[Updated October 19, 2017]

Recently there has been renewed interest in fiber as a dog food ingredient. One pet food manufacturer published an article on the Internet condemning beet pulp in dog food as unhealthy, if not downright dangerous. There is a lot of myth and misunderstanding concerning fiber, so let’s take a closer look at this controversial ingredient.

The term “fiber” (or “roughage”) applies to complex carbohydrates that are resistant to mammalian digestive enzymes, although certain bacteria possess the enzymes needed to break them down. Even ruminants, with their four-chambered stomachs and cud-chewing habits, rely on their symbiotic rumen bacteria to digest plant fiber.

Fiber is found only in plants – hair, hooves, bones, fish scales, and feathers do not contain any fiber. Fiber is composed of polysaccharides (complex sugars), and is found in plant cell walls, where it provides structural strength and rigidity.

While some food manufacturers use whole grains and vegetables to serve as both a source of nutrients and fiber – the method WDJ most admires – many others use dedicated fiber sources such as beet pulp, peanut shells, oat and other brans, tomato pomace, buckwheat and other grain hulls, psyllium, fruit pectin, guar gum and other gums, flaxseed, and powdered cellulose. This last one is defined as “purified, mechanically disintegrated cellulose . . . from fibrous plant materials.” I fondly refer to it as “sawdust,” which I believe is a fair description (though technically, wood contains a related fiber called lignin in addition to cellulose).

What Fiber Has to Offer Dogs

It’s true that the “wild” canine diet contains very little fiber, and the dog has no absolute physiologic need for it. However, dogs eating processed commercial foods do appear to benefit from the addition of fiber.

While fiber itself is indigestible and generally considered non-nutritive, some fibers do contain nutrients, such as vitamins and minerals, that can be extracted during digestion, either by the mechanical grinding action of the stomach and intestines, or through bacterial fermentation in the colon. However, the nutrients present in fiber are not the reason it is often included in dog fods.

Fiber’s major contribution to commercial dog food is modulation of the digestive process; the fiber content of a food greatly affects the speed of passage of food through the digestive system. Fiber’s moisture-absorbing and lubricating actions can slow down peristalsis (the muscular contractions of the intestine that push food through the tract) in cases of diarrhea, or speed it up in the case of constipation. In other words, fiber has a normalizing effect on the gut.

The presence of adequate fiber allows time for absorption of nutrients and water from the intestine into the blood. Some fibers also impart mucilaginous (slippery) qualities to the food, helping it “slide” along the gut walls. Certain fibers increase the rate of stomach emptying (this is one theory behind feline “hairball” diets), while others slow it down. Fiber binds some toxins in the gut and eliminates them in the stool.

Types of Fiber

Fiber is usually characterized by describing its solubility and fermentability. These terms are used for different properties, and any one fiber can be described in terms of either trait. Cellulose, for instance, is both insoluble and nonfermentable, while guar gum is soluble and fermentable. Others lie on a continuum between these two extremes. These terms evolved as the technology for analyzing fiber improved.

However, the method used to assay “crude fiber” as stated on a dog food label is actually a very poor technique, and fails to detect most of the lignan, hemicellulose, and even some of the plain cellulose. Thus, the actual level of fiber in a dog food may be considerably underestimated by the outdated Crude Fiber method.

Soluble fibers are considered more digestible than insoluble fibers and will dissolve in water. Soluble fiber dissolves in water to form a viscous gel, which may aid in food passage through the gut. Insoluble fiber tends to speed up gut motility.

Fermentable fibers are those that yield nutrients that can be used for energy by the body. Soluble fibers tend to be more fermentable than insoluble fibers. Bacterial digestion of these fibers produces short-chain fatty acids (SCFAs) such as proprionate, acetate, and butyrate. Butyrate is thought to be beneficial to the cells lining the colon. These SCFAs can be absorbed by the animal and used as an energy source, acidify the colonic environment, and draw water into the stool by osmosis. Basically, they keep the colon bacteria happy, and this is the reasoning behind use of fructo-oligosaccharides found in such plants as chicory and yucca in dog food.

Fiber and Medical Conditions

It has been thought for many years that high fiber diets are “more filling” and provide increased satiety. Thus, weight loss diets have traditionally included high fiber as well as less fat. However, a new study has reported that fiber appears to have no effect at all on a dog’s appetite; no matter how much fiber a food contained, all dogs were willing to eat a “challenge” meal given an hour later. Other researchers have suggested that the primary mechanism of weight loss produced by “light” diets may be decreased palatability.

