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Veterinarian Technician June 2013 (Vol 34, No 6)

Nutrition Know-How: Nutritional Management of Vomiting and Diarrhea

by Ann Wortinger, BIS, LVT, VTS (ECC, SAIM, Nutrition)

    When caring for patients with vomiting or diarrhea, it is important to remember that neither problem is a disease; rather, vomiting and diarrhea are clinical signs of disease. Few clinical studies have evaluated specific dietary manipulation for preventing or managing gastrointestinal (GI) disease in dogs and cats.1 No physical examination findings, laboratory results, or patient history is predictive of which diet would be most effective for managing vomiting or diarrhea in a particular patient.2 Even with a definitive diagnosis, individual feeding trials and regular patient assessment are essential for managing vomiting and diarrhea.2 If a patient with acute vomiting or diarrhea shows no improvement over 2 to 3 days or continues to deteriorate despite treatment, reassessment is necessary.3

    Causes of Vomiting

    Vomiting can have numerous causes that may not be associated with the stomach. Vomiting can be induced by motion sickness, ingestion of emetic substances (those that induce vomiting), GI tract obstruction, abdominal infection or inflammation, or extragastrointestinal diseases that stimulate the chemoreceptor trigger zone.4 The most important clinical sign of chronic gastric disease is vomiting.3

    Because of the dietary behavior and lifestyle of carnivores, such as cats, occasional vomiting is not considered clinically significant, especially when the vomitus is mixed with hair.5 In cats, vomiting can be a sign of a distal intestinal disorder (e.g., inflammatory bowel disease, internal parasites), even in the absence of other clinical signs.5

    Causes of Diarrhea

    Diarrhea is a nonspecific sign of many diseases, and effective management of it depends on identification and resolution or removal of the underlying cause.2 Acute diarrhea is typically caused by dietary indiscretion or intolerance, an intestinal parasite, or infectious disease (e.g., infection with Salmonella spp or Escherichia coli).4 Acute diarrhea caused by dietary indiscretion can often be treated symptomatically, resolving within 2 to 3 days with minimal treatment. Chronic diarrhea is most commonly caused by intestinal disease, although other systemic diseases may affect intestinal function and can induce secondary hypersecretion or intestinal malabsorption.5 The most common cause of chronic vomiting and diarrhea in dogs and cats is the constellation of diseases known as inflammatory bowel disease.2 Chronic diarrhea is rarely self-limiting, and treatment should be based on definitive diagnosis.3

    To Withhold Food or Not

    The standard treatment of acute vomiting or diarrhea has been to withhold food for 12 to 48 hours. The rationale has been that removing food from the upset GI tract allows it to clear itself of luminal contents that may be causing the problem; this has been thought to help (1) prevent mucosal cell abrasion by GI contents, (2) deprive opportunistic luminal bacteria of nutrients, preventing their proliferation and the absorption of dietary antigens that may be present due to maldigestion, and (3) permit restabilization of the brush-border enzyme function.1,2 Brush-border enzymes are produced along the microvilli lining the small intestinal tract and perform the final stage of digestion before nutrients are absorbed across the intestinal lining into the bloodstream. The problem with withholding food is that in almost all cases of enteritis, regardless of the cause, there is decreased motility with delayed gastric emptying and reduced segmental contractions. Therefore, fasting does not immediately provide physical rest for clearing the GI tract.1

    Studies in humans have shown that early reintroduction of feeding is associated with a quicker return of gut sounds; shorter hospital stays1,5; and stronger scar tissue and faster healing, including at surgical sites.1,5 Evidence suggests that the prokinetic effect of feeding may decrease the vomiting response in some patients.1 In addition, oral fasting can induce an intestinal insult, with mucosal atrophy occurring within 12 hours of a fasting state.1,5 While it may not be difficult to convince clients to continue feeding a pet with diarrhea, clients may be less likely to continue feeding a pet with vomiting because of the associated cleanup.


