The nutritional requirements of cats & Calculator
Following my article about the supplements that I use in my cats’ diet, I often receive questions such as “How do I know how much iodine my cat needs?”. In this article, I’m going to explain how to calculate the nutritional requirements of your cat and how to interpret them.
This article covers the requirements of adult and healthy cats. The requirements of kittens are different. Some adaptations may be necessary for sick cats, but I won't cover these here since this falls in the scope of veterinary nutrition.
Where do the nutritional requirements come from?
The nutrient requirements that I will use in this article are the ones defined by the NRC for an adult cat. I wrote an article that explains what the NRC is: I recommend that you read it first to have a better understanding. To summarize, the NRC (National Research Council) is a private and non-profit organism that publishes, among other books, the "Nutrient Requirements of Dogs and Cats". This book is an analysis of the existing nutrition studies on cats and dogs. From this analysis, the authors compile the resulting nutrient requirements. These values are then reused and adapted by some organisms (such as the FEDIAF and the AAFCO) that define the nutrient requirements used in the pet food industry.
The latest version of the "Nutrient Requirements of Dogs and Cats" was published in 2006, which means that some of the values may be outdated in light of the most recent nutrition studies. I will highlight these outdated values to the best of my knowledge, whenever needed.
Keep in mind that the nutrient requirements as defined by the NRC aren’t necessarily perfect. They are, however, the best that we have, as they come from an analysis of all the existing studies in nutrition at that time and they are established by experts in the field.
What is a "recommended amount"?
When you look at the requirements for a nutrient you will find several values in the NRC for a given nutrient: the minimum requirements (MR), the adequate intake (AI), the recommended amount (RA), and safe upper limit (SUL). These terms can sound confusing, so here is a quick explanation for each one.
The minimum requirement (MR) is the smallest amount of a bioavailable nutrient that was shown to support a given life stage. The word "bioavailable" is important in that sentence: when the MR is used, you assume that the nutrient in the food is entirely available. This isn’t always the case, in particular in industrial pet food.
The adequate intake (AI) is used when the minimum requirement is not defined, and it’s an amount that is presumed to support a given life stage but we don’t know if it’s a minimum.
The recommended allowance (RA) is the amount of the nutrient which is present in a diet that supports a given life stage. It’s based on the minimum requirement (MR) and includes a safety margin to take into consideration that nutrients may not be perfectly bioavailable. When the minimum requirement is not known, the RA is based on the adequate intake (AI). The RA is the value that is generally used when formulating a diet.
Finally, the safe upper limit (SUL) is the maximum amount of a nutrient that we know is safe for the animal, or at least nontoxic. For most nutrients, a safe upper limit isn’t defined. This doesn’t mean that the nutrient can’t be toxic in high quantities but, rather, that we don’t know what is the safe upper limit.
The different ways to express the nutrient requirements
The nutritional requirements are usually expressed in 3 different ways: keep in mind that they are all equivalent, but some may be more convenient based on your needs.
Based on the dry matter
One way to express a nutritional requirement (which is also the most popular) is to express it on 1 kg of dry matter of the diet. For example, you may have seen that a cat needs 2.9 g of calcium per kg DM (dry matter). This is the amount of needed nutrients when the water is removed from the diet. This is particularly important as different diet types have different water contents. For example, kibble contains around 8% of moisture (so 92% of the diet is dry matter), while in a raw diet the moisture content is around 70%.
This way to express the nutrient is often used as it makes it easy to visualize what is needed when feeding kibble.
However, the NRC also specifies that this recommendation is valid for a diet containing 4000 kcal per kg of DM. So, if the diet contains more or less energy per kg, the nutrient needs to be proportionally adjusted. In fact, as I explained in the article about energy, a cat will instinctively stop eating when it reaches its daily calorie needs. For example, if a diet contains more than 4000 kcal/kg of DM, the cat will likely eat less (grams of) food, so the nutrient needs to be more concentrated in the diet.
This way to express a nutrient requirement is mainly useful for kibble manufacturers, as 4000 kcal per kg of DM is the average calorie density of kibbles.
Based on the energy
The second way to express the nutrient requirement is by 1000 kcal of the diet. As explained before, as a cat will stop eating when it reaches its energy requirement, it makes sense to express the amount of a nutrient based on the energy intake.
You can find the requirements on this website. Raw Fed and Nerdy has a calculator for nutrient requirements based on the calories ingested by your cat.
