The Slim-Fast 1-2-3 Meal Replacement Diet is arguably one of the easiest and cheapest diets around. The concept is simple, you have 1 sensible nutritious meal per day, 2 meal replacement shakes or bars and 3 snacks that are each around 100kcals. If you followed the diet exactly your daily calorie intake would be 1360Kcals, which is 640 calories less than the average woman needs. In order to loose 1lb of body weight you need to cut out or burn 500 calories, based on this the diet should help you shred weight pretty quickly.