The topic of processed foods is incredibly interesting. Processed foods are something we encounter every time we shop at the grocery store, and we’re understanding more and more about the negative impacts of consuming a large amount of ultra-proceed foods on human health. Just last month, the British Medical Journal published an impressive systematic umbrella review (an umbrella review is a little bit like a review of other reviews) that found a higher risk of death (all types and those specifically due to cardiovascular disease), mental disorders (poor sleep, anxiety, depression), obesity, and type 2 diabetes in people who eat a lot of ultra-processed foods (1).
So, what are these unhealthy ultra-processed foods? A processed food is a food that has been altered in any way from its natural form. The NOVA classification system splits food based on how processed they are (2). This system is not perfect, but it’s the one most commonly used. At the beginning is unprocessed or natural foods. An example of this would be an apple in its natural state. The next level is minimally processed, so this would be packaged, pre-sliced apples that you can buy in the grocery store.
Then you have processed foods, which would be the apple made into apple sauce. To make the apple sauce, the peel is removed, water is added and the mixture cooked and then blended. The last category is ultra-processed, in which case the applesauce would then be sweetened with high fructose corn syrup or an artificial sweetener. Foods that fall into this ultra-processed category include things like chips, instant soups, cakes, chocolates, candies, energy drinks…things that are pretty far away from the foods that they originally started off as.
If we applied these definitions to kibbles and canned pet food, how do they turn out? Well, traditional kibbles are made through an extrusion process where a dough is formed from powdered meats, oils, grains, vegetables, a vitamin/mineral mix, etc. and cooked at a temperature between 80 – 200°C for a few seconds to a few minutes. After cooking, the dough is pushed through a small hole and cut into shapes. From there, the kibbles are dried in temperatures that can reach up to 150°C. Once dried, the kibbles are enrobed with fats and palatants before it is packaged.
For canned food, the process is similar. Fresh meats are mixed with fats, vegetables, grains, vitamins & minerals, and water. This mixture is heated to 25 – 85°C to gelatinise the starches (making them more digestible) and to start denaturing protein. Denaturing proteins can be helpful by creating texture and making the proteins more digestible (e.g. egg whites). However, denaturing proteins can also affect digestibility in a negative way as well. In one study, there was no difference in in-vitro digestibility of pork meat that was cooked to 60°C compared to raw meat, and a small decrease (3%) when the meat was heated to 75°C (3). Higher though (at 95°C), digestibility decreased by 21% compared to the raw meat. Therefore, it’s a balancing act to get the cooking right. After this initial cook, packages are filled with the mixture, and then they undergo sterilisation. How long they're heated for depends on the temperature they're heated to. But heating it to 120°C for several minutes is common. Just as a comparison, we tend to bake our food in ovens at a temperature of 180°C or so.
So, are kibbles and canned pet food processed foods? Yes. Are they ultra-processed foods? Yes. But they’re not quite the same thing as the ultra-processed foods of the human world. The biggest issue with foods in this category is that they provide little nutritive value. Nutrients are stripped along the way as the food becomes more and more processed. Kibbles and canned food though, if they are complete and balanced, have added vitamins and minerals to ensure that they at least meet the minimum nutrient requirements for dogs and cats. The topic of whether added synthetic nutrients are less ideal than their natural counterparts is another topic for another day. But the main point here is that while nutrients are lost when the kibble is extruded or the canned food is sterilised, manufacturers account for that in their formulation so that the final product is not devoid of nutrients.
Another concern with processed foods is that they contain something called “process” contaminants. These are chemical by-products that are created when heating, drying, or fermenting foods. They can occur anytime we’re cooking our foods – a classic example is toast. Toast is super tasty because heating the bread creates a change in the texture and caramelisation, which is due to a Maillard reaction. However, this heating also creates unwanted compounds, such as acrylamide. Acrylamide is formed between sugars and an amino acid, asparagine, and eating a lot of acrylamides has been shown to cause cancers and other undesirable effects in lab animals.
There is no safe dose of acrylamide so we can’t say what would be the “tolerable dose” or “safe upper limit”. Instead, some government agencies have quantified the dose range where it could cause cancers and other neurological changes. EFSA sets their range to start at 0.17 mg acrylamide/kg body weight/day (4). What would mean in practical terms? Well, that would be like me eating 1700 pieces of toast or 2.5 kg of potato chips a day! It’s a lot and unrealistic amount - but let's also remember that there is no safe amount of acrylamide, so it’s certainly not a target!
There are a small number of studies examining levels of acrylamide in pet food; kibbles have been found to have a higher concentration than wet food (5). Overall, a range of 15 – 360 ng/g of food has been described (5,6). Assuming a 20 kg dog eats 260 grams of dry food a day, that would mean an intake of 94 micrograms of acrylamide per day. This is far below what is believed to cause cancers in other species.
So, where does this leave us? It’s clear that by definition, kibbles and canned foods are the ultra-processed foods of the pet world. Are they just as unhealthy as the cakes, cookies, and fast foods that are also in this category? Not necessarily as at least complete and balanced kibbles and canned foods are fortified with supplements. Does processing create unwanted chemical compounds? Definitely yes. But the levels found in kibbles and canned foods are below what we think are needed to cause disease. There is no safe level though, so if you want to reduce the amount of acrylamide your pet is eating, adding in wet food and/or fresh food would help.
Thanks for reading! Please keep an eye out for the next blog in this series. Also, if there’s something in particular you’d like us to cover, please let us know in the comments below!
1. Lane MM, Gamage E, Du S, et al. Ultra-processed food exposure and adverse health outcomes: Umbrella review of epidemiological meta-analyses. BMJ. Published online 2024. doi:10.1136/bmj-2023-077310
2. Braesco V, Souchon I, Sauvant P, et al. Ultra-processed foods: how functional is the NOVA system? Eur J Clin Nutr. 2022;76(9):1245-1253. doi:10.1038/s41430-022-01099-1
3. Han Y, Liu H, Li Q, et al. The degree of doneness affected molecular changes and protein digestibility of pork. Front Nutr. 2023;9. doi:10.3389/fnut.2022.1084779
4. European Food Safety Authority. EFSA Explains Risk Assessment : Acrylamide in Food. EFSA; 2015.
5. Sugita K, Yamamoto J, Kaneshima K, et al. Acrylamide in dog food. Fundam Toxicol Sci. 2021;8(2):49-52. doi:10.2131/fts.8.49
6. Šucman E, Veselá H. Determination of acrylamide in dry feedstuff for dogs and cats. Acta Veterinaria Brno. 2013;82(2):203-208. doi:10.2754/avb201382020203