They say that burning carbs is the "primary" system of getting energy, and burning fat is secondary. I am curious what is the basis for putting one first and another second.
If you eat both, your body burns the carbs and stores the fats.
The only time it's the other way is if you're following a cyclic diet like UD2 and you're going from ketosis and full glycogen depletion to a high-mostly-carb post-workout repletion, in which case it will use the carbs for glycogen and continue burning fat. But, that's a forced anomaly that only lasts a short time.
