Kale is one of the few vegetables that has gone from almost unheard of to immensely popular in a very short period of time.
Some of that pattern is connected to the many examples of kale health benefits because the vegetable really is relevant for health
However, the pattern also comes from celebrity endorsements, with both celebrities and cookbook authors heavily endorsing the vegetable (1,2).
The hype surrounding kale has died down a bit since the initial buzz, but there is still a lot to be said about getting kale health benefits in your diet.
Some Background on Kale
Kale is a vegetable that tends to have green leaves (although it can have purple leaves). The central leaves of kale don’t form a head in the way that cabbage and similar plants do.
Kale is a variety of the species Brassica oleracea, as are many other vegetables, including cauliflower and Brussels sprouts.
Vegetables from the Brassica family are collectively referred to as Brassicas or cruciferous vegetables.
Along with other related species, kale is originally descended from wild cabbage, which is the uncultivated form of B. oleracea.
The species was brought to Europe in around 600BC and was cultivated. The curly variety was an important food in Europe during the Roman times and also in the Middle Ages. In the 17th century, kale was brought to the United States by settlers.
Types of Kale
The plant has continued to be cultivated in multiple parts of the world, which has resulted in the development of new varieties. These vary in appearance and in taste.
If you are shopping at a grocery store, you might only find a few of these varieties. However, farmers’ markets are a good place to go for a wider variety.
After all, if you’re going to include kale in your diet regularly, it’s worth taking the effort to find the variety that is the most appealing to you.
Studies haven’t focused too much on the specific varieties of kale, but it’s likely that the kale health benefits are pretty similar across the various varieties.
This is by far the most common and recognizable type of kale and you can find it in most grocery stores.
The leaves can be either bright green or dark green, and in some cases they are purple. With this type of kale, the leaves are very crinkly, which makes the kale very easy to recognize.
The curls of the leaves can be so intense that they make it difficult to chop the kale effectively.
This type of kale is sometimes called dinosaur kale and has dark wrinkled leaves. Even after cooking, the leaves have a firm texture.
Some say that the taste of the kale is a little sweeter than curly kale, although it does also have an earthy and slightly bitter kale.
When buying this variety a good approach is to look for large bunches with wide leaves.
Some people argue that this variety of kale is the best choice if you plan on making kale chips, because it crisps more evenly.
However, kale chips made with curly kale are equally common and are still very popular.
Russian Red Kale
This type of kale is less common and you probably won’t find it at grocery stores.
The leaves of this type of kale are similar to oak leaves in appearance, and the stem is tinged red/purple.
This variety of kale has some appeal because it is sweeter than any other variety.
However, the stems of the kale are very tough and fibrous, which makes them hard to chew and hard to digest.
There are also some other varieties of kale, such as Kamome Red Kale, Rebdor Kale and Siberian Kale. The other varieties tend to be more challenging to find and are not commonly used in cooking.
Kale Health Benefits
Cholesterol is a nutrient that does play important roles in the body. Nevertheless, lowering cholesterol is often cited as a way to reduce the risk of cardiovascular disease.
Kale has the potential to help lower cholesterol by binding bile acids. There are compounds that play a role in fat digestion and are formed from cholesterol. Typically, these compounds are reabsorbed once they are used.
However, the process of binding bile acids acts to prevent some of this reabsorption. In turn, this helps to lower levels of cholesterol (3).
Interestingly, the process of steam cooking kale actually helps to improve kale’s ability to bind bile acid (4).
One study on kale juice supplementation found that supplementing with kale juice for 12 months significantly improved risk factors coronary heart disease. This included decreasing levels of LDL (the ‘bad’ cholesterol) and increasing the levels of HDL (5).
One of the more unusual kale health benefits is that it is a good source of ALA (also known as alpha-linoleic acid).
This is a healthy fat that plays a significant role in reducing the risk of type 2 diabetes, as well as providing benefits to both heart and brain health (6).
Protecting the Eyes
One of the challenges with aging is that eyesight tends to get worse, which can be a frustrating situation.
Kale hosts two carotenoid phytonutrients that can play a large role in protecting eyesight. These are zeaxanthin and lutein.
In particular, if you can get enough of these two compounds in your diet it has the potential to reduce your risk of cataracts and macular degeneration (7,8).
Kale is actually a good choice for weight loss because of its low calories and high fiber content.
This combination is significant because the fiber content can help to make you feel full, despite offering low energy. Many people choose to include kale in smoothies to help promote weight loss, along with other ingredients like whey protein.
Cancer is a terrible disease and complex disease, and one that we understand so little about. Because of this, we don’t have many good ways of fighting cancer or even decreasing its likelihood. Despite this, some natural compounds, including those in kale, have some potential to fight cancer.
