Kale is a green, leafy, cruciferous vegetable that is rich in nutrients. It may offer a range of health benefits for the whole body.
It is a member of the mustard, or Brassicaceae, family, as are cabbage and Brussels sprouts.
This article looks at the nutritional content and health benefits of kale, how to include it in the diet, and reasons why some people should not eat too much of it.
Antioxidants help the body remove unwanted toxins that result from natural processes and environmental pressures.
These toxins, known as free radicals, are unstable molecules. If too many build up in the body, they can lead to cell damage. This may result in health problems such as inflammation and diseases. Experts believe that free radicals may play a role in the development of cancer, for example.
Learn more here about antioxidant foods.
Fiber: A 2018 study concluded that people who consume the highest amounts of dietary fiber appear to have a lower risk of developing type 2 diabetes. Consuming dietary fiber might also lower blood glucose levels, the authors note.
Antioxidants: Authors of a 2012 article note that high blood sugar levels can trigger the production of free radicals. They note that antioxidants, such as vitamin C and alpha-linolenic acid (ALA), can help reduce complications that may occur with diabetes. Both of these antioxidants are present in kale.
Various nutrients in kale may support heart health.
Potassium: The American Heart Association (AHA) recommend increasing the intake of potassium while reducing the consumption of added salt, or sodium. This, say the AHA, can reduce the risk of high blood pressure and cardiovascular disease. A cup of cooked kale provides 3.6% of an adult’s daily needs for potassium.
Fiber: A Cochrane review from 2016 found a link between consuming fiber and a lower blood lipid (fat) levels and blood pressure. People who consumed more fiber were more likely to have lower levels of total cholesterol and low-density lipoprotein (LDL), or “bad” cholesterol.
People need both soluble and insoluble fiber. Learn more here about both types.
Chlorophyll: Kale and other green vegetables that contain chlorophyll can help prevent the body from absorbing heterocyclic amines. These chemicals occur when people grill animal-derived foods at a high temperature. Experts have linked them with cancer.
The human body cannot absorb much chlorophyll, but chlorophyll binds to these carcinogens and prevents the body from absorbing them. In this way, kale may limit the risk of cancer, and pairing a chargrilled steak with green vegetables may help reduce the negative impact.
Antioxidants: The vitamin C, beta carotene, selenium, and other antioxidants in kale may help prevent cancer. Studies have not found that supplements have the same effect, but people who have a high intake of fruits and vegetables appear to have a lower risk of developing various cancers. This may be due to the antioxidants these foods contain.
How does a person’s diet affect their cancer risk? Find out here.
Calcium and phosphorus are crucial for healthy bone formation.
A cup of cooked kale provides almost five times an adult’s daily need for vitamin K, around 15–18% of their calcium need, and about 7% of the daily phosphorus requirement.
Get some more tips on increasing bone density.
Kale is high in fiber and water, both of which help prevent constipation and promote regularity and a healthy digestive tract.
Skin and hair
Kale is a good source of beta-carotene, the carotenoid that the body converts into vitamin A as it needs it.
Beta-carotene and vitamin A are necessary for the growth and maintenance of all body tissues, including the skin and hair.
The body uses vitamin C to build and maintain collagen, a protein that provides structure for skin, hair, and bones. Vitamin C is also present in kale.
A cup of cooked kale provides at least 20% of a person’s daily need for vitamin A and over 23% of the daily requirement for vitamin C.
For more tips on what to eat for eye health, click here.
The table below shows the amount of each nutrient in a cup of boiled kale, weighing around 118 grams (g), without added salt.
It also shows how much an adult needs of each nutrient, according to the 2015–2020 Dietary Guidelines for Americans. Requirements vary according to the individual’s sex and age.
|Nutrient||Amount in 1 cup||Daily adult requirement|
|Carbohydrate in grams (g)||6.3, including 1.4 g of sugar||130|
|Calcium in milligrams (mg)||177||1,000–1,200|
|Selenium in micrograms (mcg)||1.1||55|
|Vitamin C (mg)||21||75–90|
|Folate (mcg DFE)||76.7||400|
|Betaine (mg)||0.4||No data|
|Beta carotene (mcg)||2,040||No data|
|Lutein + zeaxanthin (mcg)||5,880||No data|
|Vitamin E (mg)||1.9||15|
|Vitamin K (mcg)||494||90–120|
|Vitamin A (mcg RAE)||172||700–900|
Kale also provides a range of antioxidants and B vitamins.
