Is Kale Safe For Your Dog? Experts Give Their Advice

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When it comes to staying healthy, it seems like every day brings something new to worry about. And it doesn’t stop with your own diet. Each new piece of information helps guide not only what you eat … but what you feed your dog as well. 

In case you weren’t already stressed enough, there’s another food up for debate … and that’s kale (along with other cruciferous vegetables like broccoli, cabbage and cauliflower). 

There’s some advice from experts below. But first here’s some background on kale …

Why Kale May Not Be The Right Choice For Dogs

Back in 2015, several articles were published describing how molecular biologist Ernie Hubbard discovered cruciferous vegetables may be hyperaccumulators of toxic heavy metals like thallium. This includes kale. The source of heavy metals is the soil the vegetables are grown in. 

This is on top of concerns that too many cruciferous vegetables can lower thyroid levels, according to a 2005 paper by Jane Higdon PhD at the Linus Pauling Institute at Oregon State University (1). 

So does that mean you should stop feeding your dog kale? Because kale has a lot of nutritional benefits too.

Why Kale Is Good For Dogs

Kale has been popular with health enthusiasts for a while. Everyone adds kale to smoothies and salads, or baked kale chips in the oven. Some even share this superfood with their pets. 

After all, kale is full of healthy nutrients. It’s a good source of fiber, vitamins C. K and E, iron, calcium, potassium and magnesium.

It’s also filled to the brim with antioxidants that fight cancer and disease.

Benefits Of Antioxidants In Kale

Your dog needs antioxidants to prevent oxidative stress. Oxidative stress happens when there’s an imbalance of free radicals and antioxidants in your dog’s body.   

Free radicals are unstable molecules with an odd number of electrons. They’re a natural byproduct of everyday processes … like metabolism and exercise.  But they’re also caused by environmental toxins like pollution, pesticides, or secondhand smoke.

To stabilize themselves, free radicals interact with other molecules. This can damage proteins, DNA and other cells. And eventually this damage will lead to diseases like …

Antioxidants stabilize free radicals and stop them from reacting with your dog’s cells and DNA.

So your dog needs to get enough antioxidants to fight free radical damage. Kale is an excellent choice. It’s full of antioxidants with potent health benefits …

RELATED: Why Your Dog’s Food Needs More Antioxidants …

1. Carotenoids 

Carotenoids are plant pigments. They’re responsible for the colors red, orange and yellow in plants, algae, bacteria and fungi. Yellow daffodils, red tomatoes, even the warm hues of autumn leaves, are full of carotenoids. They’re also one of the reasons the reason flamingos, salmon and shrimp who eat foods rich in these compounds are pink. 

Carotenoids are rich in antioxidants that protect your dog from free radicals. 

Kale has three major carotenoids … lutein, zeaxanthin and beta-carotene. 

Beta-carotene is a pro-vitamin A carotenoid. This means it converts into vitamin A in your dog’s body. And vitamin A is important for your dog’s skin, coat, muscles and nerves. 

Beta-carotene also helps …

  • Improve vision health
  • Restore the immune system (2)
  • Improve cognitive function
  • Protect skin from sun damage (3)
  • Prevent cancer (4)

Like beta-carotene, lutein and zeaxanthin are great for the eyes and skin. 

Lutein and zeaxanthin are most effective in supporting retina health. In fact, they’re the only carotenoids you can add to your dog’s diet that will accumulate in his retina (5). 

Research shows that this helps protect against …

  • Age-related macular degeneration (AMD) (6)
  • Cataracts (7)
  • Diabetic retinopathy (8)
  • Retinal detachment (9)
  • Uveitis (10)
  • Blue light damage (11)

Lutein and zeaxanthin can also protect your dog from the sun’s UV rays. This reduces skin inflammation (12) and slows aging (13). 

Studies show that lutein and zeaxanthin improve heart health (14). They reduce the buildup of plaque that hardens the arteries (15). This lowers the risk of stroke and heart attack. 

