Kale – The Secrets of a new Superfood

Kale – The Secrets of a new Superfood

Kale is a vegetable that has gained fame and consumption for its renowned support to the organism in recent years. It is an ideal vegetable to include in the daily diet, thanks to its nutritional and anti-inflammatory properties and its help to lose weight

What is Kale?

Kale is a variant of cabbage characterized by its typical curly leaf. It belongs to the family of the brassica or cruciferous plants, which also include red cabbage, Brussels sprouts, cauliflower, broccoli, and turnip. But it differs quite a lot in its aspect from the rest of its relatives, since kale is elongated instead of rounded and its leaves are more similar to those of lettuce.

Its scientific name is Brassica oleracea var. acephala and its origins are found in the coastal countries of the south and west of the old continent.

What is the Kale for?

It is a vegetable that, as a result of successive discoveries about its nutritional benefits for health, has ended up being labelled among the so-called superfoods, which are understood as those foods that combine an enormous amount of nutrients while providing a scarce energy supply, which is why they could be regarded as food concentrates.

Its leaves, which cover almost the entire vegetable, draw attention for its intense color and its clearly rough texture. It has, for most of those who have tried it, a delicious flavor, which has greatly boosted its success in the diet of Western countries, including Spain. It is also useful in preventing overweight and obesity since it is a remarkably hypocaloric food.

Properties of Kale Leaves

Traditionally, it has gone unnoticed among the many existing edible vegetables, being given a low value and not being recognized for its immense virtues, which we will dwell on later. It was only a few years ago that it entered the scene of new dietary trends, gaining an unusual and well-deserved popularity in a short time.

One of the reasons that have lifted the protagonism of kale is the current trend of consuming green juices on a daily basis, which is where this vegetable plays a very significant role for health.

The different types of Kale

There are mainly the following types, whose differences lie in their texture and morphology:

  • Green Kale: its leaves, always green, can have a shade of matt or gloss, since there are subvarieties within it. This disparity of varieties is also manifested in the form they take which can be rounded, oval, wide, smoother, more curly…
  • Lacitano kale or toscan kale, also known as dinosaur (because it resembles the skin of a dinosaur): it has sharp, long, narrow leaves, characterized by a fairly dark greenish-blue shade. Their consistency is such that they do not give way during cooking, staying firm in the kitchen. In terms of its taste, it is the type that least produces the bitter aftertaste that characterizes this species.
  • Redbor kale: they are red or of an intense purple color due to their richness in anthocyanins, which gives them an aesthetic that apart from the culinary use, makes them suitable as ornamental plants in gardens and floral arrangements.
  • Red Russian Kale: its irregular long flattened parts have a reddish color with the presence of purple tones in the ribs. Its slight spicy touch does not prevent it from being considered the kind of kale that provides the sweetest taste on the palate.
  • Curly kale: a moderately spicy and bitter tone prevails in this variant, which is why the young and dark green ones are the most appreciated, since they accumulate less intensity of flavor.

Kale Species

Culivation of Green Kale

First of all, it can be said that the green kale is a vegetable that is easy to grow and it can adapt to any urban vegetable garden that are so popular nowadays. In fact, the cultivation of kale hardly differs from that of other species of crucifers: it is a matter of choosing a soil with good drainage, fertilizing it properly and trying to locate it in areas with temperatures within the optimum growth range of this vegetable, which moves between 10 and 20 ºC.

It is not very common to grow it in summer in family orchards, although it is able to resist in semi-shaded places where it does not receive excessive hours of direct sunlight (as long as it is not the southern and interior peninsular areas that suffer pronounced summer peaks).

It is important to make a sowing forecast in line with the calendar, which means preparing the seedbeds at the beginning of summer so that when September comes (or at most in the middle of the month), the seedlings that have emerged are ready to be transplanted to the orchard.

