Dietary considerations for dogs with chronic enteropathies

Introduction

Chronic enteropathy (CE) is a poorly defined term in veterinary medicine. In its most basic definition, it is a descriptor of all gastrointestinal (GI) disorders which are chronic in nature. The designation of “chronic” disease should be made on an animal-by-animal basis through a thorough assessment of the patient’s individual history and clinical signs ( Figure 1 ). Signs should be persisting in the animal for at least ten to fourteen days in duration before the classification of chronic is made. This distinction between acute and chronic GI disorders is important from both a diagnostic and therapeutic perspective; this article deals with chronic GI disorders and cannot necessarily be extrapolated to acute GI disorders and their associated dietary management. In addition, this broad definition of CE inherently includes all chronic GI disorders, including those that may result from inflammatory, autoimmune, metabolic, neoplastic and infectious etiologies. 

As a practicing clinician, achieving a correct diagnosis and establishing what is causing the CE is essential to allow for targeted application of both dietary and medical therapies. A definitive diagnosis can be accomplished by assessing patient factors, utilizing a targeted diagnostic testing approach (e.g., clinical pathology, fecal testing, molecular diagnostics, imaging ( Figure 2 ) and GI biopsy), and performing therapeutic trials as indicated on a case-by-case basis. One of the primary goals when evaluating the patient should be to eliminate the systemic, infectious and neoplastic disorders which may be largely clinically indistinguishable from food-responsive CE and require specific treatment in conjunction with, or separate from, dietary management.

Understanding diet categories for dogs with GI disease

Understanding the variety of dietary options available for treating GI disease is the first step in being able to properly implement dietary therapy in CE cases. There is no “one size fits all” approach; each dietary category is suited for specific disease syndromes and situations while potentially not advisable in others. The proper implementation of specific dietary strategies is imperative for successful use of diets as a therapeutic tool. Canine CE can often be effectively managed with diet, and may avoid some of the problems that can develop with the use of long-term antibiotics (e.g., alteration of the gastrointestinal microbiome) or immunomodulatory medications (e.g., altered immune status and risk of infection). The clinician should always consider three things when making a diet selection, namely: (I) diet history (II) diet strategy, and (III) diagnosis ( Figure 3 ). The following diet types (therapeutic classes) are the most commonly employed and are readily available through many petfood companies for treatment of canine GI diseases: easily digestible, limitedingredient, hydrolyzed, low-fat, and fiber-fortified diets ( Figure 4 ). Identifying which category or categories a potential diet falls within is best done based on information provided by the manufacturer and the individual patient’s complete dietary history. Amongst GI diets available on the market, many overlap and meet the requirements for multiple of the above categories at the same time, and such overlap can be to the clinician’s benefit. It is also vital that clinicians are aware that the nutrient profiles of different diets may vary over time. In order to be certain that the prescribed diet meets the needs of the patient, up-to-date product information should be evaluated at least yearly. Lastly, diets in a given category (e.g., all easily digestible diets) are not the same; they often have different nutrient profiles and can have different effects in an individual animal if used interchangeably.

Easily digested diets

Easily digestible diets form a large portion of diets marketed for GI disease and are commonly associated with their frequent use in acute GI diseases. The industry currently lacks a consensus definition on what makes a diet “highly digestible” – or indeed the most appropriate and consistent way to calculate digestibility. As a result, it is best practice to utilize veterinary diets verified by reputable petfood companies and labeled for the purpose of being highly digestible. The practitioner has to trust the diet label when considering prescribing a highly digestible diet, as many companies do not report the specific digestibility profiles of their diets in product guides. Considering the diets that do provide this information, around 90% digestibility of the major macronutrients (i.e., fat, protein and carbohydrate) is common amongst this category. Multiple factors can affect the digestibility of a diet, including the ingredient source, the processing inherent to the diet, the GI physiology of the specific animal ingesting the diet, the bacterial populations in the GI tract, and chemical breakdown and anti-nutritional traits of dietary components 1. Many of these factors are separate from the diet itself and will affect how an individual diet performs in an individual animal.

