Is kibble ultra-processed? Yes, in the literal manufacturing sense, and it is worth understanding that honestly rather than as a scare. This is a companion to our guide on what to feed your roof rat, which keeps a balanced block as the base and adds fresh food on top, and to our page on ergothioneine, one of the things processing leaves out.
Start here: this is not an anti-kibble page
You will find plenty of writing online that treats kibble as poison. This is not that. A good extruded block is the easiest way to feed a rat a complete, safe, balanced diet, and on our companion page we tell you to keep it as the BASE of the diet. So why a page about processing at all? Because making that block is a genuine trade: the same high-heat process that makes kibble safe, digestible, and shelf-stable also strips out some fragile things a rat would get from whole food. Understanding the trade is what tells you exactly which gaps to refill with fresh food, instead of either trusting the bag blindly or throwing it out. Honest accounting, both columns.
One of those gaps is the reason we put ergothioneine in the drinking water, alongside taurine and betaine, and the case for all three is set out on Why We Put These Three Things In The Water.
What “ultra-processed” even means, and whether it fits pet food
“Ultra-processed” comes from a human-nutrition system called NOVA, which sorts foods by how much they are processed rather than by their nutrients; its top tier is industrial formulations built mostly from extracted ingredients plus additives.[1] By that logic, extruded kibble clearly is ultra-processed.
But be careful borrowing the alarm that goes with the term. NOVA is genuinely contested even among human nutrition scientists,[1] and a peer-reviewed review of pet-food processing concluded the human “ultra-processed” definition does not transfer cleanly to dog and cat food, because pet diets are formulated and expected to be nutritionally complete, unlike most human ultra-processed snacks. The honest position is this: the label fits in the narrow sense that kibble is made by the same high-heat industrial methods, but “ultra-processed equals bad” is a human-food slogan that has not been shown to apply to a complete pet diet. So I will not wave the word around as a scare. I will just show you what the processing does.
What extrusion actually is
Most kibble and pellets are made by extrusion: a dough of milled ingredients is pushed through a hot, pressurized barrel by screws, where friction and injected steam cook it to roughly 110 to 150 C for a matter of seconds, then it puffs and is shaped as it exits and is dried.[2] It is fast, it cooks thoroughly, and it kills germs. One side effect worth naming is the Maillard reaction, the same browning that makes toast and seared meat tasty: it improves flavor, but it also locks up some of the amino acid lysine in a form the body cannot use, so a label’s “total lysine” can overstate the usable amount.[3][4]
What extrusion trades away
- Heat-labile vitamins. Several vitamins are damaged by the heat. Vitamin A and thiamine (B1) are the best-documented losses in extruded pet food (one analysis put vitamin A loss around a third by the end of extrusion and drying),[5][6] and thiamine is genuinely unstable in finished extruded diets.[7] Vitamin C and folate are also among the heat-sensitive ones.[5] (Makers know this, which is why they overdose the vitamin premix, more on that below.)
- Fragile fats, including omega-3. Long-chain omega-3s are the most oxidation-prone fats there are, and extruded food is vulnerable to that oxidation and to rancidity during storage.[8] How much omega-3 is actually lost varies a lot with the recipe, the antioxidants present, and the packaging, so I will not give you a single number, but it is a real reason a bag of kibble is a poor omega-3 source. (See our omega-3 page for the fuller story.)
- Polyphenols and other plant antioxidants are reduced and altered by extrusion, the amount depending on conditions.[9]
- Plant enzymes. Heat inactivates myrosinase, the enzyme that turns a broccoli compound into protective sulforaphane, so a cooked diet cannot make sulforaphane the way raw or lightly-cooked crucifers can. The measurements behind that are on mustard seed rather than broccoli, and the paper’s own finding is that how much heat it takes varies a lot from plant to plant[10]. (The enzyme chemistry is well established; that extrusion specifically wipes it out in kibble is a reasonable inference, not a measured fact.)
- The whole living microbial layer. This is the subtle one. Some compounds a wild rat gets are made not by plants or animals but by fungi and soil microbes, ergothioneine being the prime example.[11] A sterile, milled, fully cooked diet would be expected to contain little to none of that layer. (No one has measured ergothioneine in kibble, so treat this as a logical inference from where the compound comes from, not a lab result. We cover it in depth on the ergothioneine page.)
What extrusion genuinely buys you (the part the scare-pieces skip)
This is the column the “kibble is poison” writing leaves out, and it is substantial:
- It makes starch digestible. Cooking gelatinizes the starch, which extruded diets digest very efficiently, far better than raw grain.[12]
- It kills pathogens and cuts mold toxins. The cook step reaches temperatures lethal to Salmonella,[13] and extrusion strongly reduces some mold toxins (deoxynivalenol by over four-fifths) but is much less effective against aflatoxin (only about 10 to 25 percent).[14] (Honest caveat: the Salmonella sometimes found in dry pet food is almost always from recontamination of coatings added AFTER the kill step, not from the cooking failing. The kill step itself is genuinely protective.[13])
- It destroys anti-nutrients. Raw legumes and grains carry trypsin inhibitors and lectins that block digestion or damage the gut; extrusion largely destroys them.[15] (This is exactly why we say to cook beans before feeding them.)
- It makes the food shelf-stable by drying it to a low moisture level.[2]
- Every bite is complete and identical. A formulated block is designed to meet all the essential-nutrient requirements for a life stage, and because every piece is the same, a rat cannot pick out the fatty, sugary bits and leave the balanced part behind, the way it can with a loose seed mix. That consistency is genuinely protective against the imbalances of a careless homemade or mixed diet.
