Camille Torres-Henderson
DVM, DABVP (Canine & Feline Practice), DACVIM (Nutrition)
Dr. Torres attended Colorado State University (CSU) for her undergraduate and veterinary education. After she earned her DVM degree in 2001, she went into small animal private practice in Albuquerque, New Mexico. She joined community practice at CSU’s James L. Voss Veterinary Teaching Hospital in 2008, and earned her feline and canine DABVP certification in 2011. As a general practitioner, she has observed the power of preventive medicine. Seeing how preventing disease can be so much easier for a pet than treatment led her to explore the effects of obesity on companion animals and nutrition’s role in obesity management. Her enthusiasm for nutrition in multiple areas inspired her to seek additional training in the field of nutrition at CSU, and she completed a residency in nutrition and became a diplomate of the American College of Veterinary Internal Medicine (Nutrition) in 2021. Her furry family consists of 2 cats, a yorkiepoo, and a French bulldog.. She enjoys spending time with her husband and their 2 boys, taking every opportunity to participate in the wonderful outdoor activities that Colorado has to offer.
Read Articles Written by Camille Torres-Henderson
Dietary fiber is a major component of veterinary nutrition. Its effects depend on key properties such as fermentability, solubility, and viscosity, which influence gastrointestinal transit, microbiome balance, and nutrient digestibility. Fermentable fiber supports gastrointestinal health through short-chain fatty acid production, and soluble and insoluble fiber affects stool bulk and moisture. Not all types of fiber are appropriate for every condition, and inappropriate use can worsen clinical signs, especially those of megacolon or obstipation. Accurate assessment of fiber content in pet food requires evaluating total dietary fiber, not just crude fiber. By understanding fiber’s multifaceted role, clinicians can tailor nutritional management strategies to meet individual patient needs and improve clinical outcomes.
Take-Home Points
- Fiber should be matched to the condition being treated; consider fermentability, solubility, and viscosity rather than using a blanket approach.
- To compare diets accurately, evaluating crude fiber is not enough; when possible, evaluate total dietary fiber.
- Not all patients benefit from added fiber; for patients with conditions such as obstipation or megacolon, fiber may worsen clinical signs.
- Response matters more than fiber amounts; tailor fiber intake to the individual patient’s tolerance and clinical response.
Dietary fiber plays a valuable role in veterinary nutrition, but the term “fiber” is often oversimplified. Its definition can vary according to specific characteristics and how it interacts with the digestive system. Fiber is commonly used to manage conditions such as constipation, diarrhea, and anal gland irritation, among others. Depending on the type, fiber can have other attributes, such as acting as a prebiotic to support microbiome health.
When recommending fiber, consider the specific goal or intended outcome and choose a fiber type that aligns with that goal. Fiber is categorized by its fermentability, solubility, and viscosity, which influence its effect in the body. Whether evaluating a diet or adding fiber to one, these 3 properties should be matched to the condition being managed. Given the diversity of fiber properties and physiological effects, dietary fiber should be evaluated on an individual basis rather than classified broadly as universally beneficial or detrimental. Finding the right balance and selecting fiber that aligns with the patient’s specific needs are essential.
Description of Fiber
Fiber is the nondigestible portion of carbohydrates. Because it is not digested, fiber passes through the small and large intestines, where it can be fermented by bacteria or affect the bulk and consistency of the feces. Fiber plays a role in supporting gastrointestinal (GI) health due to its effects on the microbiome, and it is a fuel source for enterocytes; however, not all patients respond to fiber in the same way, and thus the amount and type of fiber that is fed should be considered on an individual basis. Fiber can have several effects on the GI tract, such as altering the digestibility of a diet or transit time.1
Categories of Fiber
Fiber categorization is generally based on its characteristics and how it behaves in the intestinal tract. The main categories are fermentability, solubility, and viscosity (TABLE 1).
| TABLE 1 Type of Fiber and Its Characteristics 2,3 | ||
|---|---|---|
| Type of Fiber | Fermentability | Solubility |
| Guar gum | High | Soluble |
| Pectin | Moderate to high | Soluble |
| Psyllium | Moderate | Moderately soluble |
| Flaxseed | Moderate | Soluble |
| Beet pulp | Moderate | Mostly insoluble |
| Hemicellulose | Moderate | Insoluble |
| Pea fiber | Moderate | Insoluble |
| Soybean hulls | Low | Insoluble |
| Purified cellulose | Low | Insoluble |
Fermentability
Fermentability refers to how easily GI bacteria can ferment a type of fiber. Fermentable fiber may produce beneficial effects in some patients but induce GI signs or intolerance in others (BOX 1).