Find out more about the importance of spinach, which is another green, leafy vegetable.
Kale is a crisp and hearty vegetable, with a hint of earthiness. The flavors and nutritional content can vary between types. Younger leaves and summer leaves tend to be less bitter and fibrous.
Curly kale: This is the most commonly available type. It is usually bright green, dark green, or purple, with tight, ruffled leaves that are easy to tear. To remove the leaves from the fibrous stalk, run your hand down the stalk in the direction of growth.
Lacinato or dinosaur kale: This dark blue-green variety is firmer and more robust than curly kale. It is known as dinosaur kale because of its scaly texture. The leaves tend to be longer and flatter and maintain their texture after cooking. Less bitter than curly kale, dinosaur kale is ideal for making kale chips.
Red Russian kale: This is a flat-leaf variety that looks a little like oak leaves. The stalks are slightly purple, and the leaves have a reddish tinge. People may find the stalks too fibrous to eat, but the leaves are sweet and delicate, with a hint of pepper and lemon, almost like sorrel. People can add them raw to salads, sandwiches, and juices, or as a garnish.
Kale grows well in the colder winter months, making a good addition when other fruits and vegetables are less readily available. It is best to cook winter kale, as colder weather can turn the sugars in kale into starch, increasing the bitterness and fiber content.
People can eat kale raw, or steam, braise, boil, or sautée it, or add it to soups and casseroles.
Raw: Scrunching the leaves briefly in the hands can make them easier to digest. Add to salads, sandwiches, wraps, or smoothies.
As a side dish: Sauté fresh garlic and onions in olive oil until soft. Add kale and continue to sauté until desired tenderness. Alternatively, steam for 5 minutes, then drain and stir in a dash of soy sauce and tahini.
Kale chips: Remove the ribs from the kale and toss in olive oil or lightly spray and sprinkle with a combination of cumin, curry powder, chili powder, roasted red pepper flakes or garlic powder. Bake at 275°F for 15–30 minutes to desired crispness.
Smoothies: Add a handful of kale to any favorite smoothie. It will add nutrients without changing the flavor very much.
The Environmental Working Group, which assesses a range of products every year, put kale third on their 2019 list of fruits and vegetables most at risk of contamination with pesticides. People should wash kale thoroughly before using it.
Some people should avoid eating too much kale for the following reasons:
Beta-blockers: Doctors often prescribe this type of medication for heart disease. It can increase potassium levels in the blood. People who use beta-blockers should consume high potassium foods, such as kale, in moderation.
Kidney disease: Consuming too much potassium can be harmful to people whose kidneys are not fully functional. If the kidneys cannot remove excess potassium from the blood, consuming additional potassium could be fatal.
Blood thinners: Kale is a rich source of vitamin K, which contributes to blood clotting. This could interfere with the activity of blood thinners, such as warfarin (Coumadin).
Anyone who is taking any of these medications should speak to their doctor about foods to avoid.
Kale is a green, leafy vegetable that provides a wide range of nutrients. It is a healthful addition to a varied diet, and people can use it in numerous ways.
Learn more about other cruciferous vegetables:
Are foods like kale safe for people with a risk of a blood clot, since it contains so much vitamin K?
Those who are at risk of a blood clot should speak to their doctors about how much vitamin K is appropriate for them.
Those who use blood clotting medications, such as warfarin, should eat similar amounts of vitamin K daily to keep levels consistent, as extra vitamin K will affect the amount of medication they need.
Giving up vitamin K-rich foods is not necessary; it is more about keeping the amounts you consume daily consistent.
Natalie Olsen, R.D., L.D., ACSM EP-C Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.