Dietary management of gastrointestinal disease: Douglas Palma DVM,
DACVIM
Dietary management of gastrointestinal disease is a complicated story.
Simplistically, changes in diet can be associated with improvements in
expression of clinical disease. However, understanding what factors within a diet
resulted in the improvement of clinical signs can be much more difficult.
Alterations in diet frequently result in changes in multiple factors that may lead to
clinical improvement or lack of response.
Some factors that are affected by diet include carbohydrate concentration,
carbohydrate source, protein source, protein quality/digestibility, fiber content,
type of fiber, fat content, palatability, consistency of the diet, presence or
absence of gluten and/or additives that may be contributing to a prebiotic effect.
Therefore, it is extremely naïve to think that a particular diet is going to have a
beneficial effect in every patient. Additionally, it is extremely naïve to believe that
anyone diet is superior and that one can truly understand the interactions
between the gut and each dietary factor and more importantly their relative
contributions when given together within a specific patient and specific disease.
Currently, everybody believes that they are a veterinary nutritionists. It is
important to understand that nobody currently understands the role of diet in
veterinary medicine and that generalizations will fall short for many patients.
That being said, we must have a method for addressing patients with chronic
gastrointestinal disease.
Key dietary interventions that have been suggested in the past include feeding a
hypoallergenic/hydrolyzed diet, fat restricted/highly digestible diets or high-fiber
diets. Each one of these diet categories offer some theoretical benefits for a
given case.
Hypoallergenic/hydrolyzed diets offer limited ingredients to critically evaluate
hypersensitivity responses to proteins and/or carbohydrate sources. The
principle behind these diets is to feed dietary substrates that are unique/novel to
the patient so that allergic responses to diet can be eliminated (as dietary
hypersensitization requires preexposure). Additionally, hydrolyzed diets offer a
unique form of “hypoallergenic” diets whereby potential dietary antigens are
reduced and molecular mass to a level that the immune system does not
recognize as foreign. It is important to note as discussed above, that been diet
may alter fiber content and/or other factors that may be important/critical to
managing a condition. These diets are commonly implemented for patients with
suspected hypersensitivity and are commonly implemented in the management
of inflammatory bowel disease. The principal for their use in inflammatory bowel
disease may have to do with alterations and mucosal integrity and exposure to
the submucosal lymphoid tissue. Dietary trials usually must be approximately 24 weeks before response can be truly assessed. This is unlike dermatologic food
trials, whereby clinical response may take upwards of 16 weeks.
Another form of diets include highly digestible, low-fat diets. This is typically the
strategy implemented for patients with acute enteropathies. However, chronic
enteropathies may benefit as well. These diets offer the benefits of fat restriction
contribute to increased osmotic factors presented to the colonic mucosa for
exacerbation of diarrhea. Additionally, fat can promote gastrointestinal
discomfort from malabsorption and potentially contribute to pancreatic disease in
susceptible individuals. The highly digestible nature of these diets increases the
efficiency of the gut that may be disease by inflammatory processes. These
diets require less gastric, pancreatic, biliary and intestinal secretions for
digestion. The reduced undigested food stuffs also reduce the likelihood of
clinical signs through decreased osmotic factors. In general, most meat sources
are highly digestible with greater than 90% of the protein being digested
efficiently in dogs and cats. This may be influenced by other factors within the
diet, however. Additionally, in general, vegetable sources of protein appear to
have reduced digestibility, thereby raising concerns regarding vegetarian diets.
Highly digestible carbohydrate sources include rice >potato, tapioca, corn, pasta,
rice baby cereals.
An important aspect of gastrointestinal health is fiber supplementation. Fiber,
soluble and insoluble (fermentable or non-fermentable) can affect colonic and
gastrointestinal health through multiple ways. One predominant feature is the
generation of short chain fatty acids which provide metabolic energy to the
colonic enterocytes, enhance water resorption, increase blood flow, alter
gastrointestinal hormone release, increase beneficial mucosal proliferation and
suppress pathologic mucosal proliferation/growth. Additionally, fiber may alter
gastrointestinal motility that could affect gastrointestinal options. The benefits of
fiber are not necessarily confined to colonic disease and have been shown to
have beneficial effects on small bowel health as well. Multiple different types of
fiber sources are available, with different ratios of soluble to insoluble fiber. In
general, patients may respond beneficially to one fiber source and not another.
