This article was published in the March 2020 issue of Pet Food Processing. Read it and other articles from this issue in our March digital edition.

Pet food manufacturers have a plethora of fiber ingredient options, some more economical or functional than others. It’s all about achieving the right balance so the cat or dog has consistent, slightly firm poops on a regular basis, and allows for maximum nutrient absorption during digestion.

“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,” said Trevor Faber, companion animal nutritionist, Trouw Nutrition, Highland, Ill.

The challenge is that a lot of beneficial dietary fiber sources traditionally used in pet diets have come under scrutiny by pet parents. That is changing through education and advancements in science, along with growing interest in upcycling of food byproducts.

“Over the last decade, conversations around ingredient credibility have often focused on what an ingredient is instead of what it offers nutritionally, causing some safe and healthy ingredients to get a bad rap,” said Kurt Venator, chief veterinary officer, Nestlé Purina PetCare Company, St. Louis. “It’s important to remember that good nutrition for pets is all about nutrients, so focusing only on ingredients won’t tell the whole story and can become a distraction for well-meaning pet owners.” 

“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,” said Trevor Faber, Trouw Nutrition.

Gary Davenport, companion animal technical manager, ADM, Chicago, said, “More than 25 years ago, marketing campaigns cast fiber as a non-nutritive filler. These misleading campaigns attempted to create points of differentiation by disparaging certain ingredients in competitive products. As a result, corn, wheat, soy and animal byproduct meals often have negative consumer perceptions despite being nutritious, economical and appropriate for dogs and cats when part of nutritionally complete foods.”


Varied fiber types

While dietary fiber may come from many varied sources, it is quantified as one lump sum and reported as “crude fiber” on pet food and treat product labels. The term “crude” refers to the specific method of testing the product that measures the indigestible fractions of feedstuffs, according to the Association of American Feed Control Officials (AAFCO) – not to the quality of the nutrient.

Pets benefit from both soluble and insoluble fiber in their diet and formulators can choose from an increasing number of high-quality options.

“This method to classify dietary fibers is, as the name suggests, crude,” Faber said. “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.”

Since the turn of the century, the scientific community has gained a much better understanding of the many varied forms of dietary fiber and their different roles and benefits. The US Food and Drug Administration (FDA) defined fiber — for the first time — on May 27, 2016, as “non-digestible soluble and insoluble carbohydrates (with three or more monomeric units), and lignin that are intrinsic and intact in plants; or isolated or synthetic non-digestible carbohydrates (with three or more monomeric units) determined by the FDA to have physiological effects that are beneficial to human health.” There is discussion that AAFCO may change the pet food fiber declaration from crude fiber to dietary fiber to better align with FDA’s definition. 

“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,” Faber said. “The total dietary fiber method provides the most useful information about how these fibers will affect the animal.”

Dietary fiber is associated with varied physiological responses in humans, many of which are believed to be similar in animals. These benefits are often recognized as being specific to the fiber’s solubility.

"It’s important to remember that good nutrition for pets is all about nutrients, so focusing only on ingredients won’t tell the whole story and can become a distraction for well-meaning pet owners,” said Kurt Venator, Nestlé Purina PetCare Company.

Soluble fiber, as the term suggests, describes fiber that is soluble in water. This includes beta-glucan, fructooligosaccharides (FOS), galactooligosaccharides (GOS), gums, inulin, pectin, polydextrose, psyllium, some hemicelluloses and resistant maltodextrin. Many absorb water and form a viscous gel that traps dietary cholesterol and bile acids and carries them out of the body. This viscous solution has also been shown to trap carbohydrates, slowing their digestion and absorption. This may help prevent wide swings in blood sugar level during the day, as well as have an impact on the development of diabetes.

Some soluble fibers, such as inulin, FOS and GOS, are not viscous, rather, they are fermentable. They function as prebiotics to promote the growth of beneficial intestinal bacteria, positively impacting digestive health.

