Nutrition & Benefits

The figures come from USDA FoodData Central, entry “Kale, raw” FDC ID 168421 (SR Legacy), cross-checked with FDC ID 323505 (Foundation Foods). Actual values in any kale vary with variety, soil, season and storage.

• Vitamin K: about 390 µg — roughly 325% of the Daily Value.
• Vitamin C: about 93 mg — roughly 104% of the Daily Value.
• Manganese: 0.92 mg — roughly 40% of the Daily Value.
• Vitamin A: 241 µg RAE — roughly 27% of the Daily Value.
• Calcium: 254 mg — roughly 20% of the Daily Value.
• Fiber: 4.1 g — roughly 15% of the Daily Value.
• Iron: 1.6 mg — roughly 9% of the Daily Value.

Vitamin K

Kale is one of the richest vegetable sources of vitamin K. The body needs it to make proteins that contribute to normal blood clotting and to the maintenance of normal bones. Because it interacts with some anticoagulants, it has its own section.

Vitamin C

Vitamin C is needed for many normal body functions: it contributes to normal collagen formation and normal immune function, and it increases the absorption of iron from plant foods. It is heat-sensitive, so raw or briefly cooked kale keeps more of it.

Vitamin A

Kale doesn’t contain preformed vitamin A; it contains beta-carotene (about 2873 µg per 100 g), a carotenoid the body converts into vitamin A. Vitamin A contributes to the maintenance of normal vision and normal immune function. Carotenoids are fat-soluble, so a drizzle of olive oil helps absorption.

Kale also contains folate (62 µg per 100 g raw).

Calcium

Calcium is needed for the maintenance of normal bones and teeth. What sets kale apart is that it is low in oxalate, unlike spinach, so its calcium is relatively well absorbed for a plant source. Try pairing it with tahini or labneh, Lebanese-style.

Iron

Iron is needed for red blood cell formation and normal oxygen transport in the body. Plant (non-heme) iron is less readily absorbed than the iron in meat, but vitamin C improves its absorption — and kale contains both. A squeeze of lemon over the salad helps too.

Lutein and zeaxanthin are yellow pigments from the carotenoid family; in kale, their color is masked by the deep green of chlorophyll. Unlike beta-carotene, they are not converted into vitamin A. Because they are fat-soluble, eating kale with a little olive oil helps the body absorb them.

Researchers are interested in these compounds because they concentrate in the macula of the retina. The U.S. National Eye Institute’s AREDS2 study tested a high-dose supplement formula that included lutein and zeaxanthin in people who already had age-related macular degeneration (AMD).

Glucosinolates are sulfur-containing compounds characteristic of cruciferous vegetables. When leaves are chopped, chewed or digested, a natural plant enzyme turns them into other compounds, such as indoles and isothiocyanates, which researchers study. This conversion is also part of why kale tastes slightly bitter.

The label “antioxidant” often comes from chemical tests in a test tube. The body absorbs, transforms and regulates these compounds in complex ways, so a test-tube result is not enough to judge their health effect in people.

Values are reference values per 100 g of raw kale, and each point is labeled either “established nutrient science” or “emerging research”.

The WHO recommendation excludes potatoes, sweet potatoes, cassava and other starchy roots. Different vegetables bring different nutrients, so it helps to mix colors and families: tomatoes, cucumbers, carrots, parsley and legumes — plus a dark, leafy cruciferous green such as kale.

• Add a handful of chopped kale to soup, an omelette or pasta sauce.
• Pair it with legumes and whole grains, as in kale tabbouleh with bulgur or a kale, chickpea and tahini bowl.
• Rotate your leafy greens through the week. Ideas in 7 days of inspiration.

Read more in why eat kale?

What kale contains

Kale belongs to the cruciferous vegetables, along with cabbage, broccoli and cauliflower. These vegetables contain glucosinolates, which are broken down — when leaves are chopped, chewed or digested — into compounds such as indoles and isothiocyanates. Kale also contains carotenoids, polyphenols, vitamins and fiber.

What laboratory and animal studies show

In cell and animal studies, some of these compounds influenced biological processes that researchers link to cancer development, which is why they remain an interesting research topic.

What human studies show

Results in people are mixed: some observational studies found an association between eating more cruciferous vegetables and a lower risk of certain cancers, while others found no clear association. An association alone cannot prove cause and effect, because people who eat more vegetables often differ in many other habits too.

What we can say with confidence

Balanced diets rich in a variety of vegetables, fruits, whole grains and legumes are associated with health benefits and are recommended by major health and research organizations. Kale can be part of that variety — not a substitute for it.

We cover this topic in more depth in kale and cancer research, including how to read headlines about “superfoods”.

Warfarin works by limiting the body’s ability to use vitamin K to make clotting factors. A sudden large increase — or drop — in vitamin K from food can therefore change how well the medicine works. That is why the usual advice is about consistency, not avoidance.

If you plan to start eating kale regularly — say, several times a week — let the healthcare professional who monitors your treatment know, and ask whether this advice applies to your specific medicine.

Our references: USDA composition data, the Codex Alimentarius guidelines on nutrition and health claims, and the NIH Office of Dietary Supplements fact sheets. See also our health disclaimer.