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Kale

The beautiful leaves of the kale plant provide an earthy flavor and more nutritional value for fewer calories than almost any other food around. Although it can be found in markets throughout the year, it is in season from the middle of winter through the beginning of spring when it has a sweeter taste and is more widely available.

Kale is a leafy green vegetable that belongs to the Brassica family, a group of vegetables including cabbage, collards and Brussels sprouts that have gained recent widespread attention due to their health promoting, sulfur-containing phytochemicals. It is easy to grow and can grow in colder temperatures where a light frost will produce especially sweet kale leaves.

 


Health Benefits

Organosulfur Compounds that Prevent Cancer

As a member of the Brassica genus of foods, kale stands out as an anti-cancer food. It’s the organosulfur compounds in this food that have been main subject of phytonutrient research, and these include the glucosinolates and the methyl cysteine sulfoxides. Although there are over 100 different glucosinolates in plants, only 10-15 are present in kale and other Brassicas. Yet these 10-15 glucosinolates appear able to lessen the occurrence of a wide variety of cancers, including breast and ovarian cancers. Exactly how kale’s sulfur-containing phytonutrients prevent cancer is not clear, but several researchers point to the ability of its glucosinolates and cysteine sulfoxides to activate detoxifing enzymes in the liver that help neutralize potentially carcinogenic substances. (These detoxifying enzymes include quinone reductases and glutathione-S-transferases). For example, scientists have found that sulforaphane, a potent glucosinolate phytonutrient found in kale and other Brassica vegetables, boosts the body's detoxification enzymes, potentially by altering gene expression, thus helping to clear potentially carcinogenic substances more quickly.

Sulforaphane, which is formed when cruciferous vegetables such as kale are chopped or chewed, not only triggers the liver to produce enzymes that detoxify cancer-causing chemicals, inhibits chemically-induced breast cancers in animal studies, and induces colon cancer cells to commit suicide, but now, a new study published in the September 2004 issue of the Journal of Nutrition shows sulforaphane helps stop the proliferation of breast cancer cells, even in the later stages of their growth.(October 19, 2004)

Carotenoids that Lower Cataract Risk

In addition to its unique organosulfur compounds, kale is well-known for its carotenoids, especially lutein and zeaxanthin. These carotenoids act like sunglass filters and prevent damage to the eyes from excessive exposure to ultraviolet light. Studies have shown the protective effect of these nutrients against the risk of cataracts, where increased eye cloudiness leads to blurred vision. In one study, people who had a diet history of eating lutein-rich foods like kale had a 50% lower risk for new cataracts.

Kale also emerged from our food ranking system as an excellent source of traditional nutrients, including vitamin A, vitamin C, vitamin B6 and manganese. It is also a very good source of dietary fiber, calcium, copper, iron, vitamin B1, vitamin B2 and vitamin E. This combination of vitamins, minerals, and phytonutrients makes kale a health superstar!

Kale Gets an A+ for its Pro-vitamin A

Our food ranking system qualified kale as an excellent source of vitamin A on account of its concentrated beta-carotene content. Once inside the body, beta-carotene can be converted into vitamin A, so when you eat kale, it's like getting both these beneficial nutrients at once. One cup of kale contains just 36.4 calories, but provides 192.4% of the daily value for vitamin A.

Both vitamin A and beta-carotene are important vision nutrients. In a study of over 50,000 women nurses aged 45 to 67, women who consumed the highest dietary amount of vitamin A had a 39% reduced risk of developing cataracts. Beta-carotene has also been the subject of extensive research in relationship to cancer prevention and prevention of oxygen-based damage to cells. Beta-carotene may help to protect against certain forms of cancer since it belongs to the family of phytochemicals known as carotenoids. In population studies, consuming foods high in carotenoids is consistently found to be associated with a lower risk for various epithelial cancers. (The epithelium includes the cells that cover the entire surface of the body and line most of the internal organs.) In one study of 176 Australian men, researchers examined the diets of 88 of whom were treated for skin cancer and 88 men without cancer. The researchers found that men who ate more foods rich in beta-carotene, like kale, had a statistically lower risk of developing skin cancer.

Protection against Emphysema

If you or someone you love is a smoker, or if you are frequently exposed to secondhand smoke, then making vitamin A-rich foods, such as kale, part of your healthy way of eating may save your life, suggests research conducted at Kansas State University.

While studying the relationship between vitamin A, lung inflammation, and emphysema, Richard Baybutt, associate professor of nutrition at Kansas State, made a surprising discovery: a common carcinogen in cigarette smoke, benzo(a)pyrene, induces vitamin A deficiency.

