• Open Access

Effect of Diets Differing in Fat Content on Chronic Diarrhea in Cats


  • An abstract from this study was presented at the 2007 American College of Veterinary Internal Medicine Forum.

Corresponding author: Dottie Laflamme, DVM, PhD, DACVN, Nestlé Purina PetCare Research, Checkerboard Square, 3S, St Louis, MO 63164; e-mail: dorothy.laflamme@rdmo.nestle.com.


Background: Fat-restricted diets have been advocated for dogs with diarrhea for many years. Recommendations for cats with diarrhea have varied between low-fat and high-fat diets, but there have been no published studies to support either recommendation.

Objectives: The objective of this study was to compare the clinical responses of cats with chronic diarrhea to dietary management using either a high fat or a low fat, highly digestible diet.

Animals: Sixty pet cats with chronic diarrhea were recruited; 55 cats completed the study.

Methods: Randomized, double-blinded, controlled clinical trial. Upon completion of baseline measures, cats were fed 1 of 2 diets for 6 weeks, during which the owners recorded fecal scores daily using an illustrated fecal score chart ranging from 0 (very watery) to 100 (firm and dry). After 6 weeks, cats were reevaluated by the attending veterinarians.

Results: Fecal scores improved significantly, with 78.2% of cats improving by at least 25 points on the 100-point scale or having a final fecal score of at least 66. Over one third of the cats developed normal stools. There were no differences in clinical responses between the diets. Clinical improvement was noted within the 1st week, and maximized within 3 weeks.

Conclusions and Clinical Importance: These results show that dietary management can be helpful in cats with chronic diarrhea, but dietary fat content does not appear to affect the outcome. Cats that do not respond within 3 weeks should be evaluated further.


vitamin B12 or cobalamin


feline leukemia virus


feline immunodeficiency virus


fecal score average for week




key outcome parameters


trypsin-like immunoreactivity

Dietary management of gastrointestinal (GI) disease is an adjunct to specific or symptomatic management to control clinical signs, such as diarrhea. The appropriate dietary modifications are dependent upon the type and expression of the disease, and on which parts of the GI tract or which associated organs are affected. Recommendations also may depend on which species is affected.

Highly digestible, restricted-fat diets have been advocated as appropriate for dogs with GI disease and diarrhea for many years.1–4 Compared with protein and carbohydrate, fat is the most complex nutrient to digest and absorb. For complete digestion, fat requires lipase, colipase, and phospholipase A2 from the pancreas, as well as bile acids, which are produced by the liver, then stored and released from the gall bladder. Once inside the enterocyte, fatty acids and monoglycerides must be reformed into triglycerides. This is an active, energy-expending process, resulting in production of chylomicrons, which then enter into the intestinal lacteals and are transported via the lymphatic system to the systemic bloodstream. This differs from other nutrients, which are transported directly to the liver via the portal blood.

Despite the complexity, fat digestion is highly efficient so that most ingested fat is absorbed in healthy subjects. Yet, because of the complexity, fat digestion is easily compromised. Fat malabsorption or maldigestion may occur as a result of intestinal mucosal damage or villus atrophy, pancreatic enzymatic deficiency, or biliary deficiency. Severe fat malabsorption is evident as steatorrhea, but fat malabsorption may occur in the absence of obvious steatorrhea. When fat digestion is incomplete, bacteria in the colon can ferment the undigested fat, producing potent secretagogues and proinflammatory compounds.3–5 This results in a secretory diarrhea as well as intestinal inflammation. Thus, low-fat diets have long been recommended for patients with GI disease and diarrhea.1–6

In contrast to the recommendations cited above, recent recommendations suggest moderate to high (eg, 15–25% fat, dry basis) fat diets for cats with diarrhea.7–9 Higher fat diets usually are higher in calories, allowing a lower volume of food intake to maintain energy intake. The decreased food intake could, in theory, decrease chyme volume and increase digestive efficiency. To our knowledge, no studies have been published to support either the low-fat or high-fat recommendation for cats with diarrhea. Thus, the objective of this study was to evaluate the clinical responses of cats with chronic diarrhea of nonspecific cause to dietary management using either a high fat (45.1% of calories from fat) or a low fat (23.8% of calories from fat), highly digestible diet. Key outcome parameters (KOP) indicating clinical responses included changes in fecal score, fecal frequency, and vomiting frequency.

