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Upon the recent blood test, my cat's blood glucose is off the chart and I suspect the added sugar to my cat food is the culprit. He is only 6 years old.

Out of curiosity, I checked some popular cat foods like Whiskas and Purina One which I regularly use to feed my cat. To my surprise, they all have sugar as ingredient. Contrary to other ingredients, the quantity of sugar has not been mentioned on either of the labels. Smells really fishy!

Purina states that:

Sugars in moderation can actually serve important functions in pet foods. Small amounts of sugars in pet foods can provide a source of energy, improve palatability and help ensure a product retains its texture and softness throughout its shelf life.

I think the key term here is palatability which, in economic terms, means more $$$ for the pet food giants.

On the other hand we know that sugar has never been part of natural cat food. And we know that excessive sugar added to processed human food has caused a huge spike in type 2 diabetes and related diseases in the past 4 decades or so.

So I'm wondering if there are any studies to show the effects of sugar creeped into cat foods?

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    That Purina quote reeks of marketing speak.
    – DKNguyen
    Oct 7 '20 at 22:34
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    @karlom carnivoras synthetise all their glucose from proteins and don t need additionnal which is why they should only eat meat while us as humans needs to absorb glucose mainly from grains and other plants. Didn t figured it out until my dog had such high level that it was constantly drinking all over the day and suffered a parallelisis after eating dog foot with plain rice and corn all his life. Manufacturers add things like corn to their foods (often hidden) because their are cheaper than meat. Oct 8 '20 at 20:37
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You got most of the points right. The sugar is added to cat food for the benefit of the manufacturer, not for the cat.

Cats cannot taste sweet

You need 2 specific genes in order to have receptors for sweet tastes on your tongue, but cats lack one of those genes.

[Joe Brand, biochemist and associate director at the Monell Chemical Senses Center in Philadelphia] and his colleague Xia Li first discovered the pseudogene after decades of anecdotal evidence—such as cats showing no preference between sweetened and regular water, unlike other animals—testifying to their indifference to the sweet stuff.

This is affirmed by this meta study that I highly suggest reading because of the varied information it contains.

Neurophysiologic studies of the facial nerve demonstrated responses to salt, bitter, sour, amino acids and nucleotides taste stimuli [59,60]. No neural responses to sucrose and other sugars were detected in cats [61,62]. The sense of taste in cats is therefore similar to that of other mammals, with the exception of insensitivity to sweeteners. The molecular basis for this feline sweet blindness is the lack of a sensory system to detect sweet stimuli. Li et al. characterised the sweet receptor genes of cats and concluded that Tas1r3 is expressed and functional, but Tas1r2 is an unexpressed pseudogene. The functional sweet receptor heterodimer (T1R2/T1R3) can therefore not form, resulting in an inability to taste sweet taste stimuli [63,64]. This was confirmed in lions.

But there seem to be some cats who can sense high amounts of sugar.

Why is there sugar in cat food?

First of all, small amounts of different sugars are contained naturally in the other ingredients of the food, mostly in vegetables and grains.

Most cat foods don't contain the white sugar we are used to having in our kitchen. Instead, the sugar is caramelized to give it a deep brown color. If mixed with wet food, this caramel gives the food the color of gravy and fried meat and adds a juicy sheen to the sauce. This is only done to appeal to the humans that buy the food, not for the cats.

If mixed with dry food, the caramel also adds a rich brown color (while the kibbles would look pale grey without it) and makes the food more crispy.

It's hard to find any independent sources about this topic. The big brands only offer the kind of nonsense you've found by Purina. I did find several articles by sugar-free pet food companies:

Is sugar in cat food really bad?

I'm not a scientist, but the data seems to suggest that any amount of sugar in cat food is too much sugar.