Baybutt's earlier research had shown that rats fed a vitamin A-deficient diet developed emphysema. His latest animal studies indicate that not only does the benzo(a)pyrene in cigarette smoke cause vitamin A deficiency, but that a diet rich in vitamin A can help counter this effect, thus greatly reducing emphysema.

In his initial research, Baybutt took just weaned male rats and divided them into two groups, one of which was exposed to cigarette smoke, and the other to air. In the rats exposed to cigarette smoke, levels of vitamin A dropped significantly in direct correlation with their development of emphysema. In the second study, both groups of rats were exposed to cigarette smoke, but one group was given a diet rich in vitamin A. Among those rats receiving the vitamin A-rich foods, emphysema was effectively reduced.

Baybutt believes vitamin A's protective effects may help explain why some smokers do not develop emphysema. "There are a lot of people who live to be 90 years old and are smokers," he said. "Why? Probably because of their diet…The implications are that those who start smoking at an early age are more likely to become vitamin A deficient and develop complications associated with cancer and emphysema. And if they have a poor diet, forget it." If you or someone you love smokes, or if your work necessitates exposure to second hand smoke, protect yourself by making sure that at least one of the World's Healthiest Foods that are rich in vitamin A, such as kale, is a daily part of your healthy way of eating.(October 21, 2004)

A Healthy Dose of Vitamin C for Antioxidant Protection and Immune Support

Kale is an excellent source of vitamin C - just one cup of this cooked vegetable supplies 88.8% of the daily value for vitamin C. Vitamin C is the primary water-soluble antioxidant in the body, disarming free radicals and preventing damage in the aqueous environment both inside and outside cells. Inside cells, a potential result of free radical damage to DNA is cancer. Especially in areas of the body where cellular turnover is especially rapid, such as the digestive system, preventing DNA mutations translates into preventing cancer. This is why a good intake of vitamin C is associated with a reduced risk of colon cancer.

Free radical damage to other cellular structures and other molecules can result in painful inflammation, as the body tries to clear out the damaged parts. Vitamin C, which prevents the free radical damage that triggers the inflammatory cascade, is thus also associated with reduced severity of inflammatory conditions, such as asthma, osteoarthritis, and rheumatoid arthritis.

Free radicals also oxidize cholesterol. Only after being oxidized does cholesterol stick to artery walls, building up in plaques that may eventually grow large enough to impede or fully block blood flow, or rupture to cause a heart attack or stroke. Since vitamin C can neutralize free radicals, it can help prevent the oxidation of cholesterol. Vitamin C, which is also vital for the proper function of a healthy immune system, is good for preventing colds and may be helpful in preventing recurrent ear infections.

Protection against Rheumatoid Arthritis

While one July 2004 study suggests that high doses of supplemental vitamin C makes osteoarthritis, a type of degenerative arthritis that occurs with aging, worse in guinea pigs, another indicates that vitamin C-rich foods, such as kale, provide humans with protection against inflammatory polyarthritis, a form of rheumatoid arthritis involving two or more joints.

The findings, presented in the Annals of the Rheumatic Diseases were drawn from a study of more than 20,000 subjects who kept diet diaries and were arthritis-free when the study began, and focused on 73 subjects who developed inflammatory polyarthritis and 146 similar subjects who remained arthritis-free during follow-up between 1993 and 2001. Subjects who consumed the lowest amounts of vitamin C-rich foods were more than three times more likely to develop arthritis than those who consumed the highest amounts.(August 1, 2004)

Manganese - Energy Production Plus Antioxidant Protection

That same cup of kale will also provide you with 27.0% of the day's needs for manganese. This trace mineral helps produce energy from protein and carbohydrates, and is involved in the synthesis of fatty acids that are important for a healthy nervous system and in the production of cholesterol that is used by the body to produce sex hormones. Manganese is also a critical component of an important antioxidant enzyme called superoxide dismutase. Superoxide dismutase (SOD) is found exclusively inside the body's mitochondria (the oxygen-based energy factories inside most of our cells) where it provides protection against damage from the free radicals produced during energy production.

Cardiovascular Protection Brought to You By Kale's Vitamin B6 and Riboflavin

Vitamin B6 is involved in an important cellular process called methylation at the juncture where homocysteine, a dangerous molecule that can directly damage blood vessel walls, is converted into a helpful amino acid, methionine. Without riboflavin's assistance, however, vitamin B6 cannot change into the active form in which it catalyzes this conversion. No problem when kale is on the menu as it supplies both nutrients.

A cofactor in the reaction that regenerates glutathione, riboflavin is required to help maintain adequate levels of one of the body's most important antioxidants. Among glutathione's many beneficial activities, it protects lipids like cholesterol from free radical attack. Only after it has been damaged by free radicals does cholesterol pose a threat to blood vessel walls. A cup of kale contains 9.0% of the daily value for vitamin B6 along with 5.3% of the daily value for riboflavin.

