Fiber often gets labeled as "filler" although some people refer to all carbohydrates in pet foods as fillers and that's just silly (especially to those of you reading this blog). Now, if you are feeding a food like Ol Roy (don't tell me if you are!), yes, you are feeding way too carbohydrate and your dog (or cat) will have the fecal output to show for it.
First off, dietary fiber is not a single or simple group of compounds. In fact, they are extremely complex and diverse carbohydrates with diverse physical and chemical properties. Structurally, some fibers are soluble and some are insoluble. Some are viscous and have very high water holding capacity, while others are non-viscous. Some are fermentable in the bowel and others are not. Lastly, they can be combinations of the above. So, you can have soluble - viscous - fermentable fibers for example (those are my favorites), or you can have something like psyllium (Metamucil), which is actually a very soluble-viscous-non fermentable fiber.
The frustrating issue for me is that the label and analytics involved, don't necessarily tell you about those properties. If you look on a label of food (for you) at the grocery store, you will see that perhaps it breaks down the fiber into Soluble and Insoluble, but often gives you the Total Dietary Fiber (TDF) amount. On an herbivore diet such as for cows or horses, the label will likely (hopefully) include ADF (acid-detergent fiber) and NDF (neutral-detergent fiber). The values of TDF, ADF and NDF and obtained through totally different analyses in a lab. On our petfoods, we will see a value called "Crude Fiber" which also is a totally different analysis for fiber. Unfortunately, crude fiber is a completely worthless value to use. The assay destroys all of the soluble fibers and many insoluble fibers and only recovers portions of cellulose, hemicellulose and lignin (totally insoluble, non viscous, non fermentable). Therefore, a petfood might have a crude fiber value of 2.5% on the label but in reality, may have TDF values closer to 10% or even 20% depending on the ingredients used.
Ideally, I want fibers on the ingredient list that will provide some soluble characteristics. Soluble - viscous - fermentable fibers can alter gastric emptying and transit time (this can be good and bad), aid in management of pH along the G.I tract, provide volatile fatty acids for energy to the cells lining the gut, and aid in the management of blood lipids and glucose. These fibers can be very good in appropriate concentrations. In addition, many of these fibers provide prebiotic properties and help maintain optimal microflora populations that provide a strong basis for overall health and immunity.
Many folks like to use canned pumpkin in diets. Canned pumpkin contains about 30% TDF. That fiber is about 20% soluble and 80% insoluble; therefore, it does provide a nice blend. Due to the high TDF concentration and the blend of soluble to insoluble, pumpkin is an ingredient that I can use effectively across a huge range of species including dogs and cats, bears, elephants and primates.
My dog's raw diet does contain grain (and quite often pumpkin). I use oats and barley predominately at 10% of the the diet (as-fed). Oats and barley contain 30 and 12% TDF, respectively. Corn and wheat actually contain about 19 and 17% TDF while rice contains less than 2% (white rice). Barley has the highest percentage of soluble fiber, consisting of 30% of the total TDF. This gives barely some very viscous qualities or thickening properties. Oats on the other hand only have about 10% of the TDF as soluble; therefore, combined, I get a very nice blend of fiber qualities in my diet. Corn, wheat and rice contain 18, 14, and 20% of the TDF as soluble. Rice has such a low TDF value overall, I tend to not use it much, especially because it also has a very high glycemic index. Corn and wheat are definitely options for those animals that tolerate them. I will use fresh corn in my diet because an additional 15 - 20% (as fed) will consist of fresh fruits, greens and vegetables. If you are wondering, the breakdown looks like this:
55 - 60% muscle meat
10 - 15% organ meat (mostly liver and heart)
15 - 20% Greens, vegetables, fruit (seasonal)
I supplement with eggshells for calcium and feed raw meaty bones 2-3 times week.
No doubt, fibers have personality!!! I love them!