Trouw Pet Nutrition Outlook - Fiber

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Formulating for the correct balance of dietary fibers is arguably as important as including the proper amounts of other key nutrients, such as amino acids and vitamins.

The important role fiber plays in your PET’S HEALTH

The difference between INSOLUBLE AND SOLUBLE dietary fiber


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2 Trouw Pet Nutrition Outlook • Volume 4

Meet Dr. Faber, More like Dr. ‘Fiber’

Welcome to the fourth issue of Trouw Pet Nutrition Outook. In this issue, we’ll be explaining dietary fiber and the important role it plays in pet food. At Trouw Nutrition, we have our very own fiber expert: Trevor Faber, Ph.D. Dr. Faber is Trouw Nutrition’s Companion Animal Nutritionist, with an extensive background in fiber. Dr. Faber earned his M.S. and Ph.D. in companion animal nutrition from the University of Illinois, researching the effects of prebiotic fiber on digestive and immune health under Dr. George Fahey Jr.

After completing his degrees, he worked as a global product development scientist at Mars Petcare. Dr. Faber then joined the Trouw Nutrition team in 2015. With his strong background in fiber, he is just the expert to explain more about fiber and the role it plays in pet nutrition. In this edition, Dr. “Fiber” will elucidate the many benefits fiber plays and how it is a key dietary component for promoting and maintaining digestive health. Fiber plays a critical role in helping the gastrointestinal tract function efficiently and consistently. After reading the following, you might ask yourself, “Have I had my fiber today?”

We’d also like to introduce you to Miss Ally Mae, Dr. Faber’s furry friend.

Dietary Fiber from Beginning to End

Understanding the role of fiber in pet food

Dietary fibers play a crucial role at the very end of the digestive process – the feces. Too much and the pet owner gets frustrated cleaning it up so often. Too little and the pet struggles with laxation, which can lead to intestinal issues. If the feces are too runny, the owner perceives the pet is not tolerating the food – not to mention the complications of cleaning up after the pet. If too hard, the pet struggles to defecate, and digestive issues may result. If a diet is formulated improperly for dietary fiber, the consumer’s perception of the diet – and possibly the pet food brand –tarnishes, and they likely will never purchase the brand again.

Fiber History and Future

The key to dietary fiber formulation is understanding the analytical data and the response that fibrous ingredients will elicit in the gut. Some dietary fibers are poorly fermented but promote laxation and lead to an acceptable

stool quality. Others are rapidly fermented and provide nourishment for the intestinal bacteria, which, in turn, produce favorable metabolites that promote animal health. Dietary fiber needs to be understood from the beginning – a lack of understanding can be detrimental to pet health and brand reputation.

Dietary fiber is often perceived as one of two extremes – either as cheap “filler,” lessening the quality of the diet, or as key to digestive health. Pet food customers vilify ingredients, such as wheat middlings, soybean hulls, beet pulp and even pea fiber. The same consumers may state that digestive health is important and look for food additives, such as prebiotics.

What is lost with this assumption is that it is actually the dietary fiber profile as a whole that has the ability to improve intestinal health, promote consumer-favored stool quality, and promote overall pet well-being. Dietary fiber staples, such as whole grains and beet pulp, are falling out of favor with pet owners and the addition of fruits, vegetables and legumes are on the rise. The ever-evolving selection of ingredients and greater understanding of the gut microbiota on total health has made the focus on dietary fiber ever more important.

According to the American Association of Cereal Chemists

(AACC), “Dietary fiber is the edible portions of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine and are either completely or partially fermented in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin and associated plant substances” (AACC, 2001). However, the analytical methods available do not always align with this definition. Selecting the proper analytical method is crucial for formulating diets precisely and providing the formulator the best information about the functionality of that ingredient.

Since the creation of the Weende system of proximate analysis in the 1860s, the term “crude fiber” has described the indigestible fractions of a feedstuff (AAFCO, 2017). This method to classify dietary fibers

is, as the name suggests, crude. This methodology accounts for most of the cellulose but only a portion of the hemicellulose and lignin, resulting in underestimations of the true fiber content. Crude fiber does not account for the soluble fibers in an ingredient and provides little information about the functionality and fermentability of that ingredient or feed. Unfortunately, this method and label guarantee are still used to this day. The issue of crude fiber has gained the attention of the Association of American Feed Control Officials (AAFCO) and there is serious discussion on changing pet food labels from crude fiber to “dietary fiber” to better align with new Food and Drug Administration (FDA) regulations and to provide more meaningful information to the pet owner (AAFCO, 2018).

