With meal replacements, you can think of shakes or bars. This replaces your regular breakfast, lunch, and/or dinner. You lose weight because the bars and shakes contain fewer calories than your regular meals. Often the shakes and bars contain a lot of protein, so it's good filling. It is also important that the meal replacements are fully-fledged. They contain at least: 75 grams of protein per day, 10 grams of fiber per day, and 3 grams of carbohydrates per day.