This is a very common question, and for good reason. My preference is to have some carbs (and protein) before training if it is possible.
When you consume carbs (and some proteins), insulin levels go up. Insulin is the fuel selector switch. When it is higher, it shifts your body to use carbs. As you know, carbs are the preferred fuel for high intensity exercise. This way you are matching your nutrition to your training.
But what if I exercise early in the AM?
I totally understand that some train in the early AM and getting in much of any food is not possible. Don’t worry, as all is not lost. Your body has stored carbohydrates in the form of glycogen in the muscles and liver. As long as your stores are adequate, you can still fuel your exercise session.
Metabolic flexibility is all about using the right fuel at the right time. Your body is brilliantly designed to use stored glycogen for training when you can’t consume any carbs beforehand.
If you can get in some carbs before an intense exercise session, go for it. If you can’t, you will still be fine too.
Mike T Nelson, MSME, CSCS, PhD