Do you mean that two days a week you ONLY eat 500 calories for the whole day? And on the others you eat 1200? If so, be careful, because that is literally starving your body of what it needs to function properly. You can lose weight that way, but it can also cause other harmful physical affects. Have you looked at the ranges that spark people gives you for calories/carbs/fats/protein? Following those can result in a healthy, sustainable weight loss of around two pounds a week.
If I misunderstood your original post, please forgive me.