The ability of certain fibers to decrease intestinal transit time is the theory behind feeding high-fiber foods to diabetics. The addition of fiber slows absorption, resulting in a more stable blood glucose level over time.

While different fibers behave differently depending on the composition of the diet and the individual metabolism of the dog, it seems clear that excessive fiber increases fecal bulk, frequency of defecation, and may produce loose stools and flatulence.

Beet Pulp Fiction

Beet pulp seems to be the main target for much of the misinformation flying around about fiber. Here are a couple of the untruths currently being promulgated about beet pulp:

MYTH 1: Kibble containing beet pulp swells up in the stomach and causes bloat. This is based on the observation that extruded kibble that gets wet (i.e., dropped into the water bowl) will indeed expand, and any of us with sloppy dogs (or playful cats) have seen the evidence with our own eyes. However, baked food does not swell, and several baked foods also contain beet pulp.

The expansion of wet kibble is mainly due to the air trapped in the pellet as it “pops” from the extruder. The other thing to notice about wet kibble is how easily it breaks apart. Far from forming “an indigestible mass” in the stomach, this property of kibble probably helps speed its passage from the stomach and ultimate digestion.

MYTH 2: Beet pulp is full of sugar and can cause diabetes. Pulp is a by-product of sugar extraction from sugar beets. Sugar manufacturers, obviously, extract every last little bit of sugar from the pulp before they sell the pulp off for drying and use in dog food. There is no evidence that beet pulp causes diabetes.

MYTH 3: The saponins in beet pulp cause bloat. Saponins are basically soaps, which cause an increase in surface tension of a liquid. While normal water forms bubbles, they burst rapidly. Soap allows the molecules to stick together longer. Saponins are found in beets, legumes like alfalfa and beans (including soybeans), and hundreds of other plants. Saponins are specifically associated with one type of bloat (“frothy” bloat) in ruminants (cows and goats), but this is completely unrelated to the “gassy” type of bloat that dogs can suffer from.

MYTH 4: The saponins in beet pulp contains paralytic toxins. There are thousands of saponins; the soybean alone contains at least five different ones. The highly biased claim that all saponins (or even all soy and beet saponins) are toxic is ignorant and inaccurate. According to one expert, “From the biological point of view, saponins have diverse properties, some deleterious but many beneficial.”

Medicinal herbs such as ginseng, licorice, and alfalfa contain helpful bioactive saponins. Digitalis is a saponin that is extremely toxic in high doses, but has saved millions of lives as the basis for digoxin, a drug used to treat congestive heart failure. Saponins are largely destroyed by processing such as soaking and cooking; it is unlikely they have any biological effect when consumed in dog food.

Overall, I don’t have any objection to beet pulp. For a normal animal, I’d probably choose a food that contains beet pulp or pomace – the more fermentable fibers – over peanut hulls or cellulose. And I’d pick a food that contained a whole-food source of fiber (such as oatmeal or tomatoes) over one that included beet pulp or any other food fraction for its fiber source.

To Sum It Up

As you can see, fiber does play a useful role in commercial dog food. It probably doesn’t significantly contribute to whole body nutrition, but can provide important nutrients of value to the cells and bacteria of the colon. Fiber may actually prevent absorption of some toxins.

Most dog foods range from 1-10 percent in fiber content on the guaranteed analysis; moderate levels of fiber, in the 2-4 percent range, may be a realistic goal when selecting a dog food. In amounts of more than 10 percent, fiber increases stool volume and has a negative effect on stool firmness.

Each manufacturer uses different types of fiber to obtain specific results. Each will vigorously defend its particular source or combination as the best, but they can’t all be right! Aside from minor variations in each fiber source’s effects, which one any given healthy dog consumes will probably not matter too much. However, if your dog has any specific health issue, you may want to ask your veterinarian which type of fiber she recommends for that condition.

And, as usual, WDJ prefers foods that utilize whole foods, rather than isolated food fragments (by-products of other food manufacturing processes) that lack the balance and natural cofactors of the real thing.

Dr. Jean Hofve is the Companion Animal Program Coordinator for the Animal Protection Institute, located in Sacramento, CA.

Q: My dog drinks about a half-cup of organic milk (same as I drink) with his evening meal. He is a strong, healthy 10-year-old dog, and has never had any problems with arthritis or digestive troubles. My husband, though, is certain that milk is bad for dogs. I look at my dog and feel certain I’ve been doing things right; he looks great. Is there any reason to discontinue his milk?

