Cats and Carbohydrates: Is Dry Cat Food Bad for Cats?
- Rachel
- Mar 28
- 17 min read
Updated: Sep 15
*As an Amazon Associate I earn from qualifying purchases at no cost to you.
Are carbs good or bad for cats? Do carbs cause obesity and diabetes? Can cats eat grains and veggies or are they just cheap fillers?
The old carbs debate is getting kind of.... old.... but pet food manufacturers and veterinary nutritionists are no closer to reaching an agreement. Why?
Research into feline nutritional needs aren't as extensively researched as the domestic dog, which has been around for an estimated 30,000 years longer than cats and represent a larger share of the market. So too, cats are obligate carnivores with unique dietary requirements - this doesn't mean they can only eat meat, but they do need meat to survive.
Many studies are carried out or financed by pet food companies themselves, plus they own a large portion of the veterinary industry. Based on these factors, I wonder how transparent they are in relation to the answers they provide to the public?
Nevertheless, there seems to be a lot of focus on carbohydrate digestibility and metabolism rather than the actual benefits. Not to mention the long-term health effects, which is what we'll be covering in this article.
Take a deeper dive into commercial pet foods and the companies behind them in this eye-opening post: The Truth About Commercial Cat Food: What Really Goes into Your Pet's Food?
In this article:
Types of Carbohydrates
While the carbohydrate debate is ongoing, one thing everyone can agree on is that there are "good" carbs and "bad" carbs.
Sugars (sucrose, fructose, glucose) are known as simple carbohydrates, such as those found in fruit. Cats struggle to digest sugars, therefore they're considered to hold no biological value. Contrary to popular belief, cats are lactose intolerant, which is why you shouldn't give them milk.
Fibre, an indigestible complex carbohydrate, can aid digestive transit and the excretion of hairballs. In fact, you can get specialist food with added fibre for this very reason. Wild cats would get fibre from the bones, fur and partially digested plant matter from the stomachs of their prey.
Starch is another complex carbohydrate that the body converts into glucose to provide energy to the cells. It's easier to digest than sugar and can be found in grains and vegetables. Starch is necessary in dry foods as it acts as the "glue" that holds the ingredients together.
It gets a little more complicated because starch can be broken down further into types that are beneficial for cats and those that are less so. Regardless of ingredients, the key word is "moderation".
Carbohydrates and Energy
“Carbohydrates are one of the three categories of macronutrients, alongside fats and protein, included in diets for animals and act as the main energy source for pets.”
We already know that isn't strictly true, given that cats would be getting as little as 1-2% carbohydrates from prey in the wild. In fact, fat provides twice as much energy per gram as carbohydrates and protein, hence why it makes up a fair chunk of their natural diet.
The main purpose of starch, as quoted by pet food companies, is to provide energy in the form of glucose. Yet, cats are very special in the sense that they can synthesise their own glucose in the liver - given enough protein, of course.
Premium dry cat food with 80% fresh meat and offal. Kibble is gently air-dried to preserve nutrients. The grain-free recipe contains a small amount of fruit and vegetables, with no preservatives, colourings or flavourings.
Some would argue that the addition of carbohydrates allows cats to conserve protein for other vital functions, but it still seems unnecessary when they're efficient at utilising fat as one of their primary energy sources.
This is assuming that a natural, prey-model diet is the healthiest option for cats - which some vehemently dispute. The domestic cat has adapted in many ways, but their physiology remains the same. No amount of studies have proven otherwise, as we explore in the next example.
Grains and Veggies
“Grains, commonly referred to as ‘cereal grains’ are the edible seeds of specific grasses and include wheat, corn, rice, barley, oats and rye. To expose the most nutritious, digestible elements of grains or cereals, the raw ingredient is ground and heated in the manufacturing process. This removes the less digestible outer shell and leaves the nutrients that cats and dogs need.”
This is a perfect example of refined grains that have been processed to remove most of the fibre, vitamins and minerals. Pet food companies use them because they're more easily digested by cats, which further emphasises that they have a limited ability to digest carbohydrates.
Unrefined grains - otherwise known as whole grains - are those that haven't been processed or stripped of the nutritious parts, which you've likely seen advertised as a healthier option. Whole grains may provide more nutrients and fibre but are generally less digestible.
The main reason for this is due to a low activity of the enzymes, amylase and glucokinase, that cats use to break down carbohydrates. Cats have a short digestive tract that's designed to process animal protein quickly and efficiently.
