Intermittent fasting provides a longer fasted period during the day during which your body has to rely more on fat stores. This may take a couple weeks to get used to at first, but your body will get more efficient at releasing and using stored fat for fuel and will supply your energy needs until your first meal, usually around lunch time. Ideally you want to have about a 16 hour window from the last time you ate the day before until your first meal the next day.

Our bodies are should be very capable of providing enough energy for our day to day activities, and even some moderate exercise, with fat stores alone. Water and some black coffee or tea is fine, and will even help, during the fasted period. Moderate exercise during the fasted period will improve the training effect. This trains your fat burning metabolism, or aerobic metabolism, to work more efficiently.