A Very Good Source of Fiber

Kale's health benefits continue with its fiber; a cup of kale provides 10.4% of the daily value for fiber, which has been shown to reduce high cholesterol levels thus helping to prevent atherosclerosis. Fiber can also help out by keeping blood sugar levels under control, so kale is an excellent vegetable for people with diabetes. Kale's fiber binds to cancer-causing chemicals, keeping them away from the cells lining the colon, providing yet another line of protection from colon cancer. And the fiber in kale can help reduce the uncomfortable constipation or diarrhea in those suffering from irritable bowel syndrome.

Calcium - For A Lot Less Calories and Minus the Fat in Cow's Milk

Kale is also very good source of calcium. Calcium is one of the nutrients needed to make healthy bones, and dairy products are a heavily promoted source of this nutrient. But unlike dairy products, kale is not a highly allergenic food, nor does it contain any saturated fat - plus, a cup of kale supplies 93.6 mg of calcium (9.4% of the daily value for this mineral) for only 36.4 calories. In contrast, a cup of 2% cow's milk provides 296.7 mg of calcium, but the cost is high: 121.2 calories and 14.6% of the day's suggested limit on saturated fat.

Description

Kale is a leafy green vegetable that belongs to the Brassica family, a group of vegetables including cabbage, collards and Brussels sprouts that have gained recent widespread attention due to their health-promoting, sulfur-containing phytochemicals. There are several varieties of kale known commonly as curly kale, ornamental kale and dinosaur kale, all of which differ in taste, texture and appearance. The scientific name for kale is Brassica oleracea.

Curly kale has ruffled leaves and a fibrous stalk and is usually deep green in color. It has a lively pungent flavor with delicious bitter peppery qualities.

Ornamental kale is a more recently cultivated species that is oftentimes referred to as salad savoy. Its leaves may either be green, white or purple and its stalks coalesce to form a loosely knit head. Ornamental kale has a more mellow flavor and tender texture.

Dinosaur kale is the common name for the kale variety known as Lacinato. It features dark blue-green leaves that have an embossed texture. It has a slightly sweeter and more delicate taste than curly kale.

History

Like broccoli, cauliflower and collards, kale is a descendent of the wild cabbage, a plant thought to have originated in Asia Minor and to have been brought to Europe around 600 B.C. by groups of Celtic wanderers. Curly kale played an important role in early European foodways, having been a significant crop during ancient Roman times and a popular vegetable eaten by peasants in the Middle Ages. Kale was brought to the United States by English settlers in the 17th century.

Both ornamental and dinosaur kale are much more recent varieties. Dinosaur kale was discovered in Italy in the late 19th century. Ornamental kale, originally a decorative garden plant, was first cultivated commercially as in the 1980s in California. Ornamental kale is now better known by the name salad savoy.

How to Select and Store

Look for kale with firm, deeply colored leaves and moist hardy stems. Kale should be displayed in a cool environment since warm temperatures will cause it to wilt and will negatively affect its flavor. The leaves should look fresh, be unwilted, and be free from signs of browning, yellowing and small holes. Choose kale with smaller-sized leaves since these will be more tender and have a more mild flavor than those with larger leaves. Kale is available throughout the year, although it is more widely available, and at its peak, from the middle of winter through the beginning of spring.

Kale should be wrapped in a damp paper towel, placed in a perforated plastic bag and stored in the refrigerator crisper. It should not be washed before storing since this may cause it to become limp. Kale can be kept in the refrigerator for several days, although it is best when eaten within one or two days after purchase since the longer it is stored, the more bitter its flavor becomes.

How to Enjoy

For some of our favorite recipes, click Recipes.

Tips for Preparing Kale:

Before eating or cooking, wash the kale leaves thoroughly under cool running water to remove any sand or dirt that may remain in the leaves. Both the leaves and the stem of kale can be eaten. After removing any roots that remain, you can just cut it into the desired shape and size.

If your recipe calls for the leaves only, they can be easily removed. Just take each leaf in hand, fold it in half lengthwise, hold the folded leaves near the base where they meet the stalk, and with the other hand, gently pull on the stem. You can also use a knife to separate the leaves from the stems.

A Few Quick Serving Ideas:

Healthy Sauté kale with fresh garlic and sprinkle with lemon juice and olive oil before serving.

Braise chopped kale and apples. Before serving, sprinkle with balsamic vinegar and chopped walnuts.

Combine chopped kale, pine nuts and feta cheese with whole grain pasta drizzled with olive oil.

The taste and texture of steamed kale makes it a wonderful topping for homemade pizzas.