Additionally, titration of fiber concentration may result in the difference between
benefits and no benefits. Commonly used diets for this purpose include hills
W/D, Purina DCO and Royal Canin fiber. However, many other diets are
available over-the-counter, generally including weight control diets. Additionally,
exogenous sources of fiber through diet (vegetables, grains, fruits) or synthetic
fibers (Metamucil, Benefiber, etc.) may be used. In general, the primary role for
fiber supplementation in patients with gastrointestinal disease appears to be
predominantly colitis. The decision to use exogenous fiber supplementation vs.
dietary supplementation may be based on palatability of the diet, owners
compliance and/or concurrent diseases that warrant specific diets (i.e. renal
disease).
Nowadays, home cooking has reached an all-time high. Following several
petfood blunders (melamine, aflatoxin, vitamin D over supplementation, etc.),
consumers are leery of petfood manufacturers. Home cooking provides an
alternative to provide fresh, controlled ingredients that may be beneficial to
patient with gastrointestinal disease. Additionally, it offers a unique ability to finetune diet without preservatives and/or other “chemicals” that may be present
within a diet. In general, home-cooked diets utilizing minimal ingredients may be
helpful to determine whether or not a patient can tolerate a specific protein and/or
carbohydrate. Feeding and isolated protein source and isolated carbohydrate
source and performing slow transition/appropriate duration dietary trials may be
beneficial. Short-term inadequacies within diet are tolerated, however, once a
diet is identified, consideration to transition to a more commercially
available/comparable diet or fine-tuning of the formulation to ensure nutritional
adequacy. Considerations for protein sources might include: talapia, catfish,
white fish, white fish ostrich, venison, kangaroo, duck, etc. Consideration for
carbohydrate sources might include: couscous, rice, potatoes, lentils, peas,
barley, squash, quinoa, millet, etc. Utilization of a veterinary nutritionist and/or
Balance-IT (www.balanceit.com), may be helpful in transitioning to long-term
feeding strategies.
A common contributing factor to gastrointestinal signs and people includes
lactose intolerance. While limited study has been performed in this arena, it
seems prudent that alterations in mucosal brush border enzymes may occur in
patients with chronic gastrointestinal disease. Therefore, situationally, restriction
of lactose containing foods may be beneficial to a given patient. Some forms of
lactose containing food may contain bacterial lactase that may increase their
tolerance. Nonetheless, restriction is recommended in the setting of active
disease until stabilization can be obtained. Long-term restriction may or may not
be necessary within a given patient.
Gluten free diets or grain free diets have been the current “Holy Grail” by many
lay people. It is important to note that gluten intolerance/hypersensitivity is only
been documented in Irish setters. The presence of celiac does not appear to
exist in our patients. Additionally, documented gluten sensitivity appears to be
questionable currently. In general, gluten represents a plant-based protein that is
highly digestible in nature. It is included in wheat, rice, barley and oats but not
rice or corn. Recently, in people, FODMAP (Fermentable Oligo-DiMonosaccharides and Polyols) restriction is thought to be the cause for the
apparent “non-celiac gluten intolerance”. The significance of FODMAP restriction
or gluten restriction in animals requires further investigation before these diets
can be applied widely to our population.
Raw food diets have been suggested to be beneficial due to their enhanced
digestibility. Certainly, these diets do offer potential benefits in that they are
generally simplistic (single protein source) thereby reducing potential allergens.
Additionally, they tend to be highly digestible. However, potential contamination,
development of hyperthyroidism, a requirement for meticulous
handling/preparation and the lack of proven evidentiary support vs. commercial
diets is the basis for the argument against. Occasionally, patients may respond
to raw food when response to other commercial diets was not possible.
Therefore, one must be open to the possibility that any change in diet (even if it is
one that you typically agree with) has the potential to help a given patient with
gastrointestinal disease.
Recently, vegetarian diets have been utilized by some pet owners. In general,
they have limited role at this time in management of chronic gastrointestinal
disease. Vegetable protein sources tend to be less digestible than meat sources.
Additionally, deficiencies in vitamins (retinol cholecalciferol, taurine, niacin),
deficiencies in minerals/fatty acids (zinc, calcium, iron, linoleic acid, choline and
other trace minerals) and excessive concentrations of vitamins (A, D) have been
documented with these diets. As is recommended with home-cooked diets,
consultation with a veterinary nutritionist can be helpful to ensure nutritional
adequacy.
In general, when feeding a patient with chronic gastrointestinal disease, it is
recommended that you feed simple diets with minimal ingredients. Additionally,
strict dietary compliance without variability is essential to success. The owner
must be patient with diet trials, ensuring appropriate intervals between diet
selections (2-4 weeks, depending on the trial). My preferences are to use
hypoallergenic/hydrolyzed diets, low residue/highly digestible/low-fat diets
preferentially in patients with small bowel disease. Whereby, my general
preference is to use high-fiber initially, followed by low residue/highly
digestible/low-fat diets for hypoallergenic/hydrolyzed diets.
