A previously sedentary individual can expect a 2 fold or a 100% increase in mitochondrial content after months of regular training.
This will affect carbohydrate utilization in several ways. First, as fats can only be used for ATP production in mitochondria, having twice as much mitochondria will allow for an increase in the ability to use fats for fuel.
This will result in less carbohydrate utilization, also known as carbohydrate sparing.
Second, having twice as much mitochondria will improve our ability to use the carbohydrates that we do burn via the aerobic, or the oxidative pathway, versus the anaerobic pathway.
We get 15 times more ATP from glucose when it's used aerobically versus anaerobically. Or to put it another way, we can use 15 times less carbohydrate for the same rate of ATP production if we can use the aerobic pathway thus sparing carbohydrate.