Materials and Methods


Sixty pet cats with chronic large bowel diarrhea, small bowel diarrhea, or a combination of these were recruited by 4 primary care veterinary practices. All pet owners gave informed written consent to participate in the study. Cats were solicited for the study if they had experienced at least 3 episodes of diarrhea per week for at least 1 month before entry into the study. Cats must also have shown inadequate response, defined as continued diarrhea or recurrence after treatment, to prior therapy with a full-spectrum intestinal parasiticide, including treatment for Giardia. Cats were excluded from the study if they had an infectious disease such as feline leukemia virus (FeLV), feline immunodeficiency virus (FIV), panleukopenia virus, or feline infectious peritonitis, or if they had evidence of a systemic disease that may cause diarrhea or GI signs including, but not limited to, renal failure, hyperthyroidism, pancreatic or hepatic disease, or malignancy of any type. Cats were excluded if their clinical condition was such that they required immediate medical care to control the diarrhea or its effects, such as those with hypoproteinemia, recent weight loss in excess of 10% of their body weight, or with chronic, undesired weight loss in excess of 25% of any previous adult body weight. Cats also were excluded if they had been treated with a long-acting corticosteroid within the past 6 weeks or had received corticosteroids PO within the past 2 weeks. No corticosteroids, GI motility modifiers, oral antibiotics, parasiticides, or other medications were allowed during the study.


Two experimental diets were prepared from the same ingredients, adjusted as necessary to create diets as similar as possible except for the dietary fat content (10 or 23%, dry basis; Table 1). Both diets were formulated to provide complete nutrition and to be highly digestible. Diets were provided in plain bags, labeled to indicate Diet A or Diet B. Neither the veterinarian nor the owner knew which diet was the low-fat control or the high-fat test diet. Owners agreed to feed their cats the assigned diet, in amounts sufficient to maintain body weight, as the sole diet for 6 weeks.

Table 1.   Nutrient profile of dietsa
 Diet ADiet B
 % Dry Mattergm/100 kcal ME% Caloriesb% Dry Mattergm/100 kcal ME% Caloriesb
  • kcal ME, kilocalories of metabolizable energy.

  • a

    Key ingredients for both diets: Soy flakes and soy protein isolate; turkey and turkey by-product meal; corn starch; oat meal; oat fiber; beef tallow; vitamins and minerals.

  • b

    Percent of calories calculated as 3.5 kcal/g for protein and carbohydrate and 8.5 kcal/g for fat, as a percentage of calculated metabolizable energy.

Crude fiber1.30.3 1.80.5 
 (kcal/g dry weight)  (kcal/g dry weight)  
Metabolizable energy4.33

Study Design

All aspects of this trial were conducted in accordance with Nestlé Purina's guidelines for animal welfare. Upon entry into the study, a separate random numbers table for each study center was used to assign cats to either Diet A or Diet B. During the course of the study, cats were to receive no medications. All cats underwent baseline evaluations to rule out systemic diseases, including a complete physical examination with body weight and body condition score, serum biochemical profile, CBC, urinalysis, FeLV antigen and FIV antibody tests, serum folate and cobalamin (B12) concentrations, and serum trypsin-like immunoreactivity (TLI). Fecal samples were analyzed for the presence of intestinal parasites using a standard fecal smear and fecal floatation; zinc-sulfate centrifugation was used to detect Giardia.

A detailed medical and dietary history was obtained to include the frequency, duration, and character of vomiting and diarrhea. Fecal scores were determined using an illustrated scoring system (Fig 1), which ranked very watery diarrhea as zero (0) and firm, dry feces as 100. Client recall of fecal scores and frequency of defecations for the 3 days immediately before the initial evaluation were recorded as baseline.

Figure 1.

 Illustrated fecal scoring chart.

To measure the KOP of fecal score and frequency during the 6-week feeding period, clients were required to maintain a daily diary to record fecal scores for each defecation, thus also indicating the frequency of defecations. Daily fecal scores for the entire week were averaged (FSa) for each cat for weeks 1, 3, and 6. The occurrence and characteristics of vomitus, if any, also were recorded, and clients were to record their cat's acceptance of the diet (1 = poor; 2 = fair; 3 = good; 4 = excellent). At the end of the study, cats were reevaluated by the attending veterinarian.

Statistical Analysis

KOP included changes in vomiting frequency, defecation frequency, and FSa. For each cat, a positive response in FSa was defined as an increase of at least 25 points or an increase to a FSa of at least 66 on the 100-point scale. For this study, normal FSa was defined as a score of ≥80.

