Carbs have another not so often mentioned advantage over fat. Although carbs provide less energy PER GRAM OF NUTRIENT than fat, they actually provide more energy PER GRAM OF OXYGEN needed for metabolism. In other words, when oxygen is limited, carbs give you more energy for the amount of oxygen that is available. This naturally gives carbs an advantage over fat at high altitude.
I learned decades ago to take it easy on the fat at altitude. Now I understand much better why that works. Thanks!
