Leek is one species with some surprising relatives. Allium ampeloprasum also covers kurrat (Egyptian leek), pearl onions and the large bulbs sold as elephant garlic. Elephant garlic is no close cousin of garlic, though: a 2010 DNA study found only a distant relationship and said leek, kurrat and pearl onion should be treated separately from it.
What you eat is not a bulb. A leek builds a thick false stem from tightly packed leaf bases, and the pale lower part is the bleached part of that stem. In a plant study of four hybrids, that pale part had significantly less vitamin C than the green leaves. Shops often cut the green leaves off and throw them away, and a Monash University recipe tip tells cooks to ask the greengrocer for them.
On this site’s USDA record, raw leek has 61 kcal and 1.8 g of fiber per 100 g. The same portion gives 47 µg of vitamin K, 39% of the Daily Value, which puts leek in the top 16% of the 96 foods compared here. Leek is also one of only 28 foods in our database with a measured amount of the flavonol myricetin.
Health benefits of leeks
The top findings from 24 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★Faster recovery of white blood cells in childrenIn 97 children with cancer and fever, a leaf extract shortened recovery of infection-fighting white blood cells (neutrophils) from 6.4 to 4.0 days. The capsules held an extract of a leek species, not leeks as eaten.
- Population studyLinked to a lower risk of stomach cancerPeople who ate the most allium vegetables, including leeks, had 46% lower odds of stomach cancer in one pooled analysis. In another, the link was not seen in European studies.
- Population studyLinked to fewer heart and artery disease deathsThis was a 15-year study of 1,226 Australian women aged 70 and older. Each extra 5 g a day of allium vegetables went with an 18% lower risk of dying from atherosclerotic vascular disease.
- Population studyNo link to overall cancer riskPooling 22 studies, people who ate the most allium vegetables had about the same overall cancer risk as those who ate the least.
- Population studyNo clear link to colon and rectal cancerPooling 8 studies that followed people over time, allium vegetables as a group were not linked to colorectal cancer. A Dutch study found no link for leeks.
All 24 studies, strongest evidence first
A freeze-dried leaf extract of Allium ampeloprasum, the species leek belongs to, shortened neutrophil recovery from 6.4 to 4.0 days in children with cancer and febrile neutropenia
Double-blind placebo-controlled trial in 97 children (49 on the extract, 48 on placebo) who took 500 mg capsules twice a day for 7 days on top of standard care. Hospital discharge came about 2 days earlier, but that gap was not statistically significant, and average white blood cell and neutrophil counts did not differ. It was one center, and the capsules held an extract, not leeks as eaten.
People who ate the most allium vegetables, including leeks, had 46% lower odds of gastric cancer
Meta-analysis of 19 case-control and 2 cohort studies (543,220 people) of onions, garlic, shallots, leeks, chives and similar vegetables. Analyses of leek on its own gave similar results. Most were case-control studies, which depend on people recalling past diet, and the authors point to confounding and call for more studies.
Eating more allium vegetables was not linked to overall cancer risk in a pooled analysis
Meta-analysis of 22 studies (25 reports). The highest intake against the lowest gave a relative risk of 0.97 (range 0.92 to 1.03), with no dose-response trend, and garlic supplements showed no link either (0.97). It covers allium vegetables as a group, not leeks alone, and the authors say the finding needs further validation.
Allium vegetables were not linked to colorectal cancer risk in a meta-analysis of prospective studies
Pooled 8 prospective studies (20 reports, 5,458 cases). The highest intake against the lowest gave a relative risk of 1.06 (range 0.96 to 1.17), and a marginally higher risk of colon cancer showed up in women (1.23). It covers allium vegetables as a group, not leeks alone.
People who ate the most allium vegetables had 29% lower odds of gastric cancer, but the link was not seen in European studies
Pooled individual data from 17 studies in the Stomach cancer Pooling Project (6,097 cases and 13,017 controls). The odds ratio was 0.50 in Asian studies, 0.96 in European studies and 0.66 in American studies, and the last two were not clearly different from 1. The authors urge caution because of differences between regions and possible residual confounding. It covers total allium vegetables, with onions and garlic reported separately.
An umbrella review of allium vegetables found a 22% lower risk of gastric cancer as its strongest cancer result
Review of 16 meta-analyses covering 50 outcomes (risk ratio 0.78, range 0.67 to 0.91). Most of the findings on blood fats, blood sugar and blood pressure came from garlic, not leeks, so they say little about leeks. The side effects reported were limited, such as garlic odor and stomach complaints.
Older women who ate more allium vegetables had an 18% lower risk of dying from atherosclerotic vascular disease over 15 years
Cohort of 1,226 Australian women aged 70 and older. Each extra 5 g a day of allium vegetables went with a hazard ratio of 0.82 (range 0.73 to 0.94), and cruciferous vegetables showed a link too. It covers allium vegetables as a group, based on reported intake, and a link does not prove cause.