It is necessary to bury the seeds to 0.5 – 1cm under the surface of the ground on a tray or seedbed. It is advisable to add a combination of peat, perlite, and compost that will effectively stimulate the germination and then the vegetative development of the seedlings.
These should not be taken to the orchard until they reach at least 14-15cm; The transplant should not be rushed because it runs the risk of damaging the initial growth impulse and this can affect the evolution of the vegetable in general.

September is the right month to perform this transplant because the plant, in its early stages, needs mild temperatures to begin its vegetative growth. The beginning of the second half of autumn, in which the first days of cold are foreseeable, the plant should already be equipped with a remarkable mass of leaves.

Kales (and crucifers in general) require a lot of nitrogen, which means that you have to choose one of two options: fertilize the soil generously with an ‘ad hoc’ fertilizer before transplanting the seedlings. Or you could also use a piece of land where a legume has previously been cultivated, since this family of vegetables is well known for enriching the soil with nitrogen thanks to a very efficient symbiosis between its roots and the Rhizobium bacteria, which fix the atmospheric nitrogen.

As for the necessary space for its cultivation, it depends on the volume that its leaves accumulate as they develop and each specimen requires a minimum of 25 liters of substrate. The best dimensions are 60×40cm, allowing a minimum distance of 40cm between the plants.

As for the water needs, kale requires a constant point of humidity but not excessive.

It is a plant that is harvested continuously by removing those that are already ripe, but never forcing the pace because leaving the plant unprotected can cause problems. The ideal guideline is to collect 2 or 3 leaves per plant weekly, which is in harmony with the number of plants being cultivated that should be enough to meet the needs.

Threats to Kale cultivation

Perhaps the most common plague is the so-called cabbage butterfly (Pieris brassicae), a recurrent problem and highly annoying but easy to solve at the same time. Their caterpillars are voracious and they are capable of notably weaken the plant, apart from dirtying them by depositing their feces in the buds.

Kale Cultivation

The treatment against the cabbage butterfly can have two approaches: chemical and biological. The first uses permethrins, such as cypermethrin, deltamethrin or indoxacarb, which are effective when the plants are in their initial stage of growth.

The second one, the biological fight, consists on spreading the bacterium Bacillus thuringiensis, that fights the caterpillars by causing an infection, or with Apanteles glomeratus, a parasite that leaves them exhausted until they are killed.

Aphids, which are associated with an excess of fertilizer, as well as white flies and the typical snails and slugs, threaten the plants as well. The latter two require the use of repellent products such as granulated essential oils in order to control them. Alternatively, other ways to control their presense consists on watering in the mornings instead of at dusk or setting up a drip irrigation system, as well as surrounding the orchard with ash, orange peel, or crushed egg shell. And if it is a question of eradicating an already very extensive plague, the most effective thing is to apply some of the formulations that include ferric phosphate as an active ingredient.

In relation to the aphid (Brevicoryne brassicae), it can be said that it normally affects the weakest plants and it can be controlled with the periodic administration of Neem oil and also encouraging the presence of ladybugs to carry out a biological control in the orchard. These behave like effective aphid predators (a single larva can kill 100-150 a day). To achieve a good ladybug population, you can use a beneficial insect attractant that consists on a thin film that continuously releases essential vegetable oils.

Kale, the brand-new Superfood with pharmacological side effects

The Atlanta Center for Disease Control and Prevention (located in Georgia, United States) compiled a catalog made up of 47 foods based on their nutritional density, related to their effect on disease prevention.

In it, the kale proves to be highly abundant in 17 specific nutrients: fiber, protein, calcium, potassium, iron, zinc, vitamins A, B1, B2, B3, B6, B12, C, D, E and K and folic acid (also known as vitamin B9).

The rating awarded in that institution to each food represents the average value of the RDI or recommended daily intake that its consumption provides to the organism. Well, kale occupies an impressive fifteenth position, which corresponds to a nutritional density value of a 49%, within a list whose ‘top three’ is occupied by watercress with a 100%, Chinese cabbage with a 92% and chard with an 89%.