One such compound is sulforphane, which is a natural bioactive compound that has been linked to stopping cancer from forming (9,10,11).
Another compound is indole-3-carbinol, which has also been linked to preventing cancer (12).
Indeed, some research has suggested that cruciferous vegetables, in general, may act to lower the risk of cancer, although further research is needed (13,14).
While the compounds in kale aren’t going to be a miracle cure for cancer or a way of permanently protecting against cancer, they are still a good idea.
With so little that we can do against cancer it makes sense to do whatever we can to decrease our risk and kale is one of those options.
Kale is often called a superfood and for good reason. As you can see, kale health benefits are significant and honestly it is an important food for its nutrition alone.
The vegetable is packed with healthy nutrients, as well as bioactive compounds, fiber and antioxidants.
A single 100 gram serving of kale offers more than 100% of the recommended daily intake for vitamin A (308% to be precise), vitamin C (200%), vitamin K (1021%).
It also contains significant amounts of calcium, iron, vitamin B6, potassium, copper and manganese (15).
All of this comes from a serving that also offers 2 grams of fiber and only totals to 50 calories.
This makes kale a very nutrient dense product (16) and you’re getting a lot of nutrients into your diet for very little calories.
Many of these nutrients are things that people often do not get enough of in their diet, such as magnesium, which has been associated with protection against heart disease and type 2 diabetes (17) and potassium, which can also play a role in decreasing heart disease risk and reducing blood pressure (18).
The bioactive compounds of kale and other Brassica greens is also a very important component of their health benefits (19).
Both indole-3-carbinol and sulforphane are examples of this.
Another significant nutrient in kale is vitamin K.
For example, in just a single cup of chopped kale, the amount of vitamin K is 684% of the recommended daily amount (20).
The high levels of vitamin K are one of the reasons that kale is so significant for health.
Vitamin K plays a critical role in blood clotting by activating some proteins and promoting calcium binding. This function is the key reason why people on the drug warfarin (also known as Coumadin) have to be very careful about their vitamin K intake.
As tends to be the case with vegetables, kale contains the K1 form of the vitamin (as opposed to the K2 form in animals). Research suggests that vitamin K can help to prevent osteoporosis and heart disease (21).
Kale as an Antioxidant
Within the body, a process known as oxidative damage is thought to be connected to a wide range of diseases and negative health conditions, including many aspects of aging (22).
This perspective is known as the free radical theory of aging.
The theory is based on the behavior of highly reactive molecules known as free radicals and has since been expanded to consider other types of highly reactive oxygen species.
These highly reactive species have the potential to damage cells in the body through oxidation reactions. This can contribute to disease development and aging.
Kale contains multiple powerful antioxidant species.
This includes a number of flavonoids, such as kaempferol and quercetin (23).
Those same flavonoids also have other important roles for health and indeed, many flavonoids have multiple different areas of potential benefit for health (24). This is one of the reasons that diets high in plant-derived foods have been linked to improved health and decreased disease risk (25).
For example, quercetin has been linked to decreasing blood pressure (26).
Likewise, kaempferol has been linked to the decreased risk of cancer, cardiovascular disorders (27,28,29) and the ability to act as an anti-inflammatory agent (30).
Other benefits of the flavonoid include having neuroprotective and antidiabetic activities (31,32,33).
Additionally, the vitamin C in kale is also a powerful antioxidant.
Kale is a high source of vitamin C. For example, one cup of chopped kale contains 134% of the recommended daily intake of vitamin C (34).
One way of measuring the antioxidant properties of food is the ORAC score, which refers to Oxygen Radical Absorbance Capacity.
Scores from this test are a measure of the antioxidant activity of the sample in vitro (i.e. in the lab). The score is far from perfect, as it does not necessarily correlate to a similar level of biological antioxidant activity.
Despite this, the ORAC score is an important way of comparing the strengths of different items as antioxidants.
Kale’s ORAC score is 1,770. This is the highest ORAC score for any vegetable, and the next highest is spinach at 1,260 (35).
This makes kale one of the best choices when it comes to antioxidants from vegetables.
You can also find out more about why antioxidants are so relevant for health at the site BuiltLean.
Kale versus Swiss Chard and Spinach
Two other very similar types of greens are Swiss chard and spinach. Both of these are also considered good for health.
The three greens do vary in terms of taste and texture. Kale tends to have a taste and texture that is challenging to get used to. Both Swiss chard and spinach have a nicer taste and also wilt slower than kale, making them easier to use in salads.
The three types of greens have many similar nutritional features.
