tabby cat crouching in grass
I used to think that buying pet food was really easy to do. It is - you don't even need to go to a pet store because grocery stores stock plenty of feed, or you can buy online. Unfortunately, pet food isn't actually regulated so what you give your pets isn't necessarily good for them, especially if it's got a low price, and what's sold in stores is generally what's best-known and the most popular (usually due to marketing instead of quality). The truth is that, between vague labeling and economic forces, many brands of pet foods are often the easy choice, but not often the best one - sometimes even those that vets recommend. This is more true of kibble and other dry feed, but also wet food.

My hypothesis is that the commonly held belief - that dry food with carbs in it is bad - is true. It makes sense that animals that don't normally consume carbohydrates in the wild would not benefit, or might even be hurt by, feed containing carbs in it in more than very low amounts. In order to determine the truth, I reviewed the abstracts of 26 scientific articles, and some of the articles as well, but not all were about carbohydrates, and one had abbreviations I didn't understand.
twin cats eating kibble

Too long; didn't read (TL;DR): skip to the bottom ("Conclusion").

What's the Deal?

I recently went to Kroger and Meijer and looked at the dry foods of numerous brands there. What I discovered is that the most famous brands tended to contain a MUCH higher percentage of corn, wheat and other grains and starches. I could not find a brand that met the requirements listed below.

In looking at Aldi wet food, it's more animal by-products. Their dry food also contains a lot of carbs from corn and other sources.

The sad truth is that many pet foods are designed based on considerations other than the long-term health of your animals, such as low cost, growth, color vibrancy, etc.

Nutrition

In cats, the dietary requirements for protein, arginine, taurine, methionine and cystine, arachidonic acid, niacin, pyridoxine, vitamin A and vitamin D are greater than for omnivores due to metabolic differences. For example, a diet deficient in arginine will lead to a severe decrease in appetite coupled with an increased aversion to that food. They prefer foods containing methionine but don't require it, while they avoid food lacking in isoleucine. Kittens will consume foods with excessive amounts of leucine, but cats will continue to eat food deficient in taurine, despite the ability to taste it. In fact, it is possible that cats seek out foods rich in specific amino acids over overall protein content.

In the wild, cats primarily eat small animals up to their own size like mammals, marsupials, reptiles, amphibians, birds, eggs, insects (arthropods and annelids), and even scavenged food (e.g. carrion, human food) and small amounts of plants. However, what animals eat in the wild is heavily influenced by what they most prefer as well as what's available in abundance, as well as the instinctive drive to fulfill their needs for protein, fat, calories, and nutrients. Some studies have shown that cats will continue to hunt their favorite prey until the population of that prey is so low that they have to find another primary prey. In addition, the weather and territory felines live in affects food choices.

Taste

Please note that food exposure in early life has a definite influence on their preferences later. Also, cats prefer a variety of foods rather than the same food every time; this is probably related to their instinctive drive to eat what their bodies need - a single-source diet is likely to be missing certain things. Thus, if you notice your cat's interest in eating waning, try offering it a other types of food.

Cats can't detect sweetness, which puts them at increased risk if fed high amounts of food containing simple sugars. My conclusion is that, because they can't taste sweetness, they don't seek calories from carbohydrate sources. In addition, this "blindness" to sugar causes them to not be susceptible to sugar addiction. Interestingly, they will avoid eating foods containing sucrose, except milk. Cats also do not select food based on saltiness. They are, however, quite sensitive to bitter and sour tastes, which allows them to both identify needed amino acids while avoiding toxins.

Between their instinctive drive for a balanced diet and their taste buds, cats are more interested in nutrients than flavor. Cats usually prefer wet food over dry, possibly because the profile of caloric sources is more similar to the below. Cats prefer salmon over other fish, and prefer fish to all other animal protein sources, with chicken being their second choice. When given a choice of rats and the above, they'll take any of the above first.

In a surprising find, some cats won't hunt rats unless they are quite hungry and seem to prefer dead rats to freshly killed ones. This also adds another theory as to why cats bring home kills and leave them (aside from the "gift for their human(s) theory): that the prey they killed was done out of the hunting instinct rather than a desire for food and/or that the prey was inappropriate for its needs.

Finally, although palatability enhancer will encourage cats to eat, it won't alter the balance their body will strive to achieve nutritionally.

Fillers

Especially for cats where you need to reduce their caloric intake but can't get them to consume smaller amounts of food, undigestible fillers can be a useful solution.

