Featuring Fiber: Understanding Types of Fiber & Clinical Uses
Deborah E. Linder, DVM, MS, DACVN
Cummings School of Veterinary Medicine at Tufts University
The American College of Veterinary Nutrition (acvn.org) and Today’s Veterinary Practice are delighted to bring you the Nutrition Notes column, which provides the highest-quality, cutting-edge information on companion animal nutrition, written by the ACVN’s foremost nutrition specialists.
The primary objectives of the ACVN are to:
- Advance the specialty area of veterinary nutrition
- Increase the competence of those practicing in this field
- Establish requirements for certification in veterinary nutrition
- Encourage continuing education for both specialists and general practitioners
- Promote evidence-based research
- Enhance dissemination of the latest veterinary nutrition knowledge.
The ACVN achieves these objectives in many ways, including designating specialists in animal nutrition, providing continuing education through several media, supporting veterinary nutrition residency programs, and offering a wide array of resources related to veterinary nutrition, such as this column.
Understanding the different types of fiber—and when to implement fiber in a nutrition plan for dogs and cats—can be challenging and complicated. In addition, some cats and dogs that present with gastrointestinal conditions can be managed with diets or supplements that contain particular levels and types of fiber.
Choosing an ideal diet or supplement may involve a trial-and-error process to determine the exact fiber needs of each individual pet. Ongoing communication with clients during this process plays an integral role in successful management.
The different types of fiber can be defined in 2 ways:
- By fiber solubility
- By fiber fermentability.
Solubility describes how fibers are able to disperse in water (Table 1), while fermentability describes the rate at which fibers produce short-chain fatty acids (SCFAs) through the help of microorganisms. These definitions have some crossover as many soluble fibers also tend to be highly fermentable.
In a clinical setting, however, describing fibers by their solubility in water is the most relevant because solubility:
- Directly affects composition of feces
- Is easier to measure than fermentability, which makes information on solubility more readily available.
Soluble fibers, such as pectins and gums, are the types of fiber that best absorb water. These fibers are usually also highly fermentable, which means that bacteria convert the fibers rapidly to SCFAs, the preferred energy source for cells in the colon.
Adding soluble fiber can promote healthy colonic mucosa and immune function in the lower intestine. However, increasing soluble fiber—whether by supplement or selecting a diet high in soluble fiber—should be done slowly and incrementally to allow adaptation of the intestinal microbiome to the new amount of fermentable material.
Client Communication Tip
Insoluble “woody” fibers are more than fillers.
Insoluble fibers, such as lignin or cellulose, are frequently obtained from “woody plants” that are not generally considered food sources. Rather, these fibers are part of the cell wall that allows plants to maintain their structure. The media sometimes misconstrues this information to mean that wood or cardboard are cheap fillers used in pet food to save money. However, insoluble fibers serve many therapeutic functions and are intentionally used in pet foods to improve gut health and help, not hurt, pets.
Insoluble fibers, such as cellulose, increase fecal output and, in doing so, stimulate motility in the intestines and increase intestinal transit time. High amounts of insoluble fiber can often be found in veterinary therapeutic diets formulated for canine diabetes, feline hairball control, or weight management.
However, take caution when supplementing with large amounts, as insoluble fiber can mildly alter nutrient digestibility.2-3 Diets formulated by high-quality pet food companies, though, take this change in digestibility into account and alter the nutrient content of diets accordingly.
Client Communication Tip
What determines whether pet food companies are producing high-quality products?
The World Small Animal Veterinary Association (WSAVA) has created guidelines that help pet owners and veterinarians determine whether companies are producing high-quality products. For example, does a company employ board-certified veterinary nutritionists and PhD-level animal nutrition scientists to properly formulate and test foods? A full list of the guidelines is available at wsava.org/nutrition-toolkit.4
FIBER ON THE LABEL
The term “high fiber” can be confusing, as fiber is added and analyzed in pet foods in many different ways. Pet food labels are only required to have the guaranteed analysis—the maximum or minimum percentage of nutrients on an as-fed, or by weight, basis. This means, for example, that a pet food with maximum 12% crude fiber has no more than 12 grams of crude fiber for every 100 grams of total pet food. However, since the amount is a maximum, it could have any amount less than 12%.