This label change would require a switch from the proximate analysis method to the total dietary fiber method, which measures both insoluble and soluble fibers. The total dietary fiber method provides the most useful information about how these fibers will affect the animal.

Insoluble Dietary Fiber

IDF includes fiber types such as lignin, cellulose and select hemicelluloses that have little-tono fermentability but are very important to intestinal motility and stool

Dietary Fiber from Beginning to End

firmness. These fiber types provide little nourishment to the intestinal microbiota, but without it, the intestinal tract would strain to move digesta. They also assist with the osmotic balance inside the intestine, which helps with stool quality.

However, insoluble dietary fiber increases stool output, which can be detrimental to consumer perception of diet quality. An optimal quantity of insoluble dietary fiber promotes laxation, but also prevents excessive stool volume.

Soluble Dietary Fiber

Soluble dietary fiber includes select hemicelluloses, oligosaccharides, fructans, betaglucans, pectins and resistant starch. Most serve as important fermentable substrates for gut bacteria. Each varies in its rate of fermentation and the fermentative end product.

Soluble dietary fibers typically provide the health benefits associated with dietary fiber. The beta glucans and soluble fiber prebiotics are famously known for nurturing good intestinal health. Fermentative end products of soluble fibers include shortchain fatty acids (e.g., acetate, propionate, butyrate and lactate),


Soluble Insoluble

Makes You “Good”

Soluble in Water

Not Soluble in Water

Oatmeal, Psyllium seed husks, inulin, gum arabic, fruit pectins

Oat bran, pea fiber, cellulose

Helps blunt blood glucose and insulin spikes. Provides fermentable carbohydrates for gut microbiota. Helps promote digestive health.

Improves intestinal motility. Helps increase stool firmness. Improves laxation. Hyperglycemia (high blood sugar) Normal

Soluble and insoluble dietary fiber serve important dietary roles. Having the proper proportions of these two fiber types provides the best opportunity to enhance gut health, while maintaining acceptable stool quality.

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Table 1. Soluble vs. Insoluble Fiber
Rectum Stomach

which serve as important metabolic intermediates, energy for the host and intestinal cells, and an intestinal pH modulator. A lower intestinal pH results in an acidic environment that is inhabitable to most perceived pathogenic bacterial species. Although fiber fermentation is a positive, if excessive and not balanced with the proper amount of insoluble fiber, loose stools and flatulence can occur, causing consumer perception of the food to deteriorate.

Beyond Total Fiber Content: Dietary Ingredient Traits

Dividing dietary fibers into insoluble and soluble is an excellent way to classify them, but this division does not always explain their physiological effects, see Table 1. Dietary fiber sources are heterogeneous, and their chemical composition does not tell the whole story. Fermentability, viscosity and degree of polymerization also determine functionality in the gut.

• Fermentability

Understanding fermentability is important for predicting an ingredient’s physiological effect in the gut. An ingredient predominantly comprising insoluble fiber (e.g., wheat bran) can be

Dietary fermentable carbohydrates and various endogenous carbohydrates enter the large intestine and are fermented by the gut microbiota. The microbes produce short-chain fatty acids, metabolites, and gases as byproducts of their metabolism. These fermentative end-products are either absorbed by the intestine, utilized by other microbes, or excreted in the feces.

partially fermentable and ingredients comprising mostly soluble fiber (e.g., psyllium) are not always fermentable (Bourquin et al., 1992; Campbell and Fahey, 1997).

• Viscosity. Dietary ingredients alter digesta viscosity due to their functional properties. Many ingredients, such as guar gum and psyllium, can greatly increase the viscosity of the digesta, which can alter digesta passage rate, nutrient absorption and intestinal fermentation (Dikeman and Fahey, 2006).

