Posted : 4/9/2007 12:12:08 AM
I love conference proceedings... hope this helps!!
Dietary Management of Inflammatory Bowel Disease
Atlantic Coast Veterinary Conference 2002
Kathryn E. Michel, DVM, MS, Dipl ACVN
University of Pennsylvania, School of Veterinary Medicine
Philadelphia, PA, USA
Inflammatory bowel disease (IBD) is a general term that is applied to gastrointestinal disorders that present most commonly with diarrhea, sometimes in conjunction with vomiting, anorexia, and weight loss, and a histopathologic finding of inflammatory cell infiltration of the gastrointestinal mucosa. At times a specific etiology can be determined but more often the condition is considered idiopathic.
The pathogenesis of diarrhea in IBD involves many abnormalities, e.g., reduced absorptive surface area, reduced fluid and electrolyte absorption, increased fluid secretion, and perturbations in intestinal motility. In refractory or difficult cases of IBD, dietary and medical therapies are formulated to stimulate villus epithelial cell absorption, inhibit crypt epithelial cell secretion, stimulate circular smooth muscle cell contraction, and reduce inflammation.
Diet should play a central role in the management of IBD. Dietary factors are most certainly involved in some of the clinical manifestations of IBD and therefore it follows that dietary modification can be palliative. There is also speculation that dietary factors may be involved in the pathogenesis and perpetuation of IBD. The presence of luminal nutrients is required for maintenance of normal gastrointestinal mucosal structure and function. Food within the gut lumen provides a direct source of nutrients for the enterocytes, results in increased mesenteric blood flow, and the release of digestive enzymes and enterohormones, all of which can influence intestinal cell proliferation and differentiation. Conversely, dietary factors may cause a variety of adverse reactions including immunological and inflammatory responses, osmotic diarrhea, changes in the numbers and composition of gut microflora and altered gastrointestinal transit time.
Dietary management of IBD is primarily aimed at enhancing the absorption of nutrients and water through attention to overall diet digestibility as well as manipulation of the type and quantities of specific nutrients. The other strategies for the therapy of IBD stated above are principally achieved through pharmacologic means. However, the use of dietary fiber can influence gastrointestinal motility and absorption and diets containing novel or modified proteins could potentially reduce mucosal inflammation.
Finally, many patients with IBD have experienced some degree of malnutrition particularly if a protein-losing enteropathy is involved. Whatever dietary interventions are used, every effort should be made to insure that patients receive adequate calories and balanced nutrient intake.
Factors affecting the digestibility of a given food include the source and quantity of protein, fat, and carbohydrate, the presence or absence of nondigestible carbohydrates (i.e., lactose, various types of fiber) and how it was processed (i.e., grinding, cooking, etc.) High digestibility is desirable in diets designed for the management of IBD for several reasons. Patients with IBD usually have some degree of villus atrophy and malabsorption. High digestibility should facilitate maximal absorption in the proximal small bowel. This should lessen the potential for the development of osmotic diarrhea. By promoting complete absorption, it should limit the availability of nutrients to enteric microorganisms, potentially limiting numbers of bacteria and decreasing the production of the gaseous by-products of fermentation.
While fat is one of the most digestible components of the diet, fat malassimilation is not uncommon in patients with IBD. Fatty acids reaching the colon will be hydroxylated by bacteria, and can have toxic effects on the mucosa that result in diarrhea. Therefore diets with moderate to low fat content (<30% of calories from fat) are advisable for patients with IBD. Having said that, cats with IBD appear to tolerate relatively high fat foods better than dogs do. Medium chain triglycerides (MCT) can be used to replace some of the long chain triglycerides in the diet as a calorie source. MCT are less dependent upon micelle formation for digestion and absorption than long chain triglycerides, and are absorbed directly into the portal circulation. Most cats do not find them very palatable however, so their usefulness may be limited. In addition there is one report in the veterinary literature of cats developing hepatic lipidosis on a research diet formulated with MCT.
Fiber is a generic term encompassing the indigestible carbohydrate and lignin components of food. While it is not a nutrient, it does serve several important functions in the gastrointestinal tract including binding water, providing bulk, the modulation of nutrient absorption and digestion, and the maintenance of gastrointestinal function and mucosal structure. Fiber can be classified in several ways. Commonly fiber is divided into two broad categories: soluble and insoluble. Soluble fibers have a greater capacity to bind water and also are relatively fermentable by colonic microflora. Examples of soluble fiber include guar gum, pectins, and some hemicelluloses. Insoluble fibers have less of a water absorptive capacity, are relatively nonfermentable, and tend to decrease gastrointestinal transit time. Common examples of insoluble fiber are cellulose and lignin. The ability of fiber to bind toxins, bile acids, and water and to normalize gastrointestinal motility have all been proposed as possible mechanisms for the success of fiber in treating some individuals with diarrhea and inflammatory bowel disorders.
