5. Dietary Therapy in Gastrointestinal Disease

A number of specific diets are useful in different gastrointestinal disorders. These may involve diet restriction or supplementation, or alternatively, a change in the consistency or content of specific nutrients. In patients with steatorrhea, for example, luminal fatty acids are present and involved in the pathogenesis of diarrhea. In these patients, reduction in diarrhea can be accomplished, in part, by a reduction in the oral intake of triglycerides; a low-fat diet may be beneficial. In some patients with steatorrhea, supplementation with medium-chain triglycerides may be useful because these are hydrolyzed more rapidly by pancreatic enzymes, do not require bile acid micelles for absorption, and are primarily directed to the portal rather than the lymphatic circulation. Because medium-chain triglycerides undergo w-oxidation to metabolically nonutilizable dicarboxylic acids, the effective caloric content of medium-chain triglycerides is less than expected. Medium-chain triglycerides in a daily dose of 60 mL will provide approximately 460 calories. Low-fat dietary supplements may be provided in the form of a number of commercially available products prepared as complete nutritional supplements. Fat-soluble vitamins can be replaced using oral water-miscible formulations, if steatorrhea is present. For vitamin K, a water-soluble form is available. Fat-soluble vitamins require bile acid micelles for absorption; thus, if steatorrhea is due to bile acid depletion (as might occur in the short bowel syndrome following surgical resection for extensive Crohn's disease), increased amounts of vitamins may be required.

Bloating and cramping pain may follow ingestion of lactose-containing foods. This may be due to lactase deficiency (e.g., small bowel disease, "ethnic" lactase deficiency). Dietary lactose restriction may be indicated in patients if there is a history of lactose intolerance or a positive lactose tolerance test (i.e., rise in blood sugar less than 20 mg/dL after 50 g of lactose) accompanied by characteristic symptoms. An alternative test involves measurement of breath hydrogen; a rise of more than 20 ppm is consistent with lactose intolerance. Lactose may be found in milk, including buttermilk, even if it has been naturally fermented. Commercial yogurt should also be avoided, since this often has milk or cream added after fermentation to avoid the sour taste produced by fermenting lactose. Ice cream and sherbets have high lactose concentrations and should be avoided. Cheese or desserts made from milk or milk chocolate as well as sauces or stuffings made from milk, cream or cheese should also be avoided. Calcium supplements may be necessary with dairy product restriction, particularly in postmenopausal women. Liquid dairy products may be used to a limited extent by patients who have lactose intolerance; in these patients, a yeast enzyme preparation (i.e., lactase from Kluyveromyces lactis) added to milk at 4ºC (15 drops/L) can hydrolyze up to 99% of the lactose in 24 hours. Nonliquid dairy products cannot be treated with enzyme preparations, although lactase tablets may be chewed prior to eating solid food.

Celiac disease, also known as gluten-sensitive enteropathy or celiac sprue, is a malabsorption disorder resulting from ingestion of proteins derived from certain cereal grains of the grass family, Gramineae: wheat, rye, barley and possibly oats. It is believed that the alcohol-soluble gliadin fraction of wheat gluten or similar alcohol-soluble proteins from the other grains (termed prolamins) cause the intestinal damage. Consequently, absolute restriction is required for life. Table 6 provides some dietary guidelines for celiac disease patients. Gluten, however, is a particularly ubiquitous substance and can be found in coffee, catsup, dip, frozen TV dinners, ice cream and even in the capsules of medications! Although wheat, rye, barley and possibly oats are important, corn and rice do not appear to activate celiac disease. Data on other grains are not as clear. Buckwheat is not derived from the grass family and is usually permitted. Millet and sorghum are often allowed, but have not been thoroughly evaluated. Triticale, a hybrid of wheat and rye, should be avoided. Rye whiskey, Scotch whiskey and other cereal-derived alcohols can be consumed, since gluten is not present in distilled spirits. Similarly, brandy and wine made from fruit pose no difficulties. Beer and ale are produced from barley; it is not entirely clear if they can activate disease and would best be avoided. Malt made from barley should be avoided, as well as hydrolyzed vegetable proteins used as flavor enhancers in processed foods, since they may be made from soy, wheat and other cereal proteins.