Eating leeks was not linked to colon or rectal cancer in a Dutch cohort of men and women
Netherlands Cohort Study of 120,852 adults aged 55 to 69, using a 150-item food questionnaire. After 3.3 years there were 150 colon cancers in men and 143 in women, and onions and garlic supplements showed no clear link either. This early report followed people for a short time.
Eating the most leeks was not linked to lung cancer risk (rate ratio 1.08)
The same Dutch cohort, with 484 lung cancer cases and 3,123 people in a comparison subgroup (range 0.80 to 1.45). Onions looked protective at first, but the link faded once smoking was adjusted more closely (0.80, range 0.52 to 1.24). Garlic supplements alone went with a higher risk (1.78).
Women who ate the most leeks had no lower risk of breast cancer (rate ratio 1.08)
The same Dutch cohort, with 469 breast cancer cases and 1,713 women in the comparison group (range 0.79 to 1.48 for leeks). Onions showed no link either (0.95), and neither trend was significant.
Eating leeks was not linked to stomach cancer, while eating onions was
The same Dutch cohort, with 139 stomach cancer cases over 3.3 years. People who ate half an onion or more a day had half the rate (0.50, range 0.26 to 0.95), while leeks and garlic supplements were not associated with it.
Iranian women who ate the most leek had 72% lower odds of breast cancer
Hospital-based case-control study of 285 women with breast cancer and matched controls, using a food questionnaire (odds ratio 0.28, range 0.15 to 0.51). Garlic gave 0.41, cooked onion went the other way (1.54) and raw onion was not significant. Women with a diagnosis report diet after the fact, and one standout among many foods can be chance.
Chinese adults who ate the most allium vegetables, including leek, had 79% lower odds of colorectal cancer
Hospital-based study of 833 people with colorectal cancer and 833 matched controls in northeast China, using a food questionnaire (odds ratio 0.21, range 0.14 to 0.30). Leek, garlic, garlic stalks, onion and spring onion each showed a significant trend on their own. The effect is very large, and case-control studies depend on people recalling past diet.
Men in Shanghai who ate the most allium vegetables, including leeks, had half the odds of prostate cancer
Population-based case-control study of 238 men with prostate cancer and 471 controls (odds ratio 0.51, range 0.34 to 0.76). The top group ate more than 10 g a day and the bottom group under 2.2 g. Scallions (0.30) and garlic (0.47) showed the biggest gaps, and the abstract does not report leeks on their own.
Households that handled or prepared unwrapped leeks were far more likely to have a case of E. coli O157 infection in a British outbreak
Case-control study within an outbreak of 252 cases across England, Scotland and Wales between December 2010 and July 2011, with 80 hospitalized and one death. The odds ratio was 40 but with a very wide range (2.08 to 769.4), and sacked potatoes were also linked (13.1). It is the first outbreak tied to handling leeks, and it concerned raw leeks and potatoes, not cooked leeks.
In cooking tests on the white shaft and green leaves of leek, steaming kept more of the bioactive compounds than boiling
Lab study of blanching, boiling and steaming. Boiling lowered total phenolic content in both parts, and steaming raised the antioxidant capacity of the green leaves. Longer heating, and steaming, lowered the sulfur compounds called ACSOs, while blanching slightly raised them. These are measurements of the cooked vegetable, not a study in people.
In a simulated digestion, leek’s vitamin C fell by more than 48%, while its water-soluble sulfur compounds stayed stable
Lab model of digestion using processed leek and Brussels sprouts. Water-soluble compounds, including the sulfur compounds called ACSOs, stayed stable and were fully bioaccessible, but the fat-soluble ones (vitamin K1 and carotenoids were among those tested) were only 26 to 81% bioaccessible. This is a test tube model, not a study in people.
The pale, bleached part of the leek stem had significantly less vitamin C than the green leaves in four hybrids
Plant-breeding study of leek F1 hybrids that measured vitamin C in the green leaves and in the bleached part of the false stem, the part used as food. The gap held in all four hybrids examined in adult plants. It does not say how much vitamin C reaches people.
Adding 3% leek and 0.5% garlic to fish burgers held back cholesterol oxidation during 90 days of freezer storage
Food science test of fish burgers stored at -18°C and then grilled. Both storage and grilling raised cholesterol oxidation products, and the burgers with the leek and garlic mix rose the least (21.16%). The leek held about 1.3 mg of phenolic compounds per gram of fresh weight. This is food chemistry, not a study in people.
