What makes kale so famous? A cabbage cousin, and the secret of massaging your greens

Kale, cabbage, broccoli: one big family

Thousands of years ago, a wild cabbage grew along the Mediterranean coast, with thick, slightly bitter leaves. Farmers began breeding it.

• Those who liked big leaves kept the big-leaf plants. Over time, that became kale.
• Those who liked tight, rolled heads of leaves got cabbage.
• Those who liked the young flower clusters got broccoli and cauliflower.
• Those who liked a swollen stem got kohlrabi (su hào in Vietnamese).

All of them belong to the species Brassica oleracea. So every time you eat stir-fried cabbage or kohlrabi soup, you are eating a very close relative of kale.

In Vietnam, kale is grown mostly in Đà Lạt, the cool highland town. Some kinds have tightly curled leaves, and some have long, dark leaves known as dinosaur kale (lacinato).

Small but mighty: kale's report card

According to the USDA food database, 100g of raw kale has about 35 to 50 kcal (depending on the data version) and around 4g of fiber. But the headline is the vitamins:

The calcium story deserves a little more. Spinach is also high in calcium, but it contains a lot of oxalate, a compound that "locks up" calcium. Kale has far less oxalate. A classic 1990 study found that the share of calcium absorbed from kale was no worse than from cow's milk. The catch: to match the calcium in a glass of milk, you would need to eat quite a lot of kale.

Why is kale bitter, and why do people "massage" it?

The cabbage family has a group of compounds called glucosinolates. They are the plant's weapon against insects. When you chew or cut the leaves, glucosinolates meet an enzyme and form sharp, bitter compounds. The nose-tingling bite of mustard and of cải bẹ xanh (Vietnamese mustard greens) comes from this same family.

Scientists are studying glucosinolates and their by-products a great deal. But so far there is not enough evidence to say eating kale protects against any specific illness. We see it as one part of "eating a variety of vegetables", not a miracle food.

Kale leaves are also tough and chewy because their cell walls are thick. That is why Korea has namul: vegetables gently massaged by hand with sesame oil, salt and toasted sesame seeds.

When you massage the leaves, some of the cell walls break. The leaves soften, collapse, lose some bitterness and turn a deeper green. A full basket of kale shrinks to a small bowl.

Sesame oil is not just for flavor

Here is the most fun detail. The vitamin K and beta-carotene in kale are fat-soluble. They need a little fat alongside to be absorbed well.

Many studies found that eating leafy greens with a bit of oil boosts carotenoid absorption far more than eating the greens plain. So kale massaged with sesame oil, or a kale salad with a dressing that has some oil, is a very sensible way to eat it. Our grandparents stir-frying greens in lard were getting this right without knowing it.

How to make kale easy to eat

• Strip out the center stem if it is thick, because it is very fibrous and chewy.
• Eating it raw? Massage it with a little oil and salt for about two minutes.
• Stir-fry it fast with garlic, like morning glory. Kale handles heat better than soft leafy greens.
• Add it to soup like mustard greens, dropping it in at the end to keep the color.
• Blending a smoothie? Keep the pulp, do not strain, so you keep the fiber.

And remember: kale is not "better" than cabbage or cải ngọt (choy sum) in every way. Every vegetable has its own strengths. Rotating many kinds is the real way to eat your greens well.

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