That's exactly right. People whose fat metabolism is in working order tend to have more energy, simply because their fat cells aren't soaking up the glucose in

That's exactly right. People whose fat metabolism is in working order tend to have more energy, simply because their fat cells aren't soaking up the glucose in their bloodstream and are able to release free fatty acids to power their muscles on demand. There's good evidence that while the equation: energy consumed - energy expended = energy stored (as fat) is true, tinkering with the left hand side is likely to leave you hungry, lethargic, or both. If you can keep your insulin levels in check, you can manipulate the right hand side in your favor, allowing you to eat less, have more energy, or both.