During the week (Monday - Friday), you eat (by calories) about 55..60% fat, 30..35% protein, and no more than 30g of carbohydrates. The plentiful supply of fat causes a metabolic shift from primarily burning carbs to primarily burning fats. Insulin levels remains low (which increases GH release). Increased dietary fat is also linked to increased testosterone levels.
Despite popular belief, the human body can run pretty well without carbs (otherwise Eskimos wouldn't be doing too well). During the weekend (Saturday - Sunday, about 24 to 48 hours), you eat a high carb, medium fat (30..40%), low protein (10..15%) diet. This causes an insulin spike. While this can increase fat deposits, it moves more nutrients into your muscles, and has an anabolic effect. The important thing is to switch back to the high fat / low carb mode before you put on too much fat.