However, these values have been computed for a cat that has an energy intake as defined by the NRC for a lean cat (100 kcal x Body Weight0.67). For cats that have a much lower energy intake, this way to express the nutrient will underestimate their nutrient needs. This is often the case for indoor and neutered cats as they may eat only 50 to 75 kcal per kg of BW0.67.
This way to express a nutrient requirement is useful when formulating a diet for several cats, as well as for cats eating more calories than the NRC formulations (which is quite uncommon). However, it is less accurate for cats that have a low energy intake.
Based on the (metabolic) weight
Finally, the third way to express nutrient requirements is based on the metabolic weight of the cat. The metabolic weight is the weight of the cat (body weight, or BW) in kg elevated at the power of 0.67 (BW0.67). This is more accurate than using the weight of the cat since the metabolic weight represents the body surface area. This results in a better estimation of the requirements for small or big cats.
As the nutrient requirements depend on the body function, it makes sense that it is based on the weight of the cat in the same way that the caloric requirement is based on the weight of the cat.
However, like for the two other ways to express a nutrient requirement, this one also has a limitation. Expressing nutrient requirements based on the metabolic weight assumes that a cat is lean. An overweight or obese cat has more body fat and requires fewer nutrients. If this is not taken into account, this method of expressing the requirements will result in an overestimation. It may also underestimate the nutrient requirements for a cat eating more than the caloric intake calculated by the NRC (which is uncommon). In both these cases, using the nutrient requirement expressed on the metabolic energy (1000kcal) would be more appropriate.
This way to express a nutrient requirement is useful when formulating a diet for a specific cat, and this is why it’s the one that I will use in my example in this article. It’s also simple to use if you don’t know the calorie intake of your cat.
I wanted to give you an overview of the different ways to express the nutrient requirements so that you won't be surprised if you see them expressed in several ways. Keep in mind that they are all equivalent, but using one or another may be more or less convenient, as it may require some adjustment.
If you are interested in a more in-depth discussion on the different methods, as well as how to adjust them, I strongly recommend this article from Better Cells Nutrition.
Be careful when adding supplements
The rest of the diet
When you use the calculator to determine the amount of supplement that your cat needs for a given nutrient, be mindful that the core of the diet already brings a big part of the recommended amount.
For example, if you want to supplement iron, don’t just supplement the value that you see in the RA. Depending on what you are feeding, maybe 40%, 60%, or even 150% of the RA could be covered by the food. So, before adding a supplement, you need to audit the diet that you are feeding.
To do so, you can use, for example, the spreadsheet of Raw Fed and Nerdy. You can also calculate it yourself using nutritional databases such as the USDA. I will write more in detail about how to calculate the dosage of a supplement in a future article.
Interactions between nutrients
Additionally, these nutrient requirements don’t take into account the different interactions between nutrients. In fact, having too much of one nutrient can reduce the availability of another.
To simplify, here are the most important interactions that you need to pay attention to: the ratio omega-6:omega 3, the ratio calcium:phosphorus, and the ratio zinc:copper.
Here are the recommendations for the ratios as described by the French vet Sébastien Lefebvre in his book “Nutrition Vétérinaire du Chien et du Chat”:
The ratio calcium:phosphorus should be between 1 and 2.
The ratio omega-6:omega 3 should be between 2 and 10.
The ratio zinc:copper should be between 8 and 18.
Recent research
Finally, the data in the calculator is the same as in the NRC 2006 without any modification from myself. Keep in mind that since 2006, new studies on cat nutrition have been published, so the values may not reflect the latest research.
One notable example is the recommended allowance for the iodine which is set at 35 μg per kg of BW0.67. However, a study published in 2009 recommends an allowance of 11.5 μg per kg of BW0.67, which is roughly a third of the recommendation found in the NRC. For me details, read my article on iodine.
Another important example is the requirement in protein: a study published in 2013 has shown that the current minimum requirement and recommended allowance aren’t enough to preserve the lean body mass of a cat. The MR in the NRC is set at 3.97g per kg of BW0.67 while the study recommends 8.1g per kg of BW0.67 (5.2g per kg of BW) which is roughly the double of the NRC recommendation.
