By restricting carbs, you are training your body to use fat for fuel. You still need to supply fuel to your body, so you eat fat. No matter what type of diet you are on, the same rules apply. To lose a pound of body weight, (not water weight) you need to burn 3500 calories more than you eat. The idea is to make this a WOL, not a quick weight loss method. The high fat/low carb WOL will enable you to reduce your calorie intake to a level that will allow you to lose weight, and will also help to make sure you are losing excess fat rather than muscle tissue. Eating fat allows you to feel full. Not eating carbs maintains your blood sugar levels, which also keeps you from going through those "I gotta get food NOW" cravings"