Fruit is really good for dogs … even though some raw feeders would never include fruits in their dogs’ diets. But whether you feed raw, prey or processed kibble, adding fruit to your dog’s diet can give him an important health boost. There’s one compelling reason that makes fruits good for dogs … and that’s polyphenols.
What Are Polyphenols?
Many fruits have high polyphenol content. In berries and apples there’s up to 300 mg of polyphenols per 100 grams of fresh fruit (7). Some spices, herbs, nuts and vegetables contain good amounts of polyphenols too.
Why Are Polyphenols Important?
Polyphenols prevent degenerative diseases like cancer, cardiovascular disease and neurodegenerative diseases (3). Your dog can’t digest polyphenols but the bacteria in his colon can. Beneficial bacteria produce short-chain fatty acids (SCFA) that have many other vital roles (4) in the body. They’re a source of energy, protect the gut lining and support the immune system.
6 Important Benefits Of Fruit For Dogs
Fruits and vegetables provide your dog with hundreds of nutrients including polyphenols. Here are some reasons to give your dog fruits.
1. Manage Chronic Inflammation
Inflammation is a natural part of the body’s immune system. It’s helpful in the short term when your dog is sick or injured. Immune cells come to the affected area to fight disease and repair damaged tissues.
- Heart disease
- Joint disease
- Autoimmune diseases
In a 2014 study (6), researchers fed three groups of rats different diets for 2 months. The first group ate rat chow and the second ate a high fat, high sugar diet. The third ate the same high fat, high sugar diet but with cranberry juice as well. The researchers analyzed the rats’ livers and found the ones who had cranberry juice had fewer inflammatory markers. The polyphenols in the cranberries had two effects: they suppressed inflammatory enzymes and slowed down pro-inflammatory immune cells called cytokines.
In a 2016 review of animal studies, quercetin showed anti-inflammatory effects in obese rats (7) . A high-fat diet was supplemented with quercetin for 10 weeks and improved blood pressure, insulin sensitivity, and other factors in the rats.
2. Provide Antioxidants
Free radicals cause chronic inflammation. They’re damaged molecules that repair themselves by stealing molecules from the cells. This process can even harm DNA. If not controlled, free radicals build up and cause chronic inflammation and ultimately chronic disease and premature aging.
Antioxidants neutralize free radicals (8) that can damage cells and lead to diseases like cancer, diabetes and heart disease. Polyphenols in fruit, like curcumin and resveratrol, seek out free radicals. Feeding polyphenols found in fruit can help combat oxidative stress caused by environmental toxins, stress and poor diet.
3. Reduce Cancer Risk
Research shows that polyphenols reduce the risk of cancer (9). And researchers at Rutgers, State University of New Jersey, found they can inhibit cells that cause DNA methylation (9.1). That’s a major link to cancer. They also reactivate silenced genes in cancer cells and cause their death (apoptosis).
A 2010 study at the University of South Carolina looked at resveratrol, a polyphenol found in fruits like apples (10). Resveratrol reduced bacteria linked to colon cancer. This polyphenol, along with others, controls cancer cell growth and division. This means when your dog eats fruit, cancer cells are less likely to spread in your dog’s body.
4. Lower Blood Sugar Levels
There’s evidence polyphenols help lower blood sugar levels and manage the risk of diabetes in your dog (11, 12). Studies show polyphenols in the diet lower fasting blood sugar levels, raise glucose tolerance, and increase insulin sensitivity. These are important factors in lowering the risk of diabetes. In a 2017 study published in the British Journal of Nutrition, people eating the highest amounts of polyphenol-rich foods had a much lower risk of developing type 2 diabetes over 2–4 years, compared with those eating the lowest amounts (13). So research suggests that the anthocyanin component of polyphenols has the highest antidiabetic effect (14, 15). That’s a strong reason to feed your dog some red, purple, and blue foods like berries.
5. Support Gut Health
Feeding your dog feeds the few trillion bacteria that live in his gut. Protein and healthy fats feed the friendly bacteria in his gut. Your dog’s friendly bacteria help produce vitamins, strengthen the gut lining and modulate the immune system.