I hope this article and, in particular, the calculator will help you to understand your cat's needs. You may have noticed that carbohydrates aren’t present in the calculator: cats indeed don’t have a requirement for carbohydrates.
| Nutrient | Minimum Requirement | Adequate Intake | Recommended Allowance | Safe Upper Limit |
|---|---|---|---|---|
| Protein & Amino acids | ||||
| Protein | 0g | 0g | ||
| Arginine | 0g | 0g | ||
| Histidine | 0g | 0g | ||
| Isoleucine | 0g | 0g | ||
| Methionine | 0g | 0g | ||
| Methionine & Cystine | 0g | 0g | ||
| Leucine | 0g | 0g | ||
| Lysine | 0g | 0g | ||
| Phenylalanine | 0g | 0g | ||
| Phenylalanine & Tyrosine | 0g | 0g | ||
| Threonine | 0g | 0g | ||
| Tryptophan | 0g | 0g | ||
| Valine | 0g | 0g | ||
| Taurine | 0mg | 0mg | ||
| Fat & Fatty Acids | ||||
| Total fat | 0g | 0g | 0g | |
| Linoleic Acid | 0g | 0g | 0g | |
| Arachidonic Acid | 0g | 0g | 0g | |
| Eicosapentaenoic & Docosahexaenoic Acid | 0g | 0g | ||
| Minerals | ||||
| Calcium | 0mg | 0mg | ||
| Phosphorus | 0mg | 0mg | ||
| Magnesium | 0mg | 0mg | ||
| Sodium | 0mg | 0mg | ||
| Potassium | 0mg | 0mg | ||
| Chloride | 0mg | 0mg | ||
| Iron | 0mg | 0mg | ||
| Copper | 0mg | 0mg | ||
| Zinc | 0mg | 0mg | ||
| Manganese | 0mg | 0mg | ||
| Selenium | 0μg | 0μg | ||
| Iodine | 0μg | 0μg | ||
| Vitamins | ||||
| Vitamin A | 0μg retinol | 0μg retinol | 0μg retinol | |
| Cholecaliferol (Vitamin D3) | 0μg | 0μg | 0μg | |
| Vitamin E (alpha-tocopherol) | 0mg | 0mg | ||
| Vitamin K (Menadione) | 0μg | 0μg | ||
| Vitamin B1 (Thiamin) | 0mg | 0mg | ||
| Riboflavin | 0mg | 0mg | ||
| Vitamine B6 (Pyridoxine) | 0mg | 0mg | ||
| Niacin | 0mg | 0mg | ||
| Pantothenic Acid | 0mg | 0mg | ||
| Vitamin B12 (Cobalamin) | 0μg | 0μg | ||
| Folic Acid | 0μg | 0μg | ||
| Biotin | 0μg | 0μg | ||
| Choline | 0mg | 0mg |
Here are some notes on these values from the NRC:
0.02 g arginine should be added for every g of crude protein above 200 g for the RA of arginine
Methionine presumed to be one-half the sum of the requirement for methionine + cystine combined
To maximize black hair color, an equal quantity or greater of tyrosine to that of phenylalanine is required.
The value for taurine is the one for a purified diet (for my detail go read my article dedicated to taurine)
It is advised that eicosapentaenoic acid should not exceed 20% of the total eicosapentaenoic + docosahexaenoic
1 μg retinol = 3.333 IU (international unit) of vitamin A
1 μg cholecalciferol = 40 IU (international unit) of vitamin D3
Higher concentrations of vitamin E are recommended for diets high in poly-unsatured-fatty-acids. 1 IU of vitamin E = 1 mg all-rac-α-tocopheryl acetate.
Except when a fish-based diet is fed, adequate vitamin K is synthesized by intestinal microbes
Except for diets high in raw egg whites or for diets containing antibiotics, biotin is provided by microbial synthesis in the intestine.
Sources
National Research Council. 2006. Nutrient Requirements of Dogs and Cats. Washington, DC: The National Academies Press.
Nutrition Vétérinaire du Chien et du Chat. 2019. Sébastien Lefebvre. Seconde édition
Wedekind KJ, Blumer ME, Huntington CE, Spate V, Morris JS. The feline iodine requirement is lower than the 2006 NRC recommended allowance. J Anim Physiol Anim Nutr (Berl). 2010 Aug 1;94(4):527-39.
Laflamme DP, Hannah SS. Discrepancy between use of lean body mass or nitrogen balance to determine protein requirements for adult cats. J Feline Med Surg. 2013 Aug;15(8):691-7