Another factor to consider is the processing methods, themselves. While refined carbs are better digested, it involves heating ingredients at high temperatures. This can be problematic for a number of reasons:
Degradation of those "high-quality" nutrients, hence the mass supplementation used in commercial foods. This method of processing also helps to prolong shelf life.
Heating fats and proteins together with sugar produces compounds known as AGE's (advanced glycation end products) that can cause oxidative stress. This damages the cells and tissues, leading to chronic inflammation and lifelong diseases. The heating of seed oils, which are high in polyunsaturated fats, has a similar effect.
All things considered, it would seem as though unrefined grains are both a healthier and safer option.
Carbohydrate Digestibility
Not all studies on carbohydrate digestibility disclose which processing methods are being used or whether they are, in fact, feeding test cats the same food that they're putting on the shelves.
In Royal Canin's digestibility chart below, we can see that they're using dehydrated meat and meat meal as a comparison against wheat gluten and soy, neither of which replicate a cat's natural diet. As both are heavily processed, it's simply the worst of two evils.
These results don't mean that plant proteins are more digestible than animal protein. It shows that processed plant protein is between 3-11% more digestible than processed animal protein in this particular study.
As mentioned, a natural diet would consist of fibre from prey animals to aid digestion, which doesn't seem to be mentioned in this study, making it an unfair comparison. More to the point, we have zero information about how many cats were tested or the age, breed and health status of each cat involved.
In fact, carbohydrate studies have been criticised for deficiencies in the methods used, with small sample sizes and reliance on pet owners' observations on health and body condition. The duration of studies is important as it can take a long time to see the effects of nutritional deficiencies and accompanying health conditions.
Next, we'll take a closer look at some of these carbohydrates and why they may not be the best for cats, regardless of digestibility.
Dry "Kibble" Cat Food
Dry food has a much higher carbohydrate content than wet food at around 30-40% - not that you'll find this information on the packaging. Since cats don't need carbohydrates in their diet, there are no minimum guidelines, which means there's no legal requirement for them to appear on the label. Contradictory or what?
Psst, you can find out everything you need to know about calculating carbohydrates in this step-by-step guide: How to Calculate Carbohydrates in Cat Food and Understanding Dry Matter Basis
Protein can be as low as 26% according to pet food regulations set by the FEDIAF, which is just enough to maintain basic bodily functions. This is less than half of what cats would be getting in the wild, so while it may seem as though your kitty is getting by just fine on commercial food, that doesn't mean it's thriving as much as it could be - or that it won't have a shortened lifespan due to years of unseen damage.
Even worse, it's not always specified how much protein comes from animals as opposed to plants. These numbers speak to the excessive use of carbohydrates in pet food.
Dry food is processed using heat pressure, whereby fat and moisture are extracted from the dough that makes up kibble. Remember, fat is a source of energy so it has to be replaced with carbohydrates. Additionally, a layer of fat may be sprayed over the kibble pieces, along with preservatives and flavour enhancers to improve palpability.
If you have a kibble addicted kitty, this is probably a huge reason as to why! More about how dry pet food is made can be found on the FEDIAF website.
The fat sources used in commercial pet foods are vaguely mentioned, if at all. As with protein, we often have no way of knowing whether they're animal or plant based. Vegetable oil is commonly used for its omega-3 fatty acids, but cats are unable to convert the omega-3 found in plant sources to the usable form found in animal sources (DHA).
Let's look at the ingredients from the Royal Canin digestibility chart.
Soy
Like all legumes, seeds and grains, soy contains phytic acid which may impair nutrient intake and block the enzymes needed to digest protein, leading to potential liver damage.
Another disease that's thought to be related to soybean is hyperthyroidism, which causes an increase in a cat's metabolic rate. Symptoms include increased appetite, weight loss and restlessness. Hyperthyroidism is the most common endocrine disease of cats in the USA, and while the exact cause is unknown, evidence from studies suggests that diet plays an important role.
Wheat Gluten and Corn Gluten
Gluten is a protein found in certain grains that bumps up the overall protein content of food. Whichever type of grain is being used, there's no excuse for them to appear before animal protein on a cat food label. Ingredients are listed in descending order of weight, and first place should always go to meat.
Another point to note is that corn has been linked to inflammation in the bladder and urinary tract, also known as cystitis. While there are many non-dietary causes of feline lower urinary tract disease, studies show that the high cereal content in pet food is a contributing factor for cats and dogs developing bladder or "struvite" stones.