Lutein and zeaxanthin also help increase glutathione levels (14)  Glutathione is an antioxidant that’s produced in your dog’s cells. And it’s one of the most powerful antioxidants his body can make. It also helps with liver detox.  In fact, low glutathione may cause up to 45% of liver disease in dogs

But glutathione is depleted by …

  • Stress
  • Environmental toxins 
  • Aging
  • Diet 

And it can’t be easily replaced because dietary glutathione gets digested before it’s absorbed. So your dog needs compounds like lutein and zeaxanthin to keep up glutathione levels.  

2. Flavonoids 

Like carotenoids, flavonoids are plant pigments found in fruits and vegetables. They are also powerful antioxidants and anti-inflammatories. The two most common flavonoids are quercetin and kaempferol. And kale has both! 

Quercetin is well-known for its ability to fight allergies. It’s even referred to as nature’s Benadryl. This is because quercetin is also an antihistamine. Your dog’s body releases histamines to fight allergies. It’s what causes your dog to swell and get itchy. Quercetin reduces histamines and stops your dog from having an allergic reaction. 

While kaempferol (16) doesn’t help ease allergies, it has many benefits. Kaempferol helps …

  • Reduce inflammation (17)
  • Improve heart health (18)
  • Protect the brain (19)
  • Control diabetes (20)
  • Manage liver and metabolic disease (21)

Quercetin and kaempferol can both protect against cancer (22). 

RELATED: Read more about nature’s Benadryl, quercetin …

3. Chlorophyll

Have you ever seen your dog eat grass? If you have, there are a few reasons for it. Sometimes dogs eat grass to settle an upset stomach. Sometimes they do it just because they want to … and it’s totally normal behavior. Other times, your dog may crave an important nutrient he isn’t getting enough of … chlorophyll.

Chlorophyll is also a plant pigment. It’s the reason grass is green. Chlorophyll’s chemical structure is a lot like your dog’s hemoglobin. Hemoglobin is in your dog’s red blood cells and helps carry oxygen all over his body. Because the structures are so alike, chlorophyll can help replenish red blood cells

Chlorophyll also has many other benefits. It isn’t as powerful as the other antioxidants, but it does help with oxidative stress. That means it can protect cells from damage. Chlorophyll also helps …

  • Fight infections and heal wounds 
  • Boost the immune system 
  • Break down stones in your dog’s urinary tract
    (Caution: many foods high in chlorophyll also contain calcium oxalate, which can cause stones. More about this in a bit.)

Chlorophyll can also bind to toxins and heavy metals like mercury (23). It then carries them to your dog’s kidney, which flushes the toxins out of his system. This can help reduce organ damage and may prevent diseases like cancer.

The problem is that your dog may not digest the grass he’s eating to get his chlorophyll intake.. And that means he isn’t absorbing the nutrients he is after. Not to mention the grass may get treated with dangerous herbicides like Roundup. 

Luckily there are lots of foods you can add to your dog’s dish to increase his chlorophyll levels. Kale is one good source of chlorophyll. 

RELATED: How To Give Your Dog The Chlorophyll He Needs To Stay Healthy …

4. Vitamin C 

Vitamin C has many roles in your dog’s body. It supports tissue, cartilage, bones, blood vessels and teeth. It improves your dog’s ability to absorb calcium and iron. It also helps control the allergic response. And it’s an antioxidant that helps prevent disease and cancer. 

Unlike humans, dogs produce their own vitamin C. But sometimes your dog needs an extra boost. It may be a good idea to add vitamin C to your dog’s dish if …

  • He has allergies 
  • He needs an immune system boost 
  • You want to up his antioxidants
  • Your dog is a senior (dogs over 7 have trouble producing enough vitamin C)

It’s also helpful if your dog is stressed. That’s because vitamin C is used to produce anti-stress hormones. 

Common sources of stress for dogs can be things like new environments, travel, change in foods or other new routines, moving or loud noises. If he’s experiencing a lot of stress his body may use up vitamin C quicker than it can be produced.  Kale is full of vitamin C. One cup of kale has more vitamin C than spinach or a whole orange

So now that you know both the good and bad about kale, what do the experts have to say? 

What The Experts Have To Say About Kale For Dogs 

When you weigh the risks and the benefits, don’t get too overwhelmed by the information. This goes for any food you feed your dog, including kale. The key is moderation. 