There is accumulating evidence in animal models of IBD and some human clinical trials that fermentable fibers may be therapeutic in the treatment of colonic inflammation. One of the by-products of microbial fermentation is the short chain fatty acid butyrate. Butyrate is the preferred metabolic fuel of the colonocyte. Since butyrate uptake by colonocytes is coupled with sodium uptake, the availability of fermentable fiber may promote sodium and water uptake in the inflamed colon and ameliorate large bowel diarrhea. Currently evidence for the therapeutic effects of fiber in veterinary IBD patients is largely anecdotal. The addition of fiber to the diet of a patient who is believed to have small intestinal inflammation may be counterproductive because of the effects that it may have on the diet's overall digestibility. However, a trial of fermentable fiber may be warranted in patients with evidence of idiopathic large bowel inflammation.
Novel And Modified Protein Diets
The gastrointestinal mucosal immune system protects the host against potential pathogens crossing mucosal barriers while at the same time provides immune tolerance of the barrage of dietary antigens and normal intestinal microflora that interfaces with the mucosa. IBD is thought to be the result of dysregulation of this delicate balance. While it is unlikely that dietary hypersensitivity is the primary cause of idiopathic IBD, it is possible that food antigens may be involved in the perpetuation of mucosal inflammation. One consequence of the inflammation seen in IBD is increased mucosal permeability. There is speculation that this could lead to sensitization to dietary proteins, which would in turn contribute to the ongoing inflammatory process.
Pets with clinical signs and histopathologic findings consistent with a diagnosis of IBD often respond to treatment with limited antigen diets. . A recent study of 55 cats with idiopathic gastrointestinal problems of greater than 2 weeks in duration found that 29% of the cats had food sensitivity based on an elimination-challenge diet trial and an additional 20% had complete resolution of clinical signs with the elimination diet although signs did not reappear when challenged with their previous diet. Clinical signs resolved in a matter of days after introduction of the novel protein diet. This study underlines the importance of investigating diet when working up patients with chronic gastrointestinal problems.
There are now available a number of prescription limited antigen diets. It is important to recognize that the canned products for dogs and cats are high in fat. Most of the dry products could be considered at best, moderate in fat content. Therefore, patients experiencing problems with fat absorption will likely have difficulty tolerating these products. For these patients, one of the lower fat, dry, limited antigen formulas is the best option.
Modified protein diets have been used to treat human patients with IBD, particularly Crohn's Disease, with good success. These diets contain hydrolyzed single protein sources such as whey or casein. This type of diet has recently been developed for dogs. These are truly "hypoallergenic" diets since the protein contained in them has been broken down into fragments too small to be recognized by the immune system. If the hypothesis concerning dietary hypersensitivity and the perpetuation of IBD were correct, this type of formulation would be well suited for dietary management of acute exacerbations of the disease. Currently there are no such diets available for cats but at least one is under development.
Determination of serum cobalamin concentration has been useful in identifying and characterizing intestinal and pancreatic disease in dogs and cats. Intrinsic factor (IF), a cobalamin binding protein that promotes cobalamin absorption in the ileum, is produced by the stomach and pancreas in dogs, and the pancreas, but not the stomach, in the cat. A portion of cobalamin taken up by hepatocytes is rapidly re-excreted in bile. Cobalamin of hepatobiliary origin, along with dietary derived cobalamin, undergoes transfer to IF and receptor mediated absorption, thus establishing enterohepatic recirculation of the vitamin.
Cobalamin deficiency has rarely been reported in the cat though recent observations indicate serum concentrations can be subnormal in cats with EPI, intestinal, pancreatic or hepatic disease. Forty-nine of 80 serum samples submitted from cats with signs of gastrointestinal disease had cobalamin concentrations below the reference range for healthy cats (range 900-2,800 pg/ml; mean ± SD = 1775 ± 535 pg/ml SD; n=33). Cats with subnormal cobalamin concentrations (mean ± SD = 384 ± 272 pg/ml, range 3-883 pg/ml) were middle aged or older and were presented for weight loss, diarrhea, vomiting, anorexia and thickened intestines. Definitive diagnoses in 22 cats included inflammatory bowel disease, intestinal lymphoma, cholangiohepatitis or cholangitis, and pancreatic inflammation. Serum concentrations of cobalamin were particularly low in cats with intestinal lymphoma, 3/5 of which also had subnormal serum concentrations of folate (< 9 ng/ml). The simultaneous presence of disease in the intestines, pancreas or hepato-biliary system in many cats made it difficult to determine the cause of subnormal cobalamin concentrations. There is some evidence that cobalamin supplementation may result in clinical improvement of cats with IBD, without recourse to immunosuppressive therapy. Cobalamin can be easily supplemented parenterally (SQ or IM). Recommendations are to give 250 µg once a week for one month and then once every two weeks (D. Williams).
Folate is absorbed passively when it is present at high luminal concentrations. This may be secondary to high dietary content or intestinal bacterial overgrowth. Once absorbed, folate is methylated in the cell to methyltetrahydrofolate. It is noteworthy that cats with intestinal lymphoma have low serum folate concentrations. This may relate to malabsorption or alternatively increased utilization by neoplastic tissue.
When interpretating serum concentrations of cobalamin and folate it is important to remember that serum concentrations are labile and reflect the balance between dietary intake, bacterial utilization and production, intestinal absorption, and body metabolism and losses. Normal serum concentrations of cobalamin and folate neither exclude nor support a diagnosis of intestinal disease.