    The primary goal for managing vomiting or diarrhea is to maintain delivery of nutrition to the GI tract to prevent nutrient deficiency and malnutrition.6 The most common first step is to introduce a highly digestible, low-fat diet.2,3 TABLE 1 provides examples of appropriate diets. It is often recommended that a patient be started on small amounts of a bland diet; however, there is little evidence to support this recommendation, and the term bland is vague. For managing any inflammatory process in the GI tract, the type of diet offered is more important than the blandness of the ingredients.6 Ideally, diet selection should be based on the specific disease being treated, the affected area of the GI tract, and the ability of the diet to promote tissue healing and maintain remission of clinical signs.6 The long-term goals for managing vomiting and diarrhea are to help repair the damaged GI tract lining, restore normal GI bacterial populations, promote normal GI motility and function, support the immune system, and decrease GI tract inflammation.6

    Patients with chronic vomiting and diarrhea with subsequent loss of nutrients and energy may present with weight loss, a poor haircoat, and dry, flaky skin. These patients should respond well to a food with a high nutrient density (increased calorie content) and other nutritional modifications, such as increased omega-3 fatty acids and increased digestibility.3 When the intended results of a diet are not achieved, clients may become frustrated. Therefore, it is important to remind clients that when nutrition is provided to debilitated patients, the body decides where and how the nutrients and energy are distributed. For example, although a diet may be fed to increase a patient’s muscle mass, the patient’s body may prefer to replace intracellular protein and fat stores. The veterinary team’s job is to provide the building blocks to repair damage so that the patient can achieve full recovery.

    Adverse Food Reactions: Food Allergies and Intolerances

    There is a lot of confusion regarding the various terms used to describe adverse food reactions. Food allergies are immunologically mediated, whereas food intolerances are not. Both reactions can affect multiple body systems, but patients with food allergies commonly present with pruritus and skin excoriations (scratches).3

    Food allergies involve an immunologic response to a dietary ingredient. In humans, this is mediated by IgE type 1 hypersensitivity.7 Common signs are cutaneous manifestations and digestive disturbances. Food allergies are considered to be uncommon in dogs and cats2; however, some clinicians think that food allergies are more likely to develop during acute gastroenteritis because it allows large-molecular-weight peptides to cross the intestinal barrier, potentially sensitizing the immune system.2 For treatment, initial feeding of a novel protein may be recommended. The novel protein may eventually cause an allergic response but can allow the intestinal tract to heal in the meantime. Once the clinical signs have resolved, a long-term maintenance diet consisting of a different protein can be introduced if an allergy to the first novel protein develops.2

    Food intolerances (1) are not caused by an allergic response, (2) are characterized by diarrhea that resolves completely with appropriate dietary management, and (3) show no evidence of enteritis or of eosinophilic histologic changes on biopsy.1 Diarrhea associated with food intolerances is known as food-responsive diarrhea.2 An example is diarrhea caused by lactose ingestion: the cause is a lack of digestive enzymes for a specific sugar, not an allergic response. If a food intolerance is suspected, the current recommendation is to feed a highly digestible, single-source, novel-protein diet, such as venison, rabbit, duck, or whitefish. The rationale for this approach is that a highly digestible diet has low antigenicity because fewer intact proteins are absorbed across the inflamed intestinal barrier.6 The ideal diagnostic approach to and long-term management of suspected cases of food intolerance is based on using novel proteins or protein hydrolysates and monitoring patient response.1 Feeding elimination-ingredient diets can be used to identify the problem ingredient, but client compliance and patient cooperation are often difficult to obtain.1

    Dietary management of food allergies and intolerances can be difficult because these conditions are slow to respond and affected patients remain at risk for relapse if they gain access to the problem ingredient. Performing a food trial for a minimum of 3 to 4 weeks is recommended; some clinicians perform a trial for 3 to 4 months before making dietary changes.3 When the source of an adverse food reaction cannot be identified, an elimination diet is selected based on the history of ingredients that the animal has already been fed.3 This is why many elimination diets contain unusual protein sources, such as ostrich, duck, and hydrolyzed proteins, which are not usually found in typical over-the-counter foods.

    Food intolerances are more common than food allergies and reportedly make up as much as 29% of all cases of chronic GI disease in cats.1 Food intolerances can be due to lactose intolerance in adult animals; loss of digestibility of certain nutrients; and incomplete digestion of some fibers, resulting in flatulence.