A leek extract blocked SARS-CoV-2 infection in human lung cells in a lab dish
Test of seven plant lectins and one crude plant extract in two types of human lung cells. The leek extract and three lectins reduced infection in both, with selectivity indices from above 2 to above 299. A crude extract on cells says nothing about eating leeks.
A methanol extract of leek reduced degranulation of allergy-related immune cells in the lab
Cell study in human mast cells, rat basophils engineered to carry human receptors, and human airway cells. The extract was toxic to the airway and basophil cells only at high doses, and it lowered IL-6 release from airway cells. The authors suggest anti-allergic potential, but this is a solvent extract tested on cells.
A hydroalcoholic extract of Allium ampeloprasum at 400 mg/kg lowered triglycerides and total cholesterol in diabetic rats
Rat study, not people. Sixty male rats in five groups of 12 had diabetes induced with alloxan. The 400 mg/kg dose also lowered VLDL and a marker of oxidative stress (MDA) and raised catalase activity. It used a concentrated extract, which is not the same as eating the vegetable.
An alcoholic leaf extract of leek eased liver and kidney damage in rats given a liver toxin
Rat study, not people. The extract was given for 14 days before a single dose of thioacetamide, alone and combined with an extract of Bauhinia variegata leaves. Liver and kidney markers, oxidative stress and TNF-alpha all improved. It was a leaf extract in rats, not leeks as eaten.
A water extract of leek improved metabolic and fertility measures in rats with a model of polycystic ovary syndrome
Rat study, not women. Rats given 192, 384 or 768 mg/kg for 15 days had lower body weight, abdominal fat, LH, testosterone, total cholesterol and LDL, higher HDL and better fertility. The disease was induced with letrozole, and the dose was an extract.
Who should be careful with leeks
Most people can eat leeks freely. Take a little care if one of these applies:
- Warfarin. Leeks contain vitamin K (47 µg per 100 g), which can change how this blood thinner works. You do not need to avoid them; keep the amount steady from week to week and check with your clinic before big changes.
- Irritable bowel syndrome or a gassy gut. Monash University lists leek among the vegetables particularly rich in fructans, a type of FODMAP, and its low FODMAP recipes use only the green leaves, not the white part. Safe serving sizes for the leaves differ between sources, so check the Monash app.
- Allergy. Leek allergy is described as extremely rare, and a 2024 report was the first case of leek-triggered exercise-induced anaphylaxis. The risk is small, but see an allergy specialist if leeks ever cause a reaction.
How to choose, store and eat leeks
- White and light green part: this is the tender part most recipes use, and in a plant study it held less vitamin C than the green leaves.
- Green tops: these are tougher and usually cooked, in soups and stocks. They are also the part Monash uses in low FODMAP recipes.
- Steamed more than boiled: in a cooking test, steaming kept more of leek’s bioactive compounds than boiling, and boiling lowered total phenolic content in both the white shaft and the green leaves.
Pick firm, crisp stalks with as much white and light green as possible, and avoid yellow or withered tops. Keep leeks in a plastic bag in the fridge for up to two weeks, and wash them well between the layers to remove grit. In a 2010 to 2011 British outbreak of E. coli O157 with 252 cases, households that handled unwrapped leeks were more likely to be affected, so rinse leeks well and wash your hands after handling them raw.
Sources
- Dietary advice for patients taking warfarin. Cambridge University Hospitals NHS Foundation Trust.
- Anticoagulant medicines: considerations. NHS.
- FODMAP food list. Monash University FODMAP.
- Vegetable and chickpea soup. Monash University FODMAP.
- Takamatsu N, Nakamura K, Suzuki M, et al. Food-dependent exercise-induced anaphylaxis caused by leek and several allergens of the allium family. J Dermatol. 2024.
- Bernaert N, De Loose M, Van Bockstaele E, Van Droogenbroeck B. Antioxidant changes during domestic food processing of the white shaft and green leaves of leek (Allium ampeloprasum var. porrum). J Sci Food Agric. 2014.
- Filyushin MA, Seredin TM, Shchennikova AV, Kochieva EZ. Vitamin C content and profile of ascorbate metabolism gene expression in green leaves and bleached parts of the pseudostem of leek (Allium porrum L.) F1 hybrids. Vavilovskii Zhurnal Genet Selektsii. 2025.
- Launders N, Locking ME, Hanson M, et al. A large Great Britain-wide outbreak of STEC O157 phage type 8 linked to handling of raw leeks and potatoes. Epidemiol Infect. 2016.
- Leeks. Iowa State University Extension and Outreach, Spend Smart. Eat Smart.
History of leeks
Leek is among the oldest cultivated alliums. Dried specimens, carvings and drawings show it was part of the Egyptian diet from at least the second millennium BCE, and texts show it was grown in Mesopotamia from the start of that millennium. Its wild relative grows from southern Europe to southwestern Asia and North Africa.
