The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting

by Jason Fung

When we are not eating, insulin levels are low, allowing full access to the fat freezer—the body is able to easily get at the stored fat. With low insulin levels, you don’t even have to completely empty the glycogen refrigerator before opening the fat freezer, since it’s so easily accessible. Think about your fridge at home. Does it have to be completely empty of everything, including that half-empty bottle of ketchup and tub of yogurt, before you open that pack of burgers from the freezer? Of course not! Similarly, with low insulin levels, the body can burn fat even if there is still some glucose around. That means that if you’re cutting calories and have low insulin levels, it’s easy for your body to compensate for the reduced food energy by getting some fat out of the freezer even if your glycogen fridge isn’t completely empty. But the emptier your glycogen fridge, the more likely you will be to use what’s in the fat freezer, and the easier it is to get to the freezer, the more likely it is that you will use it.