With any major change to your diet, you will probably see a quick drop in the first week or so. Much of this loss is due to water, not actually losing fat. Many of today's most popular rapid weight loss diets see average weight losses of around 10-15 pounds and 6-10 inches on the body in the first month. Most health experts don't recommend losing more than 2 pounds a week over the long run, so don't expect those kinds of results as you progress further into your weight loss plan.