For example, they are all high in phytonutrients, have decent amounts of fiber and are low in calories.
There is some variation in how much they have of individual vitamins. The chart below highlights some of these differences (36,37,38). All of the values are for 100g of the vegetable.
Similar variations can be seen for vitamin K and vitamin A. Those ones had to go in a separate chart because their numbers are so much higher.
As you can see, there are some cases (like calcium, vitamin A, vitamin C and vitamin B6) where kale is the winner in terms of nutrients. However, there are other cases where the competition is too close to call, or where one of the other greens is superior.
Kale is highly nutritious, but both Swiss chard and spinach certainly hold their own.
All three greens can be used in a similar way and many recipes will work just as well regardless of which one you choose.
The differences in nutrition suggest that the best approach may be to switch up which green you choose. That way you get the most kale health benefits as well as benefits from the other types of greens.
Several brands offer containers of greens that contain a mixture of more than one type, including one mix that offers kale, Swiss chard and spinach. This is a fantastic option for smoothies or some recipes because it lets you get the nutrients from all three types of greens without hassle.
Despite the significant kale health benefits, actually getting kale into the diet can be a bit of a challenge.
While some people do like the taste, most of us find the vegetable barley tolerable.
Thankfully, there are some tricks that can help you get kale in the diet and actually enjoy it.
An additional thing to consider with kale is that some of the vitamins and minerals are fat soluble. In general, this means that they will be absorbed better if the kale is consumed along with some fat. One example of this is vitamin K, which requires some fat for adequate absorption (39).
How much of an impact this has on health is difficult to know. The nutritional density of kale means that even if you had lower absorption of some of the beneficial compounds, you would still be getting many health benefits from the kale.
Nevertheless, many of the recipes and ways of including kale in your diet do naturally involve some fat or can have fat added to them, so you can take this approach if you are concerned about absorption of any vitamins and minerals.
One common way of getting kale into the diet is to make kale chips.
This approach actually has two benefits. First, it can be a good way of actually eating the vegetable. Second, it makes a good alternative to potato chips or to heavily processed rice cakes or veggie chips.
Making kale chips is surprisingly simple. Basically, the chips are just kale that has been dried out in the oven. The easiest recipes just involve kale, olive oil and some salt (some people use rock salt or garlic salt, but just plain table salt works well too).
To make the chips, you make sure the kale is washed and dried, then drizzle a little bit (around 1 tablespoon) of olive oil over them, followed by salt.
The kale is then baked at 350˚F for between 10 and 15 minutes. The idea is to brown the edges of the kale, but not actually burn the final product.
Many people say that the finished product tastes a lot like potato chips, partly because of the crunch and the salt.
Making kale chips can take a bit of trial and error – and it is easy to over- or under-cook them. So, it might take more than one try to get the chips right. Every oven is a little bit different, so you might find that you need to use a slightly different cooking time or something like that.
Thankfully, the cooking time is little and there are few ingredients, so trying again isn’t too much of a challenge.
If you have trouble with burning the product, you can try a recipe that uses a lower temperature and lower cook time, like one that has the kale cook for an hour at 275˚F.
There are also some variations of kale chips that you can try. For example, one recipe calls for black pepper and grated parmesan cheese, which creates kale chips with a different taste profile
Kale chips are immensely popular, but they are still basically kale. If you don’t particularly like the taste of kale, the chips may not be appealing.
For example, a very basic recipe (basically, what I described above) for the chips on All Recipes has the following ratings:
Most of the one-star ratings came from people who make the chips without a problem but simply did not like the taste. In many cases, they had friends or spouses that did like the chips.
If you’re looking for kale health benefits, I would suggest giving kale chips a try. Just be aware that even though many people love then, this isn’t true for everyone.
Smoothies are probably the most popular way of including kale in the diet – and they are the best choice for anyone who struggles to eat the vegetable.
The nice thing about smoothies is that you can make them mask the taste of kale, or highlight the taste – depending on whether you like the taste. If you want to have some fat along with your smoothie, one way to do this is to add in full-fat milk or full-fat yogurt.
Smoothies can seem tricky, but they can be broken down into a few key steps.
1.Pick a Base
Bases are the liquid component of smoothies. Common bases include water, milk, almond milk and coconut water, although there are others. Some people use fruit juice, although this adds more sugar to your smoothie than is ideal.
2. Pick the Greens
Not all smoothies use greens, but smoothies are a great option for getting the greens. You might choose kale, Swiss chard or spinach as your greens, or a combination of all three. There are also other options, like collard greens.
