Let me explain why this is true. The human body is a very efficient organism. If it takes in more calories than it needs it will store the remainder as fat. If it is taking in too few calories it will burn what it has stored. If the body is denied too many calories (diet) too quickly it thinks that it is being starved and goes into "a conservation mode". Think of the early civilizations that had to hunt and gather for food. When people had an abundance of food they ate it and the body stored the excess as fat. Refrigeration was not available. The body then burned the fat as needed till the next feeding. Today our foods are so calorie rich that it is easy to consume more calories than needed. So many people will need to eat more calories in smaller portions more frequently in order to get the body back in synch.