Kale

What’s new and beneficial about kale

• Among all 100 of our WHF, kale tops the list in terms of lutein content. Kale is not only our most lutein-rich food at WHF, it is also the top lutein-containing food in the USDA’s National Nutrient Database that analyzes 5,350 foods that contain this carotenoid nutrient. Among the carotenoids, lutein is perhaps best known for its supportive role in eye health, and in particular, for its ability to protect different parts of the eye from potential damage by light or oxygen. A recent study on African-American women has shown decreased likelihood of glaucoma (an eye problem usually caused by increased pressure within the eye) when dietary intake of kale reaches higher intake levels. In this case, “higher intake levels” were defined as any levels exceeding at least one half-cup serving per week. Since our WHF serving size for kale is one cup, you will be getting more than this amount from one serving based on our standard. Among all of the vegetables examined in this particular study, kale and collards came out at the top of the vegetable list in this study for decreasing the likelihood of glaucoma!
• A recent study has analyzed the combination of kale with lentils and found this food combination to be especially complementary in providing us with nutrient-richness. Interestingly, this study focused on two areas of nutrition: mineral nourishment and “prebiotic nutrients.” Prebiotic nutrients are nutrients that support the growth of desirable bacteria within our digestive tract. These nutrients often involve short chains of simple sugars called “oligosaccharides.” (Glucooligosaccharides, fructooligosaccharides, and xylooligosaccharides are well-studied examples of oligosaccharides.) In this study, researchers determined that the combination of prebiotic nutrients in kale-plus-lentils and the combination of mineral nutrients in kale-plus-lentils were especially were especially complementary as each food provided the nutrients that the other one lacked. In each nutrient category, kale and lentils were able to “bring something special to the table” that the other could not, resulting in outstanding combined nutrient richness. Why not take advantage of this unique food combination by starting with our Curried Lentils? Each serving of this vegetarian entreé will provide you with 1/2 cup of kale and 1/2 cup of lentils.
• The research track record for kale in providing overall cardiovascular support is fairly strong, and not limited to improvement in blood cholesterol levels. However, research on kale and cholesterol levels is especially interesting. Recent studies show that kale can provide you with some special cholesterol-lowering benefits if you cook it by steaming. The fiber-related components in kale do a better job of binding together with bile acids in your digestive tract when they’ve been steamed. When this binding process takes place, it’s easier for bile acids to be excreted, and the result is a lowering of your cholesterol levels. Raw kale still has cholesterol-lowering ability,just not as much. Along these same lines, a recent study has examined the impact of 5 ounces of kale juice per day for 12 weeks in men with high blood cholesterol levels (above 200 mg/dL). Consumption of kale juice was determined to raise the HDL levels in these study participants, lower their LDL levels, and also improve their atherogenic profiles (which measured their likelihood of developing coronary artery disease). At WHF, we always encourage consumption of whole foods in their minimally processed forms. However, we also believe that this study on kale juice underscores the remarkable health benefits that can be derived from this cruciferous vegetable.
• Recent genetic studies on kale have shown it to have remarkable diversity, not only in terms of its physical varieties but also in terms of its nutrient content. For example, over 45 different flavonoids are known to be present in significantly differing amounts across the many different varieties of kale that can be found within the very broad kale family. One recent study has compared an Italian Lacinato-type variety of kale (also sometimes called Tuscan Black or Dinosaur kale) to a North American broad-leafed kale (often called a Napus or Siberian type kale) as well as to a German curly-leaf variety of kale (belonging to the Scotch/Scotch-Curled type of this cruciferous vegetable). As you can see, the very description of these kale types requires us to think about two continents and even more countries in which the kale was being grown. This particular study focused on sulfur-containing compounds in kale,including its glucosinolates. The researchers determined that glucosinolate content in kale can vary by as much as 10-fold depending on the specific variety in question and the conditions of cultivation and harvest. In general, this study showed that curly-leafed kale varieties and darker Lacinato varieties of kale contained higher levels of glucosinolates (and especially one particular glucosinlate called glucoraphanin) than the broad-leafed, Napus/Siberian types of kale. For glucosinolate-related health benefits from kale, you might want to focus on these varieties. In our Description section, you can find more details about each of these kale varieties.
• Kale is now recognized as providing comprehensive support for the body’s detoxification system. New research has shown that the ITCs made from kale’s glucosinolates can help regulate detox at a genetic level.

