OH and by the way, your body adjusts to some changes over time. So, something like fasted exercise will trigger the body to adapt and prepare for the fasting exercise on a metabolic level. It may be more efficient release of stored energy, but that is also likely to be paired with more efficient replacement of the stored energy. For a marathon runner, that is a good thing if not taken to extremes. For a weekend warrior, that is a bad thing if the rest of the week is spent efficiently storing energy for the weekend.