One of the main peculiarities of kale is that, while it is a leafy vegetable, it has an extraordinarily low energy content, which can be calculated at 45 kilocalories per 100 grams. This alone would not be worthy of consideration if it were not for the outstanding nutritional density contained in all the active ingredients mentioned in the previous paragraph. But apart from its immense volume of phytonutrients, kale is widely valued due to its concentration in antioxidants substances of which we will give good account during this article.

Properties of Kale

From a nutritional point of view, kale, like any leaf vegetable, stands out for its extremely high water content, which grants it an interesting role as a purifier and detoxifier of the organism. It also deviates from the general rule of the vegetables related to it by also providing an interesting protein content, which can amount to a 10% of the dry matter. In addition, this is more in line with this general rule, it can be classified as rich in fibre, which is present with a 3%, while being very poor in soluble carbohydrates and limiting the amount of fat to the essential fatty acids of the omega 3 and 6 series.

A lot of attention is being focused on its anti-cancer properties and detoxifying benefits, which to a great extent are derived from an antioxidant content much higher than usual in this type of vegetable and which is extraordinary if we take it as an absolute value. More specifically, kale is particularly abundant in flavonoids and carotenoids, the two main groups of antioxidant substances which have to the ability to prevent multiple forms of cancer. In particular, one study showed that, kale had the strongest protective effect against bladder cancer of all the foods that were used in it.

The chemical composition of kale contains an impressive list of flavonoids, including 32 polyphenolic compounds and three hydroxycinnamic acids. All of them can operate on quite a few fronts within the body, but above all they help to maintain cholesterol levels within the physiological range and to prevent the proliferation of the feared free radicals that result from oxidations in the cell membranes. Some of the most relevant flavonoids found in high concentrations in kale are kaempferols and quercetin.

Due to its richness in fiber and essential fatty acids, it is known to help to minimize the main risk factors of cardiovascular diseases. Not in vain, it has been reliably proven that its intake as a nutritional supplement compensates the balance between good cholesterol or HDL and bad cholesterol or LDL, increasing the former and reducing the latter. In addition, steamed kale drastically increases the binding effect of bile acids and is a 43 % more effective than cholestyramine, a drug that is specifically indicated to reduce the rate of cholesterol.

Its lack of substances that are labelled as anti-nutrients is also noteworthy when compared to different leafy vegetables; for example, phytates (which block phosphorus), oxalates (which do the same with calcium) and tannins (which hinder the absorption of proteins), are practically non-existent in kale, which gives additional value to some of the nutrients because they are optimally used.

What Vitamins can be found in Kale?

One of the elements that grant kale its prestigious condition of superfood are vitamins. If we take the recommended daily dose as a reference value, a single cup of kale (around 65 grams) has:

Its vitamin content has been deeply studied, concluding that it has extremely remarkable concentrations of K (one milligram per gram of kale), C (more than 20mg per 100g), A and E.

Vitamin K is closely related to the prevention of colon and lung cancer, and mainly those that have an hormonal trigger, apart from favoring the bone health. It is believed (since there still little evidence) that it helps to buffer the progress of Alzheimer’s disease.

Vitamins Chart Summary

Kale is also abundant in vitamin A (35mg per 100g), which is basic to keep a good state of the ocular health and epithelium, that is, the mucous membranes that cover endless conducts that are distributed thoughout the organism, as well as the skin. Let’s not forget that it is a nutrient that should be taken into account for the prevention of lung and mouth cancer.

It stimulates the immune system, the metabolism, and the hydration of the epidermis thanks to its vitamin C content. It is also crucial to guarantee the repair process of the epithelial cells and guarantee the formation of collagen, which is indispensable for a good integrity of skin, hair, and nails.

Another key elements from kale is folic acid. One of its most remarkable tasks is its involvement in the development of the fetal brain. KAle is rich in folic acid, which is why its consumption during pregnancy can help us gain the weight we need and form a proper neural tube, which is a precursor of the marrow bone.