3. Pick your Fruit
Fruit has its own health benefits. Fruit is also a particularly important addition to a green smoothie, because the sweetness helps to balance out the greens. If you really don’t like the taste of the greens you are adding, pick fruits that have a strong taste (like banana) to help bury some of the taste from the greens.
With fruit, you can either use fresh or frozen. Either approach works well. Frozen fruit does have the advantage of letting you skip ice in the smoothie, which can dilute the smoothie.
4. Add Protein and/or Flavor
You can tweak the flavor of your smoothie by adding in other ingredients. Some examples are vanilla extract, cocoa, cinnamon and ginger. You can also add yogurt (or frozen yogurt) to give the smoothie a nice taste and texture.
This step is also where you would add in protein. Almonds, almond butter or whey protein powder are all fantastic examples of this. As with every part of the smoothie, you really can get creative here.
5. Add Sweetness
Some people also add more sweetness to a smoothie. You may not need to do this if you have enough fruit, but raw honey is one good option. I recommend trying any smoothie idea without sweeteners first, as it may not need them and you don’t want to add needless calories.
6. Add Ice
If you didn’t use any frozen ingredients previously (like frozen fruit or frozen yogurt) then you will also need to add ice to get a smoothie texture.
If you don’t already make smoothies, they can sound like a lot of effort.
In reality, they can be a very fast and easy way to get nutrients into your diet, and it is pretty easy to take a smoothie on the go with you. Smoothies are also a very refreshing drink in the hot summer time.
There are also many smoothie recipes online, such as one for a Protein Blueberry Kale Smoothie from Damn Delicious.
Other Kale Recipes
Kale can also be used in a wide range of other types of recipes.
One common approach is simply to make steamed kale, along with various ingredients to make the dish taste more interesting.
For example, I’ve seen garlic, onion, sundried tomatoes and feta cheese used with steamed kale, which can make for a nice tasting dish.
Likewise, kale can simply be used as the base of a salad, along with typical salad additions and potentially some salad dressing.
Kale can also be braised, and cooking it this way can make it a great side for many different dishes.
Another approach is to include kale as an ingredient in a larger dish. In most cases you can use kale in the same way that you would use spinach.
So, you could use kale in an omelet, as an ingredient in a pasta dish, part of soup or even as a topping on pizza.
Tricks for Making Kale Easier to Consume
One trick for using kale is to create frozen kale ice cubes.
This sounds like an odd approach, but it’s actually really effective.
The first step in this approach is to steam the kale for around five minutes or a bit less.
Then you simply cool off the greens in cold water and then blend them up with a little water. The idea is to make a smoothie-like texture that you can easily pour.
You then pour this mixture into ice cube trays and freeze it. Once frozen, the cubes can be stored in an airtight container and will keep for several months.
When you want to use kale in a smoothie, just take a few of the cubes and add it into the blender.
This approach works really well because the steaming helps to reduce some of the challenges in digesting kale, and can even make it easier to absorb some of the nutrients. Additionally, steaming kale can help to reduce the potential for any negative interactions (which will be discussed further on).
At the same time, using frozen kale cubes like this makes the smoothie easier to drink (that fiber can be tricky first thing in the morning). It also helps to create that desirable smoothie texture. Finally, it’s easier than trying to cram handfuls of greens into your blender along with everything else you want.
Even if you aren’t making smoothies, the approach of steaming kale can help your body to digest it overall, so it is a good option.
A second trick is using younger kale. Younger kale can be a bit less bitter. Many stores sell packages of baby kale leaves, which can be an easy way of using them.
A Word of Warning
Kale has become a pretty popular fad, and because of this, there are a lot of products on the market that contain kale. Restaurants also often sell products that contain kale.
However, you’ll often find that kale-containing products aren’t as good for your health as they sound.
For example, the chain Wawa offers a Kale and Quinoa salad that sounds like it should be really healthy. However, a serving of the salad has 47 g of carbohydrates, including a huge 26 g of sugar (which is way too much for a salad).
Additionally, the product has a long ingredients list that includes additives, and kale itself is the absolute last thing on this list. So, the product has more sugar, salt and natural flavors than it actually has kale. Not encouraging.
This means that you should always be critical of any product marketed as containing kale.
Even if it does have kale, it may not be nearly as healthy as the marketing implies.
As with most other foods, if you want to improve your health the safest approach is to make the food yourself. That way you know exactly what is going into it.
Safety and Interactions
Kale is high in vitamin K, which can interact with some medications. This is particularly true for any drugs that affect blood clotting, because vitamin K plays a key role in clotting.
A common example of this is Warfarin (Coumadin), which is used to reduce the risk of blood clot formation. The drug acts to decrease the activity of vitamin K, increasing how long it takes for blood clots to form (40).