Recommendations

You’ll want to include kale as one of the cruciferous vegetables you eat on a regular basis if you want to receive the fantastic health benefits provided by the cruciferous vegetable family. At a minimum, we recommend 3/4 cup of cruciferous vegetables on a daily basis. This amount is equivalent to approximately 5 cups per week. A more optimal intake amount would be 1-1/2 cups per day, or about 10 cups per week. You can use our Veggie Advisor for help in figuring out your best cruciferous vegetable options.

Kale is one of the healthiest vegetables around and one way to be sure to enjoy outstanding nutrition and flavor from kale is to cook it properly. We recommend Healthy Steaming kale for 5 minutes. To ensure quick and even cooking cut the leaves into 1/2” slices and the stems into 1/4” lengths. While there might be potential health benefits from letting the stems and slices sit for about 5 minutes prior to cooking, the scientific research in this area is definitely mixed. You can find many key details in our article, Can Preparation Methods Impact the Benefits of Cruciferous Vegetables?.

Kale, cooked
1.00 cup
(130.00 grams)

Calories: 36
GI: very low

NutrientDRI/DV

 vitamin K1180%

 vitamin A98%

 vitamin C71%

 manganese23%

 copper22%

 vitamin B611%

 calcium9%

 fiber9%

 iron7%

 vitamin E7%

 vitamin B27%

 magnesium6%

 vitamin B16%

 potassium6%

 phosphorus5%

 protein5%

 omega-3 fats5%

 folate4%

 vitamin B34%

Food Rating System Chart

• Health Benefits
• Description
• History
• How to Select and Store
• Tips for Preparing and Cooking
• How to Enjoy
• Individual Concerns
• Nutritional Profile
• References

Health benefits

While less extensively studied than broccoli or cabbage, kale delivers exceptional nutrient density. One cup (130g) cooked provides 1,062 mcg of vitamin K (1180% DV), 885 mcg RAE of vitamin A (98% DV), and 53.3 mg of vitamin C (71% DV), placing it among the most nutrient-concentrated vegetables available.

Antioxidant-related health benefits of kale

Like most of its fellow cruciferous vegetables, kale has been studied more extensively in relationship to cancer than any other health condition. This research focus makes perfect sense. Kale’s nutrient richness stands out in three particular areas: (1) antioxidant nutrients, (2) anti-inflammatory nutrients, and (3) anti-cancer nutrients in the form of glucosinolates. Without sufficient intake of antioxidants, our oxygen metabolism can become compromised, and we can experience a metabolic problem called “oxidative stress.” Without sufficient intake of anti-inflammatory nutrients, regulation of our inflammatory system can become compromised, and we can experience the problem of chronic inflammation. Oxidative stress and chronic inflammation,and the combination of these metabolic problems,are risk factors for development of cancer. We’ve seen research studies on five specific types of cancer,including bladder cancer, breast cancer, colon cancer, ovarian cancer, and prostate cancer,and intake of cruciferous vegetables (specifically including kale). As a group, these studies definitely show cancer preventive benefits from kale intake, and in some cases, treatment benefits as well.

Kale’s cancer preventive benefits have been clearly linked to its unusual concentration of two types of antioxidants, namely, carotenoids and flavonoids. Within the carotenoids, lutein and beta-carotene are standout antioxidants in kale. As mentioned in our What’s New and Beneficial section, over 45 different flavonoids have been identified in kale. Most prominent among kale’s flavonoids are its flavonols, including kaempferol, quercetin, and isorhamnetin. Researchers have actually followed the passage of these two carotenoids in kale from the human digestive tract up into the blood stream, and they have demonstrated the ability of kale to raise blood levels of these carotenoid nutrients. That finding is important because lutein and beta-carotene are key nutrients in the protection of our body from oxidative stress and health problems related to oxidative stress. Increased risk of cataracts, glaucoma, atherosclerosis, and chronic obstructive pulmonary disease (COPD) are four such problems. Also among these chronic health problems is cancer since our overall risk of cells becoming cancerous is partly related to oxidative stress.

