This is probably going to be our shortest article: none. Well, for full transparency, "none" is equivalent to a parent's response of "because I said so", or "you'll understand when you're older"- it would be a lot easier to just accept obligate carnivores shouldn't eat any vegetables. In fact, after getting the information, you're most likely going to come to the same conclusion as "none", anyway. However, for the curious and rebellious ones out there who thrive for answers (like us), continue reading for a detailed response.
(images from Google)
If obligate carnivores can't eat vegetables, why are there so many vegetables in pet food? Is it safe- especially when you find some foods who list sweet potato and rice as some of the first ingredients. How can one obligate carnivore, like a betta fish, eat fillers and grain, when another, like a ball python, live solely off rodents?
First, let's define what "pet food" is. According to the Complete Health Guide to Pet Health, Behavior, and Happiness1, the different types of commercial pet food available are "dry food, raw food, commercial fresh, semi-moist,... [and] wet food"1.
Dry food, the most common option, has the longest shelf life as it's made with the most grains and carbohydrates. Realistically, dry food isn't the best option for obligate carnivores, who derive all their nutritional requirements from other animals. In our "What are Grains and What Does that Mean for my Dog?" article, we discuss how dogs can digest grains because they can process amylase. By comparison, obligate carnivores can't; they have shorter digestive tracts- essentially just a small and large intestine- which disallows room to properly break down complex plant sugars. While obligate carnivores can break down some nutrients from plants1, they cannot do so as efficiently as facultative carnivores, who also rely on meat for majority of their diet. Beyond the dilemma over appropriate ingredients, dry food also doesn't provide variety. The cooking process makes each individual kibble identical to the other, which can turn off fussy eaters who prefer various textures in their meals. Take, for example, the ball python mentioned above. A rat offers protein not only with meat, but also via any food being digested in its stomach, including seeds and grain. The rat's fur and bones also aids in digestion by offering fiber and texture, amongst other nutrients.
That's why although not the best, dry food is still a very viable food source. While cooked grain may not provide a lot of nutritional value, there are some benefits to it being in carnivorous diet. Like with rat fur, vegetable matter aids in digestion and can act as a laxative. Certain grasses are natural de-wormers and help rid the body of parasites. Notably, grain can even provide some protein when cooked correctly. Wysong, a popular pet food company (and arguably, one of the best commercial ferret diet providers) uses plant protein in their formulas. Here they explain their use of soy, as it is such a taboo ingredient in the pet food industry. To quote them: "heat will destroy all of these antinutritional agents, but so too does heat degrade the biological value of the nutrients. Wysong extrudes the whole bean using pressure and friction, so the bean is cooked for only 25 seconds. By so doing, the secondary protein bonds that impart the specific catalytic activity to antinutritional enzymes are broken...but the primary peptide bonds are left intact, thus retaining full protein nutrient value."4 Basically, the reason carnivores can't eat vegetables is because their bodies aren't designed to extract their nutrients, not that the vegetables *themselves* aren't nutritional. If the dry food manufacturer finds ways to keep the proteins intact, like Wysong, (and assuming your pet doesn't have an allergy nor adverse reaction) dry foods are safe to feed.
However, that isn't to say that carnivores can live solely off of safely extracted vegetables, because they absolutely cannot. Due to all the plant sugar their bodies aren't designed to digest, a diet full of vegetables and grain can lead to diabetes, especially if you're not working with a nutritionist9. They would likely be too malnourished before they reached that disease anyway. According to the American Society for the Prevention of Cruelty to Animals (ASPCA), cats (and all obligate carnivores) can't be vegan due to their high protein requirement. "Plants simply don't have high enough levels of high-quality, highly digestible protein to meet a cat's dietary requirements".6 Furthermore, these animals are physiologically designed to eat meat, and some pets will refuse foreign food like plants. Vegan diets would need to also be supplemented; there are vitamins crucial for carnivores that aren't found in plants, namely taurine, vitamin b12, and creatine10. This also isn't taking into consideration those animals with specialized diets; babies require more protein and fat than adults- how would one account for that? What about those animals who are very active and require more calories to support muscle growth? What about those who need weight loss? How easy is it supplement vegetables in all carnivore diets?
It appears to only work for giant pandas. Pandas are the exception because although built like carnivores, they have evolved to lose their umami receptors, making them dislike the taste of meat5. However, even pandas still seek out as much protein as possible. In the wild, they follow bamboo cycles, migrating so that they're always eating the younger, more protein-rich bamboo. This still doesn't provide them with much nutrition, and it can manifest in their reproduction, or rather, lack of. Due to the lack of nutrients, panda fetuses undergo a phenomenon called "delayed implantation"7. What occurs is the fetus cells will stay suspended in the mother's womb, sometimes as long as 120 days, until sufficient enough nutrients are available for them to be start forming in the uterus. In captivity, pandas have supplemented diets to give them a more complete nutritious profile. For example, at the Smithsonian National zoo in Washington DC, keepers augment their meals with special biscuits, apples, and carrots. These combined give pandas more nutrients than what bamboo alone can provide8.
Highly nutritional and minimally/non-processed meals is what makes raw food diets appealing. They have more protein, moisture, texture, and is more physiologically enticing than dry food. However, while raw food diets are the most "natural" (and this is in quotations because domesticated pets are more adapted to eating prepared food over raw) they're extremely risky due to the exposure of bacteria. It is quite easy for a family member to fall very sick if proper handling, cleaning, and sanitation isn't being followed.