Limited-ingredient and hydrolyzed diets

These two dietary classes are the next most commonly utilized categories in GI medicine and are frequently associated with their use in chronic GI disorders. Limited-ingredient diets were initially marketed for cases of food allergies manifesting with dermatologic signs 2 where they provide a balanced diet void of the ingredient to which the animal is experiencing an allergic reaction. However, in CE the prevalence of food intolerance appears to be much higher than true food allergy. While a food allergy is always an immunologic reaction, food intolerance can occur through multiple mechanisms. In animals with food intolerance, these diets may work by eliminating an offending ingredient completely or by limiting the overall dietary antigen load to the GI tract; it is unclear which of these theoretical mechanisms will work in an individual patient. Therefore, when selecting a limited-ingredient diet, it is advisable to choose one with only a single carbohydrate and a single protein source in the ingredient list, and ideally both should be novel to the patient. In order to select a limited-ingredient diet appropriately, a thorough and accurate dietary history is imperative ( Figure 5 ). It also must be emphasized to owners that many over-the-counter diets marketed for this purpose contain ingredients that are not listed on the product label and are therefore not recommended in practice 3. 

Alternatively, hydrolyzed diets are processed to reduce allergenicity and antigenicity by altering protein structure 4. If hydrolysis is thorough such diets can be effective in managing allergic cases. However, the degree to which a diet is hydrolyzed can vary depending on the manufacturing process, and with some commercial diets there may still be an allergic or antigenic potential if the processing is not complete. This does emphasize the need for a comprehensive diet history to be taken in all cases. Since each commercial hydrolyzed diet contains different protein (and other macronutrient sources), the protein source should still be evaluated – as with limited-ingredient diets – if food allergy is a primary differential. Other useful components of these diets include a highly digestible profile and reduced fiber content, which may provide additional benefits or drawbacks to the individual patient; such properties are related to the processing techniques used for these diets. Concerns over palatability and side effects related to these diets, seen occasionally in humans, appear minimal or non-existent in canine studies. 

Reduced fat and enriched fiber diets

The last categories of commercially marketed GI diets are those which have macronutrient quantities altered for therapeutic purposes. These diets are usually either reduced in fat content or enriched by dietary fiber. Fat content has been identified as an important component in the management of some canine GI diseases 5, 6. Inadequate digestion of dietary fat can promote both secretory and osmotic diarrhea 7. In animals where there is a suspicion of fat-responsive disease, diets with a fat content within the range of veterinary therapeutic low-fat diets (1.7-2.6 g of fat per 100 kcal) are advisable. This information is easily identified in company product guides, but it is again the case that there is no recognized definition of what constitutes a “low-fat” diet or at what level of dietary fat restriction a benefit should be noted in an individual patient. 

Fiber is added to diets for multiple reasons and therapeutic indications, and the fiber type and source will influence the effect that is seen in the patient. Total dietary fiber is much more informative than crude fiber, the more commonly employed descriptor 8. Crude fiber does not reveal any information about the soluble fiber in the diet, limiting its usefulness as a descriptor to guide the clinician’s ability to decide whether a diet meets the intended expectations. Benefits of soluble and insoluble fiber include fermentation, production of volatile fatty acids, benefits to enterocyte health, augmentation of the microbiota, as well as alterations in gut motility and passage of GI luminal contents.

Nutritional management of common canine chronic enteropathies

Food intolerance

Inflammatory bowel disease (IBD) is a complex disease where the GI tract mounts an aberrant response to genetic, microbial, immune, and environmental factors, with the classical clinical sign of diarrhea. Such cases are often referred to as having food responsive diarrhea (FRD). Interestingly, two thirds of affected dogs will respond to nutritional management when empirical diet trials are systematically applied 9, 10. The most frequently cited dietary strategy for these dogs include the use of either a hydrolyzed or limited-ingredient diet. Although initial case reports and expert opinion in published proceedings have supported these choices for dogs, there are only three larger studies examining the efficacy of limited-ingredient diets and three larger studies examining the impact of hydrolyzed diets 9, 11,12,13,  14.

