Understanding fiber differences in the gastrointestinal tract

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Dietary fiber works in the gastrointestinal (GI) tract to regulate digestion, modulate appetite and satiety, and serve as a microbial energy source.¹ Understanding dietary fiber fundamentals is helpful to veterinary professionals managing gastrointestinal conditions. These fundamentals include, but are not limited to, terminology, measurements, uses, effects, and indications.²

Valerie J. Parker, DVM, DACVIM (SAIM, Nutrition), a clinical professor at The Ohio State University College of Veterinary Medicine in Columbus, provided an overview of how to use dietary fiber for optimizing GI health in pets, during an educational session at the 2024 Fetch dvm360 Conference in Long Beach, California.² “When we utilize fiber, it often reduces the need for other microbiome modifiers,” she said.

“We've basically got to the point in [veterinary medicine] where we have pretty good evidence to say that antibiotics really are not indicated for management of acute or even chronic diarrhea in many instances. I also think that fiber is often more effective than even probiotics for gut health,” Parker added.

Essentially, fiber is complex, nonadjustable carbohydrates that originate in plants, according to Parker. In her talk, she explained that types of fiber vary in molecular structure and size, and provide different effects on a body. They are generally classified by the functional properties: solubility, fermentability and viscosity.^1,2

Solubility is a measure by water disbursement in fiber, and fermentation by the intestinal microbiota leads to the production of short chain fatty acids.² Viscosity measures a fiber’s ability to thicken and form gels, and is typically associated with soluble fibers.¹

Soluble fiber can bind water in the intestinal tract. It is often more fermented than nonsoluble fiber.² “I think of [soluble fiber] almost like Jello powder, just kind of rolling through, picking up water, increasing viscosity, and slowing GI transit time,” said Parker. “Those short chain fatty acids are going to serve as an energy source for colonocytes, reduce colonic pH, which can impede pathogen growth, maintain a healthy epithelial cell barrier, stimulate mucus production and also interact—not just locally in the gut, but far reaching in the body—with many other organs through host micro communication.”

Parker mentioned some examples of foods high in soluble fiber and high fermentation. These include citrus pulp, and fruit pectin.²

Insoluble fiber is less fermentable. It acts more as a bulking agent, she said, and increases GI tract mobility.² “It can, in theory, stretch the intestinal wall and help stimulate peristalsis,” said Parker.

Fiber also functions as a prebiotic. Prebiotics that in­clude oligosaccharides and inulin are commonly added to pet foods, according to Parker. “The by-products of the fermentation of prebiotics serve as nutrients for commensal microorganisms and are not used by the host animal,” she noted.

Overall, Parker said, every patient being treated for a GI condition might benefit from smaller amounts of fiber, and ideally a mixture or psyllium only. Patients with stress-induced colitis, fiber-responsive diarrhea, or constipation, may benefit from higher amounts of bulking, for which soluble fiber is more appropriate.²

Takeaway

Dietary fiber is an “indispensable” factor for managing GI conditions, according to Parker. She noted that positive effects of fiber in the diet can be observed within 2 to 3 days of administration.² “[Fibers] should be considered before antibiotics, at least in mild diseases, but especially in chronic cases,” she said.

References

1. Parker VJ. How to use fiber to optimize gastrointestinal health. Presented at: Fetch dvm360 Conference; December 6-8, 2024. Long Beach, CA.
2. Moreno AA, Parker VJ, Winston JA, Rudinsky AJ. Dietary fiber aids in the management of canine and feline gastrointestinal disease. J Am Vet Med Assoc. 2022;260(S3):S33-S45. doi:10.2460/javma.22.08.0351.