Kate Mueller
Cincinnati, OH

We asked CJ Puotinen, a frequent contributor to WDJ, to answer this question. Puotinen is the author of The Encyclopedia of Natural Pet Care and Natural Remedies for Dogs and Cats.

A: Milk is a controversial food. Some pet nutritionists say milk and dairy products are perfect foods, while others blame them for every canine disorder from ear infections to cancer.

The truth lies somewhere in between. Raw, organically grown, unpasteurized, unhomogenized milk straight from a healthy cow or goat can be an excellent food for dogs of every description. After all, it has been for thousands of years. Unfortunately, America’s supermarkets stopped selling raw, whole milk long ago. Supporters of the Campaign for Real Milk, a grassroots movement that advocates a return to humane, organic dairy farming, small-scale dairy food processing, and the sale of good-quality raw milk, documents many problems with America’s milk supply. Today’s dairy cattle are often raised in crowded conditions, fed inappropriate feed, and dosed with hormones, antibiotics, and other drugs that disrupt or alter the production of milk while leaving their residues in dairy products.

But that’s not all! Most of the organically grown milk and cream sold in America’s supermarkets and health food stores is ultrapasteurized and homogenized, which makes it an inappropriate food for dogs.

The two most common methods of pasteurization heat milk to 145 degrees F for 30 minutes (low temperature, long time) or to 161 degrees F for 15 seconds (high temperature, short time). Both methods kill nearly all the bacteria, yeast, molds, and enzymes in milk. Another method, ultra-pasteurization, was developed to give slow-selling products a longer shelf life. These products are heated to 280 degrees F or higher for at least two seconds and packaged in an aseptic atmosphere in sterilized containers. The high temperatures destroy proteins as well as enzymes and bacteria, giving these products a cooked taste.

Pasteurization, which is intended to kill harmful bacteria, is ineffective against drug-resistant strains of salmonella. In addition, pasteurization and ultrapasteurization alter milk’s amino acids, promote the rancidity of unsaturated fatty acids, and destroy vitamins and enzymes. In homogenization, jets of milk collide under high pressure, breaking fat molecules into tiny particles that remain distributed rather than floating to the top. These particles can enter the human and canine bloodstream, explaining why homogenization has been blamed by some researchers for heart disease and circulatory problems.

In most states, the sale of raw, whole milk is illegal, but some states allow raw milk to be sold for pet use, and some allow consumers to buy raw milk directly from dairy farms. Your local health food store may be able to help you find a supplier, as can the Campaign for Real Milk.

Fortunately, the U.S. Food and Drug Administration considers raw milk cheese to be safe if properly aged. Connoisseurs agree that the world’s finest cheeses are made from raw rather than pasteurized milk, and some have an international following. Raw cheeses are available in specialty shops, health food stores, and a few upscale markets. Warning: Some are incredibly smelly – and expensive! Your health food store is a likely source of mild, affordable raw milk cheeses that hold their shape when cut and make high-reward treats for dogs.

Virtually every dog food on the market complies with the labeling regulations and meets the nutrient standards suggested by the Association of American Feed Control Officials (AAFCO); go look at the fine print on your dog’s food label. It will have one of two statements on it, indicating which of two AAFCO standards it supposedly met: either a “feeding trial” or chemical analysis of the food. The problem is, that particular food may have passed neither test itself.

What?

Let’s back up.

We’ve talked about AAFCO before (see “Who’s in Charge?” WDJ December 2000). It’s a nongovernment, voluntary, advisory organization of state feed control officials, who interact with and influence state and federal feed industry regulators. Most states require that dog food made and/or sold in their borders meet a standard meant to guarantee nutritional benefit to the dogs who eat it, and most states use AAFCO-developed standards.

AAFCO uses two methods to “prove” that a food is adequate to the task of keeping dogs alive. The first is a feeding trial, where the food is fed to a certain number of dogs for a certain amount of time, and as long as most of the dogs live, the food gets to go to market with a label that says something like, “Animal feeding tests using AAFCO procedures substantiate that (product name) provides complete and balanced nutrition for (life stage).” Never mind that, in our opinion, these trials are woefully inadequate; we’ve discussed that before and we will again in the future.

The second standard is basically a chemical analysis that confirms the food contains levels of nutrients that fall within a range determined by AAFCO to be sufficient to support canine life. The way it’s supposed to work is that foods that have not been tested in a feeding trial have labels that say, “(Name of product) is formulated to meet the nutritional levels established by the AAFCO nutrient profiles.” Again, never mind that we and many other pet food-industry critics take issue with the nutrient profiles. We’ve got other fish to fry today.

