Is Kale Bad For Your Health?

‘Antinutrients’ Are Nothing to Fear

By Johannah Sakimura

Earlier this year, an opinion article in the New York Times caused quite a stir when a writer revealed that beloved kale might have a dark side. The author’s troubling revelation: America’s superfood darling contains compounds that can interfere with the production of thyroid hormones.
There is some truth to this. Kale and other cruciferous vegetables contain compounds called glucosinolates, which, after processing by the body, can suppress the thyroid gland’s ability to take up iodine and convert it into thyroid hormones. Among other functions, these hormones are critical for regulating metabolism.
However, this nutritional concern is mostly theoretical, according to experts. For one, the compounds are largely destroyed by cooking vegetables. Even for people who consume large amounts of raw kale, these thyroid-interfering ingredients would only be problematic if you have an underlying thyroid disorder and an iodine deficiency. (Outright iodine deficiency is relatively uncommon in the U.S. and other developed countries. However, pregnant and breastfeeding women have a higher risk of iodine insufficiency due to increased requirements and should take a prenatal vitamin that contains iodine to protect against deficiency.)
But the controversy doesn’t stop at kale. This story illustrates a growing undercurrent of concern about so-called “antinutrients”, a term I’ve seen popping up with greater frequency on health blogs and websites. So, before antinutrient angst erupts into the mainstream discussion, I’d like to put these needless worries to bed.

What You Need to Know About Antinutrients

Antinutrient is actually a real scientific term used to refer to any compound, such as glucosinolate, that reduces the body’s ability to absorb or use essential nutrients like vitamins and minerals. However, now that this scary-sounding word is filtering into our everyday lexicon, it’s ripe for exploitation. I can just see the package labels now…boxes of sugary, refined breakfast cereal tagged “Low in Antinutrients!”
Antinutrients, which include phytic acid (or phytates), lignans, saponins, phytoestrogens, oxalates, phenolic compounds, and others, are found in all plant foods, although the types and amounts vary tremendously from food to food. They’re part of the complex matrix that makes up the growing plant tissue. While these compounds can curtail the body’s absorption or usage of certain minerals and other beneficial compounds to some extent, they don’t block it entirely. You would have to eat extremely large quantities of the same high-antinutrient foods day in and day out in order for those foods to have a significant effect on your nutritional status.
Plus, the negativity inherent in the term “antinutrient” is misleading. I’m opposed to using the word altogether, especially outside of the scientific community, because these compounds also have incredible health benefits. In many cases, they’re the very same components that are thought to give beans, lentils, whole grains, vegetables, and fruits their well-documented disease-fighting powers. In fact, you may know these “antinutrients” by another name – “phytonutrients,” the highly-prized, health-boosting compounds that we celebrate in whole foods.
Remember those glucosinolates? They’re the same compounds that are believed to give cruciferous vegetables like broccoli, cabbage, and of course kale their cancer-fighting properties. Phytic acid, found in high amounts in beans and whole grains, may help lower blood sugar, cholesterol, and triglyceride levels. In fact, increased levels of phytonutrients (in addition to high fiber) is likely one of the reasons that eating whole grains may help reduce heart disease risk.
There are special circumstances in which avoiding “antinutrient”-type compounds in foods may be warranted, but not for the reasons you might think. For example, people who get kidney stones, specifically calcium-oxalate stones, are typically advised to limit high-oxalate foods to reduce their risk of recurrence.
But the rest of us don’t need to think twice about antinutrients. As long as you eat a varied diet of nutrient-rich, whole foods and let your gut do its job, you’ll get the ingredients you need to keep your body humming along. So, you can go ahead and cross “antinutrients” off your health worry list, and focus on more important things, like whether you want your kale sauteed or steamed at dinner tonight.