Introduction
Among the timeless questions that are debated endlessly from generation to generation, such as “What is the meaning of life?” and “Does the refrigerator light go off when the door is closed?” is one that veterinarians and cat owners are particularly familiar with: “Is feeding canned or dry food better for cats?” Cat lovers, and many vets, often have strong and absolute opinions on this question, and disagreements on the subject tend to be about as amicable as disagreements about politics and religion.
The most widely held belief seems to be that canned foods are healthier for cats than dry diets. This is predicated on two key arguments:
- As obligate carnivores, cats cannot thrive on dietary carbohydrates, and canned diets are low-carb compared with kibble. Therefore, dry diets are more likely to lead to obesity and diabetes mellitus (DM), two common and important feline health problems.1–5
- Cats eating dry food don’t drink enough water, and this increases the risk of chronic kidney disease (CKD) and lower urinary tract diseases, such as feline interstitial cystitis (FIC) and urolithiasis. Feeding canned foods will maintain better hydration and promote dilute urine, and this will reduce the risk of these diseases.4,6,7
These are plausible and logically sound arguments, but the history of medicine is full of plausible hypotheses that turned out to be wrong. It is not enough to make a good argument based on general principles. To know what is really best for our patients, we must test such arguments experimentally and follow the evidence, whether or not it supports seemingly obvious, “common sense” beliefs.
The question of whether cats are healthier when fed canned or dry food is, unfortunately, far more complicated that it seems. There are many nutritional variables which affect health and disease and which are not determined solely by whether the food is dry or canned.
Macronutrient content can vary dramatically between diets, and while dry foods are typically higher in carbohydrates than canned diets, they can be higher or lower than canned foods in fat or protein. The micronutrient content of a diet is also critical, as the consequences of feeding taurine deficient diets to cats illustrates. Other variables, such as calorie density, the amount of food fed, and the feeding pattern (e.g. number of meals per day) can have as much or more impact on health than the general form of the diet.
Even the basic assumptions of the arguments in favor of canned diets are not always as clear as they might seem. Cats certainly process carbohydrates differently from more omnivorous species, but that doesn’t translate into a simple equation that ”carbohydrates = bad for cats.” The type and relative amount of carbohydrates fed make a great deal of difference. And while canned food unquestionably contains more water than dry food, the idea that cats eating canned food are better hydrated and have more dilute urine turns out not to be consistently true.
Cats and Carbs
The debate about the effect of dietary carbohydrates on cats has raged for decades. A couple of reviews have recently summarized the evidence, and simplistic, general conclusions are difficult to justify.1,8It is clear that cats do metabolize carbohydrates differently than dogs and humans. However, the type of carbohydrate (simple or complex) and the feeding pattern both have significant effects of postprandial glucose levels and other measures. Cats can utilize carbohydrates as an energy source, and they can adapt metabolically to different macronutrient ratios in the diet, so the simplistic notion of carbohydrates as “toxic” to cats isn’t supported.
Research evidence generally shows no adverse effects on resting glucose or insulin sensitivity in cats fed typical types and levels of dietary carbohydrates. Diets with greater than 50% of calories from carbohydrates, especially when fed once daily rather than ad libor as multiple meals, can generate higher and more prolonged spikes in blood glucose, but even this does not appear to achieve levels associated with harm in experimental studies.
Though there is some inconsistency among studies, most research has failed to find that dietary carbohydrates is a significant risk factor for DM in cats.1,8One study even found cats who developed diabetes were less likely to be fed dry foods than cats without DM.9There is evidence that reduced-carbohydrate diets may be useful in management of feline DM, though such diets can be counterproductive and promote obesity if they are very high in fat.1,10
Cats and Water
Cats can produce more highly concentrated urine than dogs and have lower weight-specific water requirements.6It has been argued that dry diets are associated with less overall water intake and that they promote dehydration and may increase the risk of CKD and other urinary tract diseases.4Some research has found that cats will drink less water when eating low-moisture diets.4,6However, other studies contradict this finding and identify no difference in water turnover and intake or body water content between cats fed dry and canned diets.6There are many factors that affect water intake in cats other than the form of the food, including the protein and mineral content and the energy density, so simply feeding a canned diet is not guaranteed to increase water intake or reduce urine specific gravity.6
Some studies have identified consumption of dry diets as a risk factor for FIC and urolithiasis while others have not confirmed this link.6Other research has even found that cats who develop FIC are morelikely to be fed canned food than control cats, suggesting canned foods could increase FIC risk in some cases.11Similarly, while dry diets are often cited as a risk factor for the development of CKD, research has consistently failed to support this purported association.6,12,13And while canned diets certainly have a role in the management of CKD and urolithiasis, moisture content is not the only relevant variable, and dry diets can have benefits in patients with these conditions as well.6,14
Higher moisture diets are typically less calorie-dense than lower-moisture diets, and it has been suggested that canned diets may help prevent or treat obesity in cats. Other factors are clearly also relevant, of course, such as the specific composition of the diet, the amount fed, and the feeding pattern. It is clearly possible to maintain cats in a lean body condition with dry foods and to develop and perpetuate obesity while feeding canned diets. Overall, however, it is likely that high-moisture diets, including canned foods or dry diets with added water, may be beneficial in preventing and managing feline obesity.6
Conclusions
Regular readers will not be surprised to see that the simple answer, canned foods are better/worse than dry foods for cats, is not the true answer. “It depends” is a much less satisfying response to questions about the relative merits of canned food and kibble, but it is more likely to lead us to the best dietary strategy for individual patients.