Insoluble fibers are not soluble in water. These non-viscous fibers include lignin, cellulose and some hemicelluloses. Many vegetables and cereal grains are rich in insoluble fiber, with the highest amounts in wheat and corn. Insoluble fiber is best known for adding bulk to stool, helping to prevent or alleviate constipation.

There’s a third type of fiber known as resistant starch that, as its name suggests, is a starch that resists digestion in the small intestine. It is not soluble in water yet is fermented like a soluble fiber in the colon.

Balancing the levels of these various fibers is paramount for health and wellness. That balance may vary by species, breed, gender, age and level of activity.

Recently, sweet potatoes have gained in popularity among pet parents and can be a high-quality source of fiber for formulators.
“Fiber is not considered an essential nutrient in dog or cat diets, but it is present in almost every commercial dog and cat food,” said Patrick Luchsinger, manager, marketing and business development, pet food segment, Ingredion Inc., Westchester, Ill. “While pets do not derive any energy from fiber, adding fiber to a diet for dogs and cats can help support digestive health, help with loose stools and malodorous odors.” 

Davenport said, “Inter-species differences in the ability to utilize dietary fiber is dependent on the anatomy and physiology of the digestive tract and the presence of a resident microbial population in the lower large intestine. Dogs are facultative carnivores that use dietary fiber effectively due to long digestive tracts, retention times and hind-gut fermentative capacity.”

Cats, on the other hand, are obligate carnivores and have a simple, short digestive tract. They are unable to benefit as much as dogs from dietary fiber. Regardless, dietary fiber is an important part of the cat diet.


Toolbox of ingredients

Pet food formulators have many ingredient options to achieve the best balance of fiber. While most dietary fiber sources are safe for pets, there may be some anti-nutritional factors to consider, such as tannins. This can often be overcome through processing.

Ground miscanthus grass is one example of fiber that delivers nutritional benefits but also offers a positive sustainability story for brands
“In the past, corn and peanut hulls and the like were common inexpensive fiber sources but created large stools and were not well-received by pet parents,” said Deena Krestel-Rickert, owner and principal, Four Paws Solutions LLC, Chesterfield, Mo. “Beet pulp and powdered cellulose became some of the more common fiber sources for pets. But more recently, high-quality ingredients such as sweet potato, ground miscanthus grass, fruits, peas and green beans — all rich sources of natural fiber — are the more preferred choices.”

Don Trouba, senior director, The Annex by Ardent Mills, Denver, said, “Today’s pet food manufacturers are challenged with delivering healthful, on-trend products that appeal to both pet owners and their furry friends. Incorporating ancient grains and plant-based grain alternatives like chickpeas is one way that pet food manufacturers can satisfy both.”

Ancient grains, pulses and some formats of conventional grains will provide more than fiber. Wheat middlings with ground wheat screenings, for example, is a free-flowing coarse powder that contains protein, fiber, phosphorus and other nutrients. Wheat bran contains starch and protein. Ardent Mills offers a proprietary, identity-preserved, hulless barley that is 30% total dietary fiber and 12% beta glucan.

Ingredion markets a short chain fructooligosaccharide (scFOS) that has been shown to be a highly effective prebiotic soluble fiber in pets. It encourages healthy digestive function, supports a strong immune system and helps reduce bad odors in the stool of the animal, according to Luchsinger.

“Digestive health is very important in pets because when their gastrointestinal tract is healthy, it allows for the proper absorption of vitamins and minerals, while at the same time preventing entry of pathogenic substances, which can cause them not to feel well,” said Patrick Luchsinger, Ingredion Inc.

“Digestive health is very important in pets because when their gastrointestinal tract is healthy, it allows for the proper absorption of vitamins and minerals, while at the same time preventing entry of pathogenic substances, which can cause them not to feel well,” Luchsinger said.

A unique strain of kelp seaweed is gaining traction in pet food because of its prebiotic function. It’s also been shown to contribute to a healthier skin and coat, as well as enhance growth in weaned young pets.