Toxins and starch in your dog’s diet can feed the bacteria that produce inflammatory by-products that lead to disease. A good population of friendly bacteria can crowd the harmful bacteria. Polyphenols feed the friendly bacteria so they can thrive.
The polyphenol, catechin, can stop the growth of bacteria. This includes E coli, Bordetella bronchiseptica (kennel cough bacteria) and salmonella. Quercetin can also stop E. coli from growing.
6. Detox The Liver
Natural polyphenols have attracted attention in studies for the prevention and treatment of liver diseases caused by the toxic world that surrounds your dog (16). His food contains pesticides and toxins on top of his exposure to chemicals, drugs, vaccines and cleaners. Toxins build up in your dog and cause chronic health problems. Your dog’s liver can process and remove most toxins from food and the environment. But some fat-soluble toxins are hard for the liver to metabolize. Instead, these toxins cling to liver cells and build up over time. And this can cause free radicals to accumulate in the liver as well.
Polyphenols support the liver’s two-phase detoxification process that removes fat-soluble toxins. In Phase 1 detox, enzymes neutralize toxins by converting them into less harmful molecules. But these molecules can still damage the body. So Phase 2 enzymes make these byproducts water-soluble so they can leave the body.
Which Fruits Are Good For Dogs?
Fruits, veggies, seeds and herbs can, and should, be an important part of your dog’s diet. Even wolves scour their environment for fruits and veggies. In the summer months, up to 25% of their stomach contents are fruit and other plant matter.
But variety is key! Because each fruit gives your dog different health benefits and polyphenols. To help you select a good variety of fruits (and vegetables) for your dog, you want to consider 4 major classes of polyphenols (8):
They’re anti-inflammatory, have cancer-fighting properties and improve cognitive function. There are more than 5,000 different compounds in flavonoids so it’s got many subclasses:
- Flavonols contain quercetin, which can reduce inflammation and fight cancer. Foods include apples, berries, kale and broccoli.
- Anthocyanin (15) has antioxidant effects. It’s found in red, blue and purple berries like blueberries, raspberries and cranberries.
- Flavanones contain hesperidin, a special antioxidant that can protect the brain. It’s found in citrus fruits like oranges, lemons and clementines.
- Flavanols contain catechin, which inhibits the growth of pathogenic bacteria. It’s found in berries and apples.
- Flavones: found in parsley, celery, hot peppers.
- Isoflavones: Genistein is an isoflavone, which can prevent tumor formation, and is found in soy-based foods. Other sources are legumes and alfalfa.
These are in the seeds and skin of fruits and in vegetables. They scavenge free radicals. Curcumin, the active constituent in turmeric, is one of the most notable phenolic acids. It disrupts cytokine activity to lower chronic inflammation.
They’re found in apricots, broccoli, leafy greens, and flax seeds. They’re useful in fighting hormone-associated cancers and can also be antioxidants. A 2016 Chinese study found lignans fed bacteria in the gut known to be beneficial in killing tumor cells (9).
They contain resveratrol, which is anti-inflammatory and can fight cancer. They’re found in blueberries, raspberries, and mulberries.
So you really need to add fruits (as well as vegetables, herbs and seeds) to your dog’s diet. They offer your dog valuable disease-fighting benefits.
Why Kibble Isn’t A Good Source Of Polyphenols
Kibble doesn’t even come close to providing a fraction of these benefits. Heating and processing food reduces its nutrition, changing its molecules. Cooking food destroys 5% to 50% of vitamins.
Studies (17) have found that cooking fruits and vegetables destroy many of the polyphenols. Boiling foods can remove half their polyphenols. Frying can cause a 60% loss and the loss was higher during steaming (18). And the free radical scavenging activity decreases by 60% with boiling and 30% with steaming.