Repeated measures analysis of variance was used to evaluate normally distributed data. For data that were not normally distributed, a Mann-Whitney rank-sum test was performed. Polynomial regression was used to determine the association between fecal scores and serum cobalamin concentrations. Statistical analyses were performed by SigmaPlot 11.0.a Data are shown as means ± standard deviation unless otherwise noted. Probability values of <.05 were considered significant.


Sixty cats were recruited into the study: 5 were excluded based on the predetermined criteria or withdrawn because of client preferences or noncompliance. Of the cats completing the study, 28 were fed Diet A and 27 were fed Diet B. Both diets were well accepted, although the clients' rating for Diet A was higher than for Diet B (3.8 ± 0.4 versus 3.3 ± 0.8, respectively; P < .005).

Baseline values for all KOP were similar between groups. Vomiting was uncommon in these cats. Client diaries indicated vomiting or regurgitation at some point during the study for 20 cats, but descriptions implied most of these were hairballs. Only 4 cats vomited or regurgitated more than twice over the 6-week period. Mean fecal frequency did not differ significantly over time or between diets. Data on initial fecal frequency were not available for 3 cats. Among the other 52 cats, frequency exceeded twice daily for only 5 cats at baseline, decreasing to 1 cat by the end of the study.

FSa increased (P < .001) over time from 31.5 ± 15.3 at entry to 71.0 ± 22.0 by the end of the study, but did not differ between diets (P > .10). As shown in Figure 2, FSa began to increase within the 1st week, reaching a steady state by the end of 3 weeks. By the end of 6 weeks, FSa for 43 of 55 cats (78.2%) was 66 or above or had increased at least 25 points. This result included 2 cats starting with a fecal score of 66 that did not improve further. Twenty cats (36%) had final FSa above 80. Among these 20 cats, equally split between Diets A and B, initial fecal scores averaged 34.7 ± 16.8 and improved to an average of 93.2 ± 8.5.

Figure 2.

 Fecal scores of cats with chronic diarrhea in response to dietary change. Means (+standard deviation) are based on client-assigned scores based on the system shown in Figure 1. a, b, c, means with different superscripts differ, P < .001.

Serum TLI and folate concentration did not differ over time or between diets. Fecal scores were significantly lower in cats (n = 11) with low-serum B12 concentrations (Table 2). Despite this, the proportion of cats responding positively to the diets (77.3% for cats with normal B12 versus 63.6% for cats with low B12) was not significantly different, and the final FSa was only weakly (r2= 0.201, P= .44) correlated with lower B12 concentrations (Fig 3). Seven of the 11 cats with low B12 showed improvement in fecal scores, although only 1 developed normal stools during this study. Among the 7 cats with low-serum B12 concentration fed Diet A, FSa improved in 5 cats, 1 had a weak positive response and 1 cat did not respond, with an overall significant (P<.05) improvement over baseline in this group. Among the 4 cats with low-serum B12 concentrations fed Diet B, FSa improved in 2 and did not change or became worse in 2 cats. However, statistical comparison within this group was not appropriate because of the small number of cats and low-statistical power.

Table 2.   Association between serum B12 concentration and fecal scores in cats with chronic diarrhea
  • B12, vitamin B12 or cobalamin.

  • a

    Mann-Whitney rank-sum nonparametric test performed as data were not normally distributed.

  • b

    Laboratory values shown as “>1,200” were entered as 1,200, and values shown as “<100” were listed as 100 for statistical analysis. Cats with serum B12 concentrations of <290 ng/L were considered to have low B12.

Baseline B12 concentration (ng/L)
 Low B12b11198.5221125252 
 Normal B1244954.110727441200<.001
Baseline fecal scores
 Low B121124.03316.533 
 Normal B124433.4333333.024
Final fecal scores
 Low B121151.0663366 
 Normal B124473.16666100.010
Figure 3.

 Regression showing relationship between serum B12 concentration and final fecal scores in cats with chronic diarrhea. The dotted line shows the 95% confidence interval. Best fit of the data was a third-order polynomial regression: y= 3.786 + (0.329 × B12) − (0.000468 × B122) + (0.000000203 × B123); P= .044, r2= 0.201.


This study assessed the effects of dietary fat in cats with chronic diarrhea. The majority of cats in this study responded to the diets tested with an obvious improvement in FSa. However, there were no differences in response between the 2 diets, indicating that the amount of dietary fat does not appear to be an important factor in dietary management of cats with diarrhea.

Novel protein diets often are recommended for the management of diarrhea in cats.4,10 Both diets used in this study were highly digestible and made with the same ingredients. The protein sources, soy and turkey, are commonly used ingredients. The response to these diets suggests that novel protein diets may not be important in the majority of cats with diarrhea.

