Liquid Diets can help you lose weight for a day or two, or for a couple weeks, as long as you can stay on them. The rule is that your drink must contain at least 15 grams of protein per serving, and no more than 100 calories per serving. Don’t worry about carbohydrate content or anything else. If your protein shake fits these guidelines, it’s fine. You can have 4 to 8 shakes a day. Most patients lose 5-10 pounds per week on liquid diets.