Information in this format is not very helpful to veterinarians or pet owners when comparing fiber content between diets or estimating the typical amount of fiber in each batch of food. Furthermore, crude fiber on these labels only accounts for a variable portion of insoluble fibers; it does not provide total content of fiber.
To estimate the overall fiber in diets, obtain the total dietary fiber (TDF), which includes soluble and insoluble fiber, on an energy basis (grams/Megacalorie [Mcal; 1000 kcal]) from the typical analysis—not guaranteed analysis—of the diet. This way, fiber content can be compared among diets of differing calorie or moisture content (Table 2). A typical or average nutrient analysis of TDF should be in company product guides or available by contacting the manufacturer.
Owners may be quick to look to the ingredient list to determine soluble or insoluble fiber ingredients, but the total amount of fiber in the diet is not known without the TDF. While TDF is not precise because not all insoluble fibers are measured using crude fiber analysis, a rough estimate of total, insoluble, and soluble fiber can be obtained with the TDF and crude fiber information on an energy basis. However, it is also important to note that individual animals (and their microbes) may respond differently to specific sources of fiber or combinations of specific compounds, so trial and error of diets may still be necessary for personalized care of each cat or dog.
Client Communication Tip
Pet food labels are not helpful in comparing dietary fiber.
Let owners know that the pet food label is not helpful in comparing fiber among diets. The best way to compare is to ask companies to provide the TDF on an energy basis to better understand the fiber content of a diet.
CLINICAL INDICATIONS FOR FIBER
Obtaining a full medical and dietary history helps guide diet selection and may suggest an underlying cause of gastrointestinal illness.
A medical history may suggest whether the patient has a large intestinal or small intestinal problem, which may help guide the type or level of fiber needed (Table 3). For example, increased frequency, urgency, and frank blood or mucus in stool suggests a large intestinal problem and trial-and-error management would likely start with increased insoluble fiber diets. A fecal scoring chart (Figure) provides a numeric system for accurately and consistently describing stool.
A history of previous diets may guide what ratio of insoluble or soluble fiber will benefit the patient. A dietary history that includes aspects of the home environment may also guide management; for example, diarrhea that occurs when a family member leaves for business may indicate stress colitis.
A full medical workup, such as diagnostic imaging or a dietary elimination trial, may be necessary for severe or chronic cases in which nutritional management alone cannot alleviate clinical signs.
Client Communication Tip
Obtaining a dietary history is a key component of the appointment.
A full dietary history—that includes all previous diets, treats, chews, table scraps, and food used for medication administration—can help rule out dietary indiscretion in gastrointestinal illness. This history can also elucidate any food items at risk of contamination by bacteria (eg, chews, such as bully sticks, or raw food diets).5,6 Example diet history forms can be found online at wsava.org/nutrition-toolkit.4
HOW TO GET STARTED
Which Fiber to Look for in Diets
Each pet must be considered individually when considering the amounts of each of types of fibers in the various commercially available diets; not all pets with the same condition respond similarly to nutritional management. For example, low fat, highly digestible diets (ie, low insoluble fiber) are commonly recommended for intestinal disease;1 however, one study in cats demonstrated that dietary fat content did not affect clinical outcome.7
In general, diseases affecting the large intestine (ie, colitis, anal gland or sac disease) may best be managed by trying diets higher in insoluble fibers, while diseases affecting the small intestine (ie, chronic enteritis, exocrine pancreatic insufficiency) may benefit from the addition of soluble fibers. If it is unclear which type of fiber may be helpful, a moderate mixed fiber diet can be used for an initial trial. In addition, contacting a board-certified veterinary nutritionist (a listing can be found at acvn.org) to formulate a balanced, home-cooked diet could also be elected by owners who would like more control over fiber sources and content.
Client Communication Tip
A formulated pet food or therapeutic diet is the preferred source for fiber.
Commercial pet foods or veterinary therapeutic diets are the best way to provide fiber to dogs and cats because they are formulated to provide the appropriate essential nutrients. For example, canned pumpkin is popular with pet owners as a fiber supplement, but the amount needed to be beneficial may unbalance the total diet (ie, the pumpkin would provide significantly more than 10% of a pet’s total calories).
