The Facts of Fiber

When evaluating foods for small pets, remember that the ideal level of fiber depends entirely on the animal’s dietary lifestyle.


In the world of human nutrition, there has been a great deal of discussion about the importance of dietary fiber. Studies have shown that a human diet high in fiber can help control blood sugar and prevent type-2 diabetes, reduce blood cholesterol and the risk of coronary heart disease, and prevent a number of bowel diseases, including colon cancer. Understandably, the results of these studies have people in the pet industry talking about the possible benefits of increasing fiber in small animal diets.

However, while it is tempting to try to compare the results of nutritional findings in humans to other animals, this must be done with extreme caution. The main thing to remember is that the optimal amount of fiber in an animal’s diet depends completely on the type of digestive system it has. 

Humans are omnivores, which means we eat both plant and animal matter. Among the small mammals commonly kept as pets, only the small rodents—hamsters, gerbils, mice and rats—are also omnivores. Rabbits and guinea pigs, which comprise the majority of small pets, as well as chinchillas, are herbivores and designed to eat only plants. Ferrets are carnivores, so they are designed to eat only animal matter. These differences are incredibly important. Dietary studies done on humans could possibly be applied to omnivorous rodents, but not to herbivores or carnivores.

Because most plants contain a fairly high level of fiber, the digestive tracts of herbivores are designed to deal with large amounts of plant fiber. Food that comes from animal sources tends to be much lower in fiber than that from plants, so the digestive tracts of omnivores are designed to deal with only moderate amounts of fiber. The digestive tract of a carnivore is designed to handle only low amounts of fiber. Adding too much fiber to the diet of omnivores and carnivores can cause problems. First, a diet too high in fiber can reduce the palatability of food. If a pet is not willing to eat a high-fiber food, it’s not going to provide any benefits at all. Too much fiber is also thought to interfere with the absorption of some nutrients. It can also cause abdominal discomfort, excess gas and, in extreme cases, even dehydration, intestinal blockage and death.

There are two kinds of dietary fiber: soluble and insoluble. Soluble fiber will dissolve in water and become gelatinous, where insoluble fiber can absorb water yet retains its stringy quality. Both types of fiber can increase the bulk of the feces, which helps the intestines to push it through. Soluble fiber is most commonly found in oats and barley, legumes (including beans and peas) and fruits. Insoluble fiber is found in wheat bran, the skins of many nuts, seeds, fruits and vegetables, and most importantly in the small pet world, hay. In humans, dietary fiber is defined as the portion of food that is indigestible, but some kinds of fiber can be digested by herbivores with the help of microorganisms in their lower digestive tract. These specialized intestinal bacteria aid digestion. Hay is an ideal food for herbivores, but it is indigestible for omnivores and carnivores. For them, the best type of dietary fiber is probably soluble fiber.

When comparing brands of food marketed for the different species, a good rule of thumb is to choose a diet that closely mimics the animal’s natural diet. Wild herbivores would eat mostly grass along with other types of plants. The entire digestive system of herbivores, from their teeth to their cecum, operates properly only when they eat a diet high in fiber. Without enough fiber in their diet, their teeth can become overgrown, and their digestion can become sluggish and blocked. You can almost say that the diet of herbivores cannot contain too much fiber. In fact, the biggest danger is feeding them too little fiber. The diet of an herbivore should probably consist of 25 to 30 percent fiber. Grass hay itself is about 30 to 32 percent fiber.

In the wild, ferrets would mostly eat small mammals. The only plant matter they would eat would be the partially digested contents of the prey’s digestive tract. Therefore, a ferret food should be composed almost completely of animal matter. The amount of fiber in the diet of a ferret should be no more than five percent, and it is probably best if it is only two to three percent. 

The diet of an omnivore can contain ingredients from both plant and animal sources, and because in the wild a small rodent would eat a wide variety of foods, it is probably best for a commercial diet to also contain a wide variety of ingredients. The fiber content of a diet for omnivores should probably be at least five percent fiber, but not more than seven percent. A healthy high-fiber diet recommended for humans contains about 5.8 percent fiber.

Debbie Ducommun has a B.A. in animal behavior and has worked in the animal field since 1982. She is the author of the book Rats!, the booklet Rat Health Care and, her most recent book, The Complete Guide to Rat Training: Tricks and Games for Rat Fun and Fitness.


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