Safety

Kale and Oxalates

Kale is among a small number of foods that contain any measurable amount of oxalates, naturally-occurring substances found in plants, animals, and human beings. When oxalates become too concentrated in body fluids, they can crystallize and cause health problems. For this reason, individuals with already existing and untreated kidney or gallbladder problems may want to avoid eating kale. Oxalates may also interfere with absorption of calcium from the body. For this reason, individuals trying to increase their calcium stores may want to avoid kale, or if taking calcium supplements, may want to eat kale 2-3 hours before or after taking their supplements.

Kale and Goitrogens

Kale contains goitrogens, naturally-occurring substances in certain foods that can interfere with the functioning of the thyroid gland. Individuals with already existing and untreated thyroid problems may want to avoid kale for this reason. Cooking may help to inactivate the goitrogenic compounds found in food. However, it is not clear from the research exactly what percent of goitrogenic compounds get inactivated by cooking, or exactly how much risk is involved with the consumption of kale by individuals with pre-existing and untreated thyroid problems.

Nutritional Profile

Introduction to Food Rating System Chart

The following chart shows the nutrients for which this food is either an excellent, very good or good source. Next to the nutrient name you will find the following information: the amount of the nutrient that is included in the noted serving of this food; the %Daily Value (DV) that that amount represents (similar to other information presented in the website, this DV is calculated for 25-50 year old healthy woman); the nutrient density rating; and, the food's World's Healthiest Foods Rating. Underneath the chart is a table that summarizes how the ratings were devised. Read detailed information on our Food and Recipe Rating System.

 

Kale, Fresh, Boiled
1.00 cup
36.40 calories
Nutrient Amount DV
(%)
Nutrient
Density
World's Healthiest
Foods Rating
vitamin A 9620.00 IU 192.4 95.1 excellent
vitamin C 53.30 mg 88.8 43.9 excellent
manganese 0.54 mg 27.0 13.4 excellent
dietary fiber 2.60 g 10.4 5.1 very good
copper 0.20 mg 10.0 4.9 very good
tryptophan 0.03 g 9.4 4.6 very good
calcium 93.60 mg 9.4 4.6 very good
vitamin B6 (pyridoxine) 0.18 mg 9.0 4.5 very good
potassium 296.40 mg 8.5 4.2 very good
iron 1.17 mg 6.5 3.2 good
magnesium 23.40 mg 5.8 2.9 good
vitamin E 1.11 mg 5.6 2.7 good
vitamin B2 (riboflavin) 0.09 mg 5.3 2.6 good
omega 3 fatty acids 0.13 g 5.2 2.6 good
protein 2.47 g 4.9 2.4 good
vitamin B1 (thiamin) 0.07 mg 4.7 2.3 good
folate 17.29 mcg 4.3 2.1 good
phosphorus 36.40 mg 3.6 1.8 good
vitamin B3 (niacin) 0.65 mg 3.3 1.6 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

In Depth Nutritional Profile for Kale

References

  • Baybutt RC, Hu L, Molteni A. Vitamin A deficiency injures lung and liver parenchyma and impairs function of rat type II pneumocytes. J Nutr. 2000 May;130(5):1159-65.
  • Ensminger AH, Esminger M. K. J. e. al. Food for Health: A Nutrition Encyclopedia. Clovis, California: Pegus Press; 1986.
  • Jackson SJ, Singletary KW. Sulforaphane inhibits human mcf-7 mammary cancer cell mitotic progression and tubulin polymerization. J Nutr. 2004 Sep;134(9):2229-36.
  • Li T, Molteni A, Latkovich P, Castellani W, Baybutt RC. Vitamin A depletion induced by cigarette smoke is associated with the development of emphysema in rats. J Nutr. 2003 Aug;133(8):2629-34.
  • Lyle BJ, Mares-Perlman JA, Klein BE, et al. Antioxidant intake and risk of incident age-related nuclear cataracts in the Beaver Dam Eye Study. Am J Epidemiol 1999 May 1;149(9):801-9.
  • Pattison DJ, Silman AJ, Goodson NJ, Lunt M, Bunn D, Luben R, Welch A, Bingham S, Khaw KT, Day N, Symmons DP. Vitamin C and the risk of developing inflammatory polyarthritis: prospective nested case-control study. Ann Rheum Dis. 2004 Jul;63(7):843-7.
  • Thimmulappa RK, Mai KH, Srisuma S et al. Identification of Nrf2-regulated genes induced by the chemopreventive agent sulforaphane by oligonucleotide microarray. Cancer Res 2002 Sep 15;62(18):5196-5203.
  • Wood, Rebecca. The Whole Foods Encyclopedia. New York, NY: Prentice-Hall Press; 1988.

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