Overall, concerns about the health effects of dietary carbohydrates in cats are typically exaggerated, and dry diets should not be avoided on the basis of the idea that they have too much carbohydrate and promote obesity and DM. The specific nutrient and calorie content of the diet is more important than the form it comes in.
Canned diets are higher in moisture than dry foods, and while it is unclear how much impact this has on the risk of urinary tract disease, it does seem likely this characteristic may help owners control calorie intake and weight in their cats.
So when our clients ask whether they should feed canned or dry food to their cats, rather than giving a satisfying, simple answer that is probably wrong, we should be prepared to discuss the evidence and the nuances of the issue in the context of the individual pet. This is the essence of evidence-based practice.
References
1. Verbrugghe A, Hesta M. Cats and Carbohydrates: The Carnivore Fantasy? Vet Sci. 2017;4(4):55. doi:10.3390/vetsci4040055
2. Rand JS, Fleeman LM, Farrow HA, Appleton DJ, Lederer R. Canine and feline diabetes mellitus: nature or nurture? J Nutr. 2004;134(8 Suppl):2072S-2080S. http://www.ncbi.nlm.nih.gov/pubmed/15284406. Accessed June 14, 2019.
3. Buffington CAT. Dry foods and risk of disease in cats. Can Vet J = La Rev Vet Can. 2008;49(6):561-563. http://www.ncbi.nlm.nih.gov/pubmed/18624064. Accessed June 14, 2019.
4. Zoran DL. The carnivore connection to nutrition in cats. J Am Vet Med Assoc. 2002;221(11):1559-1567. doi:10.2460/javma.2002.221.1559
5. Gomez-Mejias Y. Does Grain Actually Predispose Our Cats to Gain Weight? Vet Evid. 2019;4(2). doi:10.18849/ve.v4i2.201
6. Larsen JA. The role of water in disease management. In: 2018 ACVIM Forum. Seattle, WA; 2018.
7. Markwell PJ, Buffington CT, Smith BHE. The Effect of Diet on Lower Urinary Tract Diseases in Cats. J Nutr. 1998;128(12):2753S-2757S. doi:10.1093/jn/128.12.2753S
8. Laflamme D. Cats and carbohydrates: Why is this still controversial? In: 2018 ACVIM Forum. Seattle, WA; 2018.
9. Sallander M, Eliasson J, Hedhammar A. Prevalence and risk factors for the development of diabetes mellitus in Swedish cats. Acta Vet Scand. 2012;54(1):61. doi:10.1186/1751-0147-54-61
10. Nguyen PG, Dumon HJ, Siliart BS, Martin LJ, Sergheraert R, Biourge VC. Effects of dietary fat and energy on body weight and composition after gonadectomy in cats. Am J Vet Res. 2004;65(12):1708-1713. http://www.ncbi.nlm.nih.gov/pubmed/15631038. Accessed June 14, 2019.