The largest study involving limited-ingredient diets was a retrospective study that looked at 131 FRD dogs, of which 73 responded to a limited-ingredient diet 9. Diet selection was not controlled and was potentially influenced by clinician, owner or animal preference, but it still provides good retrospective data demonstrating a proof of concept in a large cohort of animals. The second largest study involved 65 dogs, which underwent a 10-day limitedingredient diet trial 11 where a response rate of 60% was observed. In this study, the diet response rate was not compared to another diet type, however it was similar to the general dietary response rate reported in other studies. The final study reported a cohort of dogs that responded to a limited-ingredient diet 12. The trial was initiated to investigate the effects of a probiotic, but the noted clinical improvement was attributed to the diet and not the probiotic. 

In the same previously cited retrospective study of 131 FRD dogs, hydrolyzed diets were successful in 58 cases, once again providing proof of concept in a larger population of dogs 9. A second, separate prospective study looked at 26 dogs fed either a highly digestible diet, or a hydrolyzed protein diet 13. These dogs were then followed for sustained response up to 3 years after study inclusion. In both groups, approximately 90% of dogs were controlled based on clinical signs at 3 months. Long-term, only the dogs on the hydrolyzed diet maintained remission status through the first year of the study. The dogs on the easily digestible diet saw a 28% control rate at 6 months and a 12% control rate at 12 months, indicating a more robust long-term response to the hydrolyzed diet. The final study reported a cohort of dogs that responded to a hydrolyzed diet and was investigating impact on GI histopathology 14. 

In summary, the currently published data regarding dietary options indicate that limited-ingredient and hydrolyzed diets should be the primary strategies for FRD management. There may be a potential benefit to easily digestible diets, but further study will be necessary to determine this approach. The question as to which diet type is best is unknown. A recent informal poll asked whether clinicians prefer a hydrolyzed or a novel ingredient diet as their firstchoice dietary strategy¹ . The results were mixed, with 60% of responders choosing hydrolyzed diets as their first strategy, and the remainder choosing limited-ingredient diets. Unfortunately, the literature is lacking comparative studies to determine if there is a benefit to one diet type over another in a controlled, comparative study in dogs. It is also possible that some FRD dogs will only respond to one diet type while being unresponsive to others. Therefore, until additional information is available, it may be beneficial to attempt multiple dietary approaches before ruling out FRD. 

¹ personal communication – conducted by Dr. Katie Tolbert with members of the Comparative Gastroenterology Society

Food allergy

Food allergies are likely to be less common than food intolerance in dogs with chronic GI signs. However, the author is not aware of any study which has examined the relative prevalence of these two disorders. If a true food allergy is suspected, a complete and accurate diet history is vital to successful implementation of nutritional management. The selection of the diet needs to take into account whether the diet provides novel macronutrient sources and/or a hydrolyzed protein source. It is also hard to predict which ingredient is the offending agent without elimination and challenge trials. Experimentally, most macronutrients – and specifically proteins – can be antigenic, but a set group of antigens are more commonly implicated in canine disease, namely beef, dairy products, and wheat 15, 16. 

Studies examining food allergic dogs with primarily GI signs are scarce, as most have focused on strictly cutaneous adverse food reactions. Animals with food allergies can exhibit variable clinical signs, however in a patient exhibiting both cutaneous and GI clinical signs the clinician should have a raised suspicion of a food allergy. A clinical diagnosis can be confirmed with a positive response to an appropriate diet trial, with a relapse in clinical signs after reintroduction of the offending ingredient 16. The diet trial can be completed with either a hydrolyzed or a limitedingredient diet, as both appear to be effective for food allergies, again despite the lack of a comparative studies 2, 17, 18, 19, 20. In cases where there is a high suspicion of food allergy, an 8 week dietary trial – similar to what is performed in dogs with a cutaneous adverse food reaction – is recommended; for dogs with suspected FRD a 2-4 week diet trial may be sufficient 21, 22.

