Foods a clear liquid diet allows include water, clear broth and gelatin, according to Mayo Clinic. Doctors prescribe a clear liquid diet before surgery, as it is easier for the patient to digest and helps to clean out the digestive tract. The diet is also useful after surgery, when a patient still may not be able to handle eating solid foods.
Broths for a clear liquid diet should be fat-free, such as bullion or consommé, reports Mayo Clinic. Fruit juices should be free of pulp. Fruit-flavored drinks, carbonated water and soda are allowable. Vegetable juices, such as tomato, require straining to remove any pulp. Coffee and tea are acceptable, but milk, cream and creamer are not. The diet also allows hard candies, honey and sugar.
The purpose of the diet is to maintain hydration while allowing the digestive tract to empty, according to Mayo Clinic. If a doctor prescribes the diet, he may ask the patient to avoid foods that interfere with the test, such as those containing red dyes, during the preparation time.
Clear liquid diets are very low in calories and do not provide sufficient nutrition to meet the normal needs of the patient, and Mayo Clinic indicates it is not for long-term use. Patients who do not follow the diet exactly risk the chance of inaccurate test results or having to reschedule a surgical procedure.