Within the flavonoids, kaempferol is a spotlight antioxidant in kale, followed by a flavonoid called quercetin. You’re likely to be getting about 60 milligrams of kaempferol in the one-cup serving of kale that we use as the standard serving size on our website, as well as 29 milligrams of quercetin. Alongside of these spotlight flavonoids, however, it is probably the very broad spectrum of flavonoid antioxidants in kale that are largely responsible for kale’s cancer-preventive and other benefits, owing to their ability to reduce oxidative stress.

Anti-inflammatory health benefits of kale

We have yet to see research on kale’s omega-3 content and inflammation, but we would expect this kind of research to show the omega-3s in kale to be an important part of kale’s anti-inflammatory benefits. It only takes 100 calories of kale to provide over 350 milligrams for the most basic omega-3 fatty acid (alpha-linolenic acid, or ALA). We suspect that this amount will be plenty to show direct anti-inflammatory benefits from routine kale intake.

We also have yet to see specific research on inflammation and kale’s vitamin K content. But we know that kale is a spectacular source of vitamin K (one cup of kale provides far more micrograms of vitamin K than any of our World’s Healthiest foods) and we also know that vitamin K is a key nutrient for helping regulate our body’s inflammatory process. Taken in combination, we expect these two facts about vitamin K to eventually get tied together in health research that shows kale to be an exceptional food for lowering our risk of chronic inflammation and associated health problems.

Glucosinolates and cancer-preventive benefits of kale

What we have already seen in the health research on kale is ample evidence that its glucosinolates provide cancer-preventive benefits. Kale is a top food source for at least four glucosinolates, and once kale is eaten and digested, these glucosinolates can be converted by the body into cancer preventive compounds. Kale’s glucosinolates and the ITCs made from them have well-documented cancer preventive properties, and in some cases, cancer treatment properties as well. At the top of the cancer-related research for kale are colon cancer and breast cancer, but risk of bladder cancer, prostate cancer, and ovarian cancer have all been found to decrease in relationship to routine intake of kale. The chart below presents a summary of the unusual glucosinlate phytonutrients found in kale, and the anti-cancer ITCs made from them inside the body

Glucosinolates in kale and their detox-activating isothiocyanates

Glucosinolate

Derived Isothiocyanate

Isothiocyanate Abbreviation

glucobrassicin

indole-3-carbinol*

I3C

glucoraphanin

sulforaphane

SFN

gluconasturtiian

phenethyl-isothiocyanate

PEITC

glucopaeolin

benzyl-isothiocyanate

BITC

sinigrin

allyl-isothiocyanate

AITC

* Indole-3-carbinol (I3C) is not an isothiocyanate. It’s a benzopyrrole, and it is only formed when isothiocyanates made from glucobrassicin are further broken down into non-sulfur containing compounds.

In addition to the glucosinolates listed above, scientists have also identified glucobrassicanapin, glucoiberin, and gluconapin as glucosinlates present in kale.

Kale’s cardiovascular support

One set of health events that most people would like to avoid is clogging of the arteries (arteriosclerosis). Since plaque formation along the walls of the arteries is required for clogging, and since the plaque formation process is usually preceded by chronic inflammation and chronic oxidative stress, it is not surprising to see a food like kale lessening our risk of arteriosclerosis. The reason is simple: kale is a concentrated source of antioxidants and anti-inflammatory nutrients, as already described this Health Benefits section.

