Do our pets need vegetables?
Discover why feeding your pets vegetables and fruit supports health, immunity, and cancer prevention in dogs and cats.
The Cancer Council recommends we eat at least five serves of vegetables and two serves of fruit daily, to reduce our risk for cancer and other chronic diseases. However, in conventional veterinary nutrition, we are taught that neither dogs nor cats require vegetables in their diet. Digestible carbohydrates and fibre are commonly included in pet foods. Fibre may be required for proper gastrointestinal function. Fermentable fibre provides energy sources for beneficial microbes in the gut and nourishment of intestinal cells. Insoluble fibre provides bulk to the stool and helps promote gut movement. Soluble fibre is used to soften stools.
But are there other reasons to offer your pet veggies? There is a trend these days towards feeding ancestral or grain-free diets and some raw diets that are vegetable-free. (Note: this discussion does not include keto diets, which tend to be low in vegetables and may have benefits for some neurological or cancer conditions.)
The bright colours of fruit and vegetables are due to four classes of plant chemicals: chlorophyll (green), carotenoids (yellow, red, orange), flavonoids: anthocyanins and anthoxanthins (red, blue, purple), and betalains (red, yellow, purple). Other phytochemicals (or phytonutrients) include isoflavones (in soybeans) and polyphenols (in berries, cloves and cacao).
Phytochemicals are not essential to plants, but they perform important secondary tasks such as repelling pests or protecting from sunlight as well as growth regulation. For thousands of years, these effects have been harvested to be used in foods, medicinal herbs and spices, teas and topical treatments.
There are a few studies to support the health benefits of adding vegetables to canine diets. One is the Scottish Terrier study that showed the risk of developing bladder cancer was significantly reduced in dogs that consumed green and orange vegetables at least three times weekly. Another recent case study not yet published is of dogs with hemangiosarcoma. This study showed improved outcomes in dogs on fresh diets (meat and vegetables) compared to ultra-processed diets. Preclinical studies show that sulforaphane (SFN), found in raw cruciferous vegetables, may have an anticancer effect against bone cancer cells.
What about general wellness? Studies have shown benefits in cognitive, vision, kidney and immune health in dogs fed a variety of foods containing phytochemicals.
So, what vegetables can we offer our pets?
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Green leafy vegetables: spinach, broccoli, kale, lettuce, Italian parsley, Swiss chard, collards, bok choy, turnip greens
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Yellow-orange vegetables: butternut pumpkin, carrots, other pumpkins, yellow beets, yams, sweet potatoes
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Red capsicums, green beans and asparagus.
Small amounts of fruit can also be fed, including apples and blueberries. I generally avoid very starchy vegetables such as white potatoes, green peas and corn. And no onions (or chocolate).
I recommend starting slow. As a rule of thumb, root vegetables such as sweet potato, carrot and even pumpkin may be best cooked and mashed. Greens and other above-ground vegies can be lightly cooked and finely chopped. Raw vegies can be grated, and I often use the pulp from a juicer as long as it’s fresh (if fermented, it may cause gut upset).
How much should you feed? This may depend on the type of food you are already offering your dog or cat. There are no rules, but too many vegetables may reduce absorption of important nutrients and may cause unpleasant side effects such as flatulence. As a rule of thumb: for dogs, up to 30 per cent of the volume of food fed daily. Cats are finicky, so not so much — 10 maybe 20 per cent of the diet. Even half a teaspoon once a day will have some benefits. Cats may not digest raw vegetables. My go-to for cats would be cooked pumpkin, cooked and finely chopped spinach and maybe a tiny bit of cooked zucchini.
What about fruit and vegetables as a treat? These are a great substitute for processed treats. Phytonutrients and antioxidants are not the same thing, but some phytonutrients act as antioxidants and may aid in protecting the body from damage caused by free radicals. I think adding antioxidants in the form of fruit and vegetables is a much healthier way than adding antioxidant supplements.
Adding vegetables to a dog’s diet is an easy way to provide nutritional support for cancer treatment. In cancer co-care, we may be careful not to give strong antioxidant supplements at the same time as some chemotherapy and radiation therapy due to the potential for negative interactions. However, feeding antioxidant-rich food is unlikely to interfere with conventional cancer treatments.
The advice given to us is to eat a rainbow of foods, and this is often what I recommend for my four-legged patients as well.
