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

by Jason Fung

The reason the body has to resort to decreasing metabolism and increasing hunger is because insulin remains high, so it doesn’t have access to the energy stored as fat. Your body has no other option but to slow metabolism—it’s trying to conserve energy because it can’t get at the fat freezer. This is why insulin resistance plays such a crucial role in obesity: the high insulin levels tell your body to hang onto body fat and simultaneously trigger the body to lower your metabolism. This inexorably erodes weight-loss efforts. Body weight plateaus and then ruthlessly climbs back up, even as the proper diet is maintained. For some of us, changing what we eat is clearly not enough. Let’s take an example. Suppose you eat 2,000 calories per day. Your weight is stable, so you are burning 2,000 calories per day. There are 3,500 calories in a pound of fat, so if you carry 100 pounds of fat, there are 350,000 calories in fat stores.