However, some research suggests that they will avoid food with peat, pectin, dried apple, sugar-beet pulp as well as with kaolin or cellulose in it, although another study found that they'd accept small amounts of cellulose in wood meal at 5% or less. They will only accept wheat bran, horn mean, rumen content* and grass meal at 10% of volume, or less, and hydrolized feather meal at 15% or less. Most of the tests of fillers were done by mixing fillers with meat or meat/fat meal, with meat being limited to 100g per serving and meal being unlimited.

Unfortunately, in one study, fillers other than cellulose caused a significantly reduced ability to digest organic materials, including proteins, with rumen content and raw starch being somewhat worse than the other fillers tested.

*Rumen content is what is in a ruminant's rumen (paunch), a part of the digestive system (i.e. grass, leaves, bark, etc.).

Caloric Sources

For cats, because they are "obligate carnivores" as are dogs, ferrets and some other pets, the balance of food sources must be almost entirely from animals. Dr. Pierson (2017) suggested the first column, based on calories. Another source (Verbrugghe and Hesta, 2017) suggests the second set of numbers, which are based on wild cats' diets. A third source (Watson, 2011) provided the 3rd set of numbers, which is based on unspecified cats and showed a caloric balance of 420kJ protein, 280kJ fat and 100kJ carbohydrate. The last column is from a test of different carb-level diets by Salaun, Blanchard, Paih, Roberti & Niceron, 2016.

Source	Pierson	Verbrugghe & Hesta	Watson	Salaun et al
animal (not plant)-based protein	>50%	52%	52%	53%
fat	~20-40%	46%	36%	36%
carbohydrates	1-2%	2% (nitrogen-free)	12%	11%

Dr. Pierson also recommended that food be water-rich (~70%).

Most cats, excepting primarily those who haven't been traumatized or otherwise caused to develop the habit of greedy eating, will eat as needed and in appropriate amounts. If they are given a variety of choices, they tend to instinctively choose to eat a balance of foods that mimics that of cats in the wild. Thus, it is important that you offer them as much variety as possible to ensure their good health. If your cat is a greedy eater, you should seek the help of an expert to retrain your cat.

Carbohydrates

However, although a small number of studies have shown a detrimental relationship between dry foods and health, several studies have been unable to find a strong link between carbohydrates and diabetes mellitus (DM). These studies suggest that complex carbs, like starches and fibers, are a better choice for cats than are simple sugars, and also better than a high-fat diet. Some suggest that cats with a mixed diet of wet and dry food are less likely to develop DM, as well as if your cat eats several small meals instead of a few large ones (the same is true for humans) because blood sugar cannot spike as much from a small meal, unless the food is high in sugar. Other sources claim that a high (over 33%) level of carbs, again especially simple sugars, is bad for feline health, and others claim that the long-term consumption of dry foods leads to digestive and kidney problems, possibly due to the manufacturing process and lack of moisture, but I was unable to find substantive research to support this claim (which doesn't mean it's not true - maybe I didn't use the right keywords). That said, carbs more efficiently meet the energy needs of a cat's muscles and brain, requiring less food be eaten; however, we should remember that a cat that gets too much high-calorie food can have health issues just like humans, such as insulin resistance (if there is a genetic predisposition), diabetes mellitus (DM), lower urinary tract disease, osteoarthritis and skin problems.

Processed carbohydrates in low to low-medium (33% or less) amounts should be fine, although poorly processed or raw carbohydrates may cause gas, diarrhea and bloating. I am somewhat concerned about the long-term effect of high-carb diets on animals, which doesn't seem to have been studied, if the digestive system and gut biome is regularly disturbed by too many carbs in the diet. However, we also need to keep in mind that middle to old age is when cats are more likely to become obese or develop DM, with a definite majority being males, especially if they're neutered; certain breeds are more likely to get one or the other (and obesity increases the risk of DM by a multiple of 4). Indoor and inactive cats are much more at risk, especially if the diet doesn't meet their needs, contains excessive calories or if given inappropriate human food.