We as humans are very good at digesting carbohydrates and sugars, so good in fact that it causes obesity and diabetes on a large scale. When we taste sweet food, our body produces a number of different enzymes that break down the longer molecule chains of carbohydrates into smaller bits, starting in our mouth and continuing the work in the small intestine. The long chains are called starches, the smaller bits sugars, and the chains need to be broken down to a length of 1 - 2 sugar units to be absorbed into the blood stream. Since our bodies are so good at breaking down the chains and absorbing them into the blood, our blood gets flooded with sugar after a carb rich meal, which can cause diabetes.

This study found that, despite the evolution of cats as carnivores, they seem to be just as good at digesting carbohydrates as humans are.

Early studies by Morris et al. observed that adult cats could efficiently digest all carbohydrates added to a meat-based diet, despite the described evolutionary adaptations along the feline gastrointestinal tract [28]. The total apparent digestibility of starch is reported to be 40–100%, depending on source and treatment [28,29,30], which proves that cats can digest and absorb carbohydrates.

AND cats are actually better at absorbing sugars of different chain lengths into the blood stream, which may cause diabetes:

Anatomically it may seem as cats have a limited ability to absorb monosaccharides because of the limited length of the small intestine. However, partial compensation for this relative deficit in absorptive surface occurs. First, the mucosal area per unit serosal area in the cat’s small intestine is greater compared to rats and dogs [24]. Second, the d-glucose transport across the feline intestinal brush border appears to have a considerably higher capacity in cats than in cattle and rabbits, despite the similar amounts of glucose reaching the small intestine when these species are fed a natural diet. Although omnivorous species can adapt glucose transport to dietary carbohydrate intake, it was found in kittens that the glucose transport system in the intestinal brush border does not adapt to varying levels of dietary carbohydrate.

But since cats cannot regulate the amount of digestive enzymes to the amount of carbohydrates in their digestive tract, they cannot metabolize big meals:

Wild cats eat small vertebrate prey with low carbohydrate content (NFE 1–2%ME) [1,48], and must catch 8–12 of these small rodents every 24 h to provide their energy requirement [53]. Similarly, domestic cats in an experimental setting also spread their daily intake of food and macronutrients over 12–20 small meals, evenly spread between light and dark periods [53,54]. Because of the limited intestinal enzyme capacity, consumption of excessive amounts of digestible carbohydrates will not lead to a massive increase of glucose absorption, but will provide substrate for microbial fermentation in the colon, and cause gastrointestinal adverse effects.

Does sugar in cat food cause diabetes?

This is still subject to debate. Several studies have been conducted that either found no clear correlation or contradict each other.

An excerpt from the aforementioned meta study:

The effect of diet type remains a topic of debate. Slingerland et al. failed to find evidence that the energy percentage of dry food in the cat’s diet is a risk factor for the development of feline diabetes [121]. Also, in the study by Sallander et al. healthy controls consumed a higher portion of dry food compared to diabetic cases [117] and McCann et al. observed that cats eating a combination of dry and wet food are at higher risk compared to cats fed only dry or only wet food [111]. More recently, dry food feeding has been associated with increased risk of diabetes mellitus in normal-weight cats, while diet type was not found to be a risk factor in obese cats [110]. Body condition was, however, reported by the pet owners in this study, which may have skewed the body condition classification, as previous research has shown that pet owners underestimate their cat’s body condition [86,90,98,100,108]. As with the epidemiological research on risk factors for obesity, dietary macronutrient content and food intake were not assessed, so conclusions relating to dietary carbohydrate content, which are often made in these publications, cannot be drawn. Other dietary factors increasing the risk for diabetes include greedy eating behaviour and free choice feeding [110], which could be linked to higher energy intake and obesity.

