Kale: Health Benefits, Uses and Risks
If you have not tried kale yet, now may be the time. This super green is packed to the max with nutrition that puts it high on the list of the world’s healthiest foods.
Even spinach cannot come close in comparison to the number of nutrients that kale provides. Including kale in your diet provides nutrients that support healthy skin, hair and bones, as well as healthy digestion and a reduced risk of heart disease.
Other possible health benefits of kale include improving blood glucose control in diabetics, lowering the risk of cancer, lowering blood pressure and lowering the risk of developing asthma.
This MNT Knowledge Center feature is part of a collection of articles on the health benefits of popular foods, all written and reviewed by our qualified nutritionist. It provides a nutritional breakdown of kale and an in-depth look at its possible health benefits, how to incorporate more kale into your diet and any potential health risks associated with its consumption.
Possible health benefits of consuming kale
Studies have shown that people with type 1 diabetes who consume high-fiber diets have lower blood glucose levels and that people with type 2 diabetes may have improved blood sugar, lipids and insulin levels on a high-fiber diet. One cup of chopped fresh kale (about 16 grams) provides 0.6 grams of fiber. A cup of cooked kale (about 130 grams) provides 2.6 grams of fiber.
The Dietary Guidelines for Americans recommends 21-25 g/day for women and 30-38 g/day for men.
Kale contains an antioxidant known as alpha-lipoic acid, which has been shown to lower glucose levels, increase insulin sensitivity and prevent oxidative stress-induced changes in patients with diabetes. Studies on alpha-lipoic acid have also shown decreases in peripheral neuropathy and/or autonomic neuropathy in diabetics.3
It is important to note that most studies have used high doses of alpha-lipoic acid administered intravenously. The same benefits have not been sufficiently demonstrated for oral supplementation.3 Kale can contribute to a healthy daily intake of alpha-lipoic acid from a variety of fresh fruits and vegetables.
Kale is packed with nutrition that puts it high on the list of the world’s healthiest foods.
The fiber, potassium, vitamin C and B6 found in kale all support heart health. An increase in potassium intake along with a decrease in sodium intake is the most important dietary change that a person can make to reduce their risk of cardiovascular disease, according to Mark Houston, M.D., M.S., an associate clinical professor of medicine at Vanderbilt Medical School and director of the Hypertension Institute at St. Thomas Hospital in Tennessee.2
In one study, those who consumed 4069 mg of potassium per day had a 49% lower risk of death from ischemic heart disease compared with those who consumed less potassium (about 1000 mg per day).2
High potassium intakes are 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.2
For blood pressure, increasing potassium intake may be just as important as decreasing sodium intake for lowering blood pressure because of potassium’s vasodilation effects.
According to the National Health and Nutrition Examination Survey, fewer than 2% of US adults meet the daily 4700 mg recommendation.2 One cup of chopped fresh kale provides 79 milligrams of potassium, while a cup of cooked kale provides 296 mcg of potassium.
Also of note, a high potassium intake is associated with a 20% decreased risk of dying from all causes.2
Because the human intestinal tract does not absorb chlorophyll in any great amount, kale and other green vegetables that contain chlorophyll can help to inhibit the absorption of carcinogenic heterocyclic amines, which are generated when grilling animal-derived foods at a high temperature.4
The chlorophyll in kale binds to these carcinogens and prevents their absorption, thereby limiting the risk of cancer. If chargrilled animal foods stay on your plate, be sure to pair them with green vegetables to help negate at least one of the negative effects of these foods.
Low intakes of vitamin K have been associated with a higher risk for bone fracture. Adequate vitamin K consumption is important for good health, as it acts as a modifier of bone matrix proteins, improves calcium absorption and may reduce urinary excretion of calcium.5
Kale is high in fiber and water content, both of which help to prevent constipation and promote regularity and a healthy digestive tract. It also contains vitamin, which promotes iron absorption, and B vitamins, which 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 17707 International Units of vitamin A. This nutrient is essential for the growth of all bodily tissues, including skin and hair, as well as 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.
