What is a filler and does pet food actually contain “fillers”? Certain ingredients often get blamed for being of low nutritional value and simply filler ingredients. A filler is something that contains no nutritional value and is added to create bulk in the diet. In pet food, this actually doesn’t exist. Everything included in pet food is in there for a reason, and because of this AAFCO doesn’t define “fillers”.

Not only is placing a filler ingredient into a food essentially a waste of money, adding a product that contains no nutritional value to a carefully balanced diet simply doesn’t make sense. If fillers were a thing, they would make pets feel fuller, thus eating less and they would probably also suffer from a number of nutritional deficiencies. Foods containing so called “filler ingredients” are often accused of trying to make money by using cheap, unfulfilling ingredients to make pets eat more…but this also doesn’t make sense – using filler ingredients would mean the owner would actually spend less money on food, as they would purchase it infrequently – the pet would eat less as it’s “filling up” the pet thus going through bags of food slower. So if the aim was to increase food sales, adding fillers is not the way you’d do it.

The ingredients often accused of being fillers are generally carb or cereal based ingredients such as corn, wheat, rice and beet pulp. Many naysayers state that all these ingredients do is ‘bulk up’ or provide fibre to pets to make them feel full of empty calories – as a nutritionist, I don’t understand how these ingredients have gotten such a bad name. As in my previous posts, fibre is not an inert, bulky, space filling ingredient that offers no nutritional value – in fact, it’s a wonder product for gut health! Fibre is not a nutritional requirement for pets, but a diet lacking in fibre will have a significant impact on your pet’s overall health.

So let’s have a look at what these “filler” ingredients offer and WHY they are actually included in pet food.

Corn
Corn is the first ingredient that is regularly slammed as being indigestible and a filler. However, corn is added into pet food for a number of reasons; when used in the form of corn gluten meal, corn meal or maize flour it is actually 98% digestible! As far as carbohydrates are concerned, corn contains less sugar than rice or potato. It is also one of the richest sources of linoleic acid (an essential fatty acid) and is a wonderful source of protein with a fantastic amino acid profile comparable to chicken. Corn also provides Vitamin E, beta carotene and lutein! So…this ingredient definitely doesn’t fit the definition of a filler.

Wheat
Wheat, despite its bad name, is a nutritious source of fibre and protein. Wheat gluten, despite being an allergen in humans, is unlikely to cause any issues in pets (see my post about food allergies) and is actually also a highly digestible (99%) source of protein for pets. Using wheat as a protein source reduces indigestion, faecal odor and flatulence – it’s very good for the colon as it prevents the toxic effects of undigested meat protein damaging the mucosa and lubricates the bowel so stool can easily pass through. It is also low in saturated fat and cholesterol.

Rice
Rice is highly digestible and is a good source of bland carbohydrate, used especially in diets for gastrointestinal conditions; white rice has a good effect on binding the stool when diarrhea is present, as it’s starchy and the sugar content also gives a little bit of an energy boost. Brown rice can also sometimes be used in pet foods, which is a little higher in fibre and nutrients than white rice, and has a much lower glycaemic index than white rice. Again, neither are fillers but are used for different purposes.

Beet pulp
Fibre, fibre, fibre! Beet pulp is one of the best sources of prebiotic fibre available to pets. As in previous posts, prebiotic fibre feeds the good bacteria in the gut and promotes the production of host-specific probiotics. Beet pulp is also the the perfect blend of soluble and insoluble fibres, meaning it provides a whole host of benefits to gut health and the microbiome. It’s a highly sustainable ingredient that is a byproduct of sugar beet processing, once all the sugar is removed the pulp is left behind to be used as a fibre supplement. This is often also included in horse feeds aswell for the same purpose. Occasionally you may seen FOS or fructooligosaccharide included in a pet food instead; this can also be a derivative of beet pulp, chicory root or other fibre-rich fruits and vegetables.

Tomato pomace
Another ingredient I’ve seen labelled as a filler, is tomato pomace. This ingredient is actually skin, pulp and crushed up tomato seeds that are then dried which creates tomato pomace – this is essentially a by-product from manufacturing tomato sauce or pasta sauces. Tomato pomace is mainly used as a source of soluble fibre – it’s a very rich source in dog food for the volume required, so it is a very economical way of increasing the fibre content of the diet. This product also lowers cholesterol and stabilises blood sugar levels so is particularly helpful in patients who are diabetic. The other wonderful things that tomato pomace offers, is very high in antioxidants aswell as Vitamin C, K1 and Potassium. Also, tomato pomace is also used as a tasty natural flavouring.

So in summary, there are no fillers! Every ingredient in pet food is there for a reason and provides a unique nutrient profile. If you aren’t sure why an ingredient has been included, you can ask the pet food company, or check out their website; both Hills and Purina have websites that actually explain what their ingredients are and what they provide to their formulations. These nutrients are what your pet needs, not the ingredients. And if they provide something nutritionally, they cannot be fillers.

What ingredients do you see called fillers? Have you ever wondered why they actually are included in the diet? Why not leave me a comment below on an ingredient you think is a filler and I’ll explain why it’s in pet food!

References

AAFCO Talks Pet Food. [website] Available at: https://talkspetfood.aafco.org/whatisinpetfood

Freeman & Heinze (2012) Deciphering fact from fiction: Corn. [pdf] Available online at https://balaclavavet.com.au/sites/default/files/files/attachments/deciphering_fact_from_fiction_-_corn.pdf

Gajda M, Flickinger EA, Grieshop CM, Bauer LL, Merchen NR, Fahey GC Jr. Corn hybrid affects in vitro and in vivo measures of nutrient digestibility in dogs. J Anim Sci. 2005 Jan;83(1):160-71. doi: 10.2527/2005.831160x. PMID: 15583056.

Kempe, Riitta & Saastamoinen, Markku & Hyyppä, Seppo & Smeds, Kurt. (2004). Composition, digestibility and nutritive value of cereals for dogs. Agricultural and Food Science. 13. 5-17. 10.2137/1239099041838067.

Pet Nutrition Alliance (2021) Why is corn an ingredient in pet food? Is it used as a filler? Is corn a major cause of allergies? [website] Available online at: https://petnutritionalliance.org/site/pnatool/why-is-corn-an-ingredient-in-pet-foods-is-it-used-as-filler-is-corn-a-major-cause-of-allergies-2/

Holloway, C. (2019) Nutrition Know How: Corn. available online at: https://www.vetfolio.com/learn/article/nutrition-know-how-corn-nutrient-or-filler-busting-common-nutrition-myths