    Gluten, especially wheat gluten, has received a lot of attention for causing problems in some people. Now there are grain- or gluten-free diets for pets. Gluten is a plant protein that is an excellent source of amino acids. Gluten is 80% to 82% protein, is low in dietary fiber, and has a digestibility of ~99%. Gluten is an important source of the amino acid glutamine, which has been shown to be important for maintaining digestive integrity and conserving lean muscle mass during intense activity.3 Rice and corn do not contain gluten, but wheat, rye, barley, and oats do contain it.3 The Irish setter is the only breed of dog or cat in which gluten sensitivity has been documented.3 Therefore, a gluten-free diet is recommended for Irish setters that have been shown to be gluten intolerant. A gluten-free diet is not recommended for other animals because gluten can be an excellent source of protein.3


    Patients with vomiting and diarrhea should be fed a protein source that is high quality, is easily digested and assimilated (i.e., absorbed through the intestinal wall and incorporated into body tissue), and contains all the essential amino acids in the correct proportions. The quality of a protein is measured by digestibility, as determined by feeding trials and by the biologic value of the protein. Biologic value is a determinant of the availability of the essential amino acids within a protein.6 Eggs are the protein source with the highest biologic value (100). Protein digestibility varies between healthy and ill animals and can be affected by food-processing methods.6 Protein is the largest source of dietary antigens, which generate an immune response.6

    Dietary protein is essential for secretion of hormones and enzymes required for digestion. This includes pancreatic enzymes and the hormones insulin, gastrin, and cholecystokinin.1,5 Insufficient caloric availability in the diet, intestinal protein loss, increased catabolism, and decreased absorption of dietary protein can all result in a low protein level in the body.1 To ensure that sufficient protein is available for use by the body, a minimum total diet digestibility of 85% to 88% dry matter and a protein digestibility of >92% are recommended for animals with GI problems.5


    Although fat is the most calorically dense nutrient and can therefore benefit malnourished patients, absorption of fat through the intestinal lymphatics may be impaired in cases of GI disease; therefore, fat could contribute to a postprandial increase of fluid influx into the intestinal tract, contributing to secretory diarrhea.1,6 Nevertheless, high-fat diets may be beneficial in slowing gastric emptying in cats, especially those with diarrhea.2 Slowing gastric emptying may be beneficial for decreasing the flow of chyme into the GI tract and reducing the incidence of diarrhea. Increasing soluble fiber in a diet can have the same benefit but does not provide the calories that fat does.2 The recommended total dietary fat content is ~11% to 15% dry matter for dogs and cats with GI disease.6

    Omega-3 fatty acids have been found to be helpful for managing inflammatory responses in the body, including those in the GI tract.6 Omega-3 and -6 fatty acids are essential and are therefore required in canine and feline diets. Manipulating the ratio of these two fatty acids in diets can decrease the inflammatory response.


    As with protein, carbohydrate should be easily digested and assimilated by the intestinal tract when fed to patients with vomiting and diarrhea. The carbohydrate with the highest digestibility is cooked and blended white rice.6 Alternatives to rice include potato, tapioca, and corn. Before feeding, these should be blended or ground to break down the cellulose outer shell of the plant material and allow digestive enzymes to reach the nutrients within the plant’s cells. Although cooked rice is often recommended for inclusion in homemade diets, the whole rice grain may pass through the entire GI tract relatively intact due to a patient’s impaired ability to access the contents through the fiber shell. Blended rice and baby food flaked rice are more digestible than plain cooked rice.


    Fiber is useful for managing GI disease and maintaining GI health. The type and level of fiber in the diet are important.6 Fiber that results in production of the short-chain fatty acid (SCFA) butyrate (butyric acid) is preferred. Butyrate is the preferred energy source for colonocytes (cells that line the colon), which obtain ~70% of their energy from luminally derived SCFAs.6 Fiber can increase peristaltic contractions and may inhibit colonic contractions. SCFAs have been shown to protect intestinal tissue and promote restoration of normal intestinal function.6 However, dietary inclusion of highly fermentable fiber that produces a high level of SCFAs can cause diarrhea and flatulence and may interfere with digestion and absorption of other nutrients.6

    Both soluble and insoluble fiber may be beneficial for symptomatic treatment of large-bowel diarrhea by allowing modulation of water retention.5 Examples of soluble fiber include beet pulp, pea fiber, and tomato pomace. Examples of insoluble fiber include cellulose, peanut hulls, and most hemicelluloses. Which fiber is most beneficial depends on patient response. Unfortunately, no single fiber is ideal. Feeding highly fermentable fibers such as guar gum, lactulose, and pectin may increase the incidence of diarrhea and flatulence and may interfere with nutrient digestion and absorption.6