So fresh is always best when it comes to fruits for dogs. You can add fruit directly to kibble to boost your dog’s nutrition. But there are a few things to know …
Cautions With Fruit
Never feed unripened fruit, and introduce new fruits in small amounts. Too much, too soon can cause an upset stomach and diarrhea. Always remove stones in fruit like plums as they can cause blockages. And finally, don’t overfeed fruit to diabetic dogs or a dog with severe inflammation.
Don’t forget that some fruits can be toxic to dogs! Always double-check to make sure he can eat the fruits and vegetables you’re giving him.
Now you know how polyphenols can help your dog, add some fruits to his meals and watch him flourish!
1. Williamson G. The role of polyphenols in modern nutrition. Nutr Bull. 2017 Sep;42(3):226-235.
2. Gharras, El Hasna. Polyphenols: food sources, properties and applications – a review. Int. Journal of Food Science & Tech. N. 2009.
3. Tsao R. Chemistry and biochemistry of dietary polyphenols. Nutrients. 2010 Dec;2(12):1231-46.
4. den Besten G, et al. The role of short-chain fatty acids in the interplay between diet, gut microbiota, and host energy metabolism. J Lipid Res. 2013 Sep;54(9):2325-40.
5. Hunter P. The inflammation theory of disease. The growing realization that chronic inflammation is crucial in many diseases opens new avenues for treatment. EMBO Rep. 2012 Nov 6;13(11):968-70.
6. Kim MJ, Kim JH, Kwak HK. Antioxidant effects of cranberry powder in lipopolysaccharide treated hypercholesterolemic rats. Preventative Nutrition and Food Science. 2014;19(2):75-81.
7. Kim Y, et al. Polyphenols and Glycemic Control. Nutrients. 2016 Jan 5;8(1):17.
8. Gharras, Hasna El. Polyphenols: food sources, properties and applications – a review. Int Journal of Food, Science & Tech. Vo 44, Iss 12, 2009.
9. Zhou Y, Zheng J, Li Y, et al. Natural polyphenols for prevention and treatment of cancer. Nutrients. 2016;8(8):515. Published 2016 Aug 22.
9.1. Fang M, Chen D, Yang CS. Dietary polyphenols may affect DNA methylation. Journal of Nutrition. 2007;137(1 Suppl):223S-228S.
10. Cui X, et al. Resveratrol suppresses colitis and colon cancer associated with colitis. Cancer Prevention Res (Phila). 2010 Apr;3(4):549-59.
11. Xiao JB, Högger P. Dietary polyphenols and type 2 diabetes: current insights and future perspectives. Curr Med Chem. 2015;22(1):23-38.
12. Anhe, Fernando, et al. Polyphenols and type 2 diabetes: A prospective review. PharmaNutrition. Volume 1, Issue 4, October 2013. Pages 105-114.
13. Grosso G, et al. Dietary polyphenol intake and risk of type 2 diabetes in the Polish arm of the Health, Alcohol and Psychosocial factors in Eastern Europe (HAPIEE) study. Br J Nutr. 2017 Jul;118(1):60-68.
14. Khoo HE, et al. Anthocyanidins and anthocyanins: colored pigments as food, pharmaceutical ingredients, and the potential health benefits. Food Nutr Res. 2017 Aug 13;61(1):1361779.
15. Azzini E, et al. Antiobesity Effects of Anthocyanins in Preclinical and Clinical Studies. Oxid Med Cell Longev. 2017;2017:2740364.
16. Li, Sha, et al. The Potential and Action Mechanism of Polyphenols in the Treatment of Liver Diseases. Oxidative Medicine and Cellular Longevity. vol. 2018, Article ID 8394818, 25 pages, 2018.
17. Hwang IG, Shin YJ, Lee S, Lee J, Yoo SM. Effects of different cooking methods on the antioxidant properties of red pepper. Prev Nutr Food Sci. 2012;17(4):286-292.
18. Gunathilake KDPP, et al. Effect of Different Cooking Methods on Polyphenols, Carotenoids and Antioxidant Activities of Selected Edible Leaves. Antioxidants (Basel). 2018 Aug 30;7(9):117.