Calories, Carbohydrates and Fat

Multiple studies show that carbohydrates are less likely to cause health problems than are inactivity, living indoors (which probably means less activity because of a non-conducive environment and sedentary lifestyle) and high-fat diets, but the ratios above are likely very appropriate for a cat with DM. High-carb, low-protein diets are not recommended and a protein-from-high-fat-content (relative to other parts) diet is also not healthy because a cat will eat to fulfill its protein needs, even if that means consuming more fat than is healthy for it {leading to a significant rise in the plasma triglyceride, FFA, beta-hydroxybutyrate and cholesterol concentration}. Several studies have shown that two much fat in the diet is worse for cats than too many carbs, especially when combined with living indoors, being inactive and having been desexed (i.e. spayed: removal of the ovaries; neutered: removal of the testicles/ovaries) - especially males, and these factors can lead to a higher risk of DM and obesity, especially among certain breeds and especially starting around middle age. Feline intestines have (relative to other animals) a slightly inferior ability to digest carbohydrates compared to other animals. {Enzymatic production of amylase in the intestines; maltase and isomaltase in the pancreas; and maltase and isomaltase, sucrase in the intestines are low, and there is no sucrase (for sucrose) and lactase (for dairy's lactose) in the pancreas, and much more. In addition, there are some deficiencies of glucokinase in the liver.} However, they are sufficiently able to digest carbs.

Interestingly, it is reported that cats will self-limit carbohydrate consumption to about 300kJ/d
(20.5g/d), but will go over normal limits of animal parts and fat to assure a balanced diet.

Fatty acids were also noted in one study to be increasingly difficult to digest as cats age, with saturated fatty acids being the most difficult for young and senior cats.

Risk factors for developing diseases related to food consumption include: high-fat (skin, fat, organs) diets; diets high in saturated fats; low-protein from meat diets; high-byproduct diets; medium-to-high-carb diets; middle-aged or older; male; desexed; certain breeds; genetic abnormalities, living indoors; inactivity; obesity; and human foods.

Pet food packages have a guaranteed analysis (GA) that shows you the percentage of the amount of these four things, as well as certain other things. You can use this as a baseline, as well as look at the ingredients list. Unfortunately, since the vast majority of brands do not tell you the actual ratios on the packaging, you'd have to contact each company and hope that they'd tell you. I'm not saying that manufacturers universally produce foods that are unbalanced nutritionally but, certainly, some are bowing to undereducated consumer trends and budgetary constraints, while others use clever marketing strategies to command a higher price without necessarily being worth it.

My hypothesis was wrong, and I had to rewrite parts of this article to reflect the truth of my research. The myth that cats can't process carbs has been debunked in part: because carbs are okay but simple sugars (glucose, galactose, sucrose, frucose, etc.) and saccharides shouldn't be given to them.

Food Types & Sources

Fish

We know that cats enjoy eating fish, but is it actually good for health? In the wild, cats don't eat much, if any fish, and there may be nutrients absent in fish. Most cats do not naturally have the option to "go fishing" for fish. Thus, it seems that it shouldn't be the sole source of protein in a cat's diet, but inclusion is undoubtedly fine. There wasn't much information specifically about fish in the research I looked at, but a palatability study showed that cats prefer food with fish over all others, thus suggesting that their instinct for a balanced diet is demonstrating that fish are superior.

Large Animals

What about cows and other large animals? Have you ever seen a cat large enough to take down a large animal? I can imagine a cat taking down an immature turkey, but even a pig is too big, unless it's a tiny piglet. If a cat, which is naturally solitary, cannot take it down in the wild, it may be questionable, but it is still a valid protein source. I looked briefly for information and found a study about the palatability of beef vs lamb, but it didn't include other meats. However, the results showed that lamb parts and meat were preferred over beef, except for hearts and livers, which were equally liked from both animals. Testing a porterhouse steak bone on my cat, I noticed that he didn't avidly go after the scraps of meat and gristle on it, in contrast to his love of chicken bones - not much meat and gristle was eaten, and he didn't try to chew the bone.

As for corn-fed beef, it shouldn't even exist because corn isn't the cow's natural diet and results in a less nutritious meat compared to grass-fed, including an excessive amount of omega-6, which is bad for health! For those with ethical concerns, feeding corn to cows often leads to digestive and other problems with E. coli and others. That said, a lot of farm-raised animals, especially when raised by factory farms, are raised on feed that promotes growth instead of health, be it fish, chickens, opossums or other animals, which means that the meat is still a problem. If you can, find sources that use REAL "free-range" animals (as opposed to animals in a big building that acts as the communal cage for hundreds to thousands) and that eat natural food that is appropriate for their species.

Raw

Some people advocate this, while others say it's too dangerous. Some studies claim that raw is easier to digest than cooked products but others claim the opposite. However you have to make sure that the meat is free of bacteria (e.g. Campylobacter, E. coli, Salmonella), fungi and parasites (e.g. Toxoplasmosis gondii, Bartonella henselae), or your pet can potentially get them, which could lead to you getting them through their feces. I have a permanent eye infection that likely came from this very source. Thus, given the risks both to your pets and yourselves, it is best that food given to your pets be cooked to the point that no germs will be left alive.