TABLE 6 Dietary guidelines for celiac disease patients

Foods to avoid
Wheat, rye, barley, oat products
Triticale (wheat-rye hybrid)
Millet and sorghum
Malt and hydrolyzed vegetable protein

Acceptable foods
Corn, rice, buckwheat products
Wine and distilled alcoholic beverages
Fruits and vegetables
Meat
Nuts
Dairy products (unless lactose-intolerant)

For both symptomatic and asymptomatic patients with celiac disease, a lifelong gluten-free diet is recommended. Multivitamin supplements are frequently required and specific vitamin, mineral and trace element deficiencies should be corrected. Iron and folate supplementation may be needed and poor absorption of oral iron may sometimes necessitate parenteral administration. Supplements of calcium and vitamin D may be required to prevent mobilization of skeletal calcium, and in some patients magnesium may be needed.

Malnutrition in patients with inflammatory bowel disease, especially Crohn's disease, is a frequent problem. Weight loss may be seen in over 65% of patients and growth retardation may be observed in up to 40% of children. As shown in Table 7, there are multiple causes for malnutrition, especially in patients with Crohn's disease with small bowel involvement. The goal of nutritional management is to ensure adequate nutrient intake with modifications that reduce symptoms. Although only limited studies are available, evidence suggests that energy expenditure is no greater than one would predict for a healthy individual unless the disease is complicated by fever or sepsis. There may be increased caloric as well as nutrient requirements, however, particularly if gastrointestinal losses are substantial and malabsorption is significant. Attention should also be placed on micronutrient deficiencies in these patients, particularly if concomitant malabsorption is present. For example, patients with significant ileal disease or resection require regularly administered parenteral vitamin B₁₂.

TABLE 7 Malnutrition in inflammatory bowel disease

Reduced oral intake
Disease-induced (e.g., postprandial abdominal pain and diarrhea, sitophobia, anorexia, nausea and vomiting)
Iatrogenic (e.g., restrictive diets, 'fad' diets)

Malabsorption
Reduced absorptive surface (e.g., shortened small intestine due to prior resection, diseased segments)
Bacterial overgrowth (e.g., associated with strictures and bypassed loops, stasis)
Bile salt deficiency after ileal resection (e.g., impaired micelle formation and steatorrhea)
Lactase deficiency (e.g., associated with small bowel disease)
Drug-induced malabsorption

Increased nutrient loss
Protein-losing enteropathy
Diarrhea losses of electrolytes, minerals and trace elements (e.g., potassium, zinc)
Gastrointestinal blood loss (e.g., iron loss)

Drug-induced malabsorption
Cholestyramine (e.g., bile acids; fat; fat-soluble vitamins, including vitamins D and K)
Sulfasalazine (e.g., folic deficiency associated with reduced absorption and increased requirement related to hemolysis)
Steroids (e.g., calcium absorption and mobilization)

Increased requirements
Chronic inflammatory disease, fever, superimposed infection

Frequently, the diet consistency or form will require modification to permit intake of adequate amounts of various nutrients. Thus, a low-fiber or low-residue diet may be recommended if symptoms are associated with stenotic bowel segments. In some, symptoms may be improved by a diet with increased fiber. Increased amounts of pectin or guar, for example, may be helpful in patients with increased stool water content, as these fibers tend to have a significant water-retaining capacity.

Lactose intolerance may be common in patients with inflammatory bowel disease, particularly with small intestinal involvement, as well as in ethnic groups with a high frequency of primary lactase deficiency. Recent reports suggest that lactose intolerance in Crohn's disease is not as common as previously thought. In patients with a limited ileal resection, diarrhea may result from impaired ileal bile salt reabsorption. With more extensive ileal resection, particularly if over 100 cm, bile salt depletion may occur. As a result, micelle formation may be suboptimal, and fat malabsorption results. In addition, fecal fat and/or fatty acids may bind to calcium, magnesium, zinc and copper; increased fecal losses of these divalent cations may result. Increased fat-soluble vitamin loss may occur. Finally, patients with Crohn's disease and an ileal resection with steatorrhea are more prone to develop calcium oxalate kidney stones. This is due to increased urinary oxalate concentrations associated with enhanced absorption of dietary oxalate, largely in the colon. Steatorrhea causes enteric hyperoxaluria because calcium binds to unabsorbed fatty acids. As a result, more oxalate is available for passive colonic diffusion. In addition, fatty acids appear to increase colonic permeability to oxalate. By reducing dietary fat, oxalate absorption is also reduced.

Specific drugs may also alter nutrient absorption. For example, sulfasalazine is a competitive inhibitor of intestinal folate absorption. In addition, patients on sulfasalazine may have hemolysis secondary to red cell oxidant injury from sulfapyridine. Thus, folate requirements are increased.