Phytonutrients for Dogs: What Plants Give Your Dog That Meat Cannot

By Caroline Buck, Co-founder of Petaluma

Ancestral diets, raw feeding, and grain-free all share one idea: plants are filler, and a dog would be better off without them. The argument usually runs through what plants lack. It rarely asks what plants supply that meat does not. Carotenoids, polyphenols, and phytosterols are made by plants and by nothing else, and AAFCO does not require a single one of them. Below: what phytonutrients are, which foods carry the most, what the canine research has actually measured, and what it still needs to answer.

What phytonutrients are

Phytonutrient means a compound made by a plant. Thousands exist. Three groups come up most in canine nutrition.

• Carotenoids are the pigments that make carrots orange and kale dark green. Beta-carotene, lutein, zeaxanthin, and lycopene are the ones you have heard of.
• Polyphenols are a large family that includes the flavonoids in berries and the catechins in tea.
• Phytosterols are plant compounds structurally similar to cholesterol, found in seeds, nuts, and vegetable oils.

A dog can get every AAFCO-required nutrient from animal ingredients, plant ingredients, or a mix. Phytonutrients are the part of the plant column with no animal equivalent.

Why "non-essential" is a misleading word

In nutrition, essential has a narrow technical meaning: remove it from the diet and the animal develops a deficiency disease. Taurine is essential for cats: a deficiency can cause blindness. Phytonutrients fail that test, so they are classed non-essential and no requirement exists for them.

In 2021, a team led by Jirayu Tanprasertsuk reviewed the canine evidence on phytonutrients for the Journal of Animal Physiology and Animal Nutrition. They put the problem with the label plainly:

The term "non-essential" is somewhat misleading to the general public. Although no intake requirements have been established for phytonutrients, it should not be interpreted that these compounds have no benefits on health. Rather than just meeting the minima that have been proven to be essential to maintain normal function, these phytonutrients may be useful for health optimization and longevity.

Fiber and antioxidants are under the same 'non-essential' label, but there are clear benefits to the presence of both in a dog's diet. Fiber doesn't have a current AAFCO minimum, and labeling rules require crude fiber, which misses doesn't give the consumer much insight into soluble fiber. AAFCO's label modernization rules replace that with a total dietary fiber guarantee, alongside a new total carbohydrate guarantee. They took effect in 2024, with full compliance due by 2030.

Which foods carry the most

Carotenoids do two different things in a dog, depending on the compound.

Convert to vitamin A Alpha-carotene, beta-carotene, cryptoxanthin Your dog's body splits these to make vitamin A, which supports vision, immune function, and skin and coat. AAFCO requires vitamin A, and plants are one route to it.

Serve as antioxidants Lutein, zeaxanthin, lycopene These neutralise free radicals, the reactive molecules that damage cells during normal metabolism and hard exercise. AAFCO sets no minimum for that protective work.

The review compiled carotenoid content across common foods, measured in milligrams per 1,000 kilocalories, which is how nutritionists compare foods of different energy densities. It lists each carotenoid separately, so the two groups have their own rankings.

Beta-carotene, which converts to vitamin A

Food	Beta-carotene (mg/1,000 kcal)
Spinach	245
Carrots	202
Sweet potatoes	124
Pumpkin	119
Butternut squash	114
Kale	82
Cantaloupe	59
Red sweet peppers	52

Beta-carotene is not the only route to vitamin A. Pumpkin leads the alpha-carotene list at 155 mg per 1,000 kcal, ahead of carrots at 85 and butternut squash at 28, and butternut squash leads on beta-cryptoxanthin at 78.

Lutein and zeaxanthin, which serve as antioxidants

Food	Lutein + zeaxanthin (mg/1,000 kcal)
Spinach	530
Kale	179
Collard greens	135
Asparagus	36
Green peas	31
Green beans	21
Sweet yellow corn	9

Spinach tops both tables, at 245 mg of beta-carotene and 530 mg of lutein and zeaxanthin, which is why it does both jobs at once. Kale places sixth on one list and second on the other. We have written separately about pumpkin, carrots, and spinach for dogs.

What the canine research has measured

The canine phytonutrient studies are scattered across decades and journals, and most are small. That is the problem the 2021 review set out to solve. Jirayu Tanprasertsuk, Devon Tate, and Justin Shmalberg collected the trials into one place for the Journal of Animal Physiology and Animal Nutrition and sorted them into ten health areas. All three work for a fresh pet food company that makes meat-based food, so they had no commercial reason to argue for plants.