Animal Meat

A cat's food, wet or dry, should contain at least 50% protein from MEAT, but most brands do NOT tell you what parts of an animal are used. That it says "chicken" or some other animal can means meat and skin, but it doesn't indicate the ratio, which is important because it should be a natural ratio of mostly meat, not mostly the cast-off skin from "skinless, boneless" chicken we buy for ourselves.

Animal By-Products

This is every other part of the prey animal, except some bones, the stomach, intestines and at least some of the fur and feathers. Although animals eat organs, bones, feet, eyes, etc., this shouldn't be the first item listed, especially since you don't know the ratios. If chicken feet are rarely sold for human consumption, you can bet they're in this

Meal

If there is "meal," for example, that means that the manufacturer bought pre-dried and processed animal parts, which means a larger amount (1 truck is the equivalent of 5 trucks of raw animal), and could be the skin and meat, by-products, or both. Since it's pre-processed, it's also less expensive to use. Animal meal isn't, by itself, bad, unless the ratios of meat, skin, fat, bones, organs, etc. are unnatural.

Bone meal is ground-up bones. Cats naturally eat bones, both for calcium and for the nutrients in the marrow, but I'm sure you realize that bone meal shouldn't be a large proportion of a feed.

For a more in-depth look at the use of meat, by-products, and meal, read the Pets Magazine article I listed in the resources.

Moisture in Feed

If you do find a good kibble, make sure to wet it when you serve it as cats normally get most of their water from their food. I find that my cat is more interested in dry food when it's moistened, and definitely prefers wet food. Excessive consumption of dry foods that haven't been moistened can lead to digestive and kidney problems.

Vegetables, Grains, Fruits and Vegetarian/Vegan Feed

No vegetarian/vegan feed! Cats are "obligate carnivores," meaning that they MUST consume meat. This doesn't mean that they are 100% carnivores because they will eat small amounts of green plants in the wild, just like dogs do, and enjoy corn (I only allow mine to chew on discarded corn cobs); however, grains, veggies and fruits should be a relatively part of the recipe. Vegetables should be mostly greens, be pre-cooked because cats don't have the enzymes needed to digest most vegetables, and constitute no more than 5% of the total if your cat has DM.

Vets

Should you ask your vet for advice on what food to feed your pet? Unless that vet has been trained in pet nutrition and has the ability to analyze brands to determine relative quality, your vet may be giving you advice based solely on input from pet food manufacturers. I was unable to find much on 3 different veterinary association websites on feed, and my vet didn't even seem to have anything bad to say about dry food - not even that some brands are more carbs than animal!

I've included an excellent, brief letter (see 1st resource) about dry cat food and its impact on feline health, as well as the role of the veterinarian.

What Should We Do?

So what should us pet owners do? I'm focusing on felines for this article, but I can guarantee you that the problems apply to dogs, ferrets, rabbits, rodents, and even fish! Even live food (or frozen whole animal) are not necessarily a good source of nutrition because they are, all too often, given nutrient-poor, unbalanced feed that keeps them alive and growing without much thought to the nutrition content for your animals that eat them. If the ASPCA and PETA want to help animals, they should be focusing on feed for pets, farm(ed) animals and more! Growth feeds do not produce animals that are anywhere near as nutritionally beneficial to us as wild animals and those fed on proper diets mimicking wild diets of stable, healthy populations!

Unfortunately, I don't have the training to make specific recommendations about what to eat, so I gave the link to Dr. Pierson's recommendations for cats in the resources section below, which is very helpful. I can tell you that:

Make sure that your cat has ample opportunities for exercise and ways in which to burn off calories, and consider slowly reducing the amount of food you give them each time.
Animals need stimulation in their lives, and there are feeding dishes that help provide challenges for them. You can also make sure that they have enough activities through playing with them, as well as giving them the ability to explore (such as by installing tunnels, steps, ladders, shelves, etc.).
Meat should always be listed first on the label.
The best source of carbohydrates for cats is from starch; simple sugars (lactose, galactose, glucose, fructose, etc.) should always be avoided.
If you see by-products listed first and animal names listed somewhere later, then it's inappropriate.
If you see carbohydrate sources or fats in the first 2-3 ingredients, avoid that product. If both of them dominate the top 5, you're best off avoiding it, while more omnivorous animals might be okay.
Cats and some other animals function better on 6 smaller meals a day than 3 larger ones.
If your pet is of a social breed, you should have an appropriate number of them.
Fish should never be fed so much that more than a tiny amount ends up on the bottom of the aquarium. Also, most fish can go for a day or two without food.
Many reptiles and amphibians don't need to eat daily; check with a vet or pet expert. A local herpetological society is probably your best resource.
Some animals have trouble moderating their appetite, but most will eat in moderation in the absence of addictive substances in the food. Carnivorous fish are known to swallow so many prey in rapid succession that the first ones in start coming out the anus completely undigested.
Not all animals actually need to be fed on a daily basis, including some reptiles and fish.
If breaking up feeding times proves to be challenging for you, there are automated, precise feeders for a variety of types of animals, including fish.
Just because a brand of feed is popular or famous doesn't mean it's good for your pets!
If you spay/neuter your pet, keep in mind that some alterations to diet may be necessary for optimum health.