Pet food ‘families’
Here is our problem: AAFCO recently amended its regulations to allow foods that are comparable in nutritional adequacy to a food that actually passed a feeding trial to bear the exact same label claim.

A food that has passed an actual feeding trial can now serve as the “lead food” for a “family” of foods; and the standards required for the “family members” are not nearly as rigorous (if we can use that verbiage in relation to pet food production) as for the lead food.

To be in “the family,” a food must meet the following criteria:

• The moisture content must be similar to the lead food. This requirement simply ensures that dry foods stay in a dry food family, a canned food is in a canned food family, etc. For example, both the lead food and any family members must be under 20 percent moisture (“dry” foods), 20-65 percent moisture (“semi-moist” foods), or over 65 percent moisture (canned foods).

• The “metabolizable energy” (ME) content of the family member must be within 7.5 percent of the tested food – which more or less means they should have similar calorie counts. This must be validated by feeding the family member food to six animals for 10 days. The first five days are so the animals can acclimate to the food. During the last five days, the animals’ stools are collected and their energy content assayed by calorimetry. The difference between the amount of food eaten and the amount of stool excreted, with a correction for urinary losses, equals the ME of the food.

This is the only time that the “family member” foods must be fed to live animals before they arrive at the retail store shelves.

There is an optional test for ME that uses calculations rather than the feeding protocol, but it is unlikely that any manufacturer will ever use it, because it would have to state outright on the label that the food is “comparable in nutritional adequacy to a product which has been substantiated using AAFCO feeding tests.” Rather than admit that on the label, manufacturers will most assuredly use the relatively lenient 10-day ME test.

• The family member must also meet the levels contained in the lead food for a few crucial values: crude protein, calcium, phosphorus, zinc, lysine, and thiamine. (For cat foods, the family members must also meet specified minimums of potassium and taurine.)

• The family member may claim adequacy for only the same or a less-demanding life stage than the lead food. (Life stages are, in descending order of demand: “all life stages,” “gestation/lactation,” “growth,” and “maintenance.”)

• Finally, the family member must meet or exceed the nutrient levels of the lead food or as specified by the AAFCO Nutrient Profiles for all other nutrients, whichever is lower.

Good news for manufacturers
This is very good news for the pet food manufacturers, because they no longer have to perform expensive feeding tests in order to market a food with the feeding test claim – a “higher” standard in most consumers’ eyes. This gives family member foods a potential marketing advantage over foods that “only” meet the requirements of the AAFCO Nutrient Profiles.

The new family rule also allows food makers to fast-track the development and marketing of new formulas. In case you were wondering, this is the mechanism that has permitted the rapid proliferation of such things as special formulas for dogs with sensitive skin or tender tummies, breed-specific formulas, and odor-reducing formulas on the shelves of your local pet superstores and grocery stores.

Bad news for consumers
Is it good news for you? True – it has resulted in a much wider selection of foods to choose from at the store.

But until recently, we used to be able to trust that, if a food claimed it had been tested using AAFCO feeding protocols, it had at the very least kept a handful of dogs alive for six months. Now, we have no assurance at all, because we can’t tell which food is a lead food that was really tested, and which one is the copycat. This is particularly bad news because the lead food, which has passed feeding tests, is not itself required to meet the AAFCO Nutrient Profiles. Thus, a family member food could be significantly below the recommendations of the Nutrient Profile for many nutrients, yet never be required to prove it can keep animals going, even for six months. Small differences in formulation could mean big differences in how digestible and bioavailable certain nutrients are to the dog, but the only way you’ll find this out is when your dog develops a problem because of it!

I know I keep saying this, but it’s another case of “let the buyer beware!” Always keep an eye on your dog when trying out a new food to make sure it’s working for him. He should have good energy, a normal appetite, clear eyes, a shiny coat, no dandruff, and normal stools. If anything seems “off,” look to his food first for the cause.

On the other hand, if your dog displays every sign of good health and has no worrisome symptoms of chronic health problems (such as recurrent ear infections, “hot spots,” or digestive troubles), don’t give in to the impulse to switch to the newest food on the pet store shelves just because its bag is newer, shinier, or cheaper, or labeled as just right for Airedale-crosses from the East Coast or all dogs with “sensitive skin.” It’s probably an untested newcomer to a over-accepting “family.”

-By Jean Hofve, DVM

Dr. Jean Hofve is the Companion Animal Program Coordinator for the Animal Protection Institute, located in Sacramento, California.