The review collected these studies rather than running them itself. Each used a small number of dogs, and each tested a supplement instead of actual vegetables.

• Immune response. Chew and colleagues (2000) fed beagles 0, 2, 20, or 50 mg of beta-carotene a day. Immunoglobulin G, the most common antibody in blood, rose with the dose up to 20 mg and then levelled off. Those dogs also had more of the helper T cells that coordinate an immune response, and they responded more strongly to a vaccine.
• Oxidative damage. Baskin and colleagues (2000) supplemented 62 Alaskan sled dogs with beta-carotene, lutein, and vitamin E, then ran them for three days. Antioxidant levels in their blood rose, and a marker of DNA damage fell.
• Body composition. Wang and colleagues (2017) gave growing beagle puppies a supplement containing carotenoids alongside DHA, taurine, and vitamins. Those puppies carried less fat mass at six months, with better cholesterol and triglycerides, and they burned fat more readily.

The review also covers gut health and the microbiome, bone and joint health, kidney health, skin and coat, vision, and cognition. Its conclusion: excluding plants removes both certain essential nutrients and these phytonutrients. Plant foods also raise levels of some vitamins and minerals that run low in meat.

What the research still needs to answer

Most of these studies measured biomarkers rather than outcomes. A rise in antibodies is not the same as fewer infections, and burning fat more readily is not the same as a longer life. Many trials used isolated supplements, and a carotenoid capsule is not a bowl of pumpkin. Sample sizes are often small, and no requirement has been established for any phytonutrient, so there is no target intake to aim at.

The longest-running canine work shows how hard attribution gets. Starting in the 1990s, researchers at UC Irvine and the University of Toronto studied cognitive ageing in beagles. Dogs accumulate the same beta-amyloid protein in the brain that people do, which makes them a useful model for human ageing. The team fed aged dogs a food fortified with antioxidants and mitochondrial cofactors, then tested their learning for years. Those dogs handled progressively harder learning tasks better than controls (Cotman et al., 2002). A later two-year study of 48 aged beagles got its best results when the food was paired with exercise and enrichment (Milgram et al., 2005).

That work is often cited as proof that plant antioxidants protect the ageing brain. It does not show that. The food was a bundle that included vitamins and mitochondrial cofactors, the strongest effect required exercise alongside it, and the researchers concluded that combinations beat single ingredients. It is good evidence that antioxidant-rich food matters, and no evidence about which part did the work.

Settling any of this takes a different kind of study: long feeding trials built on whole plant foods rather than extracts, measuring disease and lifespan rather than blood markers. Those trials are slow and expensive. Until they exist, the case for phytonutrients rests on mechanism and short-term markers, which is enough to make plants worth including and not enough to promise an outcome.

How this shows up in our food

We build recipes from whole plant foods rather than extracts.

• Sweet potato and pumpkin: 124 and 119 mg beta-carotene per 1,000 kcal in the review's table. Sweet potato anchors our Roasted Peanut Butter & Sweet Potato adult recipe, pumpkin our Baked Pumpkin & Peanut Butter senior recipe.
• Carrots, spinach, and kale: carrots are in all three recipes, baked into the adult and senior bites alongside oats, parsley, and nuts. Spinach and kale are in our Whole Food Mixer. Spinach and carrots are the top two foods in the beta-carotene table above, at 245 and 202 mg, and spinach also leads on lutein at 530 mg.
• Whole foods, not extracts: chickpeas, oats, barley, flaxseed, and applesauce each arrive with their own mix of compounds. The review notes that the nutrient profile of a food is more complex than that of a supplement.
• Baked and dehydrated, not extruded: plant ingredients need some cooking before their nutrients are fully available, and the method matters. We bake the adult and senior recipes at a solar-powered bakery in Illinois, and dehydrate the Whole Food Mixer at a vegan, human-grade facility. Neither goes through the high heat and pressure of extrusion.

A diet built on plants gets these compounds by default. That is not the reason to feed plants, and long-term health is what matters most to us, but it is a real difference and it belongs in the conversation. For more, see our review of whether dogs thrive on plant-based diets, our look at whether dogs need meat, and the evidence on whether dogs are omnivores or carnivores.

Frequently asked questions

What are phytonutrients for dogs?

