The food you eat is converted to glucose, which your body can use for energy. Without
it, your muscles
will fatigue more rapidly. Some people can tolerate this muscle fatigue better than others, but it still occurs. Feed your muscles. They need it, poor things.
What should you eat, and when should you eat it?
Again, people differ on this. But you don't need a lot of food. This is a common pitfall of the chronic dieter and beginning exerciser. We get a diety mentality.