Grain-Free Diets
Based on all of the information above, it's no surprise that many opt for a grain-free diet under the assumption it's healthier. However, "grain free" doesn't necessarily mean "carbohydrate free". The grains used to bulk out cat food have to be replaced - and not with animal protein. Instead, the food comprises of vegetables such as potatoes, carrots and peas; lentils and berries. This means they can contain as much, if not more carbs than grains.
Most veterinary nutritionists argue that grain-free diets are little more than a marketing tactic, but perhaps the most significant benefit is avoiding those dietary allergens. Wheat, corn, gluten and soy are common culprits; although the biggest factors influencing digestibility are more likely related to ingredient quality and processing methods.
Other Health Conditions
Chronic Kidney Disease
Some health conditions, such as chronic kidney disease, require low-protein diets to limit the amount of work the kidneys have to do, in which case carbohydrates are necessary. Vets may prescribe a specialist renal diet, while some experts suggest feeding a higher quality animal protein to compensate for the reduced amount.
It's also important to feed cats wet food, as hydration is essential for proper kidney function. Kibble isn't a direct cause of kidney disease, but it can contribute to conditions that increase the risk.
Dehydration
Inadequate water intake can weaken the immune system and increase susceptibility to dietary allergens and digestive problems. As mentioned, UTI's and bladder stones are common in male cats, but there's another reason why kibble may not be the best choice.
Carbohydrates are alkaline which creates a perfect environment for struvite stones to form, whereas meat is acidic. If, like me, you have a kitty on a urinary diet, you may know that food is designed to be more acidic in order to dissolve struvites!
Periodontal Disease
Pet food companies claim that the abrasive surface of kibble helps with dental hygiene, but dry food contains no moisture and is more likely to get stuck between the teeth, causing a build-up of plaque and tartar. When you consider the difference between eating a rare steak and a digestive biscuit, it's not hard to see which is more likely.
Irritable Bowel Syndrome
IBS and IBD (irritable bowel disorder) can be related to food that's hard to digest, although there are many other causes. It's important to keep a record of symptoms so your vet can perform the necessary tests to make an accurate diagnosis. Sometimes the cause is unknown, so changing a cat's diet (under the guidance of a vet or veterinary nutritionist) may be a good option.
Impaired Protein Absorption
High amounts of carbohydrates causes food to move through the digestive tract faster than normal, decreasing protein digestibility. Furthermore, refined carbohydrates feed the "bad" intestinal bacteria, which creates an overgrowth in the colon. This bacteria breaks down dietary protein, leading to the production of ammonia which puts pressure on the liver to eliminate.
In relation to intestinal bacteria, we should talk about the stinky poops that cats are notorious for. Contrary to what you might think, this isn't normal and can be due to the overpopulation of bad bugs diminishing the good bugs' ability to survive. The result being flatulence, cramping, vomiting and diarrhoea - which over time can lead to inflammatory bowel disease and other conditions.
Obesity and Diabetes
Obesity is often associated with carbohydrates, yet pet food companies state that these conditions are more likely a result of inactivity or overfeeding. There's an element of truth here, but it could be argued that low energy levels are a result of low-quality food - at least in part.
The consumption of glucose from carbohydrates leads to a spike in blood sugar, which in turn causes high insulin levels - more than the pancreas (the insulin-producing organ) can handle. This extra pressure on the pancreas can lead to degenerative conditions like diabetes over time, which is precisely the issue I raised at the beginning of this article.
Furthermore, the overconsumption of carbohydrates causes fat cells to convert glucose into fat and store it for later use, eventually leading to weight gain. Conversely, low insulin levels signal fat to be taken out of storage and used as energy, the result being that reducing carbohydrates has shown to lose weight in both animals and humans.
Some evidence suggests that carbohydrates aren't a risk factor for cats developing diabetes, but how are we to know whether a cat is diabetic from the offset? Surely, it'd be more viable to study the effects that a natural diet has on diabetic cats to see if the condition is reversed.
When considering the different types of simple and complex carbohydrates, it can be helpful to know their effects on blood glucose as not all will be the same. Starches with a high glycaemic index raise blood sugars quickly and are considered to be even worse than sugar!
Potatoes, which are found in a lot of grain-free pet foods, and refined grains are examples of starches with a high GI. Low-GI food, such as whole grains and legumes, are digested slower and result in a smaller increase in sugar, as well as keeping cats feeling "fuller" for longer. Yet we know that whole grains come with their own set of problems.
Summary
So, the ultimate question is: do grains and fillers deserve their bad rep?
