Speaking as the husband of a constantly-dieting wife, I can assure you that if it were ever remotely possible to lose 8kg in 12 days (which it is not), the resultant shock to your body would probably kill you within a few weeks. That is an almost impossible and highly-dangerous rate of loss, and any diet sponsors that promise it are lying, or risking your life, or both. Some things just don't change. One of them is, The only guaranteed way to lose weight in a safe and efficient manner is to eat progressively less food, and take progressively more vigorous exercise.