“This marine plant contains a unique blend of polysaccharides,” Faber said. “When added at 0.25% of the diet, it positively modulates the gut microbiota and provides numerous polyphonic compounds that promote the immune system.” 

Miscanthus grass is another new option in functional fiber for pet food. It is a perennial plant that is non-GMO. It is being grown for the sole purpose of being a source of insoluble fiber for pet foods and is recognized as an environmentally responsible crop. This allows for traceability of the ingredient as well as price stability.

“Many pet food brands use miscanthus grass fiber at 3% to 10%; however, specific high-fiber diets will use more,” said Eric Allphin, vice president, business development, Renew Biomass, Aurora, Mo. “Unlike soluble fibers that are fermented in the small intestine, miscanthus grass fiber makes it all the way through the small intestine and into the colon so the entire digestive tract benefits from all the nutrients moving through the entire tract.”

Citrus fiber is another ingredient being used in a variety of pet foods and treats. It is multifunctional because of its unique composition of insoluble and soluble fibers, as well as pectin.

“Our citrus fiber is a byproduct or upcycled material procured from citrus juicing companies,” explained Brock Lundberg, president of research and development, Fiberstar Inc., River Falls, Wis. “The fiber’s functionality is created by the patented mechanical process.”

Beet pulp, the fibrous material left over after sugar is extracted from sugar beets, is a common source of dietary fiber in pet foods.
The high pectin content helps bind moisture and oil in pet foods and treats to enhance processability, moistness and final texture. In certain applications, it may replace chemical emulsifiers and moisture-binding agents, he added.

Beet pulp and cellulose are common sources of dietary fiber used in commercial dog and cat foods, too. Beet pulp is composed of soluble and insoluble fibers, which results in a moderate rate of microbial fermentation in the large intestine. 

“In contrast, cellulose is predominantly insoluble fiber and passes through the digestive tract essentially undigested prior to fecal excretion,” Davenport said. “This insoluble fraction provides the necessary bulk to maintain intestinal passage and desirable stool consistency.

“Cellulose is commonly used in feline hairball control foods to minimize hairball occurrence,” he continued. “The undigested cellulose associates with ingested hair derived from grooming to move the hair through the intestinal tract for excretion in the feces.”

Soybean hulls are a widely available, economical co-product of the soybean oil extraction process. Despite their low cost, soybean hulls are rarely used in today’s pet foods because they are assumed to be inert filler with no nutritional value, according to Davenport. However, research conducted at the University of Illinois demonstrated soybean hulls provide similar nutritional health benefits to dogs and cats as beet pulp.

Education directed toward pet owners helps to counter misconceptions concerning the use of dietary fibers in pet food formulas.


Final considerations

With so many fiber ingredient options, processing modifications may be necessary. Some fibers may impact product formulations, others may be added seamlessly at defined usage rates.

“In extruded pet treats, for example, fiber is often an essential ingredient as it aids both the extrusion process as well as the product texture and can be incorporated in a large amount,” Luchsinger said. “For dry kibbles, care must be taken as the amount and type of fiber will affect the expansion, texture, aroma and palatability.

“Fiber use in wet food may be more challenging,” he continued. “Only a small amount may be able to be incorporated because of process difficulty.”

Keep in mind that regardless of the fiber type, most fiber ingredients are low- or no-calorie nutrients. Their inclusion reduces the overall energy value of the food.

“For pets who need a dense form of energy, such as from a performance or puppy formula, too much fiber may dilute the energy content so much that they can’t consume enough to meet their energy needs,” said John Dickerson, animal nutritionist, Cargill Animal Nutrition & Health, Minneapolis.

“Everything we include in a formula contributes to a healthy, well-balanced diet,” Dickerson concluded. “While not all types of fiber are created equal, the right fibers [in the right balance] can provide desirable benefits.”

Ultimately, this is the goal of all pet diets.

Read more about product development, ingredients and formulation.