, much simpler ways to do it much more effectively. 4. That being said, implants are getting more and more common, it won't be too long before finger pricks are replaced by injected sensors, as the latter is already a deployed technology, for instance. 5. It will happen on some level, but weight loss / gain isn't just energy in and out.