Protein-losing enteropathies/ lymphangiectasia

Dietary fat restriction is most commonly used in dogs with protein-losing enteropathies (PLE). The initial basis for this presumption was based upon research demonstrating that dietary fat increases lymphatic flow. When there is increased lymphatic flow – which can be seen with various diseases, including lymphangiectasia – this can theoretically worsen protein loss and destabilize disease control 5, 6. PLE is also a heterogenous group of diseases which include IBD, lymphangiectasia, infectious etiologies (e.g., histoplasmosis), and GI lymphoma, among others, and the role of dietary therapy varies between these diagnoses. 

Initial reports on the responsiveness of PLE cases to low-fat diets were published in case reports, case series, and proceedings. Larger case series and studies have also reported on the efficacy of feeding low-fat diets to dogs with PLE. However, these studies are limited by a lack of control groups, study design, and concurrent treatments. As a result, they are intriguing and make a strong initial argument for dietary fat restriction. However, it is once again imperative that these early findings are substantiated with more robust research on the topic. Lastly, as mentioned before, the underlying etiology in PLE cases is variable and therapies should also be directed at the definitive diagnosis. For example, if an animal is diagnosed with IBD and PLE, it would be wise to choose a diet that could also provide either a hydrolyzed nutrient source or limited-ingredient list, thus allowing the clinician to meet the needs of the PLE patient as well as the routine IBD patient from a dietary perspective.

Large bowel disease

Variable dietary strategies have been employed for cases of canine large bowel disease. Six larger studies have investigated the topic of chronic colitis in dogs 10, 23, 24, 25, 26, 27. As with the available PLE literature, these studies are also often limited by a lack of control groups, study design, and concurrent treatments. Three of these studies in particular provide specific interesting information. In the first study the authors compared three diets (low-fat, high-fiber, or “hypoallergenic”) in dogs with colitis 25. All dogs in the study were concurrently managed with anti-inflammatory medications, but there was a different response rate based on diet type. An 85% response rate was seen with the hypoallergenic diet, 75% response rate with the fiber diet, and an 18% response rate with the low-fat diet. The other two studies provided strong evidence for the role of fiber-fortified diets or fiber supplementation to traditional GI diets (easily digestible, low-fat, and/ or limited-ingredient) in cases of chronic colitis 26, 27. In one study, the dogs had previously failed low-fat dietary therapy 27. In summary, responses have been seen with home-cooked, easily digestible diets, limited-ingredient diets, low-fat diets, and high-fiber diets. A review of this limited evidence should be in conjunction with an analysis of the robustness of the studies reporting results, as most are uncontrolled, but they demonstrated fiber-supplemented diets and/or novel or limited ingredient diets are best first-line options in the management of chronic colitis. As with previously cited disease, larger comparative studies are needed to determine the optimal approach in these cases, if one exists.

Canine CE can often be effectively managed with diet and this approach may avoid some of the potential problems that can be encountered with the use of long-term antibiotic or immunomodulatory medications, as many studies have demonstrated (Table 1). Diet should therefore be a focus during treatment planning for the CE patient. A variety of options exist, and patient factors and clinical signs may guide empirical dietary management choices for the clinician. Each patient should be evaluated independently, and diets chosen to best suit their needs based on the current literature. Dietary response times are well documented and there is some evidence that multiple diet trials may be advantageous in patients that fail to respond to initial empirical choices. Longterm, establishing control of canine CE with dietary modification and proper monitoring can lead to a strong, stable therapeutic response.