Properties of Kale

The role of Carotenoids in Kale

Carotenoids are a group of pigmentation substances that are only present in the plant kingdom, they play an important role in stopping the formation of free radicals, which are the main responsible for cell deterioration and, therefore, aging and many degenerative and chronic processes.

Lutein and zeaxanthin are two carotenoids that give kale its characteristics colors among other properties, and both elements are renowned for their efficacy to prevent two degenerative processes of sight: macular degeneration and cataracts.

More specifically, lutein plays a role that is similar to a sunscreen in the depth of the eye, helping to prevent the loss of visual acuity which happens naturally with aging.

The macrominerals from Kale

Its richness in minerals is what makes it an ideal food for sportspeople after the effort, since it can help the to recharge the electrolytes that are lost through the sweat. Now let’s see what are the minerals that kale substantially provides.

Calcium, a star mineral in the nutritional composition of Kale

Its richness in calcium is useful to prevent osteoporosis due to the loss of bone density which specially affects post-menopausal women and old men.

Apart from the fact that this mineral is extraordinarily abundant in this food, it is also effectively absorbed in the intestine (which is better than that of dairy products, since it is somehow hindered by casein and lactose) which is mainly due to what we have been mentioned in previous points: the absence of oxalic acid and oxalates which tend to steal it by forming chelates which are excreted through the stool. Nevertheless, the best way to take advantage of its calcium content is to eat it raw or in powder instead of cooking it.

Iron, another important element from Kale

Iron for Sportspeople

It is one of the most exclusive vegetable sources of iron, which should be specially taken into account by vegetarians and vegans, since products from animal origin tend to be the main supply of this mineral and avoid anemia.

Iron is vital for the synthesis of proteins and blood pigment, as well as other enzymes that are involved in oxygen transport and utilization processes in the body. However, we should take into account that the iron from kale is found in a chemical form that is called “no hemo”, which is less available than the one from animal origin. This deficiency can also be countered by consuming some acid food, like a citrus fruit.

If we express it in terms of nutritional density, kale has twice more iron per kilocalorie than beef, for example (beef provides 1.3mg and kale 3mg per 100 kilocalories).

Potassium, another remarkable mineral

Its high levels of potassium have a positive diuretic effect that includes several benefits for the body, this is why it helps to eliminate excess fluids that unbalance the electrolyte metabolism, apart from serving as deposits of toxins. Therefore, consuming kale is particularly convenient in cases of diabetes, obesity, gout (due to excess of uric acid) and heart and kidney failure. One of the best known effects of potassium is its ability to reduce blood pressure in cases of hypertension.

We will complete this list of minerals that are found in kale by pointing out a trace element (no longer a macromineral) that is found in quite significant quantities, boron. This mineral develops its main function in the female organism, since it contributes to reduce the deficit of estrogens that characterizes the menopausal phase, thus lessening the difficulty of fixing the calcium in the bones that becomes a crucial metabolic problem in women over 50.

Kale as an ideal ingredient in weight-loss diets

Its richness in fiber and proteins and its low energy supply make up a cocktail that is very advisable for weight-loss diets. Regarding fiber, the popular belief is that it is important only in cases of constipation, which does not conform to the reality because every organism demands a systematic supply of soluble fiber. This guarantees an adequate intestinal transit and fulfills a purpose as a cleaner of molecules that are not suitable for the organism, especially saturated fats.

Kale is a life insurance for the liver

Kale helps to keep the liver in a proper functional state, which is vital for the correct development of the body overall, because it is nothing less than the body’s laboratory. How does it work to achieve this effect? By means of sulfur-rich molecules called sulfides that activate certain enzymes that play a specific role in the production of bile.

This takes place through the conversion reactions of cholesterol into acids and bile salts, which are released through the common bile duct into the small intestine each time you eat fats. Once they have been metabolized, bile acids are reabsorbed into the bloodstream to be reused when necessary, behaving like a cholesterol reserve.

