A few other comments on metabolisms:
- Before breakfast you have less sugar in your system so you burn up to 3x as much fat than later in the day after you start eating.
- I have about 11 pounds of fat and thus 38,500 calories of fat fuel in me, in theory enough to run well over 300 miles continuously, now, if I wanted.
- I have hit the wall in the 400, 800, 5000, 10,000, and a number of 15+ mile long runs, notably an 18 miler in Colorado on Gold Hill. So our bodies are complicated.