11. Lund HS, Sævik BK, Finstad ØW, Grøntvedt ET, Vatne T, Eggertsdóttir A V. Risk factors for idiopathic cystitis in Norwegian cats: a matched case-control study. J Feline Med Surg. 2016;18(6):483-491. doi:10.1177/1098612X15587955
12. Finch NC, Syme HM, Elliott J. Risk Factors for Development of Chronic Kidney Disease in Cats. J Vet Intern Med. 2016;30(2):602-610. doi:10.1111/jvim.13917
13. Bartlett PC, Van Buren JW, Bartlett AD, Zhou C. Case-control study of risk factors associated with feline and canine chronic kidney disease. Vet Med Int. 2010;2010. doi:10.4061/2010/957570
14. Roudebush P, Polzin DJ, Ross SJ, Towell TL, Adams LG, Forrester SD. Therapies for Feline Chronic Kidney Disease. J Feline Med Surg. 2009;11(3):195-210. doi:10.1016/j.jfms.2009.01.004
Thanks for this, skeptvet, this is a very informative article. If only it would put to rest the endless (and sometimes vitriolic) debates unless or until we discover more 🙂
I split the difference: my cat (we think she’s part Maine Coon) gets both. In the morning, she gets kibble (Fromm Gold Adult) and in the evening, she gets a can of I and Love and You. She seems to be doing quite well on this, which makes me pretty happy. (I try to do the best for my cat, for obvious reasons.)
Like Silverwynde, I also split the difference, BFF wet food in the pouches, it is a hit and soup-like, so there definitely is extra hydration, but I use because it was the texture preferred by felines, not me.
Since no weight issues or diabetes, dry food is always available, Fromm 4 star nutritionals and Farmina, both varieties with grain. I rather rice, etc than spiking the protein content with legumes.
I highly recommend a water fountain for felines, it definitely increased water intake. The Catit fountain is good, easy to clean and inexpensive. I prefer over Petsafe version I first bought since the water is covered by the filter vs water exposed that gets filthy quickly.
“It depends” is, of course, the right answer. Start from the premise that a diet of nutritious real foods is likely to be healthier than a mere fortified diet of “fillers” and preservatives.
Dry food is unlikely to be healthy by this standard, but wet food can also contain fillers and preservatives and little in the way of nutrition.
We feed our cat a “formula” of two kinds of meat-based, grain-free, fortified wet food combined with egg yolks, sardines, and coconut oil. We supplement her diet with occasional bits of liver and heart.
She has a voracious appetite and maintains a fairly stable weight of between 7 and 8 pounds no matter how much of this diet she consumes. Before adopting this diet about six years ago, her weight peaked at about 15 pounds, mostly eating a “veterinarian recommended”, “clinically proven” dry cat food.
“Start from the premise that a diet of nutritious real foods is likely to be healthier than a mere fortified diet of “fillers” and preservatives.”
This, of course, is a premise that contains numerous unproven assumptions, so it is not a rational place to start. Your definitions of “nutritious,” “fillers” and “preservatives” are all suspect, and there is no evidence that the kind of diet you are talking about has concrete health benefits. It is possible, of course, but the proof is not in an argument that assumes the truth of its own conclusions or in individual anecdote and trial-and-error experience but in legitimate scientific research.
As a premise, it certainly contains one or more assumptions. And yes, I did not provide “proof” and do not have “proof”.
But you then go on to state that my definitions of “nutritious”, “fillers”, and “preservatives” are all “suspect”. I did not provide definitions, so your characterizations of them as “suspect” is, at best, “unproven”, or worse, not applicable. You could have asked.
In fact, the definition of “nutritious” that I assumed (but did not state) was “contains substances science shows are beneficial when consumed”. As for “fillers” and “preservatives”, you can infer, now that I have defined “nutritious”, that they are substances included for reasons (e.g. texture, preservation, or low cost) other than nutrition. If their purpose is not nutrition, they may nonetheless be nutritious by accident, but they are less likely to be.
Finally, you go on to criticize my description of my experience with my cat as lacking scientific legitimacy. Yet I made no claim of scientific legitimacy, and I certainly did not mean to imply that an n=1 uncontrolled experiment constitutes “proof”.
It is important not to be so “scientific” that common sense – and even the ability to discern what someone is trying to say – go by the wayside.
The implied definitions of your terms is present in their use, otherwise you would have to assume nobody could understand your meaning without a lexicon. You are contrasting “nutritious” with “fillers and preservatives,” which implies the latter are somehow in conflict with nutritious or healthy food. On the contrary, preservatives often increase the nutrient and health value of food by reducing spoilage. And “fillers” is not a recognized term in pet nutrition. It is not defined by AAFCO or used by nutritionists. It is a term almost exclusively used as a pejorative description for commercial pet foods by people who believe (without evidence) that unconventional diets, like the one you describe for your cat, are healthier than commercial diets. There is no misunderstanding of your meaning or intent here, but a recognition of the biases clearly evidence in your original post.