Throughout the process, substances called bile acid sequestrants can interfere, which can prevent their reabsorption, when chemically linked to them. When this happens, the total amount of cholesterol is reduced. Well, kale contains these sequestrants, which gives it the power to reduce the cholesterol levels.

A natural toxin purge based on isothiocyanates

We have mentioned a property of kale in which it is worth to spend some time because of its importance for our organism. We are talking about its work as a natural detoxifier, mostly due to the isothiocyanate contained in the glucosinolates, which are very abundant in crucifers and perform a defensive function against aggressions.

The environmental and alimentary environment in which we move subjects us to a persistent aggression by means of the toxins that we consume through processed food, atmospheric pollutants, pesticides, synthesis medicines… Our organism has to defend itself by setting in motion detoxifying mechanisms that protect it from diseases, and kale is a natural tool of unmeasurable value with its glucosinolates, which enhance the power of prevention of its antioxidants, flavonoids and carotenoids.

The anti-inflammatory power of Kale from its essential fatty acids

It would not be an exaggeration to say that one of the greatest benefits of eating kale regularly is to take advantage of its anti-inflammatory properties.

If we consider that one of the main factors that condition the anti-inflammatory power is to respect the ideal ratio between omega-3 and omega-6 fatty acids, we could say that kale is the anti-inflammatory food par excellence. A chronic inflammatory state is a common denominator of many well-known degenerative or neoplastic diseases, such as rheumatoid arthritis, Crohn’s disease, or cancer. Kale manages to produce an imbalance between the pro-inflammatory effect of omega-6 (mainly represented by linoleic acid) and the anti-inflammatory effect of omega-3 in favor of the latter. Its composition keeps an omega-3-omega-6 ratio of 1.1:1, which counteracts the negative effects of a regular consumption of foods loaded with vegetable oil in which omega-6 predominates.

Kale Anti-inflammatory Effect

As it has already been mentioned, kale contains very little fat, but a good part of it is ꬰ-linolenic acid from omega-3. It is one of the few foods that has more omega-3 fatty acids than omega-6. In short, it is important to know that a diet based on processed and refined foods will contain excessive omega-6 and few omega-3, which will stimulate inflammatory processes.

This description of the anti-inflammatory potential of kale would not be complete without mentioning the role played by other sulfur compounds, the so-called sulforaphanes (3). These can be released by bacteria in the large intestine and absorbed by the body, producing an additional effect as anti-cancer elements.

The trend of green juices rich in Kale

In the United States, the so-called green juices or greeners have been in vogue for some time now. Kale leaves are an essential ingredient of this recipe and the protagonists of dietary approaches against cancer due to their enormous concentration of antioxidants, B vitamins such as folic acid, and minerals like iron, zinc, magnesium… which vary in proportions depending on the exact composition of the juice. They are not only meant for a long-term anti-cancer treatment, but also in the context of treatments of existing cancers since they facilitate the therapeutic work of chemotherapy.

But we must not only limit its usefulness in the context of cancer. Their regenerating properties hinder the lethal action of the free radicals which trigger the oxidation of cell membranes. This property makes them highly interesting in effective and inexpensive detox diets.

Kale Juice

Side effects and contraindications of Kale

Kale is a highly beneficial food, which should be clear after reading this entire article. But in spite of this, its abundance in certain minerals and vitamins and other active principles can be a double-edged sword depending on the following situations.

People who suffer hypothyroidism could compromise the absorption of iodine due to the consumption of sulfur compounds like the glucosinolates and sulfopharanes, which interfere in this part of the metabolism. More specifically, the glucosinolates produce goitrin when they are consumed, this is a compound that hinders the synthesis of thyroid hormones, causing hypothyroidism.

At the same time, those who are taking anti-coagulant medication (like acetylsalicilic acid) should also be careful when consuming kale due to its high percentage of vitamin K.

Kale, like other leafy vegetables, absorbs a lot of heavy metals like cadmium, thallium, or arsenic through its roots. However, these contaminants should not cause any problem if it is consumed moderately.

