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At the pet store this weekend, we were approached by a sales representative marketing a "gourmet" pet food brand. One of the biggest selling points was apparently that the food contains "wholesome whole grains, garden veggies and healthy fruit", in addition to meat.

While I understand that vegetable products such as corn meal are frequently used as fillers for dry pet food, I question the value of fruits and vegetables being added to cat food, since cats are obligate carnivores.

The main selling point was that the first ingredient on the list of each of their foods were "real meats" (as opposed to meat by-products), so presumably the food contains enough crude animal proteins to meet the cats primary dietary requirements, but does adding fruit and vegetables have any actual health benefits to a cat? Or is it just a marketing gimmick, playing on people's assumption that if the food sounds appealing to them, it might be more appealing to their cats?

  • related: pets.stackexchange.com/questions/1601/… – ratchet freak Jan 8 '14 at 13:48
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    @ratchetfreak I don't think that the two questions are related at all. This question is about feeding cat normal food and adding some fruits and vegetables to it. But the question you have mentioned in your link is about feeding a cat food that is completely vegetarian. – Sonevol Nov 30 '18 at 7:38
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Most of the relevant work seems to indicate that the nutrients found specifically in vegetables/fruits aren't digestible by cats, and the nutrients that they need are found in animal tissue (usually muscle or fatty tissue). So the inclusion of these ingredients in their food is not poisonous, but adds indigestible mass that they don't need.

For example, in The carnivore connection to nutrition in cats (JAVMA, Vol 221, No. 11, December 1, 2002) Dr. Debra L. Zoran states:

Vitamin A is found naturally only in animal tissues, and it must be provided as the biologically active form in diets formulated for cats because of the fact that cats cannot convert β-carotene (which is plentiful in plants) to retinol (the active form of vitamin A); this conversion is not possible, because cats lack the necessary intestinal enzyme.

In high enough levels, being unable to digest some materials can actually be harmful to the cat. For example, benzoic acid is one of the components in cranberries (a popular fruit to add to cat food because of its folklore status as a cure for urinary tract infections in humans). Too much benzoic acid can be fatal for cats.

Outbreaks of poisoning affecting 28 cats have followed ingestion of meat containing 2.39% benzoic acid. The effects were nervousness, excitability, and loss of balance and vision. Convulsions occurred and 17 cats either died or were killed. Autopsies showed damage to intestinal mucosa and liver. The sensitivity of the cat may be due to its failure to form benzoyl glucuronide and toxicity may develop with quantities greater than 0.45 g/kg single doses or 0.2 g/kg repeated doses (Bedford & Clarke, 1971).

However, you'd have to feed your cat a LOT of cranberries to get to this level of toxicity, so I don't believe your cat would be in any danger from a commercially produced food that included cranberry.

Cranberries are somewhat of an unusual case. Their inclusion is often to promote urinary health, not just to increase the "nutritiousness" of the food. Skepvet summaries his findings:

There is weak theoretical justification for using cranberry products for UTIs, though none of the supporting preclinical evidence involves dogs or cats. There is conflicting clinical trial evidence in humans, and no clinical studies in dogs and cats. There are weak theoretical safety concerns.

Peas and pumpkin can also be included not for nutritional value, but to bulk up the stool and relieve constipation. I don't generally recommend feeding fiber to an otherwise healthy cat and prefer to monitor the situation myself. GI symptoms can be the first sign of an illness, so I prefer to know as soon as possible that something may be wrong.

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    So maybe the meat byproducts are actually a healthier choice for the cat than lean chicken meat? A wild cat would eat the feathers, etc. – James Jenkins Jul 26 '14 at 0:03
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    @JamesJenkins many raw/homemade recipes caution against using solely muscle meat because of micronutrients that are missing in muscle meat that cats would get if they were eating organs and such. I wouldn't go far as to say byproducts are healthier, but they shouldn't be avoided because we find the thought of them disgusting. Like everything else, it's a matter of balance. – Zaralynda Jul 26 '14 at 1:22
  • Can you add that to your answer? The product in question specifically mentions that byproducts (i.e. organs) are excluded. – James Jenkins Jul 26 '14 at 9:44
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    @Sonevol do you have some evidence of the benefits? If the nutrients aren't digested, they aren't beneficial. I discussed the use of fiber under the heading peas and pumpkin, but can modify that to "peas, pumpkin, and other sources of fiber" if that's what you mean. – Zaralynda Dec 7 '18 at 19:29
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    @Sonevol in plants Vitamin A is found as β-carotene. Cats cannot convert this into retinol, the form they can use. – Zaralynda Dec 12 '18 at 17:45
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It is a common misconception that house cat and other cat species (read lions, tigers, etc.) don't need green food. Although being obligate carnivores with 95% of dietary requirement being meat, they do need green food. But in wild they don't need to eat green food separately. They hunt and eat herbivores. Their digestive tracks have some half digested green food. And that is enough for the cat species.

Sources claiming that cats do eat digestive tracts of prey -

Lions, for instance, often tear open large prey right away to get at and eat the internal organs before they start eating the muscles (meat) of the animal. Depending on the hunger and fitness of the lion in the pride, they will also eat the intestines -- Do carnivores eat the digestive system?
Although cats are meat-eaters, when they hunt and eat their natural prey, they eat the vegetable matter in the prey’s gut. -- Feeding Vegetables to Cats
Cats tend to consume the whole of a small prey animal like a mouse, with its tiny amount of fermented stomach content. I have seen cats eat the stomach content of larger prey like rabbits - Answers: The Stomach Contents of Prey

But in case of house cats, unfortunately most are fed commercial cat food which is totally void of green food. So house cats do need to consume some amount of green food separately.