As for my critique of your anecdote, you clearly provided it as evidence that the diet you are feeding has health benefits compared with the commercial diet you fed previously. I hardly think it unfair to point out that the implied cause/effect relationship here is not, in fact, demonstrated by this anecdote or, for that matter, any other extant evidence.
No, I did not provide my anecdote as “evidence”, at least not in any way intended to suggest scientific rigor.
Nor did I imply – despite any unscientific and baggage-laden interpretations you may have projected on my words – that fillers and preservatives are “in conflict” with nutritious or healthy food. As I stated in my last comment, the contrast (as opposed to “conflict”) was with ingredients intended to provide nutrition.
It is a tautology that a preservative is for preservation, and yes, preventing food spoilage is generally a benefit. But introducing an agent solely for that purpose dilutes – and renders dubious – its intrinsic nutritional value compared to, for example, liver, which is nutritionally dense and requires no chemical preservatives when prepared and served appropriately.
It is ironic how much confidence you have expressed about your interpretations of my words without applying your prized scientific skepticism and rigor to your own judgments.
What benefit do you believe that coconut oil is nutritious, particularly for cats?
v.t. > What benefit do you believe that coconut oil is nutritious, particularly for cats?
I don’t know whether coconut oil is nutritious, but I speculate that cats (and most mammals) benefit from consuming a variety of fatty acids. Coconut oil adds a few more fatty acids to her diet, some of which differ from the predominantly long-chain fatty acids in the rest of the ingredients. It is possible it is beneficial, harmful, or has no significant health effect.
One of the other reasons I include it in her formula is that she really seems to like it.
Toxic plants, antifreeze and other poisonous hazards “taste” good to pets too, that of course doesn’t mean your pets should be exposed to them.
skeptvet.com/Blog/2015/04/coconut-oil-for-pets/
sciencebasedmedicine.org/coconut-oil-warning/
sciencebasedmedicine.org/of-mice-and-men-and-coconut-oil/
http://www.hsph.harvard.edu/news/hsph-in-the-news/is-coconut-oil-healthy/
(Above are not hyperlinked due to spam restrictions, just copy to your browser)
v.t. > Toxic plants, antifreeze and other poisonous hazards “taste” good to pets too, that of course doesn’t mean your pets should be exposed to them.
I didn’t state that my cat’s affinity for coconut oil was evidence of beneficial health effects, only that it was one factor in my decision to include it in her formula.
As for your self-described “science based” citations, we could go down a deep rathole about saturated fat, HDL, LDL, etc. there. Or you could go to PubMed.
There is a great deal of sophistry here, and I’m not seeing any discussion of substance, just word games. I’ll leave the subject for now, but you are perilously close to trolling here.
Again, the last sentence here is pointlessly snarky and not a substantive response to the information provided. Last warning.
This is the best article on cat food I have ever read. Thank you.
Thank you for this. This has been one of the more reasoned discussions on the topic I have come across. Even in talking to various vets about food for my cats, I have come across the hard liners vehemently advocating wet or raw only. But, I’ve also had vets who admit it’s not that simply. They say, feed dry if that works better for my cat and myself. If I have doubts about water intake, it’s simple enough to add water if the cat likes it that way.
This fits better with my own knowledge of how science should work as an evidence based tool. I also grew up on a farm with outdoor cats and had plenty of opportunity to watch what they actually ate on their own. Insects and small reptiles were the bulk of what I saw them eat. Rats and mice of course; dive-bombing mockingbirds. Our big cat was fond of rabbits. They would also browse on green vegetables in our garden. Despite the above knowledge, even I fell for the wet only doctrine for about a year and a half.
I do like to feed wet food, but a major problem I find in wet food is consistency of product. Not only do pet stores randomly stop selling your choice of canned or fail to keep it in stock, but manufacturers can up and change the formula without notice. I also have my own observations that my cats were perfectly healthy on a well chosen dry food for years, but after transitioning to wet food, I started encountering a host of health problems related to teeth, kidneys, and thyroid very quickly. No idea why, but it made me stop and reassess the information sources.
I’m back to feeding mostly dry. But I supplement wet a couple times a week as an almost ‘treat’. I make it myself from a framework recipe a local vet gave me. One who also studies nutrition. I do this more for consistency sake and my own interest in cat nutrition. Thank you again for the well written post on this topic
Can you please tell me which wet and dry food you feed, as well as the recipie? Thanks so much! 🙂 I’d love to try it with my kitties.
I don’t have a brand preference since there is little evidence to show one is superior to another. I typically recommend following the World Small Animal Veterinary Association guidelines on choosing a pet food.