As noted above, vitamin C also aids iron absorption, and kale is rich in both iron (1.17 mg per cup, cooked) and vitamin C, which could help prevent hair loss associated with iron-deficiency.
On the next page we look at the nutritional breakdown of kale, how to incorporate more kale into your diet and the health risks associated with kale.
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Kale’s nutritional breakdown
Kale is a leafy green cruciferous vegetable that is chock-full of essential vitamins C and K, vitamin A in the form of beta-carotene, and minerals like copper, potassium, iron, manganese and phosphorus. A cup of chopped fresh kale has only about 8 calories but contains 24 mg of calcium, 79 mg of potassium, and 17 mcg of folate.
One cup of cooked kale has over 1000% more vitamin C than a cup of cooked spinach and, unlike spinach, kale’s oxalate content is very low which means that the calcium and iron in kale are highly absorbable in the human digestive system.1
How to incorporate more kale into your diet
Kale can be enjoyed raw in salads or on sandwiches or wraps, it can be added to green juices, braised, boiled, sautéed or added to soups and casseroles. Many people also like to make kale chips by briefly toasting lightly marinated kale in an oven.
A member of the mustard family (Brassicaceae), kale has a spicier and more pronounced flavor than lettuce. It is also heartier and crisp with a hint of earthiness. Different types of kale have slightly different flavor profiles and nutrient profiles, and younger leaves and summer leaves tend to be less bitter and fibrous.
Curly kale is the most commonly available variety and is usually bright or dark green or purple in color. It has tight ruffled leaves that are easy to tear. To remove the leaves from the fibrous stalk, simply run your hand down the stalk in the direction of growth.
Lacinato kale, or dinosaur kale (so-called because of its scaly texture), is a dark blue-green variety that is firmer and more robust than curly kale. These leaves are generally longer and flat and maintain their texture after cooking. Not so bitter as 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 leaves have slightly purple stalks and a slight red tinge to the leaves themselves. 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 including in salads, sandwiches, juices and for adding as a garnish.
Kale grows well in the colder winter months, so can be a great addition to your fruit and vegetable intake when other produce is not as readily available. Winter kale is usually better cooked as colder weather can turn the sugars in kale into starch, and increase the bitterness and fiber content of the leaves.
If using kale raw in salads, it is a good idea to massage the kale (scrunch it briefly in your hands) to begin the breakdown of the cellulose in the leaves, thereby helping to release the nutrients for easier absorption.
Kale can be enjoyed raw in salads or on sandwiches or wraps, braised, boiled, sautéed or added to soups and casseroles.
Sauté fresh garlic and onions in extra-virgin olive oil until soft. Add kale and continue to sauté until desired tenderness.
Kale chips: Remove the ribs from the kale and toss in extra-virgin olive oil or lightly spray and sprinkle with your choice or a combination of cumin, curry powder, chili powder, roasted red pepper flakes or garlic powder. Bake at 275 degrees Fahrenheit for 15-30 minutes to desired crispness.
In a food processor or a high-speed blender, add a handful of kale to your favorite smoothie for a nutrient blast without a big change in flavor.
Potential health risks of consuming kale
Beta-blockers, a type of medication most commonly prescribed for heart disease, can cause potassium levels to increase in the blood. High potassium foods such as bananas and cooked kale should be consumed in moderation when taking beta-blockers.
Important note: consuming too much potassium can be harmful for those whose kidneys are not fully functional. If your kidneys are unable to remove excess potassium from the blood, it could be fatal.
A cup of cooked kale provides 1062.1 mcg of vitamin K, which could interfere with the activity of blood thinners such as Warfarin. Speak to your doctor about foods to avoid when taking these medications.
Information about other vegetables
If you’ve enjoyed reading about the possible health benefits of kale, why not take a look at our collection of articles about other fruits and vegetables.