• Degree of polymerization (DP). The DP value indicates the number of sugar units found in an oligosaccharide chain. As DP increases, transit rate and rate of fermentability decrease,

causing the fiber to be fermented more distally in the large intestine (Rumessen and GudmandHøyer, 1998; Stewart et al., 2008). This, in turn, affects microbial activity because some bacterial species only possess the enzymes to ferment longer chain oligosaccharides. Dietary fibers with varying DP values can foster microbial diversity in the large intestine, particularly in the more distal regions.

A solid understanding of ingredient traits is imperative to diet formulation. It helps ensure nutritional success for the pet, but also for the gut microbes, see Figure 1.

When carbohydrates are not available, particularly in the distal regions of the colon,

Microbial •
Mucin Microbiota Short-chain Gases-H2, CO2, CH4 Fermentable CHOs Figure 1. Carbohydrate Compound Effects

Dietary Fiber from Beginning to End

bacteria depend on protein and amino acids for nourishment, which can be detrimental to gut health. Protein and amino acid fermentation produces nitrogenous compounds, such as ammonia, biogenic amines, phenols, indoles, and gases, such as methane and hydrogen sulfide (Yao et al., 2015). These compounds can be proinflammatory and/or carcinogenic. Gases, phenols and indoles result in flatulence and stool odor, which affect the consumer perception of diet quality (Yao et al., 2015). These detrimental compounds can be diluted and reduced by promoting dietary fiber fermentation instead of protein fermentation, see Figure 2.

Microbial Diversity and Populations

The intestinal tract is a natural ecosystem, and the health of an ecosystem is measured by evaluating the diversity of plants

Undigested dietary and endogenous proteins and peptides are fermented by the gut microbiota. These microbes produce various compounds, such as ammonia, biogenic amines, phenols, indoles, branched-chain fatty acids, and gases (e.g., methane, hydrogen sulfide). These are absorbed and detoxified or excreted in the feces. Dietary fiber dilute these compounds and provide beneficial carbohydrates for fermentation.

and animals and their ability to live in a symbiotic relationship.

Greater diversity is typically indicative of a healthier ecosystem. Grazing animals need plenty of plant life and variety to meet their nutritional needs. With ample vegetation, grazing animals consume a healthy diet and easily reproduce, providing plenty and a variety of food sources for the predators, enabling them to thrive. All this animal activity promotes soil health by providing vegetative control and compost for the plants. The plants then thrive and the cycle continues.

These organisms live in a symbiotic relationship and depend on one another for food and health. If one species is out of balance, the food chain is disrupted,

which affects all other living organisms in that ecosystem.

A similar symbiotic ecosystem lives in the intestinal tract of all animals. Intestinal microorganisms ferment undigested nutrients into energy and metabolites that can be used by the host to improve host health. In addition, these organisms release hormones, antimicrobial compounds, and pro- and antiinflammatory compounds that affect the behavior and health of the host. In return, the host provides nourishment and an anaerobic environment in which the microorganisms can thrive, see Figure 3. Scientific understanding of the microbiome is in its infancy, but one major concept

Disposal • • by epithelium Undigested Protein Microbiota Gases-H2, CO2, CH4, H2S NH3, Amines, Phenol, Indoles Branched-chain Structural Proteins Endogenous Protein Figure
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2. Nitrogenous

When adequate dietary fiber is provided and carbohydrate fermentation is favored over protein fermentation, digesta compounds are diluted, transit rate is altered, and a microbial shift occurs. The microbes produce beneficial metabolites, less nitrogenous compounds are produced and absorbed, and microbial diversity is increased.

that is becoming apparent is that a diverse, strong microbial population results in better health for mammals (Xu and Knight, 2015). Microbial diversity and populations are dictated by the type and amount of foodstuffs available for fermentation. Each microbe has its niche diet, and when food is plentiful, the population will thrive. A diverse, robust population decreases the risk that pathogenic bacteria (e.g., salmonella, E. coli) may colonize the intestinal tract and/or become virulent causing gastrointestinal upset (Stecher and Hardt, 2008). (For more information on the gut microbiome, please refer to Trouw Pet Nutrition Outlook, Volume 3, “The Role of Prebiotics in Pet Food.”)

