Kale vs spinach: two greens, two different jobs

Kale is Brassica oleracea, the same species as cabbage, broccoli, cauliflower, Brussels sprouts and kohlrabi. It belongs to the Brassicaceae — the cruciferous vegetables — whose sulfur-containing glucosinolates give kale its peppery, slightly bitter edge. Unlike cabbage, kale never forms a head: it grows as loose leaves, and the curly type sold by 3adan has the ruffled, bright-to-deep green leaves most people picture.

Spinach, Spinacia oleracea, belongs to the amaranth family (Amaranthaceae), alongside chard and beetroot. It contains no glucosinolates and tastes milder and more mineral; it can even leave a faintly chalky feel on the teeth, a hint of its oxalate content.

For the full family tree, read what are cruciferous vegetables? or our introduction to what kale is.

Notice what the table does not say: neither green “wins”. They simply do different jobs on the plate. The comparison below adds lettuce and cabbage to the picture.

Oxalate (oxalic acid) is a natural plant compound that binds calcium in the gut and makes it harder to absorb. Spinach is one of the best-known high-oxalate vegetables, so although it contains calcium, the body absorbs relatively little of it. Kale is low in oxalate, which is why its 254 mg of calcium per 100 g is considered relatively well absorbed for a plant source.

This does not make spinach a poor choice; it brings its own nutrients and a very different texture. It simply means that if you count on greens as one of your calcium sources, kale — alongside foods such as yogurt, labneh or tahini — is the more useful leaf. If you have been advised to limit oxalate for medical reasons, follow your healthcare professional’s guidance.

And iron?

Both greens contain non-heme (plant) iron, which the body absorbs less readily than iron from meat. Pairing either with vitamin C — lemon juice, tomato, sweet pepper — helps, and kale brings plenty of vitamin C of its own (about 93 mg per 100 g).

Raw

Young spinach leaves go straight into a salad. Curly kale needs a minute of preparation: strip the thick stems, cut the leaves finely and massage them with a little oil, lemon and salt for 1–3 minutes. The reward is a salad that stays lively after dressing instead of collapsing — see how to prepare raw kale.

Quick cooking

Spinach wilts in a minute or two and releases a lot of water; a big pile shrinks to a few spoonfuls. Kale leaves take roughly 3–5 minutes in a hot pan with oil and garlic and lose less volume. Chopped stems go in a few minutes earlier.

Long cooking and the oven

In soups and stews, kale keeps its shape and a pleasant chew, while spinach melts into the broth. In the oven, only kale turns into crisp chips; spinach is too thin and wet.

• Spinach recipe, kale instead: remove the stems, chop the leaves more finely and cook a few minutes longer. In fatayer-style fillings, salt and squeeze the chopped kale as you would spinach.
• Kale recipe, spinach instead: skip the massage, add it at the very end and expect it to shrink far more.
• Use both: a mix gives you tenderness and structure at once — try our kale and spinach omelette.
• Don’t swap for chips: crispy kale chips only work with kale.

If you take warfarin or a related anticoagulant, switching suddenly from occasional spinach to daily kale salads, or the reverse, can change how much vitamin K you eat. Keep your usual intake of leafy greens steady and talk to your healthcare professional before major dietary changes. More detail on our nutrition page and in vitamin K in leafy greens.