If you’ve made dramatic changes to your diet and exercise routine, you may feel the effects of weight loss within a week. Although a 1- to 2-pound-per-week loss is normal and recommended, in the first week or two of beginning a plan, you may lose slightly more.
A lot of this initial weight loss is water. Your fluid levels fluctuate often and can change dramatically when you alter your diet. For example, when you start a low-carbohydrate diet, you deplete the stored glycogen in your muscles. When you lose this glycogen, you also lose the water it retains. As a result of this loss of water weight, you may experience a flatter-feeling tummy and the first pounds lost on your scale. Lose just 2 cups of water, and it results in a pound lost on the scale, but it’s not actual fat loss.