If you feed a varied diet of clean whole foods, you’re already way ahead of the game. Here’s what some highly respected experts had to say about kale:

“Kale is rich in some minerals that when compared with AAFCO, FEDIAF or ancestral standards, are short in many meat-based diets. So the choice often comes down to use moderate amounts of kale and similar vegetables, find other foods that provide the minerals, add mineral supplements or have a diet that may be deficient in some important minerals. Mineral-rich vegetables reduce the number and amount of supplements that we need to add to meet standards.” – Steve Brown, Pet Nutrition Expert, Author of UnLocking The Canine Ancestral Diet

“The facts have always been there, if we saw them or not: Thallium is a renowned and vicious toxin, and kale appears to be an efficient accumulator of thallium. So this current interest in thallium is basically the intersection of two recent trends; our ability to detect smaller and smaller amounts of an element or molecule (rapidly improving lab sophistication) and devout foodies more able to follow extreme diets of their choice. I don’t see that pets are at increased risk from dietary thallium if they are fed prudent diets. All mammals have effective systems for neutralizing the occasional toxin. Unless fed a predominately vegetable diet, that itself was predominantly kale, for several months, I would not worry about thallium.” – Dr Richard S Patton PhD, author of Ruined By Excess, Perfected By Lack

“Follow your grandma’s advice: everything in moderation! The crucifers are the warrior veggies that knock out cancer; don’t deny your dogs the benefits of the indole-3-carbinol found in these healing foods, but use them in rotation. Buy crucifers grown in organic soil to avoid thallium contamination from environmental pollutants. If dogs have been fed conventionally grown cruciferous vegetables, both cilantro and chlorella can be used to naturally bind and excrete (chelate) thallium from the body.” – Dr Karen Becker DVM

What about the thyroid problems? Thyroid expert Dr Jean Dodds DVM has an easy enough fix …

“Cruciferous vegetables if fed raw have goitrogenic properties and can lower thyroid activity. But, once they are cooked, even lightly steamed, the goitrogenic activity is minimized.”

And lightly steaming them is the best option. If you boil them, you will destroy the nutrients that make broccoli so great for your dog. (Goitrogens are substances that lower thyroid hormone production. This can cause the thyroid to enlarge.)

How To Feed Kale To Your Dog

To help your dog reap the benefits of kale with the lowest risks possible, follow these feeding tips …

  1. Always buy organic, this will lower the risk of toxins and heavy metals in your kale.
  2. If you buy non-organic kale, add some chlorella or cilantro to help get any thallium out of your dog’s body.
  3. Lightly steam the kale to reduce its effect on thyroid hormone production.
  4. Make it a part of a balanced diet and introduce kale slowly to avoid gastric irritation.

Other Cautions

As mentioned earlier, chlorophyll in kale can help break down bladder stones. The problem is, kale also contains calcium oxalate, which can cause kidney and bladder stones.  Dogs who are prone to stones should eat food rich in calcium oxalate (like kale) in moderation. 

Kale also contains isothiocyanates. These are compounds that may lower the risk of cancer in humans. But in dogs, it can cause gastric irritation and in large amounts may be toxic. It’s safest to keep kale and other cruciferous vegetables to no more than 10% of your dog’s diet

So … should you feed your dog kale? The experts say … 

Let your dog enjoy some kale or other cruciferous veggies. They’re a healthy addition to his meat-based diet. But don’t overdo it! Include some other veggies in the rotation. That way your dog will stay healthy and enjoy all the goodness kale has to offer.

