It takes about three weeks for your metabolism to retool so that you switch from being a “sugar burner” to a “fat burner.” Once your body and brain have made the switch, you will feel the difference. You will have more energy, better mental focus, and you’ll even be sleeping better! In my experience, I have found that after feeling the difference, and "retooling" the brain's needs and desires, few people want to go back to their old eating patterns. NOBODY’S PERFECT It is far better not to, but IF YOU DO SLIP UP...EXERCISE IT OFF. If you “forget” and eat a sandwich with two slices of bread, or eat a cookie, go for a brisk 20-30 minute walk or undertake other exercise immediately after eating. If you don’t burn off those starchy calories right away, they will raise your blood sugar, raise your leptin and insulin levels, prevent fat burning, and turn to fat, all of which get you right back to a deranged metabolism.