The main risk factors for diabetes in cats are:

  • Breed (Tonkinese, Norwegian Forest, Burmese Russian Blue, and Abyssinian)
  • Age (older than 7 years)
  • Sex (male and neutered cats have a higher risk)
  • Housing and activity (inactive indoor cats are at higher risk, obese cats at much higher risk)
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  • I'm not sure that it's accurate to say there's only sugar in pet food to appeal to humans since sugar can be used in foods as a preservative. The one part I'm not entirely sure on is if the amount used in cat food would actually act as a preservative? I did find this one article that did say there are dog foods that use salt and sugar as a preservative though. It's probably the same for cat food?goodnesspetfood.com/…
    – Kai
    Oct 7 '20 at 8:30
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    @Kai: the overwhelming information out there is that both salt and sugar are toxic to both cats and dogs. They (sugar and salt) suddenly become "good" when they have to improve the marketing of a product (as preservatives, color, etc.). If you have any information against my understanding, please point me to the right direction, I am really interested.
    – virolino
    Oct 7 '20 at 8:37
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    @kai I have to agree with virolino. In order to act as a preservative, the amount of sugar must be much higher than what is found in commercial pet foods. That's why I didn't include this reasoning in my answer, because it doesn't make sense in my oppinion. If I'm wrong with that assessment, I will edit my answer, but I haven't found any reliable information that point in that direction.
    – Elmy
    Oct 7 '20 at 8:57
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    On a side note: This is one of the reasons it is very hard to make a proper vegan diet for cats. It is incredibly easy to overdose carbs in their food.
    – T. Sar
    Oct 8 '20 at 13:49
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As someone who reversed type II diabetes there is a part that your question misses.

For 24 to 48 hours after exercise muscles become insulin sensitive, diabetes is insulin insensitivity.

Reversing diabetes is diet and exercise. So make sure your cat is moving a lot.

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    Have you ever tried to make an adult domestic cat exersise? Quite a challenge, it is.
    – fraxinus
    Oct 7 '20 at 22:56
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    @fraxinus It can be. On the other hand, my grandmother had a mongrel cat who used to have a wild half-hour running around the place every evening, all the way past her 17th birthday. (The cat, not the grandmother. She was well over ninety.) Oct 8 '20 at 16:01
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Here is a website created by a vet with great info about cat food, what to feed cats, and what illnesses can result from feeding them the wrong food: CATINFO.ORG

Cats should only eat species appropriate food. I have 3 cats, they have never been sick. We only feed them grain free wet food, and occasional greenie snacks. They never throw up besides the occasional hair ball. Carrageenan is known to cause cancer, we avoid cat food that has it in the ingredient list, and we don't feed them cat food that contains fish (cats systems can't process fish). Cats are strict carnivores and don't eat carbohydrates in the wild. You may pay more for quality can food (Wellness is a good one), but it will save you a lot because you'll have less vet bills from sickness.

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The FEDIAF has reviewed carbs in pet food (see page 8 for cats, includes further references)

It has been suggested that high dietary carbohydrate levels could alter energy metabolism and reduce insulin sensitivity but this has not been confirmed. Many studies have been conducted regarding the impact of dietary carbohydrates on biomarkers for disease risk and they have not found a clear association of carbohydrate intake with diabetes mellitus risk in cats. Diet can increase the risk of this disease mainly due to its association with obesity rather than to its nutritional composition.

Epidemiological studies found that dry foods (which likely contain more carbohydrates than wet ones, and also can have increased energy density) do not affect diabetes risk, or are associated with a reduced risk; however, one study found that dry diets were associated with a higher risk of diabetes in lean but not fat cats.

There is a new study (summary) showing that cats showed a strong preference for food containing oligosaccharides. Mannan oligosaccharides (MOS) are naturally occurring in cat's milk and are widely used in animal feed. As producers are extremely vague about the "various sugars" in their cat food, I wonder if some of these might be used as attractants?

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  • FEDIAF is the lobby of European pet food industry. It's like asking Suger lobby if sugger is fine for human body. They are heavily biased.
    – Karlom
    Mar 11 at 5:02
  • @Karlom I'm aware of that, hence the note about the further references; also see the second part of my answer; it might explain what these - not further specified - sugars are, how they add to palatability or even make cats crave certain products despite not having a taste for sweetness, at least not in the same way humans have.
    – Jens
    Apr 18 at 0:36

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