- Speeds up gastrointestinal transit time
- Reduces fecal bulk
- Increases short-chain fatty acid production to support intestinal health
- Can increase gas production and flatulence
Fermentable fiber supports healthy bacteria within the GI tract and can help promote balance within the microbiome.4 When fiber is fermented, bacteria produce short-chain fatty acids (SCFAs), which serve as an energy source for cells in the intestinal tract. Fermentable fibers such as inulin and fructooligosaccharides produce several SCFAs but tend to generate higher concentrations of the SCFA butyrate compared with other types of fermentable fiber. Butyrate is considered one of the preferred sources of energy for enterocytes and has been shown to promote a healthy intestinal barrier and improve water and electrolyte absorption.5 Butyrate has also been shown to be beneficial for humans with ulcerative colitis due to its anti-inflammatory effects, which inhibit activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in macrophages.6 When NF-κB is activated, it can promote inflammation; its activation has been shown to promote inflammation within the lamina propria in dogs with chronic enteropathy.7 Using fermentable fiber to modulate inflammation in patients with chronic enteropathy is an example of how diet can be used to support intestinal health.
Although highly fermentable fiber offers many benefits, it can also increase gas production, which may lead to undesirable side effects such as intestinal distension, discomfort, and flatulence. For patients with excessive flatulence, it is helpful to review the diet ingredient list for fermentable fiber sources that may be contributing to the flatulence. Another consideration is that highly fermentable fiber can increase methane production, which may worsen signs of colitis.
Solubility and Viscosity
Fiber is also categorized by solubility (soluble or insoluble), which is associated with its viscosity as well. Viscosity refers to the ability of fiber to thicken or form a gel when mixed with liquid and has been suggested as an alternative way to describe soluble fiber.2 Soluble fiber, or that with higher viscosity, has a greater water-holding capacity than insoluble fiber and is generally more susceptible to bacterial fermentation. However, although it may seem logical to link solubility with fermentability, the 2 properties are not always directly associated.2 For example, beet pulp is considered an insoluble fiber, but it is also considered to be fermentable. To avoid confusion, solubility and fermentability should generally be considered separately when evaluating fiber sources (TABLE 1).
Fiber with higher viscosity can increase the water content and bulk of feces. Highly viscous fiber can also slow gastric emptying and intestinal transit time. However, the effects of fiber on transit time reported in the literature can vary depending on the study, which may be influenced by the amount of fiber used. For example, 1 study found that adding 30 g of purified cellulose to dog food slowed intestinal transit time, whereas another study found that feeding a diet containing 9% α-cellulose (as fed) resulted in faster intestinal transit time compared with that in controls.2 It is generally accepted that soluble and viscous fiber typically delays gastric emptying and, conversely, insoluble fiber tends to speed up transit time through the small intestine and colon, meaning that contents pass more quickly; however, variations are possible.3
Fiber also affects digestibility. It has been shown that higher-fiber diets tend to decrease total dry matter digestibility and may influence protein digestibility as well.8,9 Thus, therapeutic diets that are formulated to be highly digestible tend to be lower in fiber, but every diet should be examined individually as fiber variations between highly digestible diets certainly exist (TABLE 2).
