Since kale is relatively new in our repertoires, many of us don’t know why it is fast becoming so popular. Nutritionally speaking, kale is a powerhouse. One cup (about 2 1/4 ounces or 67 g) has 34 calories, and 300 mg potassium, with only 29 mg sodium, and is very rich in beta-carotene and vitamin C. It has 90 mg of calcium which is very highly absorbed, even much better than from dairy.
Spinach is also full of nutrients. Two-and-a-quarter cups (the same 2 1/4 ounces or 67 g) has 15 calories, 53 mg sodium, 377 mg potassium, but less beta-carotene and much less vitamin C. It has more iron and less calcium than kale. However, the iron and calcium is very poorly absorbed from spinach. Spinach is very high in oxalic acid which binds calcium and iron so tightly that very little is absorbed during digestion. Not only does it reduce the absorption of calcium from the spinach, but it will also bind calcium from other foods that are consumed at the same time.
Bottom line? Choose kale for salads, to add to lasagna or pizza, or to incorporate in omelets. That will give you the biggest payoff for vegetable sources of calcium. Recipes for the kale salad, shown right, and more delicious foods based on kale are in the soon-to-be-published book, The Everyday DASH Diet Cookbook, by Marla Heller, MS, RD, with Rick Rodgers.