In this current age, much misinformation is propagated throughout the general
public. One such argument is the use of corn in diets. Corn gluten meal
provides high-quality proteins while cornmeal provides an a highly digestible
carbohydrate source. The digestibility of the carbohydrate is greater than other
carbohydrate sources (rice, week, barley, sorghum). Additionally, corn is replete
in essential fatty acids as well as other antioxidants. Veterinary literature has not
been able to convincingly prove that corn sensitivity (food allergy) exists in any
significant quantity, in fact recent literature suggested a lower incidence of
allergies when compared to other protein/carbohydrate sources. The concept of
protein complementation or balancing of proteins within a diet to ensure
appropriate quality of proteins (that which meets the individual animal’s
demands) is implemented when corn is incorporated into the diet. Therefore, this
concept of it being a poor protein or carbohydrate source or acting as a filler is
inaccurate. Additional terms that are frequently used inappropriately include
digestibility of the diet. Digestibility references the amount of protein that is
absorbed vs. that which is ingested; frequently citing that the digestibility of many
commercial diets is poor. In reality, digestibility of many commercial diets and
protein/carbohydrate sources are quite high (>90%) disease. Additionally protein
quality is commonly used in discussions regarding pet foods. The quality of the
protein has to do with the ability of the animal to utilize the protein for growth and
maintenance of tissue and/or production of products (meat, eggs, etc.). This of
course depends on the type of protein relative to the individual species/animal.
Utilization of multiple protein sources within a diet allows for a high quality diet;
one that meets all the demands of the animal. The term is commonly
misconstrued with the argument suggesting that selection of meat cuts, etc. are
the sole factors in making a diet “high quality”. Additional terms/statements
frequently used in public include the use of “fillers”, ------ “meal”, byproducts and
lack of meat as the number one ingredient. Fillers are generally meant to imply
that cheap sources of protein are used, when in reality digestibility of some
proteins (i.e. corn) are quite high. The use of “meal” only means that the meat
source has been broken down into reduced particle size. The same cut of meat
may be used to create a “chicken meal” vs. “chicken”; the manufacturers use this
technique to save costs in shipping. The use of “byproducts” suggests that neck,
feet, underdeveloped eggs, intestines (not feathers) can be in part included in the
meat source. The digestibility of some of these sources can still be quite high
and certainly utilized in nature to complement dietary needs. And finally, a
common argument as to site that meat is not the first ingredient. It should be
noted that petfood manufacturers may use dry weight or wet weight basis which
can significantly alter the order of ingredients. Therefore, in short, critical
evaluation of a diet is difficult enough, without all the misconceptions in the
public.
Common disease processes and appropriate dietary suggestions are
below:
Disorders associated with reduced gastric motility (gastritis, inflammatory bowel
disease), gastroesophageal reflux, alterations in outflow tract diameter may be
benefited by altering dietary consistency and fat content within the diet.
Increasing fluidity of the food will increase gastric emptying time and potentially
modify disease processes. Additionally, restricting fat also might encourage
gastric emptying in patients with the aforementioned conditions.
Disorders associated with altered swallowing or esophageal dysmotility may
benefit from modifying food consistency as above. Patients with these conditions
being tolerate liquids better than solids or vice a versa. Experimentation with
consistency of food might result in the difference between the expression of
clinical disease or not. In rare cases, hypoallergenic diets can be considered for
patients with regurgitation. Eosinophilic esophagitis has been documented in
both dogs and cats and may be a manifestation of allergic disease; thereby
responding to dietary trials. This represents an unusual disease process in small
animal patients when compared to our human counterparts.
Management of acute gastritis/gastroenteritis is typically treated with an initial
phase of bowel rest (to reduce degree of osmotic factors contributing to diarrhea)
followed by a “bland diet”. This so-called bland diet is characterized by highly
digestible relatively fat restricted diet. As noted previously, fat and poorly
absorbed material results in exacerbation of gastrointestinal symptoms through
osmotic properties. Additionally, modification of feeding strategies; feeding small
volumes more frequently may reduce gastric distention and/or signs of nausea in
this setting. Of course, commercially available and noncommercially available
home-cooked options exist (boiled chicken, cottage cheese and rice). The
concept of feeding through diarrhea is frequently employed in people but may be
better suited to secretory diarrhea vs. the more common osmotic diarrhea seen
in animals.
Pancreatic disorders may require dietary modifications as well. Exocrine
pancreatic insufficiency frequently is cited as an indication for fat restriction.