    Prebiotics are specific short-chain carbohydrates that are usually classified as fibers based on their digestibility by the GI tract. The most commonly available prebiotics include inulin, galactooligosaccharides, lactulose, fructooligosaccharides, and manooligosaccharides.6 The benefit of these fibers to the intestinal tract is their ability (1) to be broken down by intestinal bacteria during SCFA production and (2) to help modulate GI motility. Butyrate has been shown to have antiinflammatory effects on enteric and colonic tissue.3 The prebiotic fibers used in the diet can help modify the composition and metabolic activity of GI bacteria and allow nonpathogenic bacteria to overcome pathogenic bacteria, allowing readjustment of small intestinal bacteria. While prebiotics exert their primary effect on the colon, in dogs, enterocytes are also able to digest prebiotics, producing SCFAs in the small intestine.1,3 The bacteria responsible for fiber digestion change the gut pH resulting from SCFA production; this makes the digestive environment more favorable for ”good” bacteria and less favorable for “bad” (pathogenic) bacteria.1


    Probiotics are bacteria that are introduced into the GI tract to reestablish a population of “good” bacteria and overcome “bad” bacteria that contribute to disruption of the GI tract.6 When including probiotics in a diet, it is imperative to ensure that they survive exposure to stomach and bile acids and are alive when they enter the duodenum. Not all probiotics are equal; if they are not alive when they enter the small intestine, they are not worth their cost. Feeding trial results regarding the survivability of bacterial strains included in a product should be obtainable. It is important to explain to clients the advantages of veterinary-specific strains of bacteria compared with over-the-counter, usually human-based products. Using products that have been developed and tested specifically for dogs and cats helps ensure that the bacterial populations will be beneficial and will survive the GI environment. If a product does not survive introduction into the GI environment, it becomes a very expensive protein source. Bacteria that have not been shown to benefit dogs and cats could be “bad” or have no positive effect.


    For managing patients with vomiting or diarrhea, diet selection is ultimately determined by the cause of clinical signs and by individual patient response. Many commercial therapeutic diets offer options (e.g., low fat, novel protein, modified fiber) for managing intestinal diseases. Because no physical examination findings, laboratory results, or patient history is predictive of which diet will be most successful, individual patient response and regular patient assessment are necessary for optimal success.

    Suggested Reading

    Saker K, Remillard RL. Critical care nutrition and enteral-assisted feeding. In: Hand MS, Thatcher CD, Remillard RL, et al, eds. Small Animal Clinical Nutrition. 5th ed. Topeka, KS: Mark Morris Institute; 2010:441-442.

    Ms. Wortinger is the Nutrition Know-How editor of Veterinary Technician.

    1. Cave N. Nutritional management of gastrointestinal diseases. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. Ames, IA: Wiley-Blackwell; 2012:175-204.

    2. Buffington CA, Holloway C, Abood SK. Clinical dietetics. In: Manual of Veterinary Dietetics. St. Louis, MO: Elsevier Saunders; 2004:82-89.

    3. German A, Zentek J. The most common digestive diseases: the role of nutrition. In: Pibot P, Biourge V, Elliott D, eds. Encyclopedia of Canine Clinical Nutrition. Aimargues, France: Royal Canin; 2006:103-123.

    4. Willard MD. Clinical manifestations of gastrointestinal disorders. In: Nelson RW, Couto CG, eds. Small Animal Internal Medicine. 4th ed. Maryland Heights, MO: Mosby Elsevier; 2009:355-361.

    5. Zentek J, Freiche V. Digestive diseases in cats: the role of nutrition. In: Pibot P, Biourge V, Elliott D, eds. Encyclopedia of Feline Clinical Nutrition. Aimargues, France: Royal Canin; 2008:85-92.

    6. Case L, Daristotle L, Hayek M, Raasch M. Nutritional management of gastrointestinal disease. In: Canine and Feline Nutrition. 3rd ed. Maryland Heights, MO: Mosby Elsevier; 2011:455-472.

    7. Outerbridge C. Nutritional management of skin diseases. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. Ames, IA: Wiley-Blackwell; 2012:166.

    References »

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