Just a caveat: make any changes to your cat’s diet slowly and gradually, and if your cat has any health issues, talk to your vet first. I’m not a veterinarian or a vet tech, I’m basing this on a one-year program as a vet assistant (one step down) and on a long history of research due to cats with special needs. I’m hoping this is helpful and to the best of my knowledge it’s accurate, but your mileage may vary.
It should go without saying that diet is immensely important in making sure your cat stays healthy. Poor-quality diet can lead to deficiencies or excesses causing a variety of conditions. Obesity can lead to diabetes and heart problems among other things — a fat cat (or dog, or any other animal!) is not cute.
One factor to consider is how much your cat should be eating.
The kilocalories listed on the cat food bag/box/can are the same as the calories we think of for humans. It should say it has X kilocalories per ounce, cup, or some other measurement.
Approximate recommended (by bodyweight)
|Age||kcal per kg||kcal per lb|
|1 yr+ active||85||35-40|
|1 yr+ inactive||70||32|
If they’re getting less than that, they’ll lose weight. If they’re getting more, they’ll gain weight (obviously). Active cats use more than sedentary cats; young adult cats use more than middle-aged or senior cats; cats with health issues usually have special needs; cats that are outdoors a lot or otherwise exposed to seasonal changes will usually need more in colder temperatures; there are other factors, but they’re all pretty common-sense.
What do you do with this? Brace yourself for a little math, but if you go step by step, it isn’t really all that difficult. Make sure you have your cat’s weight, to start with (weight in kg = weight in lbs divided by 2.2; weight in lbs = weight in kg multiplied by 2.2). Then multiply the weight by the above numbers to find out how many kcal your cat should be getting in a day. For example, a 1.8 kg (4 pound) kitten who is roughly 12 weeks old should be getting 450 kcal per day (1.8 kg x 250 kcal per kg = 450 kcal per day).
If the food is 300 kcal per cup, she should be getting 1.5 cups of food (450 kcal needed / 300 kcal per cup = 1.5 cups).
If it’s 100 kcal per 85g/3oz can (Fancy Feast sized), she should be getting 4.5 cans per day (450 kcal needed / 100 kcal per can = 4.5 cans).
If you want to combine them, then, say, two 3 oz cans of food at 100 kcal each would be 200 kcal of her diet (100 kcal per can * 2 cans = 200 kcal), leaving 250 kcal to be supplied by the dry food, so she’d need 0.85 of a cup of dry food (250 kcal needed / 300 kcal per cup = .833 cups) (that’s slightly less than 7/8ths of a cup).
Another factor to consider is what’s in the food you’re providing.
Just like with human diets, the value of those kcal varies. You can get a thousand calories easily at MacDonalds but they aren’t going to have a lot that you’d want to give a growing kid or that would be healthy maintenance for an adult. Corn and wheat are cheap fillers in cat food, mostly providing carbs, not the kinds of meat-based nutrients that a cat’s body needs.
Cats, unlike dogs or humans, are obligate carnivores: their digestive system is evolved in specific ways to deal with a meat diet exclusively. Cats also need almost twice the protein, on average per weight, that dogs do. As examples, their bodies cannot turn linoleic acid, an omega-6 fatty acid common in some vegetable oils, into arachidonic acid, essential for cell membranes and in the brain; they cannot convert beta-carotene, found in plants, into vitamin A, which is found in animal tissue. They need to get both arachidonic acid and vitamin A directly from meat sources.
A lot of what they need comes from what we consider by-products – internal organs, for example. However, in cheaper foods, ‘byproducts’ can be some pretty vile things (I won’t get into the details here) that are either hard to digest or not from healthy sources, and ‘meat byproducts’ is about as vague as you can get; you could be getting pretty much anything, and the cheaper the food, the less actual useful value there’s likely to be in it.
It is, realistically, a pain in the tail trying to get a fussy cat to eat what you want them to eat instead of what they like the taste of. It’s ALWAYS most important to make sure that a cat is eating SOMETHING. Extended fasting, especially in overweight cats, can lead to liver issues that can be fatal. In underweight cats, well, they just don’t have the resources to go without eating. So ultimately, it’s a hard ideal to try to reach. One of mine will only eat a single flavour of a single brand of wet food and it isn’t a quality I’m happy with, but since I want him getting some kind of wet food, I compromise.
Basically, if you can afford it, I really recommend foods with low or no grains, especially corn and wheat; low or no unspecified byproducts, or at least byproducts from named animals; high-quality digestible meat proteins. They do tend to be more expensive, but there’s a substantial body of evidence that it can prevent (expensive and stressful and possibly terminal) health issues later in life. Many pet stores offer free or inexpensive sample sizes of various foods, so you can find out if your cat is interested without spending a fortune. If you do happen to buy a larger bag and your cat decides not to eat it, check for local feral colonies, they may be happy to accept it as a donation even if it’s open.
Wet foods help supply water, which is something cats do have trouble drinking enough of – their kidneys don’t concentrate it very well, even when healthy. The water does tend to decrease the kcal the cat gets per serving, though, so they have to eat more volume to get equal nutrition. This is a good thing when you’re trying to help a cat lose weight, but not so good with an underweight cat. Any cat that will eat wet food at all, I’d suggest they get it as at least part of their diet.
And, the really obvious stuff: lots of cool fresh water that’s changed at least once a day if not more; change food gradually so there’s no GI upset; make sure the food you’re using says it’s formulated as a complete diet and not as a supplement (unless you are, in fact, using it just as part of the diet, in which case go to it).
Incidentally, I’ve observed, and have talked to others who have observed, that the better quality the food, the less waste the cat passes, because more of it is actually being used instead of just passed through as indigestible.