If you want to see an example of very biased marketing on behalf of multiple brands, check out (but don't believe - just use it to help identify brands by their parent companies) Top 15 Pet Food Brands & Treats

Feeding Your Fish (Aside)#

I CAN tell you this when it comes to fish feed - feed used for commercial fish farms doesn't necessarily produce nutritious fish. It'll likely be more focused on increasing growth and size. This often comes at the expense of nutritional value on the plate. I met a university professor in Indonesia who specialized in fish and we discussed the use of feed that is often used there. He explained that it's not nutritionally balanced, and thus has several negative consequences aside from the fish becoming nutritionally inferior to wild fish, including thinner blood, flesh that starts to rot faster, decreased immune system and an off taste. In Indonesia, fish like the Giant Gourami, Catfish, Carp and Tilapia are commonly farm-raised and, most often, they are cooked by frying them because the flavor of fish raised on this inferior feed is muddy unless you fry them or know the right spices to use. So, if you can add some fresh veggies and fruits, even piranhas have been found to eat them when they are available, and a varied diet will produce healthier fish.

Conclusion

The expression "You are what you eat," doesn't just apply to you - it applies to your pets, too.

The myth is false - cats can eat carbohydrates. Complex carbohydrates are okay for cats, as long as the caloric percentage from carbs doesn't exceed about 33%, and simple sugars, especially sucrose (which cats tend to avoid) and saccharides are not used.
A high-protein (~53%, about 6 g of protein/kg body weight/day) diet, from smaller animals and insects is required.
The protein profile should be mostly meat, followed by byproducts (organs), bone, fat and skin, in approximately that order. Excessive amounts of byproducts and fat for protein will be eaten by cats in the absence of sufficient meat, but this will put them at increased risk of illness.
Fat should be limited to about ~36% of diet.
Carbohydrates should be about 11% of the diet, based on discovered preferences of cats when given choices.
In other words, the "ideal" diet (based on scientifically observed cat preferences) seems to be 53% protein, 36% fat and 11% carbs. Starches are best, but not raw starches, nor simple sugars/saccharides. When choosing dry and wet food, or making food at home, be sure to try to achieve this balance.
If the right balance of proteins, fats and carbs is achieved, you will reduce your cat's risk of illness and increase its lifespan.
Exercise and activities that stimulate your feline are important for physical and mental well-being.
The older a cat becomes, the more the digestive system has trouble doing its job.
Cats don't care about/can't taste spicy, sweet or salty flavors, but can detect salty and bitter and while flavor enhancers will improve their appetite, it won't fool their instinctive search for their required nutritional balance.
Felines are not pure carnivores but they must eat meat. Do NOT put them on a vegetarian or vegan diet!
Cooked meat is easier to digest than raw and, if cooked properly, much safer due to the lack of bacteria, fungi, viruses and parasites.
They can only taste sour and bitter, but they eat based primarily on nutrients, not taste.
Felines have olfactory (smell) and gustatory (taste) senses that are highly tuned and help them to make sure they get the right balance of food, if available, which they instinctively seek out by consuming various sources of food.
You should provide a varied diet of wet, dry and home-prepared (preferably cooked) meals for your cat to avoid nutrient shortages.
Loss of appetite is probably because of an imbalanced diet lacking in certain nutrients, such as arginine, if diseases are ruled out. In older kittens, teething can cause temporary decreases in appetite due to pain (as with children). Diarrhea and/or an upset stomach can also impact appetite.
Moisten dry food.

Offer

This article took several days to finish the research for. If you'd like me to research the different brands and find out their relative worth, please support me with an upvote and resteem, and comment that you'd like to know which brands to choose and which to avoid. If enough people will do that for me, then I can continue to do this kind of research. I'll even do it for other kinds of animals, if there's enough interest.

Also, if there are specific brands you want me to be sure to include other than what is typically in grocery stores, let me know.

Resources

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