Every time I pass by that colossal bag of kale at the grocery store or our local farmers market, I have the distinct feeling that I should be eating more of the dark, leafy green. But I’m not sure if that’s because celebrities such as Gwyneth Paltrow and Ryan Seacrest say I should, or because the trendy veggie has any real, exceptional health benefits.
Turns out there’s quite a bit of science behind this super food hype: “Kale is rich in so many different things," says registered dietitian and nutritionist Cheryl Harris, of Harris Whole Health in Fairfax, Va., who notes that the cruciferous veggie — which is in the Brassica family, along with broccoli, cauliflower and cabbage — is an excellent, potent source of vitamin K, vitamin A, vitamin C, fiber and carotenoids, and that’s just to start. Research has also shown that kale contains 45 — count ’em, 45 — different flavonoids with a variety of antioxidant and anti-inflammatory effects.
“Any vegetable that has a very deep color the way kale does, that means there is a high concentration of nutrients, and that translates into a range of antioxidant and anti-inflammatory effects in the body," says Deirdre Orceyre, a naturopathic physician at the Center for Integrative Medicine at the George Washington University Medical Center.
This wide array of vitamins, nutrients and minerals results in several documented, distinct health advantages.
“Brassica vegetables are known to help with general health as well as heart disease and cancer, but even among this group kale stands out" because it has the broadest range of antioxidants and also the highest levels of several specific ones, along with vitamin K and a type of vitamin E that seems to be heart-healthy, Harris says. It has been shown to lower cholesterol and may reduce the risk of certain types of cancer, although there is evidence that a person’s specific genetic makeup also comes into play. A new laboratory study also found that kale extract inhibits the production of existing colon cancer cells.
Orceyre highlights the fact that the green contains indole-3- carbinol, a nutrient that seems to play a role in how estrogen is metabolized in the body and may play a protective role against breast cancer. “We sometimes use it as a supplement in patients with breast cancer, anyone who has a reason to be concerned about developing breast cancer and for those with estrogen-dominant illnesses like fibroids, fibrocystic breast disease or endometriosis, to try to help modulate negative estrogenic effects in the body," she says. “Eating kale is a natural way to do that."
Meanwhile, the fiber in kale can aid digestion in general, says Baltimore dietitian Angela Ginn, a spokeswoman for the Academy of Nutrition and Dietetics. Eating kale, she says, “revs up your body’s natural detoxification ability."
Notes of caution
Still, it’s probably best not to go overboard with kale and to simply integrate it into an overall healthful diet full of other fruits and vegetables.
“There are a couple of controversial things about kale that are worth mentioning," says Orceyre, who explains that its large concentration of vitamin K can be a problem for people taking blood thinners and other medications because it promotes clotting; the green also contains oxalates, which in lab tests have been associated with kidney stones and some gallstones.
Raw kale in particular “can be hard on the digestive system" — meaning it can cause bloating, gas and other abdominal issues — “and also contains a compound that can suppress thyroid function in certain people," she adds. That’s why she doesn’t recommend eating the vegetable uncooked or juicing it more than once or twice a week, though she says you can eat as much of the cooked veggie as you like.
Finally, Orceyre cautions that kale crops are often sprayed with pesticides, so buy organic if you can manage it, and in all cases be sure to clean vegetables well to wash away any surface chemicals.
Indeed, good overall preparation is essential if you want to enjoy that giant bag of kale, which has a well-deserved reputation for being tough and bitter.
“One mistake people make is that they don’t cut the center stem out: That’s what makes it really tough," says Ginn, who suggests cutting out the larger stems and slicing the leaves into strips, then washing them thoroughly and sprinkling with baking soda or baking powder to tenderize.