While some patients with this disorder may do better with fat restriction, the
restriction of fat does not universally seem to help these patients. In fact,
significant variability within a patient ranging from high-fiber/poorly digestible to
low-fat/highly digestible diets may be needed to aid in management of these
conditions. Therefore, dietary transition is not recommended at initial diagnosis
but will be considered in a refractory patient. An additional pancreatic
disturbance; pancreatitis has raised considerable discussion regarding fat
restriction. Current evidence suggesting pancreatitis is directly linked to fat
consumption is relatively weak. While anecdotal evidence suggesting high-fat
meals may trigger pancreatitis is abundant, the jury still is out regarding its
significance within the population as a whole. Certainly, patients with
hypertriglyceridemia may represent a subpopulation that could potentially benefit
from fat. Other dietary strategies implemented in pancreatitis include bowel rest.
This concept is questioned as early enteral feeding has been shown to be
associated with better outcome in people and animals. Therefore, earlier
intervention is recommended, particularly when enteral nutrition as tolerated.
Due to differences in cats and dogs, cats are believed to have a much higher
tolerance for fat and thereby fat restriction does not appear to have a significant
role. Unlike acute pancreatitis, consideration to fat restriction should be made in
patients with chronic pancreatitis. Due to the inability to modify the expression of
pancreatitis in these patients, all potential benefits of fat restriction should be
considered. Equally as important, addressing obesity may affect the
development of pancreatitis. Obesity has been shown to be a risk factor for
pancreatitis in dogs and negative prognostic factor in people.
Protein losing enteropathy is a group of conditions associated with also protein
from the gut and malabsorption. It is frequently cited that fat restriction is
appropriate/essential to these patients. The evidence suggesting the diet
superiority is lacking. A recent study looking at Yorkshire Terriers did not reveal
significant difference between hypoallergenic and fat restricted diets. Fat
restriction may reduce the likelihood of secondary lymphangectasia, Whereas,
hypoallergenic diets may address allergic contribution to disease. It is important
to note that patients with PLE may have substantial reductions in efficiency due
to alterations in mucosal surface area. Therefore, highly digestible diets are
essential. Additionally, elemental diets should be considered to complement
nutrition plan. In my practice, if biopsies are obtained and evidence of significant
lymphangectasia is present (primary or secondary), fat restriction is
recommended. If the changes are predominantly inflammatory without evidence
of lymphangectasia, then I consider hydrolyzed diets preferentially.
Primary lymphangectasia is a form of protein losing enteropathy whereby fat
restriction appears to be critical to management. Commercially available fat
restricted diets may be successful however, refractory cases may benefit from
ultra low-fat diets (turkey and potato/rice or chicken and potatoes/rice). Rare
cases may benefit from not only fat restriction but marked increases in fiber (Hills
R/D).
Chronic constipation can be modified by dietary intervention. In general, colonic
stretching results in increased contractility. However, later in the stage of chronic
constipation (i.e. megacolon), fiber may result in colonic stretching without
secondary resultant bulk movements. Therefore, addition of nonfermentable/insoluble fibers could potentially exacerbate colonic obstruction in
this setting. Therefore, chronic constipation is managed to some degree based
on the stage of disease (acute, degree of colonic distention, historical
obstipation, etc.). If colonic motility is thought to still be intact, addition of highfiber diets or exogenous sources of fiber (canned pumpkin, Metamucil) may be
implemented.
Hepatobiliary disease is not uncommon. Frequently, protein restriction is
implemented in patients with hepatic disease. This is unnecessary unless
evidence of hepatic encephalopathy is present. In fact, many forms of hepatic
disease are associated with increased caloric demands. Additionally, negative
nitrogen balance can promote lean muscle mass and perpetuation of hepatic
encephalopathy from endogenous muscle breakdown. Protein restriction is
reserved for those with hepatic encephalopathy. Additional considerations
include copper restriction. Biopsies consistent with a copper associated
hepatopathy and ideally those with quantitative copper levels >1000 ppm or
those with centrolobular distribution. Copper restriction is employed through
most commercial liver diets. A list of non-copper containing foods is available
online. Several factors are commonly overlooked in management of those
patient with hepatic encephalopathy. These include: maintaining adequate
caloric intake, reducing ammonia producing protein ingestion and providing fiber
intake. As stated above, maintaining nutritional adequacy reduces lean muscle
mass breakdown (which can exacerbate hepatic encephalopathy). Different
protein sources have different volumes of ammonia production with meat based
proteins having a higher ammonia production relative to milk or vegetable
sources. Therefore, titration of protein into the diet in the form of soy based
proteins can be utilized for those patients that are stable. Additionally, titrating
fiber content can help with protein tolerance by slowing digestion and having a
effect on bacterial flora/ionization of ammonia. One final consideration are
patients with ascites; these patients must be sodium restricted.