In fact, if one isn't working with a licensed animal nutritionist, it would be quite easy for an animal to fall very sick on a raw diet, as well.
Between 2011-2012, the United States Food and Drug Administration (FDA) conducted a study where they sampled various raw pet food products. They discovered "nearly 25% [of them]…were positive for [life-threatening] bacteria...including Salmonella and Listeria".2 Even if our pet's stomach acid is able to kill harmful bacteria, if handled improperly, feeding raw still puts the entire household at risk. Cross contamination occurs whenever raw meat touches a surface that isn't sanitized afterwards. This can happen by handling the meat directly (washing, touching, cutting, etc.), not disposing of the meat wrapping properly, even from your pet eating and then
kissing you afterwards- it is very easy for bacteria to spread and infect.
Besides bacterial infections, there is also the risk of malnutrition. Along with muscle and fat, raw food diets require specific amounts of organs, bones, tissue, and supplements11. For example, cats require supplemental vitamin A because their bodies can't produce it themselves. Liver is a fantastic source of vitamin A, but how do you know how much to feed? Do kittens need more liver than adults? What if the cat suddenly develops vitamin A toxicity after months of consistent feeding? What if the cat develops allergies because they're fed the same meat source repeatedly? Without extensive research and partnering with a veterinarian, a raw food diet can be very detrimental to your pet's health. The inconvenience of it is one of the reasons why it is not vet-recommended, and fed at a risk.
The pros and cons of raw food are quite well-known, but what are the issue of commercial fresh foods? Commercial fresh foods are the foods that may look like "fancier" wet food, as they're chunkier, have easy to identify ingredients, and have to be refrigerated.
(images from Google)
They're minimally cooked, made with fewer preservatives, and all the ingredients are human-grade.3 What's the risk? Due to their relatively shorter shelf lives and high moisture, it is common for mold to form in these foods, especially the ones that have more meat and less vegetables. Some are also more difficult to obtain than other food options. Spot and Tango, for example, is subscription based, meaning you wouldn't be able to get some immediately if you need to replace it. Due to the fresher ingredients, they can also be more expensive, further making them not an ideal choice for some pet owners. Even if you had the money and were able to feed a majority commercial fresh food diet, there's not a wide variety of options that aren't catered to dogs, anyway.
For nutrition, price, availability, and appeal, the best choice for most is wet food. It also has the highest moisture, and many obligate carnivores are notorious for being underhydrated. Dr. Gary Weitzman, President and CEO of the San Diego Humane Society, says "...the best food for a cat is wet food...Canned foods provide that extra water they need. In addition, dry foods have more carbohydrates and oils and can lead to more obesity in cats."1.
With all this information, how should you choose an appropriate pet food? Regardless of whether you're doing homemade or buying food off a shelf, it's important to pay attention to the ingredients. Below is a chart on how to pick the safest food source for your obligate carnivore. As always, if you have any further questions or are making any changes to your pet's diet, be sure to consult your veterinarian.
Dr. Weitzman, Gary. Complete Health Guide to Pet Health, Behavior, and Happiness. National Geographic, April 2 2019.
Dr. Hunter, Tammy. Dr. Downing, Robin. Avoiding Raw Food in Cats. VCA Hospitals. https://vcahospitals.com/know-your-pet/avoiding-raw-food-in-cats
Sprankle, Haley. What Is Fresh Pet Food and Is It Actually Better? New York Times, August 6 2020. https://www.nytimes.com/wirecutter/blog/best-fresh-pet-food/
Wysong. The Soy in Pet Foods Myth. Wysong. 2022. https://www.wysong.net/TheSoyinPetFoodsMyth
Sekar, Sandhya. How Pandas survive on their bamboo-only diet. Science, July 9 2014. https://www.science.org/content/article/how-pandas-survive-their-bamboo-only-diet#:~:text=%22In%20areas%20with%20only%20one,different%20times%20of%20the%20year.
ASPCA News. Why Can't My Cat Be Vegan? ASPCA, May 2 2018. https://www.aspca.org/news/why-cant-my-cat-be-vegan
Zhang, Hemin. Li, Desheng. Wang, Chendong. Hull, Vanessa. Delayed implantation in giant pandas: the first comprehensive empirical evidence. Reproduction, Volume 138: Issue 6, December 2009. https://rep.bioscientifica.com/view/journals/rep/138/6/979.xml#:~:text=1989).,around%20107.15%C2%B119.75%20days.
Smithsonian National Zoo and Conservation Biology Institute. Giant Panda FAQS. Smithsonian, 2022. https://nationalzoo.si.edu/animals/giant-panda-faqs#:~:text=In%20the%20wild%2C%20giant%20pandas,nutritious%20biscuits%2C%20carrots%20and%20apples.
Head of Veterinary Services Blue Cross. Can cats be vegan? Blue Cross, September 17 2020. https://www.bluecross.org.uk/advice/cat/can-cats-be-vegan#:~:text=The%20short%20answer%20is%20no,environment%2C%20health%20or%20ethical%20reasons.
Arnarsan, Atli. 7 Nutrients You Can't Get from Plants. Healthline, Nutrition, June 9 2021. https://www.healthline.com/nutrition/7-nutrients-you-cant-get-from-plants#_noHeaderPrefixedContent
Nestle Purine, Raw Food Diets for Cats. Purina, 2022. https://www.purina.com/articles/cat/nutrition/raw-food-diet-for-cats
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