Surely if it’s complete and balanced, mixing two different diets shouldn’t matter, right?
I see a lot of pet owners struggle with this concept, that if feeding two diets from different brands, at any ratio, it won’t matter because the diets are complete and therefore you won’t have nutritional deficiencies or excesses.
Well, let’s test this theory, with some simple maths. But first;
What does complete and balanced mean?
A diet that is complete and balanced means it contains all the necessary nutrients in the right amounts and ratios necessary, based on the pet’s daily intake.
Diets can be complete and balanced based on two different sets of nutritional requirements – AAFCO or FEDIAF. It depends where the product is manufactured or formulated, so most diets in the US will follow AAFCO while products manufactured in the EU will use FEDIAF.
Now why is that important? They have different values. These two sets of requirements vary, AAFCO has mins and maxes of most nutrients, whereas FEDIAF actually has much narrower ranges or more specific pinpoint values for nutrients based on the National Research Council’s values (NRC).
So while both AAFCO and FEDIAF diets are complete and balanced, those values will look completely different to each other. While they are both balanced, the values are not identical.
But what about two diets using the same model?
Even two AAFCO or two FEDIAF diets will not be the same, because we are modulating the nutrient levels within the allowable range to create a unique formulation in every diet. Because nutrient values exist on a scale or range, no two diets will ever be the same even if they use the same nutrient requirements whether that is AAFCO or FEDIAF – a different diet is, in fact, different.
Nutrients also operate based on ratios – they are not considered in isolation. So when you split a diet 50:50, that ratio of nutrients is no longer the same. For example, calcium levels need to be increased when zinc is increased, but when zinc is increased, copper absorption decreases, so this level needs to also be adjusted.
So when you mix two diets, let’s say they are both adult maintenance diets, they will be balanced in relation to themselves – not in combination with other foods because the formulators cannot take into account what you might add on top. So unless you are mixing two IDENTICAL diets (what would be the point), then you are upsetting the ratio of nutrients.
Why is this a problem?
So, when you mix two diets it has a completely unexpected result, as we are creating new gaps and holes in the overall diet that could potentially affect the pet’s health, as the ratios of these nutrients are no longer controlled when the diet is mixed and the diets have never been tested when combined.
But the ingredients are identical, so why aren’t the diets the same?
It’s also worth mentioning that a similar effect described above can occur with certain ingredients – for example high levels of fibre can block the absorption of some nutrients, or certain combinations of ingredients can be a problem as they don’t play nice together (see Diet Associated DCM).
When you mix eggs, milk, flour and water – what do you get? It totally depends. While the ingredients are the same, the end product depends on the amounts of each ingredient.
I see this argument quite often with prescription or therapeutic diets – how can they possibly be able to manage disease or medicate a pet when the diet uses the same ingredients as regular pet food?
At the end of the day, your pet still needs to eat and their diet should resemble food. But the nutrient values are what actually impacts disease. For example, while an adult food and a renal food use similar ingredients, what makes the renal food “therapeutic” is that it has lower levels of phosphorus and protein, higher levels of essential fatty acids and oils, slightly increased levels of digestible carbohydrates as the main energy source, adjusted pH levels to produce an alkaline environment, etc. For more on this topic, see my post about this here.
What if I mix wet and dry from different brands?
The difference between wet and dry diets is even more stark – unless you are feeding the same diet in its wet and dry form, the values between different diets and different brands will be worlds apart. It also makes it really hard to compare unless you convert everything to dry matter.
Always use the associated wet and dry products from the same brand and line of food you’ve chosen, and check with the manufacturer if the diet you want to mix with is compatible (some dry foods can be fed alongside a number of wet foods within the same brand, but only the manufacturer can advise which ones are suitable).
The same dry or wet food that comes in multiple flavours, textures or varieties for example is generally fine to mix as they use the same formulation just in a slightly different format or flavour. But again, it’s always best practice to double check with the manufacturer before mixing.
Is there any other reasons I shouldn’t mix and match diets or brands?
Logic tells us most pet food manufacturers aren’t testing their diets when combined with other pet food formulations – only their own brand of foods or those designed to be fed in combination. So, in reality we don’t actually know what the potential implications of combining diets could be, but when we apply formulating expertise (like above) we can look at the potential issues we could run into if we mix and match formulas.
The other reason I recommend steering clear of this practice is the calorie density; every diet will be different whether that’s between kibble diets, kibble and wet, or different types of pet foods. Not only can this lead to over or under feeding, because the combination of calories can be hard to manage, and it can also impact the nutritional profile of the diet;
Often some nutrients are listed on a per energy basis (per 1000kcal), which means if the pet isn’t fed the right amount of the food in question, they won’t be meeting their needs for that specific nutrient. It’s also for this reason we don’t recommend pet owners heavily restrict food intake to induce weight loss in overweight pets – not only is it ineffective, it’s also potentially damaging nutritionally.
Again, when we look at prescription diets we need to remember that each brand has its own philosophy in managing specific disease states, so not only will the nutrient levels between diets differ, they may be incompatible due to the inclusion of certain ingredients or the way in which the diet works. The most common reason prescription diets fail is because of mixing brands or adding toppers/treats to the diet which dilutes the benefits of the food.
So what should I do?
If you want to mix feed, I recommend sticking with the one diet/brand and following the manufacturer’s guidelines. If the diet you are feeding comes in a wet and dry format, you can absolutely mix feed these diets – even better if the same wet food comes in multiple textures (loaf, mousse, gravy, jelly, stew etc) or different protein sources/flavours (chicken, beef, lamb, fish, etc). If you aren’t sure which wet food is suitable to match your dry food, ask the manufacturer or check the feeding guidelines.
If adding toppers or treats, as always stick to the 10% rule – do not exceed 10% of the pet’s daily caloric intake with treats. If you aren’t sure how to work this out, I recommend using the PNA Calorie Calculator which makes it super simple to work out.
References
Nutritional Guidelines
Remillard, R. L., & Crane, S. W. (2010). Making pet foods at home. Small animal clinical nutrition, 207-223.
Koppel, K., Monti, M., Gibson, M., Alavi, S., Donfrancesco, B. D., & Carciofi, A. C. (2015). The effects of fiber inclusion on pet food sensory characteristics and palatability. Animals, 5(1), 110-125.
National Research Council, Division on Earth, Life Studies, Committee on Animal Nutrition, Subcommittee on Dog, & Cat Nutrition. (2006). Nutrient requirements of dogs and cats. National Academies Press.
Gagné, J. W., Wakshlag, J. J., Center, S. A., Rutzke, M. A., & Glahn, R. P. (2013). Evaluation of calcium, phosphorus, and selected trace mineral status in commercially available dry foods formulated for dogs. Journal of the American Veterinary Medical Association, 243(5), 658-666. Retrieved Jun 9, 2024, from https://doi.org/10.2460/javma.243.5.658
You must be logged in to post a comment.