Leeks: Nutrients, What Research Shows and Safety

Leeks are the long, white-to-green stalks of Allium ampeloprasum (leek group), in the onion family. People eat the white shaft and the pale-green lower leaves, cooked in soups and stews or sliced raw in small amounts. They are eaten for flavor and as a source of vitamins. This page keeps the food apart from supplements and from hype, and says plainly where evidence is thin.

Read this first

• Warfarin (Coumadin): vitamin K affects how this medicine works, and MedlinePlus advises keeping vitamin K intake about the same from day to day. Leeks contain vitamin K (see the table), so tell the person who manages your warfarin if you eat them often or are about to change how much you eat. [1][2]
• Gut comfort: leeks are an onion-family vegetable, and onion-family vegetables contain fructans, a type of FODMAP that can bother some people with irritable bowel syndrome. We could not read a leek-specific figure, so this is a general caution. [3][4]
• Grit: leeks grow with soil trapped between their layers. Rinse them well, and see the food-safety notes below. [5][6]
• Allergy: for trouble breathing or swelling of the face or throat, call 911.
• Evidence in one line: leeks are a useful low-fat, vitamin K and folate source; we found no leek-specific trials showing they prevent or treat any disease.

What is in it (USDA values)

Source: USDA FoodData Central, raw leeks (bulb and lower leaf portion), item 169246, SR Legacy. [1] USDA household portions: 1 cup or 1 leek, each 89 g; 1 slice, 6 g. Per-serving figures are our own arithmetic from the per-100 g values. % Daily Value uses the FDA 2016 Daily Values; values vary with variety, ripeness and storage.

Leeks, like onions and garlic, are described in reviews as containing sulfur compounds and flavonoids (plant pigments), and flavonols such as kaempferol and quercetin are discussed in a 2026 lab-chemistry study of onion and leek. [7][8] Those are laboratory findings; the review says clinical validation in people is limited. [7] USDA also lists carotenoids (beta-carotene and lutein plus zeaxanthin) in raw leeks. [1] We did not find a source giving a leek-specific kaempferol amount that we could read, so we give none.

What research says

Eaten as food vs taken as a supplement or extract. The human data above come from people eating allium vegetables as part of ordinary diets, and they are observational: they cannot prove cause. The mechanism studies use extracts or isolated compounds in the lab. A leek extract or powder is a different product; we found no trial of one that we could read, so we make no claim about it. For garlic, which has its own supplement questions, see Garlic.

How much is a normal serving

• The WHO healthy-diet fact sheet (26 January 2026) says people older than 10 should eat at least 400 g of fruits and vegetables a day. [11]
• The NHS "5 A DAY" guide (last reviewed 9 June 2026) counts 80 g of fresh, canned or frozen vegetables as one portion. [12]
• USDA's household portion for leeks is 1 cup or 1 leek, both 89 g. [1]
• These are official figures for information, not a prescription for you.
• Cooking changes allium compounds in ways that depend on the vegetable, the method, time and temperature, and the authors call for more research on each one. [13] We found no source on how cooking changes the vitamins in leeks, so we make no claim.

Safety, allergy and medicines

• Vitamin K and warfarin. MedlinePlus (reviewed 21 January 2025) says vitamin K, or foods that contain it, can change how warfarin works, and advises keeping vitamin K levels steady day to day by eating about the same amount of vitamin K foods every day. [2] It names leafy greens such as kale, spinach and collards and some other vegetables; it does not name leeks. USDA lists 42 µg of vitamin K in one cup (89 g) of raw leeks, 35% of the Daily Value. [1] The point is steadiness: do not suddenly add or drop a food that is high in vitamin K without telling your care team. This is information, not dosing advice.
• Fructans and IBS (FODMAPs). Fructans are a type of FODMAP, short-chain carbohydrates that ferment quickly and can worsen symptoms in people with irritable bowel syndrome. A 2024 measurement of 40 foods found onion highest in fructans; leeks were not reported in the abstract we read. [3] The NHS says a dietitian may suggest a low FODMAP diet that cuts back on certain vegetables, among other foods (page reviewed 17 March 2025). [4] Leek-specific portion figures: Proper evidence not found in the sources we read (the Monash University tables were not reachable). Ask a dietitian, rather than guessing, if leeks bother you.
• Food allergy. Allergy to onion-family foods is possible; the NCCIH garlic page, summarized on our allium overview, notes that some people react to garlic. We did not find a source on leek-specific allergy that we could read. Call 911 for trouble breathing or swelling of the face or throat.
• Kidney disease and potassium. USDA lists 180 mg of potassium per 100 g, 4% of the Daily Value. [1] People on a restricted potassium plan should follow their own team's list; see Foods, kidney disease, potassium and oxalates.
• Pregnancy. The sources we read did not single out leeks as eaten in meals; ask your prenatal care provider about your whole diet.
• Soil on the plant. Leeks pick up soil between their many layers as they grow. [5] Produce can carry germs from soil, and washing reduces but does not remove them. [6]
• Pesticide residues. We did not read a leek-specific source, so we say nothing about residue levels.

Choosing, storing and food safety

• Washing the grit out. Rinse leeks well. One university extension method is to trim leeks into thin rings and rinse them under cool water to remove soil trapped between layers. [5] The FDA says to wash produce under running water, not with soap, detergent or produce washes, and to dry it with a clean cloth or paper towel. [6]
• Storing. Illinois Extension says to keep unwashed leeks in the refrigerator and use them within a few weeks. [5] The FDA says to refrigerate cut or packaged produce, and keep perishable produce at 40°F or below. [6]
• Cutting boards. After handling raw meat, poultry or seafood, wash boards, knives and counters with soap and hot water before preparing produce. [6]
• After cutting. The CDC lists cut vegetables among perishable foods to refrigerate within 2 hours (1 hour in very hot weather above 90°F). [14]

Related pages

• Onions
• Onions, garlic and allium vegetables as food
• Foods and medicine interactions: vitamin K, grapefruit and others
• Prebiotic foods: inulin, onions, garlic and more
• Fresh, frozen and canned produce
• Garlic