Full Nutrient Profiles
Unless the patient has a proven food allergy (diagnosed through a dietary elimination trial), the overall nutrient profile should determine the diet rather than ingredients. For further consideration, diets high in fiber may have a lower caloric density; therefore, energy needs may also need to be taken into account. An underweight diabetic dog, for example, may have difficulty consuming enough low calorie, high fiber food to maintain weight. In this example, consideration of the fat and calorie content, as well as the fiber content, is of importance.
Fiber can be supplemented outside the diet, but there is limited guidance for standardized dosages. One study found benefits in dogs with a median dosage of 2 tablespoons per day of a common human psyllium supplement, although there was a range of 0.25 to 6 tablespoons per day.8
If supplemented, fiber should always be given gradually over a few days until the stool reaches the desired composition. Use fecal charts (Figure), which allow clients to objectively chart their pets’ stool production and quality and provide more objective feedback.
Prebiotics and probiotics are also commonly used supplements: Prebiotics are fermentable carbohydrates—also called oligosaccharides—and, because of their ability to foster beneficial (“the good”) bacteria in the intestinal tract, are considered beneficial for pets. There are many commercially available prebiotic supplements to help cultivate healthy gut bacteria. Meanwhile, probiotics are not actually a source of fiber, but are ingested microorganisms (the “good” bacteria themselves) that are associated with benefits for humans and animals. It is important to note that quality control can vary and only products that are independently tested should be used.9
More Client Communication Tips
Clinical Management with Fiber.
- When adding insoluble fiber, tell dog owners in advance that the increased fecal bulk may mean that they will need to schedule more walks during the day to avoid accidents.
- For clients that really want to provide treats, they can use a portion of their pets’ daily kibble as treats until stool has reached desired consistency.
- Because gut bacteria take time to adapt during diet changes, encourage clients to transition between diets slowly (7–10 days).
- Let clients know that mild loose stool is expected with any diet change.
- Setting expectations is crucial, and it is helpful to tell clients that dietary management alone may not be successful.
- Home-cooked diets are commonly sought by clients who suspect a gastrointestinal issue in their pets. Recommend a consult with a board-certified veterinary nutritionist (ACVN.org) to ensure the diet is formulated properly without any deficiencies.
Fiber can be an integral part of nutritional management for many disease conditions in dogs and cats. Understanding the different types of fiber and how to determine the fiber content of commercial diets for cats and dogs can guide optimal diet selection. Because each animal (and their gastrointestinal microbes) may react differently, trial and error is often necessary to determine the exact fiber needs of each individual pet. Ongoing communication with clients during this process plays an integral role in successful management.
- Cave N. Nutritional management of gastrointestinal disease. In Fascetti AJ, Delaney SJ (eds): Applied Veterinary Clinical Nutrition. Chichester (UK): Wiley-Blackwell, 2012, pp 175-220.
- Harmon DL, Walker JA, Silvio JM, et al. Nutrient digestibility in dogs fed fiber-containing diets. Vet Clin Nutr 1999; 6(1):6-10.
- Prola L, Dobenecker B, Mussa PP, Kienzle E. Influence of cellulose fibre length on faecal quality, mineral excretion and nutrient digestibility in cat. J Anim Phys Anim Nutr 2010; 94:362-367.
- Freeman L, Becvarova I, Cave N, et al. WSAVA nutritional assessment guidelines. Compend Contin Educ Vet 2011; 33(8):E1-E9.
- Weese JS, Rousseau J, Arroyo L. Bacteriological evaluation of commercial canine and feline raw diets. Can Vet J 2005; 46(6):513-516.
- Freeman LM, Janecko N, Weese JS. Nutritional and microbial analysis of bully sticks and survey of opinions about pet treats. Can Vet J 2013; 54:50-54.
- Laflamme DP, Xu H, Long GM. Effect of diets differing in fat content on chronic diarrhea in cats. J Vet Intern Med 2011; 25(2): 230-235.
- Lieb MS. Treatment of chronic idiopathic large-bowel diarrhea in dogs with a highly digestible diet and soluble fiber: A retrospective review of 37 cases. J Vet Intern Med 2000; 14:27-32.
- Ridgway MD. Probiotics. Clin Brief 2013; 2:21-23.