An uncommon side effect which should be taken into account is that drinking kale juice can produce certain intestinal discomfort, which tends to produce flatulence and diarrhea. These symptoms seem to be related with the intake of sorbitol, a polyalcohol that is frequently used as a sweetener. Those who suffer irritable bowel syndrome should be careful with this vegetable.

People have also reported hyperpotassemia cases which cause muscle weakness, fatigue, diarrhea, and chest pain. Those who follow a low-potassium diet should avoid consuming kale, as well as bananas, potatos, beans, oranges, broccoli, and spinach, among others foods.

Using Kale in recipes and the kitchen

It is very common to include kale in traditional recipes of spoon dishes like stews.

Kale is easy to handle in the kitchen and its recipes, which also allow its raw use, as long as it is thoroughly washed or cooked. It has the advantage that, unlike other crucifers, it does not produce flatulence or abdominal swelling. You should consume it as soon as you can after purchasing it, since it turns bitter as it dries.

The part that is commonly used are its leaves which is the most nutritious element, even though the stems are also edible and appetizing. They do not need a lot of water to be boiled and we will also preserve more water-soluble vitamins in this way. So, instead if boiling it, it is advisable to use it for dishes that combines other vegetables and even with meat. At the same time, it is ideal to match pasta and rice along with a delicious sauce, or mixed with some mashed potatos to enriched the nutrient supply and improve the texture.

Kale in the Kitchen

There is a very appetizing combination that consists on making a sauté with the kale, some coconut oil, fresh garlic, and onion.

Another alternative would be to make juices, shakes, or smoothies. In this case, the Spanish Academy of Nutrition and Dietetics advises to consume it in this liquid or semi-liquid elaborations, slowly and intermittently to avoid digestive problems.

To adapt the consumption to your likes, you should know that the soft leaves have a softer taste, while the ripe ones have a more intense taste. If you want to use it for salads, remove the central rib of the leaves, and macerate them for a while with some lemon juice and olive oil in order to smooth its flavor.

Kale chips are made by spraying the leaves with some avocado or olive oil, then add a pinch of salt and bake them until they are dry.

If you want to store and preserve them, there are several ways to do so:

  • Just like you purchased it, put it on a plastic bag in the fridge covered with a wet towel. It will not last longer than a week, and this may change if you did not purchase it a fresh product.
  • Cut in slices once it has been washed and dried: remove the stems and cut it. Then put it on hermetic bags in the fridge.
  • Dehydrated, you can do this with a food dehydrator or just with a conventional oven at a low temperature, letting it cook for several hours. Once they are dehydrated, they are ground and stored in a closed glass recipient (or similar). This hydrated kale is ideal to season different dishes and recipes, it will barely add any flavor and we will still be able to benefit from all its nutrients.
  • Frozen: they have to be washed and dried, then stored them on food containers or a similar recipient and put them on the freezer. Leave them for a few hours, then get them out to put them on bag, which will be frozen and edible for more than a month.

Last but not least, it is advisable to purchase kale from ecological agriculture, which will guarantee that the vegetable has no pesticides. Always make your purchase from a reliable store or as a nutritional supplement with an ecological agriculture certification.


  1. https://www.ncbi.nlm.nih.gov/pubmed/16142557
  2. https://www.sciencedirect.com/science/article/pii/S0895398808600124
  3. http://therapy.epnet.com/nat/GetContent.asp?chunkiid=201344
  4. https://www.conasi.eu/blog/consejos-de-salud/kale-y-sus-competidoras/
  5. https://www.nutri-facts.org/es_ES/news/la-luz-azul-luteina-y-zeaxantina-para-la-salud-ocular.html
Kale Review

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About Alberto Ricón
Alberto Ricón
Alberto Ricón is a specialist in nutrition and food hygiene with a lot of experience in this field. He works as a Food Safety Technician in Castilla La Mancha.
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