Katherine MaGrath, student dietitian, Queen Margaret University.

Leeks are the stuff of legends, widely recognised as the national symbol of Wales and long associated with the Welsh Saint David. To this day a leek is worn on the cap of Welsh solders on St David’s Day and myth once had it that girls who slept with a leek under their pillow on St David’s Day would see their future husband in their dreams (1).

Packed with antioxidants and vitamins, leeks are a delicious, nutritious and exceptionally versatile vegetable, best enjoyed between the months of November and April. Although it is a native to the Mediterranean and Middle East, it is now successfully grown locally and seasonally in Britain during the winter months, when homegrown produce can be difficult to find. Leeks are a member of the maryllis family (Amaryllidaceae) and are relatives to the onion, garlic, shallots, and scallion plants (2). With larger yet similar features to scallions, leeks are typically around 12 inches long with a small bulb and long white cylindrical stalks  that are layered and fade into darker green flat leaves.

They have a delicate, sweet onion-like taste and can add a subtle, comforting quality to a variety of dishes without overpowering other flavours present. They can be enjoyed raw, finely chopped in a salad with vinaigrette, however they are typically best enjoyed cooked in a variety of ways, including soups, roasts, stir-fry’s and more, which may alter the nutrient content slightly.

Eating leeks can contribute towards reaching the UK dietary recommendation for having at least five portions of fruit and vegetables per day (3). One portion is equal to 80 grams or three heaped tablespoons of the vegetable and contains approximately 18 calories, 2.3g carbohydrate, 0.4g fat and 1.28g protein (4).

Table. The full nutritional composition and reference nutrient intake (RNI) of an 80 gram portion is outlined in the table below:

Reference Nutrient Intake (RNI)
Nutrient Amount per 80g Adult

(19+ years)

Adolescents

(11-18 years)

Children

(1-10 years)

Calories (kcal) 17.6
Carbohydrate (g) 2.32
  of which sugars (g) 1.76
  Fibre (g) 1.76 30 25-30 15-20
Fat (g) 0.40
Protein (g) 1.28
Vitamin K (µg) 8.08 70
Vitamin C (mg) 13.6 40 35-40 30
Folate (µg) 44.8 200 200 70-150
NSP non-starch polysaccharide; AOAC American Association of Analytical Chemists

ᴥValue provided in NSP. AOAC value not available as there is no reliable information on the amount at this time. ♦RNI provided as AOAC where 1g AOAC = 0.76g NSP

References:  SACN 2011; EFSA 2017; DoH 1991

Macronutrients

Leeks are low in calories and fat and contain a good amount of dietary fibre, making them a fantastic addition to anyone’s diet, in particular for weight management. Nutritional requirements vary based on your gender, age and physical activity, however the Scientific Advisory Committee on Nutrition (SACN) recently reported the estimated average requirement (EAR) as 2065kcal/day for men and 2079 kcal/day for women (5). For that reason, leeks can contribute towards reducing the overall calorie content of meals, while still providing a wide range of micronutrients.

Micronutrients

Leeks are jam-packed with antioxidants and vitamins and should be included regularly in the diet. Those present in the highest quantities are flavonoids, folate and vitamins K and C.

Flavonoids

Leeks are a great source of flavonoids, most notably, the flavonols kaempferol and quercetin (6). Flavonoids are a group of phenolic compounds found in plants that have potential health benefits.  The flavonols present in leeks are found in greatest quantities in the lower leaf and bulb of the leek. Both are potent antioxidants, due to their structure and ability to scavenge potentially damaging oxidizing agents known as free radicals (6).

Folate

Folate, also known as Vitamin B9, is a member of the B vitamins complex. This is a water-soluble group of vitamins that play a role in our cells metabolism. Folate occurs naturally in foods, while the term folic acid relates to a synthetic form of folate found in supplements and fortified foods. Folate is involved in several essential functions in the body. It has a very important role in the production of DNA and other genetic material, especially during times of rapid growth, for example: childhood, adolescence and pregnancy. Folate intake is especially important both prior to and during pregnancy to ensure proper foetal growth and reduce the risk of neural tube birth defects (7). Folate affects our brain’s functioning ability and may impact on mental health. It is also closely associated with another B vitamin, vitamin B12, for the production of red blood cells and the effective use of iron in the body. As it is a water-soluble vitamin, it cannot be stored in our bodies and must be consumed daily from our diets. Leeks provide a valuable source of folate, with one portion (80g) providing between 30-64% RNI for children aged 1-10 years and 22% RNI for children and adults (11+ years) (8).