It's fair to say that carbohydrates can provide a source of energy and fibre in moderation; however, this is nothing that can't be offered by a prey-model diet that doesn't need to be processed or contain a bunch of harmful ingredients.
Prey-model diets refer to fresh food consisting of 100% animal protein including meat, muscle tissue, organs and bone. There are, as of now, a limited amount of fresh pet food companies that cater to felines, which is just as well because we can't all be board-certified nutritionists!
The biggest issue for most is budget, as meat is far more costly than plants. For a lot of pet parents, the commercial option is affordable and easily attainable. While it's not perfect, wet food is much closer to what cats should be eating, with high moisture and protein levels; and usually a small amount of carbohydrates. Once cats start eating kibble, it can be difficult to transition them to anything else.
Related post: How to Change a Cat's Food with 10 Tasty Tips
Finally, let's go over some tips for selecting the safest, most species-appropriate food that your budget allows.
Helpful Tips
As we know, the most common grains in cat food are wheat and corn. Unless specifically labelled as whole grain, they're likely to be refined. Either way, it's recommended to avoid foods that contain these ingredients, along with soy and gluten, due to the issues mentioned in this article.
Some unrefined grains that veterinary nutritionists approve of include:
Brown rice (as opposed to refined white rice).
Whole grain oats.
Whole pearled barley.
This list isn't extensive but already rules out a lot of cheaper food on the shelves. You may be wondering what the heck you should be feeding your cat and, unfortunately, there's no simple or straightforward answer.
If your cat is able to digest whole grains, we know they're generally safer and more nutritious than refined grains in small amounts. It always concerns me when the ingredient list on pet food is as long as a child's Christmas list, especially when there are more plant based than animal based.
Grain-free diets rely on vegetables as supplemental protein, and we know that potatoes have a high glycaemic index. Sweet potatoes are slightly better, or you can look for lower GI ingredients such as broccoli, cauliflower, carrots and spinach. Peas are also common, but make sure pea protein isn't a main ingredient.
A high-quality recipe should be made with a named source of animal protein (poultry, beef, fish) as the primary ingredient. Animal fats are just as important and further reduce the need for plant-based products. Look for chicken fat or salmon oil as a source of omega-3 fatty acids.
Below are some examples of grains and vegetables used in commercial cat foods.
*Carbohydrate contents are estimated based on calculations from the crude amount of protein, fat, fibre, ash and moisture.
Ingredients: Fresh chicken (65%), chicken liver (5%), potato (21%), egg, chicken gravy, flaxseed, cellulose, minerals, prebiotic (fructoligosaccharides 0.7g/kg), Italian cheese, seaweed, carrots (0.02%), cranberries, bilberries, parsley (0.02%), fenugreek seeds. |
Analytical Constituents: Protein: 27% Fat: 17% Fibre: 3% |
Lily's Kitchen is a great example of what we want to see on a pet food label, with fresh chicken and chicken liver as the first ingredients, and at a whopping 70%.
The carb-loaded potato comes in at number three (21%) with a small amount of herbs, fruit and vegetables to provide fibres and vitamins. The recipe does contain cheese, which isn't great for our lactose-intolerant cats; and cellulose which they struggle to break down.
Lily's Kitchen comes with a high price tag due to the fresh meat content, which is rare to see in dry foods. Yet there's a catch: if we look at the guaranteed analysis, the overall protein content is only 27% (of which at least 70% is animal based). This is an important factor to consider when reading a cat food label.
Carbohydrates are around 36-38% but the high meat content makes it a good trade off - if you can afford it!
Ingredients: Cereals, meat and animal by-products (including 4% chicken in the light brown kibbles*), oils and fats, vegetable by-products, minerals, vegetable protein extracts, various sugars, vegetables (including 0.5% dried carrots, equivalent to 4% carrots, in the orange kibbles and 1% dried peas, equivalent to 4% peas, in the green kibbles*). |
Analytical Constituents: Protein: 30% Fat: 12.4% Fibre 1.8% |
Whiskas is pretty bog-standard but makes a great comparison to Lily's Kitchen in terms of transparency. The first ingredient is cereal - not meat - so I'd avoid it straight away. None of the animal protein is named, apart from a measly 4% chicken (which only applies to the light brown kibbles). This is followed by more unspecified oils, fats and vegetable by-products.
While the overall protein level in the guaranteed analysis is higher than Lily's Kitchen (30%) there's no way of knowing how much is animal based vs grains and vegetables, let alone what those mysterious "by-products" are.
Carbohydrates are an estimated 37-40% but, again, we're left guessing what that actually consists of. Given the low fibre content, they're clearly poor quality.
