Often labeled as a superfood, kale is one of the healthiest and most nutrient-dense foods you can eat.
This leafy green comes in a variety of colors, shapes, and textures. It’s often eaten raw in salads and smoothies but can also be enjoyed steamed, sautéed, boiled, or baked.
Along with broccoli and Brussels sprouts, kale is a cruciferous vegetable that offers an array of potential health benefits.
However, raw kale also contains a compound called goitrin, which can affect thyroid function.
This article examines whether raw kale is safe to eat.
Kale is a nutrient-dense food, as it’s low in calories and high in many important vitamins, minerals, and antioxidants.
For example, 1 cup (21 grams) of raw kale contains only 7 calories but is an excellent source of vitamins A, C, and K. It’s also a good source of manganese, calcium, copper, potassium, magnesium, and several B vitamins (1).
This vegetable is likewise packed with antioxidants. These molecules help counteract oxidative damage caused by compounds called free radicals and may reduce your risk of conditions like heart disease, Alzheimer’s, and certain forms of cancer (2Trusted Source, 3Trusted Source).
Due to kale’s nutrient composition, eating it may offer several health benefits, including promoting eye and heart health and protecting against certain forms of cancer (4Trusted Source, 5Trusted Source, 6Trusted Source).
Cooking affects the nutritional value
Raw kale has a bitterness that can be reduced by cooking it.
Still, studies have shown that cooking it may reduce its content of nutrients, including antioxidants, vitamin C, and several minerals (2Trusted Source, 7Trusted Source).
One study evaluated the effects of five cooking methods on the antioxidant and nutrient composition of kale (7Trusted Source).
Compared with raw kale, all cooking methods resulted in a significant reduction in total antioxidants and minerals, including calcium, potassium, iron, zinc, and magnesium (7Trusted Source).
While raw kale may boast the highest nutrient content, the study found that steaming retained the most antioxidants and minerals, compared with other cooking methods (7Trusted Source).
As a result, for those who prefer cooked kale, steaming it for a short duration may be the best way to preserve its nutrient levels.
Kale is a nutrient-dense food that’s high in several vitamins, minerals, and antioxidants. While cooking kale makes it less bitter, it also significantly reduces its antioxidant, vitamin C, and mineral content.
Raw kale may be high in goitrin
Raw kale may be more nutritious, but it may also harm your thyroid function.
Kale, along with other cruciferous vegetables, contains a high amount of goitrogens, which are compounds that can interfere with thyroid function (8Trusted Source).
Specifically, raw kale contains a type of goitrogen called goitrins.
There are some concerns about eating raw kale, as goitrins can decrease the uptake of iodine, which is essential for the production of thyroid hormones (8Trusted Source).
This is worrisome, as thyroid hormones help regulate your metabolism. As a result, thyroid dysfunction can lead to reduced energy levels, weight gain, sensitivity to cold, and irregularities in heart rate (9Trusted Source).
One review of goitrin concentrations in cruciferous vegetables found that only an excessive intake of 2.2 pounds (1 kg) of kale per day for several months significantly impaired thyroid function in otherwise healthy adults (8Trusted Source).
However, research has shown that a moderate intake of goitrin-rich vegetables, including kale, is likely safe for most individuals.
Additionally, animal and human studies indicate that eating broccoli and Brussels sprouts doesn’t significantly affect thyroid hormone levels or functioning, suggesting that moderate amounts may even be safe for those with thyroid issues (10Trusted Source, 11Trusted Source).
Furthermore, regular intake of cruciferous vegetables has only been associated with an increased risk of thyroid cancer in women with very low iodine intake (12Trusted Source, 13Trusted Source).
Still, given that cooking vegetables deactivates the enzyme responsible for releasing goitrin, those with thyroid problems may benefit from cooking kale before eating it, as well as ensuring adequate intake of iodine from foods like seafood and dairy (14Trusted Source, 15Trusted Source).
Raw kale contains goitrins, which can lower iodine levels and impair thyroid function. Yet, research shows that a moderate intake of kale is unlikely to have any serious effects on thyroid health.
The bottom line
Kale is one of the healthiest foods on the planet due to its high concentration of vitamins, minerals, and antioxidants.
Despite being high in goitrins, research shows that a moderate intake of raw kale is unlikely to affect your thyroid health. Plus, raw kale may be more nutritious than cooked varieties.
To reduce your risk of potential side effects from goitrins while reaping all the nutritional benefits that kale has to offer, consider incorporating both raw and cooked kale into your diet.
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