The Romans rated leek, which they called porrum, above garlic and onions, and the cookbook attributed to Apicius has four leek recipes. The English word comes from Old English lēac, an old word for onion-like plants that lives on in garlic.
In Wales the leek is a national emblem, worn on St. David’s Day with the daffodil. One legend says King Cadwaladr of Gwynedd had his soldiers wear leeks to tell friend from foe in a battle against the Saxons fought in a leek field, and another says Saint David lived on leeks while fasting. Shakespeare’s Henry V, around 1599, has the Welsh captain Fluellen describe Welshmen wearing leeks in their caps as an honorable badge.
Leeks also gave the world a famous cold soup. Chef Louis Diat of the Ritz-Carlton Hotel in New York wrote that vichyssoise came from his mother’s simple leek and potato soup. The date is disputed: 1917 is often given, but the earliest printed mention found is from 1923, in the French journal La Revue culinaire.
Modern science has caught up with the vegetable. A 2025 study produced the first reference genome of leek, which is about 15.2 billion DNA letters long with four copies of each chromosome. In comparisons with onion, bunching onion and garlic, leek looked closest to garlic.
Sources
- Hirschegger P, Jakše J, Trontelj P, Bohanec B. Origins of Allium ampeloprasum horticultural groups and a molecular phylogeny of the section Allium (Allium: Alliaceae). Mol Phylogenet Evol. 2010.
- Nieuwenhuis R, Voorrips R, Esselink D, et al. High-resolution genome and genetic map of tetraploid Allium porrum expose pericentromeric recombination. Plant Genome. 2025.
- Filyushin MA, Seredin TM, Shchennikova AV, Kochieva EZ. Vitamin C content and profile of ascorbate metabolism gene expression in green leaves and bleached parts of the pseudostem of leek (Allium porrum L.) F1 hybrids. Vavilovskii Zhurnal Genet Selektsii. 2025.
- Leek. Wikipedia.
- Allium ampeloprasum. Wikipedia.
- Vichyssoise. Wikipedia.
- Henry V, Act 4, scene 7. Folger Shakespeare Library.
- Vegetable and chickpea soup. Monash University FODMAP.
Frequently asked questions about leeks
Are leeks good for you?
For most people, yes. Raw leek has 61 kcal and 1.8 g of fiber per 100 g, with 47 µg of vitamin K (39% of the Daily Value), 0.48 mg of manganese (21%) and 64 µg of folate (16%). The research is thin: no study here reaches strong or moderate evidence, and in a Dutch cohort of 120,852 adults leeks were not linked to colorectal, lung, breast or stomach cancer.
Can you eat the green part of a leek?
Yes, but the dark green tops are tougher, so they are usually cooked in soups and stocks. Iowa State University Extension advises cutting them off before cooking, which is a matter of texture. Monash University uses them in low FODMAP recipes, and in a plant study they held more vitamin C than the pale stem.
Are leeks low FODMAP?
Only the green part is the usual low FODMAP choice. Monash University lists leek among vegetables particularly rich in fructans, and its low FODMAP recipes use just the green leaves, for example 3 cups (220 g) in a soup that serves 10. Sources disagree on safe serving sizes for the leaves, so check the Monash app.
Can you eat leeks raw?
Yes. Iowa State University Extension says leeks can be eaten raw or cooked, and their onion-like flavor lets them stand in for onions. Slice them thin and wash the layers well to remove grit. A cooking test found steaming kept more bioactive compounds than boiling, though that was a lab measurement, not a trial in people.
What is the difference between leeks and onions?
Both are alliums, but a leek makes a long false stem of leaf bases while an onion makes a round bulb. Their flavors are similar enough for leeks to replace onions in cooking. In a 2025 genome comparison, leek looked closer to garlic than to onion or bunching onion.
Are leeks high in vitamin K?
Yes. A 100 g portion has 47 µg, or 39% of the Daily Value, and one leek (89 g) has 41.8 µg, or 35%. Gram for gram, leek is in the top 16% of the 96 foods compared on this site. If you take warfarin, keep the amount steady from week to week and ask your clinic.
Are leeks good for weight loss?
No study here tested weight loss. One leek (89 g) has 54 kcal, and 100 g has 61 kcal and 1.8 g of fiber. Leeks add flavor and bulk to a dish for few calories, which is a swap effect and not a proven effect of leeks themselves.
How do you clean and store leeks?
Keep them unwashed in a plastic bag in the fridge for up to two weeks, and wash before cooking. Soil collects between the layers, so cut the root and dark tops and rinse with cold water while separating the layers. Rinsing matters for safety too: in a British outbreak of E. coli O157, households that handled unwrapped leeks were more likely to have a case.