Although cats will not be able to digest the green food, still it is very beneficial. Some of the benefits are:

  • Cats don't need to break down the starch to absorb vitamins and minerals from plant leaves
  • Adding a few select vegetables to her diet is a great way to give her more selection, while sneaking in a few additional (essential!) vitamins and minerals as well. -- 6 Best Vegetables for Cats
    common lawn grasses like St. Augustine offer fiber and trace minerals -- Leafy greens for dogs and cats
  • Green foods helps in weight control of overweight cats
  • If your cat is overweight, adding some veggies to her diet can help keep her weight down. -- Feeding Vegetables to Cats
  • Green foods boost immune system and lessen the effect of ageing
  • Feeding your cat vegetables can also boost her immune system and can lessen the effects of aging. -- Feeding Vegetables to Cats
  • Vegetables, especially those obtained from gut of prey are the main source of useful bacteria in cats. As such house cats have to be fed probiotics separately.
  • The stomach content of an herbivore, such as a mouse or rabbit, contains fermented vegetable matter which is a mix of symbiotic bacteria and volatile fatty acids.¹ The VFAs become the energy source for the herbivorous animal and the symbiotic bacteria. In turn, the symbiotic bacteria keep the intestinal mucosa healthy.

    So, for a cat, the consumption of fermented gut content from a mouse or rabbit aids in the management of the cat's own intestinal flora. The intestinal flora in turn maintains the integrity of the mucosal surface. It is likely the VFAs contribute little as an energy source to the cat, but the bacterial load is likely very beneficial.² The microorganisms perform a host of useful functions: preventing the growth of harmful bacteria, producing vitamins for the host such as biotin and vitamin K and maintaining the integrity of the mucosal surface of the gut.

    -- Answers: The Stomach Contents of Prey
  • Grass is a great source of folic acids in cats
  • The juices in grass contain folic acid, a vitamin essential to a cat's well-being. Folic acid, also present in the mother cat's milk, aids the production of oxygen in the cat's bloodstream. A folic acid deficiency may lead to anemia, and a young cat's growth can be stunted if she doesn't get enough of it. -- Why do cats eat grass?
  • Green foods remove waste and detoxify the colon
  • Green food helps a cat to expel hairballs by either pushing them into the digestive track or enabling vomiting
  • It may add fiber and bulk to their diet, helping them pass worms or fur through their intestinal tract. If broader-leafed varieties offer a laxative effect, thinner-leafed grass induces cats to vomit. -- Why do cats eat grass?
  • Some green foods detoxify liver and urinary track
  • Dandelion greens are packed with nutritious compounds that detoxify the liver and urinary tract -- Leafy greens for dogs and cats
  • Some green food like kale and chard helps prevent constipation, fecal impactions and spastic colons
  • -- Leafy greens for dogs and cats
  • Fiber in green food helps prevent the buildup of gas and waste in colon
  • -- Leafy greens for dogs and cats
  • Green leafy vegetables can prevent cancer of digestive tracks
  • Human studies have demonstrated that leafy vegetables can even prevent cancers of the digestive tract. Considering the cancer epidemic among companion animals, this should not be overlooked or underestimated. -- Leafy greens for dogs and cats
  • Some green foods can ease the pain of arthritis
  • the proteolytic enzymes found in some leafy greens are anti-inflammatory, and may ease painful conditions like arthritis. -- Leafy greens for dogs and cats

Regarding claims of detoxification,

As given in moderncat

The food that help detoxify the body of a cat are -

  1. Milk Thistle - It helps in regenerating and protecting the liver, the organ responsible for detoxifying the whole body.
  2. Vitamin E - Many plant food are rich in Vitamin E, which seeks out and destroys free radicals. Free radicals cause cancer, skin problems, infectious illness and ageing.
  3. Vitamin C - Yet another nutrient which is abundant in many plant food, It boosts immune system, relieves bowel problems, prevents cancer, gum diseases and skin diseases
  4. Green Tea - It is high in anti-oxidant which eliminates free radicals, remove carcinogens and thus prevent cancer
  5. Zinc - A mineral that is abundant in plant food, it reduces inflammation and speeds up healing process. It also helps liver to produce detoxifying enzymes.
  6. SAMe - S-adenosylmethionine, known as SAMe for short, is another supplement that helps to clear the liver of toxins. It is present in Milk Thistle.
  7. Dandelion - It helps strengthen the liver and clear out toxin.
  8. Support the Lymphatic System - Lymph contains white blood cells, and helps get rid of toxins in the body. Red clover support the lymphatic system.
  9. Support the kidneys - Kidneys are also important for detoxification. Marshmallow, corn silk, and cranberry are good for kidney health
  10. Support the immune system -
    • Echinacea
    • Astragalus
    • Garlic

So, in short the answer is YES, cats do need to eat a certain amount of green leafy vegetables in their diet.

However always consult the vet before giving any green leafy vegetable to a cat so as to ensure that the particular vegetable has no harmful side effects.

RELATED:

What are some green vegetables that I can safely feed to my cat?

How to prepare vegetables to feed a cat?

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  • Thanks for the edits/sources! Unfortunately, many of the sources you cite do not provide sources for the claims. Interestingly enough, the citations that do back their claims up with sources seem to indicate that the vegetables packaged directly into cat food is typically so processed that it provides little-to-no actual benefit to the cat. The claims backed by the strongest references seem to focus primarily on gut bacteria/probiotic and roughage benefits, which vegetables in canned foods do not provide. Still, great research on you part, so +1 from me, thanks! – Beofett Nov 30 '18 at 18:04

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