Because of this, patients on Warfarin have to have their dosage of the drug balanced with their consumption of vitamin K.
The key with Warfarin is to keep vitamin K consumption consistent. So, you can’t suddenly start including kale in your diet and you can’t suddenly stop including it. In both cases, you would want to consult with your doctor.
Excessive amounts of any type of food is always something to be careful about.
With kale, there is some concern that that too much kale can contribute to the development of thyroid issues. This concern actually applies to all cruciferous vegetables and it’s only related to very high intakes (41).
For example, there was one case where a woman ended up in a coma after eating between 1 and 1.5kg (2.2 – 3.3lbs) of raw bok choy for several months. In that case, the women had been using the bok choy as an attempt to control her diabetes (42).
This does mean that you need to be careful about extremely high levels of kale intake, but honestly, it’s pretty difficult to eat excessive levels of kale. After all, even if you like the vegetable, it is difficult to consume large amounts of it every day.
However, this interaction does mean that people who are concerned about their thyroid or have thyroid issues should talk to their doctor before adding significant amounts of kale (or any cruciferous vegetable) to their diet.
The second problem from high doses comes from high levels of oxalates in raw leafy greens.
Interestingly, kale is low in oxalates compared to most other leafy greens (43) and this amount is lowered even more if you steam the kale before consuming it.
However, people can decrease their absorption of oxalates by consuming calcium at the same time (44). Likewise, research suggests that people should not consume a diet high in oxalates if their calcium intake is low (45).
The main cause for concern with oxalates is their potential to contribute to the development of kidney stones, although not all research supports this perspective (46).
Overall, if you are concerned about oxalates, kale is a good choice for a leafy green because of its lower oxalate composition.
Again, if you are not consuming excessive amounts of kale each day, this really isn’t an area to worry all that much about.
Kale is high in fiber, which is a good thing for most people.
However, some groups of people may find that the fiber in kale makes it challenging to digest. This can also result in digestive issues, especially for people with irritable bowel syndrome or similar health conditions.
Steaming kale can make it easier to digest, but even then, people who find digesting the vegetable to be challenging may want to limit how much they consume.
Can You Freeze Kale?
Kale can be frozen without many issues.
The freezing process does change the taste of kale, making it sweeter and giving it a more intense flavor. Some people prefer this taste to the taste of kale before it is frozen.
Despite this, the freezing process can significantly decrease some of the phytochemicals in the kale, potentially decreasing kale health benefits.
In contrast, the nutritional composition of kale and many similar vegetables are mostly unaffected by the majority of cooking processes, with the exception of boiling (47).
Some authors have pointed out the nutritional differences between buying fresh and frozen fruits and vegetables are largely irrelevant.
Fruits and vegetables typically lose nutrients over time. This includes the time it takes to get from harvest to the grocery store, which can often be substantial. In contrast, frozen versions are often snap frozen shortly after being picked, preventing similar deterioration.
So, both fresh and frozen versions are going to undergo some form of deterioration.
With fresh products, that deterioration is the way nutrients are lost over time.
With frozen products, it is the way that the freezing process may affect some nutrients.
Essentially, if you eat enough fruits and vegetables, the nutrient differences between fresh and frozen food isn’t significant enough to worry about (48).
Additionally, kale, spinach and Swiss chard are so nutritionally dense that you can afford to lose a little bit of nutrition from freezing kale or from its transport.
Does Steaming or Boiling Kale Make It Less Nutritious?
Most cooking processes do have some impact on the nutrients in food.
Generally speaking, you get the most nutritional benefits from raw products, because some nutrition does get lost in cooking. However, kale is more nutritionally dense than most foods, so it can withstand cooking well.
Additionally, the process of steaming kale can make it easier to digest and can reduce the amount of oxalates in the kale.
Likewise, one study found that steaming increases the ability of kale (and some other greens) to bind bile acid (49).Other research has also indicated that steaming doesn’t lower the amount of sulforphane in the vegetable. Indeed, the only cooking process that really seems to have a negative impact is boiling (51).
So, while you should probably avoid boiling your kale, steaming it may actually increase its health benefits, rather than decrease them.
Is it Worth It?
The hype surrounding kale has died down recently, but that doesn’t change the fact that the vegetable itself is a nutritional powerhouse and a fantastic addition to the diet.
Whether you use smoothies, kale chips or include kale in recipes, it is relatively easy to get kale into your diet. In fact, you can even make smoothies where you get the benefits from kale, but can’t taste the vegetable at all.
Kale is by far one of the most nutritious vegetables that you can include in your diet and it’s worth checking out – no matter what you think about the taste (and many people do love it).
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