| TABLE 2 Examples of Higher-Fiber Diets That Contain Limited-Ingredient or Hydrolyzed Protein | |
|---|---|
| Product Name* | TDF (g/1000 kcal) |
| DOGS | |
| Royal Canin Hydrolyzed Protein, canned | 57 |
| Purina Pro Plan Veterinary Diets HA Hydrolyzed, canned | 48 |
| Royal Canin Selected Protein PW Moderate Calorie, dry | 47 |
| Royal Canin Vegetarian, dry | 32 |
| Hill’s Prescription Diet z/d, canned | 27 |
| Hill’s Prescription Diet z/d Low Fat, canned | 27 |
| Hill’s Prescription Diet z/d Low Fat, dry | 26 |
| CATS | |
| Royal Canin Gastrointestinal Hydrolyzed Protein, dry | 26 |
| Hill’s Prescription Diet d/d (duck or venison), dry | 26 |
| Hill’s Prescription Diet d/d (duck), canned | 23 |
| TDF=total dietary fiber. *Product formulations can change over time. The fiber values presented in this chart (Purina 2025 Product Guide, purina.com; Royal Canin Veterinary Health Nutrition Product Book May 2024, royalcanin.com; Hill’s Product Guide 2024, hillspet.com) should be verified by using the most current product guides or by contacting the pet food |
|
Fiber in Pet Food
Determining how much fiber a diet provides can be challenging. Dietary fiber is not considered an essential nutrient by AAFCO and does not have a minimum requirement. On pet food labels, fiber is reported as a maximum percentage of crude fiber. However, crude fiber mainly reflects insoluble fiber and does not indicate whether the diet contains soluble or fermentable fiber. Because of this, crude fiber can significantly underestimate total dietary fiber (TDF).
The most accurate way to compare dietary fiber is to evaluate TDF in a diet, which indicates both soluble and insoluble fiber. The AAFCO Pet Food Label Modernization initiative will eventually require that TDF be included on labels, but this will take time.10 TDF analysis is more involved and requires laboratories to be able to process large numbers of samples.
The guaranteed analysis on labels provides percent crude fiber, which is a percentage of fiber per 100 g of food. Because this percentage is based on weight, comparing it between diets that vary in moisture and energy density is difficult. The preferred method is to compare fiber content on a caloric basis, such as grams per 1000 kcal. Grams per 1000 kcal from percent crude fiber provided on the label can be estimated as follows:
- Divide the crude fiber % by the kcal/kg of the food.
- Multiply the result by 10 000.
Example: For a diet that contains 1.5% crude fiber and 3900 kcal per kg
- Step 1: 1.5 / 3900 = 0.000384
- Step 2: 0.000384 × 10 000 = 3.84 g crude fiber per 1000 kcal
When TDF is available, comparing grams of TDF per 1000 kcal is the preferred method (TABLE 3).
| TABLE 3 Levels of Dietary Fiber in Dog and Cat Food3 | ||
|---|---|---|
| Dietary Fiber | Crude Fiber, g/1000 kcal* | TDF, g/1000 kcal |
| Low | ||
| Dog food | < 10 | < 20 |
| Cat food | < 5 | < 5 |
| Moderate | ||
| Dog food | 10–20 | 20–40 |
| Cat food | 5–10 | 10–25 |
| High | ||
| Dog food | > 20 | > 40 |
| Cat food | > 10 | > 25 |
| TDF = total dietary fiber. *Crude fiber does not reflect soluble fiber within the diet, and the preferred method of comparing fiber in a diet is to evaluate the TDF. Although this table is helpful for providing general information about fiber content, always consider the amount of fiber that is in the current diet.3 |
||
Fiber for Constipated Patients
Indications for Adding Fiber
If a constipated patient has normal colonic function and motility, fiber can offer several benefits that help reduce the risk for constipation. When managing constipation, the type of fiber is relevant. Soluble fiber, such as psyllium, is a viscous fiber that helps draw water into the feces, making it softer and easier to pass. Although insoluble fiber is not effective for dry, hardened feces, it can help maintain fecal bulk and stimulate colonic motility.
Contraindications for Adding Fiber
For patients that have dry, hard feces and are unable to defecate (e.g., those with obstipation), adding fiber is contraindicated until the patient is deobstipated. For patients with megacolon, when the colon has lost its ability to contract and move feces due to poor motility, a high-fiber diet can be harmful. Adding insoluble fiber to the diet of these patients increases fecal bulk, which the colon cannot move, thereby worsening the condition. Even soluble fiber may be ineffective because the underlying issue is the inability of the colon to contract and evacuate feces. For these patients, a highly digestible, low-residue, low-fiber diet is preferred.
Fiber for Patients with Diarrhea
Diarrhea may be lessened by modifying dietary fiber, depending on the source of the diarrhea.
