There are two issues at play for many.
1) Time of day. It's relatively, at least currently, for me as I tend towards my main gym sessions within 2 hours of breakfast. Others struggle because the majority train after a days work or at school. So it's often when their energy can drop off. Hence the use of preworkouts - which then keep them awake
2) Piss poor eating habits. Kinda obvious lol. It's better to ask not what to have before a workout but rather to consider EVERY meal as part of what's gonna give you energy. If you ate well all day yesterday and then not quite so well in the morning you'll still have a better workout than if all the meals are poor.
Stevesmi has successfully trialed fasting and found, as have others, that the body adapts. The first few sessions might be a struggle but after a while...
Finally, some of my best sessions have been when I felt tired and or hungry. It's like my body knew i was gonna try and f**k it up and saved me some 'steam' for the gym