The Dark Side of Kale (and How to Eat Around It)

Feburary 25, 2014                                                                                           by: Robert Zito

FILED UNDER: BostonMedicine/SciencePersonal Healthdietkalenutritionthyroid


If you have watched the media lately, you may have noted some pretty sensationalized headlines with regard to KALE.  Even Dr. Oz used the title, “The Dark Side of Kale“.  Which, also came from an article written over a month ago by Rachel Zimmerman. I will tell you up front that I have not written any of these findings. I only wanted to present a collection of information to help direct you to form your own opinion. What I will recommend is: Use moderation with anything you do & Always consult your physician if you have any underlying medical condition, before making any radical changes to your normal diet.

Can Kale Cause Kidney Stones?

What is an Oxalate and what is it found in? 
Oxalic acid is a naturally occurring colourless organic crystal that is found plants. Foods high in oxalic acids include spinach, chard (silverbeet), watercress, leeks, okra, purslane, parsley, beets & the leaves (beetroot), cacao, nuts such as almonds and cashews, buckwheat, some fruits such as starfruit, rhubarb, plums, figs, most berries and KALE. Most of the foods that contain oxalates are very important for good health. The root and leaves of rhubarb contain dangerously high concentrations of oxalic acid and should not be consumed raw. *kale-thyroid connection from the Oregon State University Micronutrient Information

Many charts show varying levels of oxalic acid in vegetables, fruits and other plant based foods. It has been shown that growing conditions will affect the amounts of oxalic acids found in plant foods.

Oxalic acid has been shown to bind with calcium and other minerals in the intestines and form an insoluble complex (oxalate) that is excreted via the stool (at least 70-90%), while research studies confirm the ability of oxalic acid in foods to lower availability of calcium and other minerals, the decrease is relatively small. This is also outweighed by the fact that there is so much more calcium, magnesium and iron in oxalate rich vegetables like spinach than the average vegetable in the first place that there will still be plenty of these minerals available to be absorbed! Claire Georgiou, Reboot Naturopath, B.HSc ND on July 26th, 2012


Can Kale Cause Hypothyroidism?

Very high intakes of cruciferous vegetables…have been found to cause hypothyroidism (insufficient thyroid hormone) in animals (68). There has been one case report of an 88-year-old woman developing severe hypothyroidism and coma following consumption of an estimated 1.0 to 1.5 kg/day of raw Bok Choy for several months. Two mechanisms have been identified to explain this effect. The hydrolysis of some Glucosinolates found in cruciferous vegetables (e.g., progoitrin) may yield a compound known as Goitrin, which has been found to interfere with thyroid hormone synthesis. The hydrolysis of another class of Glucosinolates, known as Indole Glucosinolates, results in the release of Thiocyanate ions, which can compete with iodine for uptake by the thyroid gland. Increased exposure to Thiocyanate ions from cruciferous vegetable consumption or, more commonly, from cigarette smoking, does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency. One study in humans found that the consumption of 150 g/day (5 oz/day) of cooked Brussels sprouts for four weeks had no adverse effects on thyroid function.

Teresa Fung, Sc.D., M.S.. an adjunct professor of nutrition at the Harvard School of Public Health and a professor at Simmons College in Boston, confirms the Kale-Thyroid link. But, she says, “normal, reasonable amounts of eating should not be a problem. A regular person [with no thyroid issues] who eats several servings of cruciferous vegetables a week should not have problems.”

Fung adds: “It’s the dose that makes a poison. If people have Hypothyroidism or they’re taking thyroid medication, then they should check with their doctor. But even in this case, reasonable amounts shouldn’t be a problem. Now, if people have a tall glass of kale juice every single day, then it gets into the unknown territory.”

1. Lightly Cook Your Kale

The goitrogenic properties of kale become dramatically lessened when kale — or any other cruciferous vegetable — is cooked. (Other veggies in this category include: broccoli, brussel sprouts, cabbage, cauliflower, collard greens, kohlrabi, mustard, rutabaga, turnips, bok choy and Chinese cabbage. Arugula, horseradish, radish, wasabi and watercress are also cruciferous vegetables.)

2. Eat Seaweed

Kale on its own does not increase the risk of thyroid problems. It’s a combination of factors; including potential iodine deficiency. (One of the most common causes of goiters is iodine deficiency.) Adding seaweed or another iodine rich food to your diet may, in some cases, help you get adequate iodine.

3. Throw a Brazil Nut Into Your Smoothie

Selenium can support normal iodine levels which in turn will support a healthy thyroid. A Brazil nut or two in your daily smoothie or as a topping to any dish might help keep selenium levels strong.

4. Switch Up Your Greens

Vary your greens. If you’re going to eat kale one day choose a non-cruciferous, non-goitrogenic veggie dish the next, like a simple cucumber and tomato salad, or beets. There are many highly nutritious vegetables that aren’t goitrogenic, including celery, parsley, zucchini, carrots and more. Our bodies need many nutrients and by eating a variety of vegetables you’ll ensure that you don’t overload on one and skip another.

January 10, 2014 | 2:36 PM | Rachel Zimmerman

See Dr. Oz’s suggestions to: Combat a Sluggish Thyroid


Possible Interactions with: Vitamin K


If you are currently being treated with any of the following medications, you should not take vitamin K without first talking to your health care provider.

Antibiotics — Antibiotics, particularly a class known as cephalosporins, reduce the absorption of vitamin K in the body. Long-term use (more than 10 days) of antibiotics may result in vitamin K deficiency because these drugs kill not only harmful bacteria but also beneficial, vitamin K-activating bacteria. This is mot likely to occur in people who already have low levels of vitamin K or are at risk for deficiency (such as those who are malnourished, elderly, or taking warfarin). Cephalosporins include:

  • Cefamandole (Mandol)
  • Cefoperazone (Cefobid)
  • Cefmetazole (Zefazone)
  • Cefotetan (Cefotan)

Phenytoin (Dilantin) — Phenytoin interferes with the body’s ability to use vitamin K. Taking anticonvulsants (such as phenytoin) during pregnancy or while breastfeeding may deplete vitamin K in newborns.

Warfarin (Coumadin) — Vitamin K reduces the effects of the blood-thinning medication warfarin, rendering the medication ineffective. Vitamin K should not be taken while taking warfarin, and foods containing high amounts of vitamin K should be avoided.

Orlistat (Xenical, alli) and Olestra — Orlistat, a medication used for weight loss, and olestra, a substance added to certain food products, prevent the absorption of fat and can reduce the body’s absorption of fat-soluble vitamins. The Food and Drug Administration now requires that vitamin K and other fat-soluble vitamins (A, D, and E) be added to food products containing olestra. In addition, physicians who prescribe orlistat add a multivitamin with fat soluble vitamins to the regimen.

The fact that vitamin K is now added to olestra-containing foods is important to know if you should not be taking vitamin K (if you are on the blood thinner warfarin, for example).

Bile acid sequestrants — These medications, used to reduce cholesterol, reduce the overall absorption of dietary fats and may also reduce absorption of fat-soluble vitamins. If you take one of these drugs, your doctor may recommend a vitamin K supplement:

  • Cholestyramine (Questran)
  • Colestipol (Colestid)
  • Colsevelam (Welchol)

Drug Interactions

  • Doxorubicin
  • Orlistat
  • Phenytoin
  • Warfarin

Alternative Names:   Menadione; Menaphthone; Menaquinone; Phylloquinone; Vitamin K

University of Maryland Medical Center 9/2007

Nature's Way Selenium
Nature’s Way Selenium



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