Meal replacement, as its name implies, refers to changing the staple food. Whole grains, the main component of meal replacement, are rich in soluble dietary fiber, which swells when it meets water, thus increasing our satiety and reducing the calorie intake in the next diet. The calorie of meal replacement itself is low, and the calorie of a pack of meal replacement is less than half of our usual intake. In short, meal replacement is to lose weight by controlling calories.