But the cardiovascular benefits of kale also extend to its cholesterol-lowering ability. What happens here is fairly straightforward. Kale contains a variety of fiber-related nutrients that can bind together with bile acids. When this binding takes place, our blood cholesterol levels go down because our body needs to replace the bile acids and they can be obtained from the breakdown of cholesterol. Studies on kale intake show that total blood cholesterol and LDL cholesterol drop with increasing amounts of kale in the diet, while interestingly, blood levels of HDL cholesterol increase. (Since higher levels of HDL cholesterol generally improve our cardiovascular health, this increase in HDL is a good thing.) Intake of both raw and steamed kale have been shown to provide cardio benefits, but the benefits seem somewhat stronger from intake of steamed kale. It’s also worth noting that a recent study on kale juice (using 5 ounces per day for 12 weeks) has shown these same cholesterol-related benefits.

Other health-related benefits of kale

Kale has a definite role to play in support of the body’s detoxification processes. The isothiocyanates (ITCs) made from kale’s glucosinolates have been shown to help regulate detox activities in our cells. Most toxins that pose a risk to our body must be detoxified by our cells using a two-step process. The two steps in the process are called Phase I detoxification and Phase II detoxification. The ITCs made from kale’s glucosinolates have been shown to favorably modify both detox steps (Phase I and Phase II). In addition, the unusually large numbers of sulfur compounds in kale have been shown to help support aspects of Phase II detoxification that require the presence of sulfur. By supporting both aspects of our cellular detox process (Phase I and Phase II), nutrients in kale can give our body an “edge up” in dealing with toxic exposure, whether from our environment or from our food.

Direct studies on kale and digestive health remain limited, though research on broccoli (a fellow cruciferous vegetable) suggests similar benefits. Kale provides 7 grams of fiber per 100 calories, a density that strongly supports digestive function. Researchers have identified key lignans in kale, including lariciresinol and pinoresinol. In raw curly kale, pinoresinol levels average about 220 milligrams per cup. Lignans are classified as polyphenols, not fibers, but lignins (the much larger molecules directly related to fibers like cellulose and hemicellulose) can contain these lignans. This connection suggests a fiber-related, digestion-supportive function for kale’s lignan content.

We predict that a second area of digestive benefits will involve kale’s glucosinolates. The ITCs make from kale’s glucosinolates should help protect our stomach lining from bacterial overgrowth of Helicobacter pylori and should help avoid too much clinging by this bacterium to our stomach wall.

Recent research

A 2021 review in Food Chemistry and Toxicology (Buscemi et al., 83 citations) examined lutein’s biological activity across multiple organ systems, substantially expanding the evidence base beyond ocular health. Lutein crosses the blood-brain barrier and accumulates preferentially in brain tissue, where it appears to modulate neuroinflammatory signaling pathways involved in age-related cognitive decline. The review also documented associations between lutein status and cardiac function, with mechanistic data pointing to lutein’s capacity to reduce oxidative modification of LDL particles and attenuate inflammatory cytokine expression in vascular tissue. Dermal protection from UV-induced oxidative damage represents a third area of interest, as does a nascent body of evidence concerning skeletal integrity. Because kale leads all foods in the USDA database for lutein content, these findings give particular weight to kale’s broader physiological relevance.

A 2021 review in Plants (Avato and Ferrara) examined how controlled abiotic stresses affect the accumulation of bioactive compounds in kale, focusing on phenolics, carotenoids, and glucosinolates. Moderate water deficit, reduced temperatures, UV-B radiation, and elevated salinity each trigger secondary metabolite synthesis as part of the plant’s adaptive stress response. The practical implication is that cultivation conditions, not just genetic variety, meaningfully determine the phytonutrient density of a given harvest. This finding has relevance for both commercial growers and researchers designing intervention studies, since the same varietal name can yield substantially different glucosinolate and phenolic profiles depending on growing environment.

The 10-fold variation in glucosinolate content across kale varieties, documented in earlier genetic studies, takes on added significance in this context. Variety selection and cultivation method together function as independent determinants of the glucosinolate dose actually delivered per serving. A consumer choosing kale based on health considerations is, in effect, making a decision that interacts with upstream choices made in the field. Where variety information is available, curly-leafed and Lacinato types have generally shown higher glucosinolate concentrations than broad-leafed Napus types, though actual values shift with the abiotic conditions the plant experienced during growth.

