What are the health benefits of kale?
The nutrients it contains support healthy skin, hair, and bones. The fiber content enhances digestion and contributes to cardiovascular health.
Here are some key points about kale. More detail is in the main article.
- Kale is a green, leafy, winter vegetable that is high in fiber.
- The potassium content of kale may help reduce the risk of heart disease.
- It can be a tasty and nutritious side dish or an addition to smoothies and salads.
- Anyone who is taking blood thinning medication or who has a kidney problem should check with a doctor before adding more kale to the diet.
Even the chlorophyll in kale may have health benefits.
It is also a good source of vitamin C and iron.
The fiber and antioxidants in kale may offer protection against diabetes.
Fiber: Studies have shown that a high intake of fiber may lower blood glucose levels in people with type-1 diabetes. Those with type-2 diabetes may see improved blood sugar, lipids, and insulin levels.
- One cup of chopped fresh kale, weighing about 16 grams (g), provides 0.6 g of fiber.
- A cup of cooked kale (about 130 g) provides 2.6 g of fiber.
The Dietary Guidelines for Americans 2015-2020 recommend a fiber intake of between 25 g and 33.6 g for adults aged over 18 years.
Antioxidants: Kale contains an antioxidant known as alpha-lipoic acid.
Studies suggest that this can help lower glucose levels, increase insulin sensitivity, and prevent oxidative stress-induced changes in patients with diabetes. It may also decrease peripheral neuropathy and autonomic neuropathy in these patients.
Most studies have used high doses of alpha-lipoic acid administered intravenously, rather than dietary sources. Nevertheless, kale can contribute to a healthy daily intake of this nutrient, which is also produced in our bodies naturally.
The fiber, potassium, vitamin C, and vitamin B6 found in kale all support heart health.
Increasing potassium intake while decreasing sodium intake is recommended to reduce the risk of cardiovascular disease (CVD).
In one study, participants who consumed 4,069 milligrams (mg) of potassium each day had a 49 percent lower risk of death from ischemic heart disease compared with those who consumed around 1,793 mg per day.
A high potassium intake is also associated with a reduced risk of stroke, protection against loss of muscle mass, preservation of bone mineral density, and reduction in the formation of kidney stones.
For lowering blood pressure, consuming more potassium may be as important as decreasing sodium intake, because potassium dilates the blood vessels.
The recommended intake of potassium is 4,700 mg a day. According to the National Health and Nutrition Examination Survey (NHANES), fewer than 2 percent of adults in the United States (U.S.) meet this recommendation.
Kale can help boost this intake.
- One cup of chopped fresh kale provides 79 mg of potassium
- One cup of cooked kale provides 296 mg of potassium
A high potassium intake is associated with a 20 percent lower risk of dying from all causes.
Kale and other green vegetables that contain chlorophyll can help prevent the body from absorbing heterocyclic amines. These chemicals are produced when grilling animal-derived foods at a high temperature, and they are associated with cancer.
Although the human body cannot absorb much chlorophyll, the chlorophyll in kale binds to these carcinogens and prevents the body from absorbing them. In this way, it may help limit the risk of cancer.
Anyone who enjoys a chargrilled steak should pair it with green vegetables to help reduce the negative impact.
Some research has suggested that a low intake of vitamin K is associated with a higher risk of bone fracture.
While the human body creates most of the vitamin K it needs, adequate vitamin K consumption is important for good health. It helps modify bone matrix proteins, improves calcium absorption, and may reduce the amount of calcium excreted in urine.
Kale is a good source of vitamin K.
Kale is high in fiber and water. Both of these help prevent constipation and promote regularity and a healthy digestive tract.
It also contains B vitamins, and vitamin C, which promotes iron absorption. These are essential for the release of energy from food.
Healthy skin and hair
Kale is high in beta-carotene, the carotenoid that is converted by the body into vitamin A as needed.
