You can do either something or nothing. Apart from 1 of my pb's in the gym, all were done fasted. None of "us" are Chris Froome (although he went low carb), Arnold Swazenegger etc, so the extremely small percentage (if anything) gain by pre or post workout food or portions is just bro-science.
There is an adjustment phase for training fasted, where energy levels are low, but this goes in time. Some electrolyte drink is good to drink, I would do water with lo salt; some low carbers put some salt on the tongue and down water.