Phytonutrients are compounds made by plants. The three groups that matter most in canine nutrition are carotenoids, such as beta-carotene and lutein, polyphenols, such as the flavonoids in berries, and phytosterols, found in seeds and nuts. Meat does not contain them, so a dog only gets them from plant ingredients.

Do dogs need phytonutrients?

Not in the way they need protein or calcium. AAFCO sets no requirement for any phytonutrient, so a diet is complete without them and no dog gets a deficiency disease from their absence. The 2021 review in the Journal of Animal Physiology and Animal Nutrition argues that "non-essential" is misleading, because no requirement is different from no benefit.

Can dogs convert beta-carotene into vitamin A?

Yes. Alpha-carotene, beta-carotene, and cryptoxanthin are provitamin A carotenoids, which a dog's body splits using an enzyme to yield vitamin A. So the carotenoids in carrots, pumpkin, and sweet potato are both an antioxidant source and a vitamin A source. Other carotenoids, including lutein and lycopene, are not converted and act as antioxidants only.

What do vegetables actually do for dogs?

In canine trials, beta-carotene raised antibody levels and strengthened vaccine response in beagles, and a beta-carotene, lutein and vitamin E supplement lowered a marker of DNA damage in sled dogs after exercise. Most of that work measured biomarkers rather than long-term outcomes, so treat it as promising rather than proven.

Which foods are highest in carotenoids for dogs?

By beta-carotene per 1,000 kcal, the 2021 review ranks spinach at 245 mg, carrots at 202, sweet potatoes at 124, pumpkin at 119, and butternut squash at 114. Pumpkin leads on alpha-carotene at 155 mg per 1,000 kcal.

Are plants just filler in dog food?

No. Plants supply AAFCO-required nutrients alongside carotenoids, polyphenols, and phytosterols that have no animal equivalent. The 2021 review found that excluding plants removes certain essential nutrients along with the phytonutrients. Plant foods also raise levels of some vitamins and minerals that run low in meat.

Should I give my dog a phytonutrient supplement?

Feed a plant-rich diet instead. No intake requirement exists for phytonutrients, so there is no established dose to target, and the 2021 review notes that whole foods carry a more complex mix of compounds than isolated supplements do. Choose a food built on plants, or add phytonutrient-rich foods like pumpkin, carrots, and leafy greens to the bowl. Talk to your veterinarian before adding any supplement.

Does cooking destroy phytonutrients?

It depends on the compound. Heat degrades some and makes others easier to absorb, which is why cooked carrots deliver more usable beta-carotene than raw ones. This is a reason to care how a food is made rather than a reason to feed raw, and any commercial dog food has been cooked.

References

1. Tanprasertsuk J, Tate DE, Shmalberg J. Roles of plant-based ingredients and phytonutrients in canine nutrition and health. Journal of Animal Physiology and Animal Nutrition. 2022;106(3):586–613. doi:10.1111/jpn.13626. PMC.
2. Chew BP, Park JS, Wong TS, et al. Dietary beta-carotene stimulates cell-mediated and humoral immune response in dogs. The Journal of Nutrition. 2000;130(8):1910–1913. Journal of Nutrition.
3. Baskin CR, Hinchcliff KW, DiSilvestro RA, et al. Effects of dietary antioxidant supplementation on oxidative damage and resistance to oxidative damage during prolonged exercise in sled dogs. American Journal of Veterinary Research. 2000;61(8):886–891. PubMed.
4. Wang W, Brooks M, Gardner C, Milgram NW. Effect of neuroactive nutritional supplementation on body weight and composition in growing puppies. Journal of Nutritional Science. 2017;6:e56. PubMed.
5. Cotman CW, Head E, Muggenburg BA, Zicker S, Milgram NW. Brain aging in the canine: a diet enriched in antioxidants reduces cognitive dysfunction. Neurobiology of Aging. 2002;23(5):809–818. PubMed.
6. Milgram NW, Head E, Zicker SC, et al. Learning ability in aged beagle dogs is preserved by behavioral enrichment and dietary fortification: a two-year longitudinal study. Neurobiology of Aging. 2005;26(1):77–90. PubMed.
7. Araujo JA, Studzinski CM, Head E, Cotman CW, Milgram NW. Assessment of nutritional interventions for modification of age-associated cognitive decline using a canine model of human aging. Age (Dordr). 2005;27(1):27–37. PMC.
8. Association of American Feed Control Officials. Pet Food Label Modernization. 2023. AAFCO.
9. Association of American Feed Control Officials. Dog Food Nutrient Profiles. AAFCO.