Description

Kale is a remarkable member of the cruciferous vegetable family known for its ability to thrive during the cooler seasons of the year and its tendency to grow wild on many different continents, and especially in countries bordering along the Mediterranean Sea. The cool-season nature of kale can sometimes be reflected in its flavor. When exposed to frost, kale can sometimes take on a sweeter taste (that is due to the conversion of some kale starches into sugars). Overall, however, the taste of kale can be surprisingly varied, from bitter or peppery to more plain and slightly sweet.

The three types of kale that we have become familiar with in the produce section of today’s grocery stores are actually domesticated versions of wild plants that took farmers hundreds of years to develop. These three types include (1) flatter, wider-leafed kale, (2) darker Lacinato-type kale, and (3) more tightly formed, curly leafed kale. The list below shows some common kale varieties belonging to each of these three types:

(1) Flatter, wider-leafed kale

• Smooth German
• Red Russian
• Beria
• Black Magic
• Tronchuda

(2) Darker, lacinato-type kale (also sometimes called napus or siberian type kale)

• Tuscan Black
• Dinosaur Kale
• Toscano

(3) More tightly formed, curly-leafed kale (also sometimes called scotch or scotch-curled kale)

• Dwarf Blue Curled
• Starbor
• Darkibor
• Winterbor

Of course, there are not always sharp dividing lines between these three types of kale, and you can expect to find varieties that blend different features. Regardless of variety, however, all versions of kale are considered cruciferous vegetables and belong to the Brassica genus of plants that also includes bok choy, broccoli, Brussels sprouts, cabbage, cauliflower, collards, mustard greens, and turnip greens.

You can find different colors of kale in all three categories described above. However, the most common leaf colors are light to dark green and lavender to dark purple. You’ll also find green-leafed kale with purple stems and veins. All of the kales discussed thus far fall into the general category of “culinary kales” that are intended to be eaten. “Ornamental kales” are also edible, but since they have been developed primarily for appearance rather than taste or texture, they may be tougher in texture and harsher in taste.

Unfortunately from a science perspective, there is not always a guaranteed connection between the genus/species/subspecies of kale plant and the looks of the leaves as described above. However, the most common genus/species types of kale are Brassica oleracea and Brassica napus. The most common subspecies (ssp.) and varieties (var.) are:

• Brassica oleracea ssp. Acephala group
• Brassica oleracea var. sabellica
• Brassica oleracea var. palmifolia
• Brassica oleracea var. ramosa
• Brassica oleracea var. costata
• B. napus ssp. napus var. pabularia

Along with broccoli, Brussels sprouts, cabbage, cauliflower, and kohlrabi, you might also hear kale being referred to as a “cole crop.” In general, this term refers to foods found in the Brassica oleracea genus/species of plant, and it comes from the Latin word “caulis” meaning “stem.”

History

Kale as we know it today was first cultivated in the Mediterranean region over 2,000 years ago. It played an important role in the food supply of Europe through the time of the Roman Empire and during the medieval period in Europe between the 5th and 15th centuries. European colonizers are believed to have brought the first kale to North America in the 1600’s, and Russian traders are believed to have first brought this vegetable to Canada a century or so later.

Several thousand farms in the United States grow kale on a commercial basis, primarily in California, Georgia, New Jersey, and Texas. Compared with its fellow cruciferous vegetable, broccoli, total kale acreage is low, and between 5,000-7,500 acres. (For comparison, broccoli acreage is noted to be 130,000-150,000 acres.)

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.

Certified organically grown kale reduces exposure to pesticide residues and heavy metals. Some local growers sell organic kale without formal USDA certification. In supermarkets, look for kale displaying the USDA organic logo.