- The vitamins are topped back up. Because makers know extrusion destroys heat-labile vitamins, they deliberately overdose the vitamin premix.[5] So a good block is still nutritionally complete on its label.
That last point is the honest hinge of the whole page: the overages refill the KNOWN nutrients on the spec sheet.
So what do you do?
Not abandon the block. Extrusion buys real things, safety,[13] digestibility,[12] shelf life,[2] and a reliably complete, balanced base, that you do not want to give up. Curious what a food that keeps more of that good stuff would look like? We put an open, public-domain recipe at the ideal rat food. The sensible move is the one our feeding page already makes: keep a good lab block as the base, and add fresh, whole foods on top to refill what processing strips. That is the entire reason the “Beyond the Pellet” approach exists. The processing is not the enemy; it is just a trade you can see clearly and then top up.
Bottom line
Kibble is ultra-processed in the literal, manufacturing sense, but “ultra-processed equals bad” is a borrowed human-food slogan that does not survive contact with a complete, formulated pet diet. Extrusion is an honest trade: it gives you safety, digestibility, shelf life, and balance, and it costs you some heat-labile vitamins (which makers top back up), fragile fats, plant antioxidants and enzymes, and the living microbial layer. Knowing both columns is what lets you keep the convenience and safety of a good block while adding back, deliberately, the handful of things the process leaves out.
This is educational information about pet-food processing, not veterinary advice.
Sources and further reading
If you want to go further, these go deeper:
- What to feed your roof rat, the block-base-plus-fresh-food approach this page points to
- Ergothioneine and omega-3, two of the things processing leaves out
- For the outside science, Tran and colleagues’ review of what extrusion does to pet-food nutrients (source) and Monteiro’s definition of the NOVA ultra-processed group (source)
Evidence note: the processing chemistry (Maillard, vitamin thermolability, lipid oxidation, starch gelatinization, anti-nutrient and pathogen/mycotoxin reduction) is species-independent and well established; the specific magnitudes come from dog, cat, and feed studies. There is no roof-rat-specific extrusion data, so all of it is extrapolated to Rattus rattus. The “kibble contains no ergothioneine” point is a logical inference, not a measurement; the “extrusion inactivates myrosinase in kibble” point is a mechanistic extrapolation; and “ultra-processed equals harmful for pets” is NOT an established claim.
References
- [1] Monteiro CA, Cannon G, Levy RB, et al. “Ultra-processed foods: what they are and how to identify them.” Public Health Nutrition 2019;22(5):936-941. DOI.
- [2] Tran QD, Hendriks WH, van der Poel AFB. “Effects of extrusion processing on nutrients in dry pet food.” Journal of the Science of Food and Agriculture 2008;88(9):1487-1493. DOI.
- [3] van Rooijen C, Bosch G, van der Poel AFB, Wierenga PA, Alexander L, Hendriks WH. “The Maillard reaction and pet food processing: effects on nutritive value and pet health.” Nutrition Research Reviews 2013;26(2):130-148. DOI.
- [4] van Rooijen C, Bosch G, van der Poel AFB, Wierenga PA, Alexander L, Hendriks WH. “Reactive lysine content in commercially available pet foods.” Journal of Nutritional Science 2014;3:e35. PubMed.
- [5] Morin P, Gorman A, Lambrakis L. “A literature review on vitamin retention during the extrusion of dry pet food.” Animal Feed Science and Technology 2021;277:114975. DOI.
- [6] Galli GM et al. “Stability of vitamin A at critical points in pet-feed manufacturing and during premix storage.” Frontiers in Veterinary Science 2024;11:1309754. PubMed.
- [7] DiSabatino B, et al. “In extruded feline diets, thiamine degraded at a similar rate when stored at -20°C, compared to room temperature.” Canadian Veterinary Journal 2021;62(4):374-378. PubMed.
- [8] Lin S, Hsieh F, Huff HE. “Effects of lipids and processing conditions on lipid oxidation of extruded dry pet food during storage.” Animal Feed Science and Technology 1998;71(3-4):283-294. DOI.
- [9] Šárka E et al. “Changes in phenolics during cooking extrusion: a review.” Foods 2021;10(9):2100. PubMed.
- [10] Okunade OA et al. “Thermal and pressure stability of myrosinase enzymes from black mustard (Brassica nigra L. W.D.J. Koch. var. nigra), brown mustard (Brassica juncea L. Czern. var. juncea) and yellow mustard (Sinapsis alba L. subsp. maire) seeds.” Food Chemistry 2015;187:485-490. PubMed.
- [11] Borodina I, Kenny LC, McCarthy CM, et al. “The biology of ergothioneine, an antioxidant nutraceutical.” Nutrition Research Reviews 2020;33(2):190-217. PubMed.
- [12] Loureiro B, et al. “Starch gelatinization implications for nutrient digestibility and fermentation products in the faeces of Beagle dogs.” Animal Feed Science and Technology 2024;309:115894. DOI.
- [13] Anderson NM, Keller SE, Mishra N, et al. “Salmonella Inactivation During Extrusion of an Oat Flour Model Food.” Journal of Food Science 2017;82:738-743. PubMed.
- [14] Cazzaniga D et al. “Mycotoxins inactivation by extrusion cooking of corn flour.” Letters in Applied Microbiology 2001;33(2):144-147. PubMed.
- [15] Pasqualone A, Costantini M, Coldea TE, Summo C. “Use of legumes in extrusion cooking: a review.” Foods 2020;9(7):958. PubMed.