Ingredients: Chicken (17%) (including bone, meat, skin), dried poultry protein, wheat (16%), corn, soya meal, wheat gluten, animal fat, corn protein meal, dried chicory root (2%), corn grits, minerals, digest (with added heat-treated Lactobacillus Delbrueckii and Fermentum powder 0.025%), yeasts. |
Analytical Constituents: Protein: 34% Fat: 14% Fibre: 2.5% |
Purina has a wide range of products that cater for all budgets and dietary needs, including specific health conditions. It places emphasis on its high-quality ingredients and is considered a mid to premium brand, which makes this product all the more disappointing.
We get off to a good start with 17% chicken (bone, meat and skin) and dried poultry protein; however, this is succeeded by a string of wheat, corn, soy and gluten - everything we don't want to see! Considering the price tag, there are much better ingredients that could have been used.
The 34% protein content and animal fat is a plus, and although it has an equal amount of carbohydrates at 34%, this is about average for dry food.
Ingredients: Dried chicken and turkey (38%, of which 23% chicken, a natural source of taurine), maize, fresh chicken (10%), millet, pork fat, dried sugar beet pulp (1.6%), chicken sauce, fructo-oligosaccharides (0.67%), fish oil, potassium chloride. |
Analytical Constituents: Protein: 35% Fat: 14% Fibre: 1.9% |
IAMS is more budget friendly than Purina ONE, yet this product only contains two grains - maize and millet - and a small amount of beet pulp. It's a shame to see maize (corn) so high up on the ingredient list, but at least we have dried chicken and turkey in prime place. It also includes 10% fresh chicken, pork fat and fish oil.
The dried animal protein may not be as high quality as Purina but there's a decent amount, and the overall protein content (35%) and carbohydrates (34.4%) are almost the same.
Ingredients: Chicken, chicken liver, brown rice, tomato, pumpkin, water, vitamins and minerals. |
Analytical Constituents: Protein: 9.5% Oils and fats: 2% Fibre: 0.2% Moisture: 82% |
Finally, let's look at a can of premium - or pricey - wet food. On first impression, I love the short ingredient list and chicken/chicken liver as the first and only sources of animal protein. This is followed by brown rice, low-GI tomato and pumpkin.
You'll notice that there's an extra line for moisture in the analytical constituents, which makes the protein, fat and fibre levels look miniscule. Comparing wet and dry food is like apples and oranges, so we have to remove the water content for a closer comparison.
After calculations, it looks more like this:
Protein: 52.78%
Oils and fats: 11.11%
Fibre: 1.11%
Moisture: 0
Carbohydrates: 26.67%
The protein level is much closer to a cat's natural diet where they'd be getting around 55%, but still higher in carbohydrates (26.67%) than I'd like to see - most wet foods contain an average of 5-15%. This could be due to the inclusion of vegetables.
However, the added value of quality animal protein, along with gentle processing methods and no additives or preservatives - all of which can degrade the quality of wet food - is better than opting for crappy ingredients just for a lower carbohydrate content.
This is why it's so important to research brands and individual products to inform yourself of how ingredients are sourced and processed. Of course, it's not all about ingredients - there's a whole other section that lists all of the additives such as vitamins, minerals and preservatives used.
Since food should be formulated according to FEDIAF standards (or AAFCO in the USA) you can rest assured that it's nutritionally balanced - at least, enough to sustain your cat which is a small comfort. There are pros and cons to everything, hence why a varied diet is best, as well as monitoring what any individual cat best tolerates.
If you feed a quality food that's a little carb-heavy one week, choose a lower carb food the next week while sticking to the rule of minimal grains, high animal protein and animal fats. If you have a kitty that's prone to obesity, a grain-inclusive diet may be better than one without, given what we know about vegetables.
Other circumstances where grains and vegetables may be forgivable is with specialist or prescription diets that have a slightly different nutritional balance to normal food. This could apply to health conditions, life-stages and other factors. For example, foods tailored to indoor cats are designed with lower calories, higher fibre and urinary tract health in mind.
If your budget doesn't stretch to a fresh food diet, there's nothing wrong with supplementing commercial food with a homemade recipe, as long as it's formulated by a veterinary nutritionist. You can choose your own vegetables and/or grains according to those "good" starches we spoke about - or even better, stick to 100% animal products and supplements.
Have you tried a grain-free diet? Do you have any great low-carb products to recommend? Are you thinking about transitioning your cat to fresh food? Share your opinions and experiences in the comments.
Comments