- Small bowel diarrhea: Large volume, watery, normal frequency
- Large bowel diarrhea: Smaller volume, increased frequency, may include mucus and/or blood, patient may exhibit straining (tenesmus)
For acute small bowel diarrhea, a highly digestible diet is usually recommended as the first step. If that does not lead to a response, clinicians can explore therapeutic diets containing novel or hydrolyzed proteins. If there is still no response, it may be appropriate to trial a higher-fiber diet. Large bowel diarrhea often responds well to a higher-fiber diet; for these patients, it can be helpful to begin by increasing the fiber in the diet. If that is unsuccessful, considering a highly digestible, novel or hydrolyzed diet is often a next step in addition to increasing the fiber.
Although it is still appropriate to consider dietary fiber supplementation for either type of diarrhea, taking a methodical approach to management with fiber can help the clinician determine the best next step. Before deciding to modify the fiber in the diet, the amount of fiber in the current diet must be considered. When managing chronic enteropathy in dogs or cats, evaluating the TDF content of the diet can be helpful. Many hydrolyzed or limited-ingredient diets are relatively low in fiber, although exceptions exist. If a patient has not responded to a diet trial for diarrhea and the current diet is low in fiber, a higher-fiber limited-ingredient or hydrolyzed protein diet may be beneficial (TABLE 2).
Comorbidities and Fiber
When managing patients with comorbidities, evaluating the fiber content of the diet is particularly valuable. A diet that provides the appropriate nutrient profile for a patient’s medical condition(s) may not contain the amount or type of fiber needed to address concurrent GI concerns.
For example, a cat with fiber-responsive diarrhea and renal disease may require a dietary plan that includes supplemental fiber. Although it can be challenging to match the fiber content of a high-fiber diet by using supplements alone, doing so may not be necessary. Both the type and amount of fiber play roles in managing fiber-responsive diarrhea. Evaluating the TDF content of therapeutic renal diets by different pet food manufacturers can help identify formulations that are higher in fiber and may better support patients with multiple conditions (TABLE 4).
| TABLE 4 TDF Content of Select Veterinary Renal Diets For Catsa | |
|---|---|
| Product Nameᵇ | TDF, g/1000 kcal |
| Purina Pro Plan Veterinary Diet NF Kidney Function Early Care, canned | 35 |
| Purina Pro Plan Veterinary Diet NF Kidney Function Advanced Care, canned | 33 |
| Royal Canin Renal Support Early Consult, dry | 33 |
| Purina Pro Plan Veterinary Diet NF Kidney Function Early Care, dry | 30 |
| Purina Pro Plan Veterinary Diet NF Kidney Function Advanced Care, dry | 28 |
| Royal Canin Feline Renal Support A, dry | 27 |
| Royal Canin Feline Renal Support F, dry | 27 |
| Royal Canin Feline Renal Support + Hydrolyzed Protein, dry | 23 |
| Hill’s Prescription Diet k/d (chicken and vegetable or vegetable and tuna), stew | 21 |
| Hill’s Prescription Diet k/d + j/d (chicken and vegetable), stew | 20 |
| TDF = total dietary fiber. ᵃAlthough many renal diets are low in fiber, some formulations provide moderate amounts of TDF, which may be helpful for management of fiber-responsive diarrhea in cats. ᵇNutrient profiles may change over time. Always consult the most current product guide or contact the pet food manufacturer directly to confirm the most up-to-date fiber content and nutrition information (Purina 2025 Product Guide, purina.com; Royal Canin Veterinary Health Nutrition Product Book May 2024, royalcanin.com; Hill’s Product Guide 2024, hillspet.com). |
|
Adding enough supplemental fiber to match that of many of the high-fiber diets can be difficult. High-fiber diets may provide 40 to 60 g TDF per 1000 kcal, whereas 2 tbsp of psyllium add only 20 mg of TDF. If a dog or cat requires more dietary fiber than supplementation can provide, feeding a high-fiber therapeutic diet can be considered.