An important observation in this study was the rapid response time. All cats that responded to the study diets began to do so within the 1st week, with maximum effect seen by the end of 3 weeks. This time frame is consistent with other studies in cats with diarrhea.11,12 Also consistent with other studies is the proportion of cats showing excellent improvement and even complete remission of diarrhea.11,12,b In this study, 36% of cats developed normal stools, with FSa > 80. Such observations highlight the importance of dietary change for the management of feline diarrhea.

Dietary changes of many types can induce physiologic adaptations within the GI tract.13–18 A partial list of such changes includes intestinal mucosal hypertrophy, alterations in gastric emptying and GI transit rate, changes in nutrient and water absorption, changes in intestinal microflora, and altered production of short chain fatty acids. Changing diets can alter the presentation of both dietary antigens and antigens from intestinal bacteria, which may be involved in dietary hypersensitivity or inflammatory bowel disease.19–21 Which, if any, of these mechanisms played a role in the clinical responses observed in the cats of this study was not determined.

There was a weak, but significant, association between low-serum B12 concentration and fecal scores in this study. Twenty percent of the cats in this study had B12 concentrations below the normal reference range. This is similar to the 16.5% reported by Reed et al,22 but considerably less than 61% reported by Simpson et al23 in their studies of cats with GI diseases. The proportion of cats with low-serum B12 concentration responding to the diets was only slightly less than the response rate among cats with normal B12 concentrations (63.6% for cats with low B12 versus 77.3% for cats with normal B12), but the magnitude of improvement was decreased in cats with low-B12 concentrations. However, in a previous study of cats with diarrhea, the mean serum B12 concentration actually was greater in cats not responding to dietary change than in cats that improved,12 so the importance of a low-B12 concentration is unclear. When low-B12 concentration is because of pancreatic or small intestinal disease, which interferes with B12 absorption, serum concentrations are unlikely to improve unless the disease is controlled. Because low-B12 concentration itself can contribute to intestinal pathology, some cats may not improve until the metabolic B12 deficiency is corrected by parenteral B12 administration. Unfortunately, repeated measurements of B12 concentration were not taken in this study to see if it improved as the cats' diarrhea resolved. Testing for and correcting low-serum B12 concentration may be important, especially in cats that do not respond to other forms of management for their GI disease.

Although vomiting is a common sign of GI disease in cats,22,23 it was not common among the cats in this study. Thus, we were not able to determine whether a high- or low-fat diet might be beneficial in the management of vomiting in cats.

A limitation of this study is that no final diagnosis for the cause of diarrhea was made in these cats. Neither endoscopic evaluation with biopsies nor other intestinal function tests were performed during this study. It would have been of interest to determine if the nonresponders had different underlying causes of diarrhea compared with those that improved. Another possible limitation is the range of dietary fat tested in this study. Although the fat content of most dry commercial cat foods falls within the range of the diets tested,24,25 some foods do have higher or lower fat levels. The effects of dietary fat might be different at notably higher or lower concentrations.


The majority of cats in this study with nonspecific chronic diarrhea responded to the diets tested with an increase in FSa. Cats with low-serum cobalamin concentrations at the beginning of the study had a slightly increased risk of not responding, or not responding as well, to dietary change.

Fecal scores began to improve within the 1st week, and achieved a maximum response within 3 weeks. However, there were no differences between the diets tested regarding the percentage of cats responding or the degree of response. Both diets were well accepted by the cats. Thus, it appears that a dietary change can be an important part of management for cats with chronic diarrhea, but the amount of dietary fat does not seem to be an important consideration.


a Systat Software Inc, San Jose, CA

b Laflamme DP, Xu H, Cupp CJ, et al. Comparison of two canned diets designed for the management of feline diarrhea. J Vet Int Med 2010;24:724 (abstract)


The authors thank the veterinarians, staff, and cat owners at the veterinary practices participating in this study (Cats Only Veterinary Hospital, Paddock Park Animal Care Center, Brick City Cat Hospital, and The Cat Doctor) as well as Denni Day and the staff of VetPharm Inc for assistance in data collection.

This study was conducted and funded by Nestlé Purina PetCare Company, (St Louis, MO), in partnership with Cats Only Veterinary Hospital (Fayetteville, NY), Paddock Park Animal Care Center (Ocala, FL), Brick City Cat Hospital (Ocala, FL), and The Cat Doctor (Thousand Oaks, CA), and VetPharm Inc (East Rochester, NY).