References
  1. Jane Higdon PhD, Linus Pauling Institute, Micronutrient Information Center, Oregon State University. Cruciferous Vegetables. Originally published in 2005, updated December 2016 by Barbara Delage PhD.
  2. Massimino S et al. Effects of age and dietary beta-carotene on immunological variables in dogs. J Vet Intern Med. 2003 Nov-Dec;17(6):835-42.
  3. Wilhelm Stahl, Helmut Sies. β-Carotene and other carotenoids in protection from sunlight. The American Journal of Clinical Nutrition. Volume 96, Issue 5, November 2012.
  4. Griffiths K, Aggarwal BB, Singh RB, Buttar HS, Wilson D, De Meester F. Food Antioxidants and Their Anti-Inflammatory Properties: A Potential Role in Cardiovascular Diseases and Cancer Prevention. Diseases. 2016;4(3):28. Published 2016 Aug 1.
  5. Widomska J, Subczynski WK. Why has Nature Chosen Lutein and Zeaxanthin to Protect the Retina?.J Clin Exp Ophthalmol. 2014;5(1):326.
  6. Eisenhauer B, Natoli S, Liew G, Flood VM. Lutein and Zeaxanthin-Food Sources, Bioavailability  and Dietary Variety in Age-Related Macular Degeneration Protection. Nutrients. 2017;9(2):120. Published 2017 Feb 9.
  7. Vu HT, Robman L, Hodge A, McCarty CA, Taylor HR. Lutein and zeaxanthin and the risk of cataract: the Melbourne visual impairment project. Invest Ophthalmol Vis Sci. 2006 Sep;47(9):3783-6. 
  8. Kowluru RA, Menon B, Gierhart DL. Beneficial effect of zeaxanthin on retinal metabolic abnormalities in diabetic rats. Invest Ophthalmol Vis Sci. 2008 Apr;49(4):1645-51. 
  9. Woo TT, Li SY, Lai WW, Wong D, Lo AC. Neuroprotective effects of lutein in a rat model of retinal detachment. Graefes Arch Clin Exp Ophthalmol. 2013;251(1):41-51.
  10. He RR, Tsoi B, Lan F, Yao N, Yao XS, Kurihara H. Antioxidant properties of lutein contribute to the protection against lipopolysaccharide-induced uveitis in mice. Chin Med. 2011;6(1):38. Published 2011 Oct 31.
  11. Roberts JE, Dennison J. The Photobiology of Lutein and Zeaxanthin in the Eye. J Ophthalmol. 2015;2015:687173.
  12. González S, Astner S, An W, Goukassian D, Pathak MA. Dietary lutein/zeaxanthin decreases ultraviolet B-induced epidermal hyperproliferation and acute inflammation in hairless mice. J Invest Dermatol. 2003 Aug;121(2):399-405. 
  13. Astner S, et al. Dietary lutein/zeaxanthin partially reduces photoaging and photocarcinogenesis in chronically UVB-irradiated Skh-1 hairless mice. Skin Pharmacol Physiol. 2007;20(6):283-91.
  14. Gammone MA, Riccioni G, D’Orazio N. Carotenoids: potential allies of cardiovascular health? Food Nutr Res. 2015;59:26762. Published 2015 Feb 6.
  15. Dwyer JH. Progression of carotid intima-media thickness and plasma antioxidants: the Los Angeles Atherosclerosis Study. Arterioscler Thromb Vasc Biol. 2004 Feb;24(2):313-9. 
  16. Calderón-Montaño JM et al. A review on the dietary flavonoid kaempferol. Mini Rev Med Chem. 2011 Apr;11(4):298-344.
  17. Kong, L., Luo, C., Li, X. et al. The anti-inflammatory effect of kaempferol on early atherosclerosis in high cholesterol fed rabbits. Lipids Health Dis 12, 115 (2013).
  18. Dabeek WM, Marra MV. Dietary Quercetin and Kaempferol: Bioavailability and Potential Cardiovascular-Related Bioactivity in Humans. Nutrients. 2019 Sep;11(10).
  19. Kouhestani S, Jafari A, Babaei P. Kaempferol attenuates cognitive deficit via regulating oxidative stress and neuroinflammation in an ovariectomized rat model of sporadic dementia. Neural Regen Res. 2018;13(10):1827-1832.
  20. Alkhalidy H, Moore W, Wang Y, et al. The Flavonoid Kaempferol Ameliorates Streptozotocin-Induced Diabetes by Suppressing Hepatic Glucose Production. Molecules. 2018;23(9):2338. Published 2018 Sep 13.
  21. Ren J, Lu Y, Qian Y, Chen B, Wu T and Ji G: Recent progress regarding kaempferol for the treatment of various diseases (Review). Exp Ther Med 18: 2759-2776, 2019
  22. Chen AY, Chen YC. A review of the dietary flavonoid, kaempferol on human health and cancer chemoprevention. Food Chem. 2013;138(4):2099-2107.
  23. Viehweger K. How plants cope with heavy metals. Bot Stud. 2014;55(1):35. doi:10.1186/1999-3110-55-35

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