Vitamin K

Leeks are a rich source of vitamin K, which is found in abundance in green leafy vegetables, where it plays a direct role in photosynthesis in the form of phylloquinone. This means that the darker green parts of the leek will contain more vitamin K (4,9). Vitamin K is a fat-soluble vitamin, stored in the body tissues and liver and best known for its activity in blood clotting functions. However, the vitamin also plays a part in maintaining bone mineralisation and health. Blood clotting is generally associated with negative outcomes, however the ability of the blood to clot is essential in stopping a bleed following a cut or puncture to the skin. Equally, vitamin K is an essential factor needed to seal calcium into the bones, increasing bone strength and density and reducing the risk of osteoporotic fracture. Leeks provide 10.1µg of vitamin K per 100g, therefore they can provide a valuable contribution towards the 70µg/day adequate intake for adults proposed by the European Food Safety Authority (10).

Vitamin C

Leeks are an excellent source of Vitamin C, also known as ascorbic acid, with one 80g portion providing as much as 34% of the recommended nutrient intake (RNI) for adults (8). The UK reference nutrient intake (RNI) recommendation for children (1-10 years) is 30mg/day and for adults (15+ years) it is 40mg/day (8). Vitamin C is a water-soluble vitamin, meaning it cannot be stored in the body; therefore, adequate amounts must be consumed through a variety of foods in the diet, including leeks. Consuming vitamin C along-side plant based forms of iron (non-haem), helps the body to absorb more than it would in its absence. Vitamin C is an essential nutrient due to its important role in the growth and regeneration of body tissues. It helps the body synthesise collagen, a protein used to give our skin strength and elasticity, but also to make cartilage, tendons, ligaments and blood vessels. It plays a part in healing wounds and in the repair and maintenance of our bones and teeth. Vitamin C is an antioxidant, thus it has the ability to remove potentially damaging oxidizing agents, such as free radicals. Build-up of these free radicals is associated with the ageing process and may be linked to development of health conditions.

Using leeks

The culinary use of leeks extends a lot further than leek and potato soup! They may be cooked in a variety of different ways to form truly delicious and heartening meals.

To prepare leeks, removed any damaged outer leaves, the tops of the dark green section and trim the rootlets at base. They can be cooked whole, or chopped in half lengthwise. Dirt can become trapped during growth so they should be given a good rise prior to cooking.

Leeks can be boiled, steamed pan fried, oven baked, roasted or eaten raw and they are a great addition to casseroles, tarts, pies and soups. However, it should be remembered that cooking them in oil or butter will increase the calorie content significantly. Not all oils are created equally, with some providing additional health benefits, for example, extra virgin olive oil and its association with heart health benefits (11). The best method to ensure the maximum nutrients are retained following cooking is to sauté the leek using as little heat exposure and duration of cooking as necessary. This can be achieved using a stock broth and allowing the leek to sauté for 5-7 minutes on a medium heat, adding some extra virgin olive oil and seasoning to serve (12).

References

(1) Historic UK. The Leek – National Emblem of the Welsh. Available at: http://www.historic-uk.com/HistoryUK/HistoryofWales/The-Leek-National-emblem-of-the-Welsh/.

(2) Encyclopædia Britannica. Leek. 2016; Available at: https://www.britannica.com/plant/leek.

(3) Public Health England. The Eatwell Guide. in association with the Welsh Government, Food Standards Scotland and the Food Standards Agency in Northern Ireland 2016.

(4) McCance RA, Widdowson EM. McCance and Widdowson’s The composition of foods : 7th summary edition [electronic resource]. 2015.

(5) SACN. Dietary Reference Values for Energy. 2011.

(6) Manach C, Scalbert A, Morand C, Remesy C, Jimenez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr 2004 May;79(5):727-747.

(7) MRC Vitamin Study Research Group. Prevention of neural tube defects: results of the Medical Research Council Vitamin Study. The lancet 1991;338(8760):131-137.

(8) Department of Health. Dietary Reference Values for Food and Energy and Nutrients for the United Kingdom. Report of the Panel on Dietary Reference Values of the Committee on Medical Aspects of Food Policy. ; 1991.

(9) Bolton-Smith C, Price RJ, Fenton ST, Harrington DJ, Shearer MJ. Compilation of a provisional UK database for the phylloquinone (vitamin K 1) content of foods. Br J Nutr 2000;83(04):389-399.

(10) EFSA. Dietary Reference Values for vitamin K. European Food Safety Authority Journal 2017.

(11) Estruch R, Martínez-González MA, Corella D, Salas-Salvadó J, Ruiz-Gutiérrez V, Covas MI, et al. Effects of a mediterranean-style diet on cardiovascular risk factorsa randomized trial. Ann Intern Med 2006;145(1):1-11.

(12) AHA. Cooking Technique: Healthy Sautéing. 2015; Available at: http://www.heart.org/HEARTORG/HealthyLiving/HealthyEating/SimpleCookingwithHeart/Cooking-Technique-Healthy-Saut%C3%A9ing_UCM_430100_Article.jsp#.WLAcuzhXVoA.