Potential Problems From Eating Too Much Kale or Spinach

I’ve been involved in the health field for a long time and have seen a few fads come and go—oat bran, carrot juice, and macrobiotic diets have all had their day. One fad food that has been around for a while is kale—mostly consumed as chips or raw in juice.

Aficionados hail kale as a superfood, rich in antioxidants, folate, biotin, vitamin C, calcium, and magnesium. But kale has a dark side because it is also rich in something else: anti-nutrients.

Goitrogens in Kale

The main anti-nutrient in kale is a goitrogen called thiocyanate. Goitrogens block the uptake of iodine by the thyroid gland, making it difficult for the thyroid gland to produce thyroid hormones. The result can be a condition called hypothyroidism, characterized by fatigue, low body temperature, constipation, weight gain, muscle weakness, hoarseness, and memory loss. At high levels and in sensitive people, goitrogens can lead to outright “goiter”—swelling of the neck and thyroid gland.

Goitrogens occur in many vegetables, such as broccoli, Brussels sprouts, cabbage, and cauliflower in the cruciferous family; and in leafy greens, particularly in some varieties of kale. (Other foods high in goitrogens include almonds, stone fruits, raspberries, strawberries, and sweet potatoes.)

If you are eating a varied diet that includes plenty of naturally occurring iodine and other thyroid-supporting nutrients (such as true vitamin A, found only in animal foods), the occasional consumption of foods containing goitrogens should not be a problem. However, even at relatively low concentrations, goitrogens can interfere with the uptake of iodine by the thyroid gland.

Goitrogens are neutralized, at least in part, by cooking. Steaming reduces goitrogen content by about 65 percent and boiling for half an hour destroys 90 percent of goitrogen content. Boiling will also take away some of the bitterness and toughness that makes kale so unpleasant to eat. In fact, there is a joke making the rounds on the Internet that to make kale tender enough to eat, add a rock and chopped kale to boiling water—when the rock is tender, the kale will be too!

Unfortunately, the goitrogens are there in full force in smoothies made with raw kale, or in chips made with dehydrated kale—and some folks are consuming a lot of these things. Thyroid disorders are a real possibility when eating so much kale, especially for those who already suffer from thyroid problems.

Oxalates in Spinach

If you add spinach to your green smoothies, you will be exposed to another menace: oxalates. Spinach is one of the highest oxalate foods—others include (but are not limited to) soy, almonds, potato skins, beets, navy beans, and dates. Moderate consumption of oxalate-containing foods is not a problem for most people—but frequent consumption of spinach, especially raw spinach, can predispose to kidney stones.

Another concern: Kale and spinach both take top spots on the “dirty dozen” list by the Environmental Working Group—deemed especially high in pesticides. Of course, you can use organic kale and spinach when making smoothies, but that doesn’t solve another recently discovered problem. Kale seems to concentrate the heavy metal thallium, with higher concentrations in organic kale compared to conventional.

A 2015 article published in the journal Craftmanship, reveals that molecular biologist Ernie Hubbard found high levels of thallium in the urine of patients at an integrative health clinic who were consuming a lot of kale (including organic kale) in green smoothies. The symptoms of thallium poisoning overlap those of hypothyroidism and include fatigue, hair loss, brain fog, and nausea.

The good news is, you don’t have to eat kale! Eggs and beef are a lot more fun to eat, and much richer in protein, niacin, selenium, and phosphorus. Eggs, in particular, are a rich source of vitamins A and D3 (there’s none in kale), vitamin E, B1, B2, B3, folate, iodine, and sodium (an essential nutrient). Beef is a great source of zinc. Beef and eggs both provide B12 (there’s none in kale).

Kale contains vitamin C, which is absent in eggs and beef, but fresh fruit is a much more pleasant way to obtain this important nutrient. Kale takes the lead in calcium and manganese, but dairy products like cheese are a more delicious way to get calcium, and many foods that actually taste good provide manganese—shellfish, berries, nuts, and grains to name a few.


per 100 grams KALE EGGS BEEF
Protein 4.7 g 12 g 17.8 g
Retinol (True Vitamin A) 0 198 ug 12.4 ug
Vitamin D3 0 1.32 ug 0.6 ug
Vitamin E 5.4 mg 3.37 mg 0.4 mg
Thiamine (B1) 0.15 mg 0.87 mg 0.04 mg
Riboflavin (B2) 0.29 mg 0.42 mg 0.15 mg
Niacin (B3) 2.8 mg 2.89 NE 3.74 mg
Vitamin B6 0.35 mg 0.11 mg 0.24 mg
Pantothenic Acid (Vitamin B5) 1.0 mg 1.72 mg 0.31 ng
Biotin 36.0 ug 23.6 ug 1.28 mg
Folate 60.0 ug 85.8 ug 9.21 ng
Vitamin B12 0 1.14 ug 1.82 ug
Vitamin C 169 mg 0 0
Sodium 35.0 mg 137mg 65.2 mg
Potassium 246 mg 132 mg 277 mg
Calcium 219.0 mg 50.4mg 8.16 mg
Magnesium 20.0 mg 11.5 mg 17.6 mg
Iron 2.0 mg 1.78 mg 1.97 mg
Copper 0.09 mg 0.06 mg 0.06 mg
Zinc 0.62 mg 1.24 mg 3.91 mg
Manganese 0.50 mg 0.04 mg 0.01 mg
Chromium 8.3 ug 0.37 ug 8.9 ug
Selenium 8.3 ug 19.9 ug 8.98 ug
Phosphorus 73.0 mg 195 mg 162 mg
Iodine 1.4 ug 25.9 ug 1.0 ug


The truth is, most plant foods contain anti-nutrients. Plants can’t run away from predators so they produce poisons to ward off pests. For this reason, we need to avoid eating any one plant food to excess and to prepare them properly. Proper preparation of grains, for example, reduces anti-nutrient content and makes them more nutritious to eat. While most of us can eat tender vegetables like lettuce and tomatoes raw in salads, we will get a lot more nutrition from less tender vegetables by cooking them—then serve with plenty of butter, of course!

How to Cook Spinach

Rinse spinach leaves and place in a pot, just large enough to hold them. Steam on medium heat for about ten minutes until well wilted. Remove from the pot to a heated serving bowl and use a potato masher to press out all the liquid—most of the oxalic acid comes out in the cooking water, so you will want to press this out as thoroughly as possible. (While some of the minerals will go out in the water, there are still plenty left in the cooked spinach.) Top the hot spinach with generous pats of butter and sprinkle with salt.

Views expressed in this article are the opinions of the author and do not necessarily reflect the views of The Epoch Times. Epoch Health welcomes professional discussion and friendly debate. To submit an opinion piece, please follow these guidelines and submit through our form here.

Sally Fallon Morell is the founding president of the Weston A. Price Foundation and founder of A Campaign for Real Milk. She is the author of the bestselling cookbook “Nourishing Traditions” (with Mary G. Enig, Ph.D.) and of many other books on diet and health.
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