A cup of cooked kale provides 885 mcg of retinol A equivalent, or 17,707 International Units (IU) of vitamin A.
This nutrient enables all bodily tissues to grow, including skin and hair. It is also essential for the production of sebum, the oil that helps keep skin and hair moisturized. Immune function, eyesight, and reproductive function also rely on vitamin A.
A cup of cooked kale also provides 53.3 mg of vitamin C, which is needed to build and maintain collagen, the key protein that provides structure for skin, hair and bones.
Vitamin C and iron are also present in kale. Vitamin C helps the body absorb iron. One cup of cooked kale contains 1.17 mg of iron. An adequate intake of iron can help prevent anemia.
Kale is a green and leafy cruciferous vegetable that is rich in nutrients and fiber.
A cup of chopped, raw kale, weighing about 16 g contains:
- 8 calories
- 0.68 g of protein
- 1.4 g of carbohydrate
- 0.6 g of fiber
- 24 mg of calcium
- 0.24 mg of iron
- 8 mg of magnesium
- 15 mg of phosphorus
- 79 mg of potassium
- 6 mg of sodium
- 19.2 mg of vitamin C
- 23 mcg of folate DFE
- 112.8 micrograms (mcg) of vitamin K
- 80 mcg of vitamin A, RAE
One cup of cooked kale has over 1,000 percent more vitamin C than a cup of cooked spinach. Unlike spinach, kale is low in oxalate, so the calcium and iron it provides are more easily absorbed by the human digestive system.
Kale is a member of the mustard, or Brassicaceae, family, as are cabbage and Brussels sprouts.
It is also hearty and crisp, with a hint of earthiness. Different types of kale have slightly different flavor and nutrient profiles. Younger leaves and summer leaves tend to be less bitter and fibrous.
Curly kale is the most commonly available type. It is usually bright green, dark green, or purple in color. It has 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 is a dark blue-green variety that is firmer and more robust than curly kale. It is known as dinosaur kale because of its scaly texture. These leaves are generally longer and flat and maintain their texture after cooking. Less bitter than curly kale, dinosaur kale is ideal for making kale chips.
Red Russian kale is a flat-leaf variety that looks a little like oak leaves. The stalks are slightly purple stalks and the leaves have a reddish tinge. The stalks are very fibrous and are not usually eaten as they can be rather difficult to chew and swallow. The leaves of red Russian kale are sweeter and more delicate than other types, with a hint of pepper and lemon, almost like sorrel. They are ideal for salads, sandwiches, juices, and as a garnish.
Kale grows well in the colder winter months, making a good addition when other fruits and vegetables are less readily available. Winter kale is usually better cooked, as colder weather can turn the sugars in kale into starch, increasing the bitterness and fiber content.
Kale can be enjoyed raw in salads or on sandwiches or wraps, steamed, braised, boiled, sautéed or added to soups and casseroles.
In salads: When using kale raw in salads, massage the leaves by scrunching them briefly in the hands. This begins the breakdown of the cellulose in the leaves and helps release the nutrients for easier absorption.
As a side dish: Sauté fresh garlic and onions in extra-virgin 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 extra-virgin 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 degrees Fahrenheit for 15 to 30 minutes to desired crispness.
Smoothies: In a food processor or a high-speed blender, add a handful of kale to your favorite smoothie. It will add nutrients without changing the flavor very much.
Beta-blockers, a type of medication most commonly prescribed for heart disease, can cause an increase in potassium levels in the blood. High potassium foods, such as bananas and cooked kale, should be consumed in moderation when taking beta-blockers.
Consuming too much potassium can be harmful for those whose kidneys are not fully functional. If the kidneys cannot remove excess potassium from the blood, consuming additional potassium could be fatal.
A cup of kale provides 1,062.1 mcg of vitamin K. This could interfere with the activity of blood thinners such as warfarin, or Coumadin. Patients who are taking these medications should speak to their doctor about foods to avoid.
Reviewed by Karen Gill, MD