Feeding the gut microbiome can be very challenging. Almost daily, scientists discover new dietary compounds that are beneficial or detrimental to gut

microbe well-being. Providing a variety of dietary fiber sources that vary in chain length, sugar composition and bonding structure can augment a diverse microbial population.

Dietary Fiber Benefits

Dietary fibers provide animals with many other health benefits directly and indirectly connected to the microbiome. Dietary fibers can promote satiety for pets on weight loss diets and glucose management for diabetic pets.

Evidence is growing for the effects of select fibers and their ability to enhance the structure of the intestinal wall. Cellulose (insoluble fiber) and pectin (soluble fiber) have been shown to promote villus development and enhance mucin production, which, in turn, alters nutrient absorption and thickens the protective mucus layer on the intestinal wall (Sigelo et al., 1984; Hedemann et al., 2009).

Dietary fibers and undigested proteins are the primary nutrients that feed the population of microorganisms in the large intestine. As we learn more about the microbiome’s role in overall health and well-being, nutritionists need to focus not only on the needs of the pet, but also the microbiome. One could argue that one needs to be a microbiome nutritionist, as well as an animal nutritionist.

We have a respectable understanding of how to meet the nutrient requirements of the dog and cat; however, we are just learning about the nutrient requirements of the gut microbiome.

As we discover more about the biological impacts of the microbiome on the host animal, the need to establish clear nutrient guidelines will grow. What we know now is that dietary fibers, in the right variety and type, result in positive health outcomes for the animal and its gut microbiome.


AACC. 2001.

The definition of dietary fiber. Cereal Foods World. 46: 112-126

AAFCO. 2017.

“Critical factors in determining fiber in feeds and forages.” AAFCO’s Laboratory Methods and Services Committee, Fiber Best Practices Working Group: 1-14.” Portals/0/SiteContent/Laboratory/Fiber_ Best_Practices_Working_Group/Fiber-CriticalConditions-Final.pdf

AAFCO. 2018.

“Pet food committee minutes – pet food label modernization.” AAFCO Midyear Meeting, July 2018. Regulatory/Committees/Pet-Food/Reports/ PFLM_Slides_for_July_31_2018.pdf

Bourquin, L. D., E. C. Titgemeyer, K. A. Garleb, and G. C. Fahey Jr. 1992. Short-chain fatty acid production and fiber degradation by human colonic bacteria: Effects of substrate and cell wall fractionation procedures. J Nutr 122(7): 1508-1520.

Campbell, J. M. and G. C. Fahey Jr. 1997. Psyllium and methylcellulose fermentation properties in relation to insoluble and soluble fiber standards. Nutr Res 17(4): 619-629.

Dikeman, C.L. and G. C. Fahey Jr. 2006. Viscosity as related to dietary fiber: A review. Crit. Rev. Food Sci. Nutr. 46(8): 649-663.

Hedemann, M. S., P. K. Theil, and K. E. Bach Knudsen. 2009. The thickness of the intestinal mucous layer in the colon of rats fed various sources of nondigestible carbohydrates positively correlated with the pool of SCFA but negatively correlated with the proportion of butyric acid in the digesta. B. J Nutr 102: 117-125.

Rumessen, J. J. and E. Gudmand-Høyer. 1998. Fructans of chicory: Intestinal transport and fermentation of different chain lengths and relation to fructose and sorbitol malabsorption. Amer J Clin Nutr 68: 357-364.

Sigelo, S., M. J. Jackson, & G. V. Vahouny. 1984. Effects of dietary fiber constituents on intestinal morphology and nutrient transport. Amer J Physiol 246: 34-39.

Stewart, M. L., D. A. Timm, & J. L. Slavin. 2008. Fructooligosaccharides exhibit more rapid fermentation than long-chain inulin in an in vitro fermentation system. Nutr Res 28: 329-334.

Stecher, B. and W. D. Hardt. 2008. The role of microbiota in infectious disease. Trends Microbiol. 16: 107–114.

Xu, Z. and R. Knight. 2015. Dietary effects on human gut microbiome diversity. Br. J. Nutr 113: S1-S5.

Yao, C. K., J. G. Muir, and P. R. Gibson. 2015. Review article: Insights into colonic protein fermentation, its modulation and potential health implications. Aliment Pharm Therap 43(2): 181-196.

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