Some clients may choose to add human food to increase dietary fiber; however, the amount needed to make a meaningful effect is often impractical to feed on a regular basis. For example, 1 cup of canned pumpkin contains approximately 7 g of total dietary fiber. If a dog is consuming 1000 calories per day and the goal is to match a therapeutic diet that provides 40 g of TDF per 1000 kcal, the dog would need about 5 ¾ cups of canned pumpkin daily, an amount that is neither practical nor recommended. That said, the amount of fiber needed to achieve a clinical response varies by individual patient. Some dogs may show improvement with as little as 1 to 2 tbsp of canned pumpkin added to their diet, highlighting the value of tailoring the fiber “dose” to the patient rather than aiming for a specific target number. However, the key takeaway is that if a client has tried adding a small amount of pumpkin and the dog’s condition did not improve, it does not necessarily mean that the dog will not respond to fiber; it may simply mean that the amount added was insufficient to achieve the desired effect.
If fiber is added and the condition does not improve, consider the type of fiber (BOX 2).
- Psyllium: mostly soluble, some insoluble
- Insoluble fiber: If psyllium is not effective, consider adding more insoluble fiber (e.g., Balance IT Firming Fiber [cellulose], balanceit.com; Nutramax Proviable fiber supplement powder [combination],
proviable.com).
- Psyllium husk powder
- Proviable fiber supplement powder (blend of insoluble, soluble, and fermentable fiber; Nutramax, proviable.com)
- FortiFlora Pro Synbiotic Action (contains psyllium and a probiotic; Purina, proplanvetdirect.com)
- Balance IT Firming Fiber (cellulose; balanceit.com)
Different types of fiber work differently; therefore, lack of improvement with one does not mean that fiber will not help. Choosing the right type is key.
Summary
Dietary fiber is commonly used to manage GI problems (e.g., constipation, diarrhea, anal gland irritation). However, this nondigestible portion of carbohydrates is not a “one size fits all” nutrient. Rather, its uses depend on the properties of the fiber (e.g., fermentability, solubility, viscosity). Not all patients respond to fiber in the same way; thus, the amount and type of fiber fed should be based on the individual patient and not generalized as being universally beneficial or detrimental.
References
- Burrows CF, Kronfeld DS, Banta CA, Merritt AM. Effects of fiber on digestibility and transit time in dogs. J Nutr. 1982;112(9):1726-1732. doi:10.1093/jn/112.9.1726
- Nutritional Research Council. Carbohydrates and fiber. In: Nutrient Requirements of Dogs and Cats. National Academies Press;
2006:49-80. -
Moreno AA, Parker VJ, Winston JA, Rudinsky AJ. Dietary fiber aids in the management of canine and feline gastrointestinal disease. JAVMA. 2022;260(S3):S33-S45. doi:10.2460/javma.22.08.0351
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Fischer MM, Kessler AM, de Sá LRM, et al. Fiber fermentability effects on energy and macronutrient digestibility, fecal traits, postprandial metabolite responses, and colon histology of overweight cats. J Anim Sci. 2012;90(7):2233-2245. doi:10.2527/jas.2011-4334
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Cave N. Nutritional management of gastrointestinal diseases. In: Fascetti AJ, Delaney SJ, eds. Applied Veterinary Clinical Nutrition. 1st ed. Wiley-Blackwell; 2012:175-219.
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Lührs H, Gerke T, Müller JG, et al. Butyrate inhibits NF-kappaB activation in lamina propria macrophages of patients with ulcerative colitis. Scand J Gastroenterol. 2002;37(4):458-466. doi:10.1080/003655202317316105
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Luckschander N, Hall JA, Gaschen F, et al. Activation of nuclear factor-kappaB in dogs with chronic enteropathies. Vet Immunol Immunopathol. 2010;133(2-4):228-236. doi:10.1016/j.vetimm.2009.08.014
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Montserrat-Malagarriga M, Castillejos L, Salas-Mani A, Torre C, Martín-Orúe S. The impact of fiber source on digestive function, fecal microbiota, and immune response in adult dogs. Animals (Basel). 2024;14(2):196. doi:10.3390/ani14020196
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Flickinger EA, Wolf BW, Garleb KA, et al. Glucose-based oligosaccharides exhibit different in vitro fermentation patterns and affect in vivo apparent nutrient digestibility and microbial populations in dogs. J Nutr. 2000;130(5):1267-1273. doi:10.1093/jn/130.5.1267
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