After 6 days of calorie reduction the body reduces the speed at which it burns fat. On a normal diet this is the point at which tiredness and sugar cravings begin.The body believes that is experiencing a time of famine. It make adjustments to conserve body fat. It is literally trying to keep the body fat so that it can survive longer without food.
In this case it is the hormone Leptin reducing the number of calories the body burns at rest. When eating as you were before your Leptin was working overtime, encouraging your body to burn fat in order to prevent you from gaining weight too rapidly.
6 days into a diet Leptin has reduced by 50% and the body is desperately trying to store fat. The selective over feed of starchy carbohydates such as sweet potato chips will boost Leptin levels back up and encourage the body to begin burning fat again.
To get the best results in the long term it can pay to place meals that include rice, potatoes, sweet potatoes and other starchy carbohydrates near your workout times.
Dieting, simply put is consuming less calories than the body requires to function. We are mitigating this with more nutrient dense food, improved digestion and reducing stress.
However, the fact remains that in order to lose weight over the long term a calorie deficit will be required. Now, the human body knows nothing of diets and it knows nothing of our desire to look a certain way, everything that it does it does with survival in mind. It only ever stores fat as a response to some sort of threat.
Under-eating is a threat.
The body believes that there is a famine, there is not enough food in the world. During a famine, those with the most fat survive. So dieting is turning your body into fat storage mode. GREAT!
The body knows there is not enough food in the world and so it must reduce its energy requirement by getting smaller. It very cleverly do this by reducing the most energy requiring part of the body. MUSCLE, along with the wasting away of muscle we get a dramatic slowing of the metabolism. This is a nut shell is the cycle of dieting and why it gets harder and harder every time.
The only way to prevent this is to provide the body with regular protein feeds so that it maintains muscle mass and elects to burn fat instead. In fact when athletes are looking to reduce body fat they will increase rather than decrease their protein intake.