The point of improving your running economy is not simply to reduce your ml O2/kg body mass/km and kcal/kg/km. That efficiency is nice, but the volume of oxyge

The point of improving your running economy is not simply to reduce your ml O2/kg body mass/km and kcal/kg/km. That efficiency is nice, but the volume of oxygen you can inhale per minute doesn't change with your diet. A competitive distance runner would use increased efficiency not to reduce their dietary intake, but to increase their speed while maintaining a high-calorie diet. It doesn't make sense that your cells could become more efficient to the degree that you "don't need to eat that many calories at all". Typical efficiency values are on the order of 1-1.5 kcal/kg/km, so your 80 mpw represents at least 1200 calories per day above baseline. Furthermore, this 1200 calories is just while running - after stopping the workout, you'll need to metabolize protein to help your muscles recover from exertion, and rebuild the glycogen stores which are larger in volume as a result of training, and which are more effectively drained as a result of training, and to rebuild the fat stores which you'll use on your long runs. And yes, I may be biased in this reasoning due to the fact that I can sit here and type this out while munching on this delicious caramel popcorn and not worry about weight gain. There's no denying that it's high-calorie.