Therapeutic Diets for the Management of Gastrointestinal Conditions and Preoperative and Postoperative Care

Clinicians often prescribe therapeutic diets to prepare patients for procedures and surgery and treat gastrointestinal conditions. Commonly prescribed diets include clear liquid, full liquid, low-residue, and bland, each with specific indications, nutritional profiles, and clinical applications. There is overlap between diet categories; for example, many foods allowed on a bland diet are also considered low-residue. This diet consists of completely transparent liquids that leave no residue in the digestive tract and is used short-term before procedures or during acute illness to maintain hydration and electrolyte balance. Clear liquids include water, ice, fruit juices without pulp, sports drinks, carbonated beverages, gelatin, tea, coffee, broth, and ice pops. Even when labeled "pulp-free," orange juice contains fine particles, natural fibers, and residual pulp and is not considered a clear liquid. This diet includes all liquids and foods that liquefy at room temperature; this diet provides more calories and nutrients than a clear liquid diet and is used during progression from clear liquids to solid foods. Full liquid diets include milk, nondairy milk alternatives (such as almond or soy beverages), strained cream soups, broths, smooth yogurt, puddings, custards, ice cream, sherbet, sorbet, plain gelatin, liquid nutritional supplements, fruit juices without pulp, and strained vegetable juices. This diet also includes cooked cereals such as cream of wheat or rice, liquid meal replacements, or nutritional formulas. This diet limits fiber and other dietary components that increase stool bulk, such as dairy products and indigestible carbohydrates. An example of the latter is cellulose, which is found in the skins and fibrous parts of raw vegetables, such as broccoli stems, kale, and celery. A low-residue diet reduces stool volume and frequency in settings such as bowel preparation for colonoscopy or during episodes of bowel inflammation. Permitted foods include refined breads and cereals, white rice, well-cooked or canned vegetables without skins or seeds, tender meats and poultry, fish, eggs, and clear fruit juices. Although low in fiber, dairy products contribute to colonic residue and fecal bulking and are therefore recommended only in limited amounts. Avoid tough or fibrous meats, corn, popcorn, coconut, raw or dried fruits and vegetables, beans, peas, nuts, and any items with seeds or hulls. In clinical practice, a low-residue diet typically contains less than 10 g of fiber daily. However, despite their distinct differences, "low residue" and "low fiber" are often used interchangeably. The American Academy of Nutrition and Dietetics removed the low-residue diet from the in 2015 because there is no scientifically accepted quantitative definition of residue or validated method to estimate the amount of food residue produced. Many protocols now focus on fiber restriction rather than total residue for managing gastrointestinal conditions. This transition reflects a need for evidence-based and clearly defined dietary recommendations in clinical practice. A bland diet consists of soft, easily digestible, low-fiber, and usually nonspicy foods that minimize chemical and mechanical irritation on the gastrointestinal mucosa to manage symptoms of gastritis, peptic ulcer disease, and other disorders. Bland foods include low-fat dairy products, nondairy milk alternatives, eggs, broth, puddings, fruit juices, cream of wheat or rice cooked cereal, tofu, lean meats (such as skinless chicken and fish), some vegetables (like beets, beans, spinach, and carrots), and tea. The diet typically excludes uncooked, spicy, and fried foods, as well as dressings and sauces, pickles, whole-fat dairy products, alcohol, caffeine, and vegetables associated with excess flatulence, such as onions, peppers, and cruciferous vegetables. Coffee is typically avoided on a bland diet because caffeine stimulates gastric acid secretion and increases gastrointestinal motility, which can exacerbate symptoms such as nausea, heartburn, or diarrhea. Decaffeinated coffee is generally not recommended either, even though it contains little caffeine, because it also stimulates gastric acid secretion and contains acids and oils that can irritate the gastric endothelium, potentially worsening gastrointestinal symptoms.