To store, place kale in a plastic storage bag removing as much of the air from the bag as possible. Store in the refrigerator where it will keep for 5 days. The longer it is stored, the more bitter its flavor becomes. Do not wash kale before storing because exposure to water encourages spoilage.

Here is some background on why we recommend refrigerating kale. Whenever food is stored, four basic factors affect its nutrient composition: exposure to air, exposure to light, exposure to heat, and length of time in storage. Vitamin C, vitamin B6, and carotenoids are good examples of nutrients highly susceptible to heat, and for this reason, their loss from food is very likely to be slowed down through refrigeration.

Tips for preparing and cooking

Preparation

Rinse kale leaves under cold running water. Chop leaf portion into 1/2” slices and the stems into 1/4” lengths for quick and even cooking.

Cooking for nutrient retention

We recommend Quick Steaming kale. We feel that Quick Steaming kale gives it maximum flavor.

Quick Steaming,similar to Healthy Sauté and Quick Boiling, our other recommended cooking methods,follows three basic cooking guidelines that are generally associated in food science research with improved nutrient retention. These three guidelines are: (1) minimal necessary heat exposure; (2) minimal necessary cooking duration; (3) minimal necessary food surface contact with cooking liquid.

It’s interesting to note that in one recent study on kale’s glucosinolate content, 96% of kale’s total glucosinolates were retained in the kale after blanching. Unfortunately, the authors did not specific the exact method used to blanch this cruciferous vegetable. However, it is very common in food science studies to blanch a food by placing it in boiling water very briefly, on the order of 1-3 minutes depending on the volume, type, and cut/uncut nature of the food. This exposure to boiling water is then usually followed by immediate submersion in ice water. So in general, we think about blanching as involving very brief exposure to heat. In this same study, it was interesting to note that about 60% of total glucosinolates in kale were lost after boiling for 5 minutes. While we cannot be certain about the exact times and percentages here,and we are clearly in need of further food science studies in this area,the glucosinolates in kale may be especially sensitive to total cooking time and this sensitivity may need to be factored in when choosing a kale cooking method.

As far as specific steps to take in your own kitchen, here are the steps that we recommend for making good overall trade-offs between nutrient retention, texture, and taste: fill the bottom of a steamer pot with 2 inches of water. While waiting for the water to come to a rapid boil chop greens. Steam for 5 minutes and toss with our Mediterranean Dressing and top with your favorite optional ingredients. We think you will love the deliciousness of these recipe results! For details see 5-Minute Kale.

How to enjoy

Serving ideas

• 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.

Recipes that feature kale

• Healthy Breakfast Frittata
• Italian Tofu Frittata
• Poached Eggs Over Sauteed Greens
• Minestrone Surprise
• Spicy Posole Soup
• Super Energy Kale Soup
• Turkey and Vegetable Chili Verde
• Sesame Braised Chicken & Cabbage
• Indian Style Lamb with Sweet Potatoes
• 5-Minute Kale
• 5-Minute Kale with Sea Vegetables

Individual concerns

Kale and goitrogens

You may sometimes hear kale being described as a food that contains “goitrogens,” or as a food that is “goitrogenic.” For helpful information in this area,including our WHF Recommendations,please see our article What is meant by the term “goitrogen” and what is the connection between goitrogens, food, and health?.

Nutritional profile

One cup (130g) at 36 calories provides vitamin K (1180% DV), vitamin A (98% DV), vitamin C (71% DV), manganese (23% DV), copper (22% DV), vitamin B6 (11% DV). Additional nutrients include tryptophan (9.4% DV), calcium (9% DV), fiber (9% DV), vitamin E (7% DV), vitamin B2 (7% DV), iron (7% DV), potassium (6% DV), vitamin B1 (6% DV), among others. Over 45 different flavonoids have been identified in kale, and especially kaempferol, quercetin, and isorhamnetin. Its glucosonolates include glucobrassicin, glucoraphanin, gluconasturtiian, glucopaeolin, sinigrin, glucobrassicanapin, glucoiberin, and gluconapin. Kale also provides the lignans lariciresinol and pinoresinol.