The bottom line is you will not perform at your peak, no matter your venue, if you don't have the proper fuel.
Picture a car, a plane a boat, you name it, if there isn't good clean fuel in it to start with and the proper lubricant to keep the engine running smoothly, you aren't go far or fast.
Water is your lubricant. Without enough of it to metabolize your sugar and fat (which needs twice as much water than sugar to burn), you aren't going anywhere. To drive the point home, if you are dehydrated while exercising your heart rate goes up 6 beats every minute, over-heating your engine quick enough to cause cardiac events in even the most healthy individuals.
Real food is your fuel. Without a properly balanced meal before exercise you will underperform. Furthermore, without a well designed post performance fueling plan, your engine won't be at its best for the next performance. No matter your task, without all the nutrients your body needs, to burn and to repair, you will not run your ship at tip-top shape for long!
What are you choosing your fuel, why are you choosing it and where did you learn this? Choose wisely, every engine is built for a different purpose and fits in a different vessel!