Leek: nutrition facts and health benefits

Leek

Leek is a vegetable plant of the family alliums (or Lily), the same as that of garlic, onion etc. Formed of leaves wrapped close to each other, its subterranean part, called white leek, is tender and most appreciated, while its green leaves from the top are hard and less used. The leek arrived in North America with the settlers who cultivated it at the end of the 18th century, but it would never take a very large place in the kitchen, as well as in Asia.

History of the leek

According to the new botanical nomenclature, plants of the genus Allium now belong to the family of alliums. They are still sometimes classified as Lily or Amaryllidaceae.

Like onion and garlic, the leek comes from the Middle East and Southwest Asia. They would have been domesticated several millennia before our era. Adopted by the Greeks and the Romans, it was spread it throughout Europe by them. The leek was, it seems, Nero’s favorite food who would have consumed it regularly for the purpose of maintaining his vocal cords.

In America, settlers and Amerindians cultivated it at the end of the eighteenth century. It will never became very important, neither in Asia. In Europe it’s mainly grown in the centre and the west. France and Belgium alone produce half of all the leeks consumed on this continent.

First leek was a bulb plant, like onion and garlic, but it has become what it is today under the pressure of selection by gardeners. Very early on, they tried to reduce the size of the bulb and to increase the length of its white bole relative to the green foliage.

Leek health profile

Leek is part of the same family as onion and garlic. Its subtle and delicate flavor charms soups and salads. The sulfur compounds and antioxidants it contains could have a protective effect against certain cancers.

The benefits of leek

Several epidemiological studies have shown that high consumption of vegetables and fruit decreases the risk of cardiovascular diseases, certain cancers and other chronic diseases. The presence of antioxidants in vegetables and fruits could play a role in this protection.

Cancer. According to some studies, the consumption of vegetables from the family of alliums (for example, leek, onion, garlic, shallot, chives, spring) would have a protective effect against cancers of the stomach and intestine. Further research has shown no connection between the consumption of different vegetables, including leeks, and certain types of cancers such as breast, lung, stomach, colon and rectum. According to the authors, the amount consumed by active compounds from the leek was insufficient to detect a tangible effect. Studies evaluating the more regular consumption of leeks will therefore be necessary to prove its beneficial properties.

Blood cholesterol. One study indicated that the leek extract, administered to rabbits, resulted in a decrease in total cholesterol and LDL-cholesterol (“bad” cholesterol). The flavonoids and saponins contained in the leek could play a role in these effects. Several studies have shown that garlic has beneficial effects on blood cholesterol among humans, further studies are needed to check if the leek could have similar properties.

What does the leek contain?

Sulfur compounds

Like all alliums, the leek has a characteristic odour due to its content in sulfur compounds (which contain one or more sulfur atoms in their chemical structure). These compounds are formed when these vegetables are cut or crushed. Many of these sulfur compounds have been associated with the decrease in the risk of cancer among animals, but the studies carried out so far target mainly those of garlic and onion. In addition, data are not available for the time being for the absorption of sulphur compounds from leek by the human body.

Antioxidants

The leek contains different antioxidant compounds, such as flavonoids and carotenoids. Sulfur compounds would also have an antioxidant action, that is, they would protect the body cells from damage caused by free radicals and prevent the development of cardiovascular diseases, certain cancers and other diseases related to aging.

The dominant flavonoid in the leek is the kaempferol, which could be one of the active principles in the potential anti-cancer effect of leeks. The dark green leaves of the outer part of the leek contain the predominant quantities of this antioxidant. Beta-carotene is one of the important carotenoids of the leek. As a comparison, the carrot, recognized as one of the richest vegetables in beta-carotene, contains six times more. The leek would not have a very strong antioxidant power compared to other green vegetables. Cooking (boiling, steaming, microwave) would result in an average loss of about 20% of the total content in phenolic compounds but would not affect the antioxidant activity of leeks.

Saponins

The leek contains saponins and sapogenins. These substances would, among other things, have the ability to reduce blood cholesterol among the animal. The different types of saponins and sapogenins isolated from the leek may have anti-cancer and anti-fungal properties (i.e., capable of preventing the development of fungal infections). However, the studies carried out on the subject do not make it possible to draw a clear conclusion as to their effect on human health.

Precautions

Allergy

The reported cases of allergy to the leek are rather rare. However, it’s possible that a person allergic to other vegetables in the Alliums family responds to leek consumption. In fact, cross reactions with garlic, onion, chives and leeks are likely to occur and could be caused by an allergen common to these vegetables. A person with allergies to one of these foods could therefore also be allergic to another food in this family.

Urinary stones

Some people may be recommended to adopt a restricted diet in oxalates to prevent recurrence of renal or urinary stones (also known as urinary lithiasis). Oxalates are compounds found in several foods, including leeks. It is therefore not advisable for these people to consume them.

Choice and conservation

Choose

The stalk of the leek must be straight, fleshy, firm, with a bright white, without brown spots. The leaves should be well green, wilted, neither yellow nor desiccated.

Keep

Refrigerator. At temperatures close to the freezing point and high relative humidity, the leek can be stored for two to three months. Its leaves will probably turn yellow, but the white remains healthy. On the other hand, the small leek can only be kept one or two weeks in the refrigerator.

Freezer. Cut into slices and blanch for a few minutes in boiling water before freezing. Consider freezing some of the green leaves for the broths.

Organic gardening

Breeders have developed varieties for the summer, fall or winter, allowing the cultivation of leeks for a good part of the year. Protected from the cold by a mulch, winter leeks can be harvested in the spring (in southern Canada).

To have young leeks throughout the summer and fall, sow in bins or boxes at regular intervals from February to the end of June. From April onwards, they can also be planted directly in the open land. On the other hand, large winter leeks must be sown very early (February or March), as they require a long season to arrive at maturity. At the time of transplantation, cut roots to 1 cm and leaves at 5 cm.

The organic fertilization is very favourable to leek, even when the manure is recent and is not well decomposed. Be careful, however, to eliminate any risk of fecal coliform contamination. In most of the specifications of the biological certification bodies, it’s stipulated that vegetables cannot be harvested on land enriched with fresh manure (i.e. not composted) only eight months or more after the manure has been landfilled.

The leek and celery association is considered beneficial for both plants. However, since celery may make shade to the leek, which would not support it, it must be grown in neighbouring flowerbeds rather than in the same. If the rows are oriented east-west, make sure the leeks are planted on the south side. On the other hand, when planted in the middle of the celery, the leeks grow higher and the white part of the stem is much longer. It’s a benefit which can be taken at an advantage, knowing however that they will never become as big as if they were grown alone or placed south of celery.

To blanch the leeks, they are butted during the season where laths are placed on either side of the keg so as to exclude the light.

At the end of the season, return the leeks that remain in a cellar by keeping as much land as possible around the foot. replanted in crates filled with land, they will quietly pursue their growth. Deprived of light, the leaves will turn yellow.

Ecology and environment

In France, thrips (insect pests) are a problem for seed-carrying leeks. A biological solution had to be found to combat them without jeopardizing pollinating insect populations. The latter are voluntarily released during this period because they are necessary for the production of seeds. Larvae of another insect, lacewing, were found to devour thrips. The results fully satisfy the producers of leek seed. Also, the environment is a little better protected from the harmful action of chemicals.

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