In terms of nutrition, spinach has more iron, twice as much magnesium, and more folic acid, says Moon. "Spinach is also much higher in choline, lutein and vitamin K, although both are really good sources."
For those who are concerned about fiber intake, kale may be the better option as it contains about twice as much as spinach. Kale also contains three times as much calcium and vitamin C. "It also contains more B vitamins that are involved in the metabolism," says Moon.
In terms of taste, spinach tends to be milder and more tender, which makes it easier to enjoy raw or cooked, she explains. Kale, on the other hand, tends to be harder, somewhat bitter and can withstand longer cooking times.
Because of these differences in texture and taste, kale can work better in a roast or stew. Spinach can, too, but it doesn't take that much cooking time and tends to wither a lot faster. Nevertheless, spinach is a good option for green smoothies due to its milder taste and delicate leaves.