These days there seems to be a million and one different options of cat food available, all claiming to be the best for your pet. It’s not a matter of just ‘wet’ or ‘dry’ food any more; there’s canned food, dry food, fresh food, frozen food, semi-wet food, single ingredient food, home-made food, raw food… How on earth do you decide? Generally, as long as a couple of key components are included, then it can often come down to a matter of personal choice. One of those to consider is the energy density of the food, but what is it and why does it matter?
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The science
Without getting too technical, energy density is the amount of energy stored by a material per unit volume. In the case of the energy density of food, this is defined as the amount of calories per unit of food, either written in kilocalories (kcal) or kilojoules (kJ), and expressed as kcal or kJ of metabolisable energy (ME) per gram (g) or kilogram (kg) of dry matter (DM). It’s the equivalent of us reading the back of a pack of crisps to look at the kcal/100g.
Cat nutrition requirements
As a general rule of thumb, cats do better with a higher protein/lower carbohydrate diet because they are what is known as obligate carnivores; their bodies are adapted to eat primarily meat. Unlike a lot of other animals, cats are unable to synthesise certain amino acids so require them in their diet. By eating meat, they are able to consume all that they need, including one of the most important amino acids, taurine. Animal protein is also the main source of energy for cats as they are less able to obtain energy from carbohydrate sources, to the extent that their bodies will actually turn to breaking down their own muscle tissue to obtain protein over using any carbohydrate in their diet. While carbohydrate in the diet can be used, it’s critical to make sure that the ratio of the different nutrients is exactly correct.
Just like in people, cats will require different diet compositions at different life stages. For young growing cats, a high protein content is preferable in order to ensure they get all the nutrients required for growth. As they age, these requirements become less, and so the need for high amounts of protein reduces. Up to around a year of age, it is advised that a cat’s diet is comprised of at least 30% protein. For adult cats, this minimum requirement drops to 26%.
Every complete cat food must also contain taurine. Taurine is an amino acid, a compound that acts as a building block for proteins. Cats are unable to synthesise taurine and even when ingested, they cannot retain it so need a consistently replenishing supply. A lack of taurine can have drastic effects including retinal degeneration which can eventually lead to blindness, a type of heart disease usually rare in cats (dilated cardiomyopathy), reproductive failure, gastrointestinal upsets and poor growth rates in kittens.
For these reasons, home-made diets, especially those that lack meat, carry high risks of not providing what a pet cat needs and could potentially lead to harm. If you wish to feed your cat a home-made diet, the advice is to consult a veterinary nutritionist who can tailor-make a diet that would still provide all their requirements.
Too much of a good thing….?
Unfortunately, just like the human population, the feline population’s waistline is enlarging. Currently, it is thought that around 40-50% of cats in the UK are overweight or obese. The definition of an overweight cat is one that is 10-20% heavier than their ideal weight; an obese cat is one that is more than 20% heaver. The risk of obesity can start as a kitten – excessive energy intake (in other words, calories) during the growing phase of life will increase the number of fat cells created. These fat calls cannot be removed therefore as the animal ages, they will be more prone to gaining weight. Surplus weight as an adult has numerous health implications, not just around joint health and urinary issues, but in cats, being overweight increases the likelihood of diabetes.
So, in short, you need to feed your cat a food that is energy dense enough to provide them with what they need nutritionally but not too much to make them overweight!
Getting the balance right
In 2020, the World Small Animal Veterinary Association (WSAVA) published a guide to the calorie need for an average healthy adult cat. In order to calculate this, they used the equation
100 kcal x BWkg0.67
or for those that tend to be prone to obesity
130 kcal x BWkg0.4
Following this, a 3kg cat would need 200-210 kcal per day, a 4kg cat 225-250 kcal per day, a 5kg cat 250-290 kcal per day, and a 6kg cat 265-330 kcal per day (the lower end of the range being for those cats prone to obesity).
So what does that mean?
Commercial cat foods can be broadly divided into ‘wet’ or dry’ diets. Typically, dry food will have a much higher calorie density that wet food, with one cup of dry food containing around 300-500 kcal compared to one can of wet food with around 150-200 kcal. Therefore, value-wise owners will get more calories for their money if they choose to feed dry food. However, this can lead to overfeeding, especially if fed ad-lib, and may mean some cats don’t take in enough water to maintain an adequate hydration. Wet food diets will help massively with water intake, which is especially vital for those cats that can suffer with urinary conditions, but they are not typically energy dense, meaning an owner may have to feed more to ensure their cat achieves appropriate nutrition. In fact, it has also been shown that if water is added to dry food, therefore diluting and reducing the dietary energy density, cats will not actually increase their energy intake (ie eat more) to make up for this and therefore either gain less weight, or actually lose weight.
The relationship between the energy density of a food and its nutrient content is a close one. In theory, cats will stop eating when they have reached their daily energy requirement so it is vital that that amount of food contains all the nutrients they need. But the nutrition label may not be as clear as it first seems.
This can be easier to explain with an example –
Food A states that it contains 40% protein and provides 400 kcal/100g
Food B states that it contains 35% protein and provides 330 kcal/100g
At first glance, it looks like food A contains more protein than food B. However, when the difference in kcal/100g is taken into account, it becomes apparent that food B contains more protein per 1000 kcal:
Food A = 400 kcal/100g = 1000 kcal/250g; while 40% of 250g = 100g protein per 1000 kcal
Food B = 330 kcal/100g = 1000 kcal/300g; while 35% of 300g = 105g protein per 1000 kcal
In conclusion, the energy density of a cat food is vital for maintaining optimum weight and health. It will have a direct impact on the quantity of food a cat will eat and is directly linked to the amount of nutrients such as taurine they will take on board. It is worth ensuring that cats are provided with a food that is calculated to have the correct energy density for their life stage and activity level in order to also discourage potential overfeeding and subsequent obesity.
Further reading and references:
FEDIAF Updated Nutritional Guidelines 2022
Alexander JE, Colyer A, Morris PJ. The effect of reducing dietary energy density via the addition of water to a dry diet, on body weight, energy intake and physical activity in adult neutered cats. J Nutr Sci. 2014 Sep 25;3:e21. doi: 10.1017/jns.2014.22. PMID: 26101590; PMCID: PMC4473177.
Calorie needs of healthy adult cats – WSAVA (2020)
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