When you're on a low-calorie diet, you usually get between 800 and 1,500 calories a day. For some people, an alternative for short-term weight loss is a very low-calorie diet.Many very low-calorie diets are commercially-made formulas of 800 calories or fewer that replace all the food you usually eat. Others, such as the well-known grapefruit diet rely on eating a lot of the same low-calorie food or foods.Very low-calorie diets are not the same as...