I think you might want to look into supplementing vitamin B1. In my personal experience sugar is not in itself the problem, but an impaired ability to process, or utilize, sugar can be. Many caffeinated beverages contain B1-inactivating tannins (tea, coffee), and consuming caffeine on an empty stomach, when blood sugar is already low, can cause mild deprivation of nerve tissues leading to impaired functioning.
Alcohol famously disrupts the metabolism of B1, making it ineffective in the body. In the extreme case it causes the Wernicke-Korsakoff syndrome which is exactly related to B1 metabolism.
The "insulinergic" role of potassium and so on in fruit juices also does make them easier to process in this way than something like coca cola.