Lettuce (Romaine & Leaf): Nutrients, What Research Shows and Safety

Lettuce (Lactuca sativa, daisy family, Asteraceae) is a leafy salad plant. We eat the leaves, raw, as romaine (also called cos) or loose green leaf. People eat it for crunch, water and a little fiber, folate, vitamin A and vitamin K. This page keeps the food apart from supplements and from hype, and it says clearly that lettuce is a different plant from "wild lettuce" sold as a herb.

Read this first

• Warfarin (a blood thinner): lettuce is a good source of vitamin K, which affects how warfarin works. The advice is to keep your usual amount steady and to tell your warfarin clinic about big changes, not to avoid greens. [5][6]
• Food safety: raw lettuce has been linked to several E. coli outbreaks, including romaine in 2018 and 2019. Wash it, keep it cold, and see the food-safety section below. [7][8][10]
• Not wild lettuce: garden lettuce is not the same as wild lettuce (Lactuca virosa), which has caused poisoning in case reports. See wild lettuce. [15]
• Allergy: lettuce allergy is uncommon but real. For trouble breathing or swelling of the face or throat, call 911. [13]
• Evidence in one line: studies of people who eat more leafy greens show links with better health, but these are observational and do not prove that lettuce itself protects you. [11][12]

What is in it (USDA values)

USDA FoodData Central (SR Legacy) values for raw romaine. [1] The serving is the USDA household portion: 1 cup shredded, 47 g.

% Daily Value uses the FDA 2016 Daily Values; values vary with variety, ripeness and storage. Serving columns are our arithmetic from the per-100 g USDA figures.

Green leaf lettuce is lighter in most nutrients per gram. USDA lists, per 100 g, 126.3 mcg vitamin K, 370 mcg vitamin A (RAE), 38 mcg folate, 9.2 mg vitamin C and 1.3 g fiber; one cup shredded is 36 g. [2] Iceberg and other lettuces are not covered by these two USDA entries.

USDA also measured two carotenoids (yellow-orange plant pigments) in lettuce: beta-carotene (5,226 mcg per 100 g in romaine) and lutein plus zeaxanthin (2,312 mcg). [1] Those are measured amounts in the food. Whether eating lettuce changes eye or other health outcomes was not shown in the sources we read: Proper evidence not found in the sources we read for lettuce specifically.

What research says

Observational studies compare people who eat different amounts of vegetables. Those people also differ in other habits, so the results are not proof that greens cause the benefit. [12]

Eaten as food vs taken as a supplement or extract. Every result above is about eating the food or the nutrients in it. We did not read any trial of lettuce extracts, powders or capsules. Do not read the leafy-greens studies as support for any lettuce product. For the herb, see wild lettuce.

How much is a normal serving

• WHO's healthy diet fact sheet (updated 26 January 2026) advises at least 400 g of fruits and vegetables a day for people older than 10. [3]
• The UK NHS counts 80 g of fresh, canned or frozen vegetables as one portion (last reviewed 9 June 2026). [4] That is roughly 1.5 cups of shredded romaine at 47 g a cup, by our arithmetic.
• Lettuce is mostly water (about 95 g in 100 g), so a cup gives few calories and little fiber. [1][2]
• Cooking effects on lettuce nutrients: Proper evidence not found in the sources we read. Lettuce is usually eaten raw.

Safety, allergy and medicines

• Warfarin and vitamin K: MedlinePlus says vitamin K can affect how warfarin works, that sudden changes in vitamin K intake can change the medicine's effect, and to ask your provider before changing your diet. [5] The NHS says foods high in vitamin K, such as green leafy vegetables, can affect warfarin; you can still eat them but should talk to your warfarin clinic, and it says not to take vitamin K supplements or St John's wort with warfarin. [6] See foods and medicine interactions. Do not change or stop a medicine on your own.
• Other medicines: we did not find a source we could read describing a medicine interaction with lettuce other than vitamin K and warfarin. Ask a pharmacist if you take other blood thinners.
• E. coli outbreaks (romaine):
• CDC's final report on the 2018 outbreak (Yuma, Arizona growing region) counted 210 people ill in 36 states, 96 hospitalized, 27 with hemolytic uremic syndrome (a type of kidney failure) and 5 deaths. The outbreak strain was also found in canal water in that region. [8]
• CDC's final report on the 2019 outbreak (Salinas Valley, California) counted 167 people ill in 27 states, 85 hospitalized, 15 with hemolytic uremic syndrome and no deaths. [7]
• FDA's list of outbreak investigations shows two further romaine E. coli O157:H7 investigations, both closed: 89 cases (posted December 2024) and 14 cases (posted July 2026). We read only that list, not the full reports. [9]
• CDC says antibiotics are not recommended for suspected E. coli infection until testing has ruled it out, because they may raise the risk of hemolytic uremic syndrome. If you get severe symptoms, contact a health professional. [7]
• Allergy: a 2025 case report describes anaphylaxis to lettuce in a florist who also had contact allergy to plants in the daisy family. [13] A 2026 review lists vegetables among sources of lipid transfer protein allergens, which are widespread plant proteins that can cross-react. [14] These sources do not say how common lettuce allergy is: Proper evidence not found in the sources we read for how common it is.
• Pregnancy: we did not read a lettuce-specific pregnancy source. Follow general food-safety guidance; see foods in pregnancy.
• Kidney disease and potassium: romaine has 247 mg potassium per 100 g, about 5% of the Daily Value. [1] A cup is small, but ask your kidney team about your own limit. See foods, kidney disease, potassium and oxalates.
• Pesticide residues, nitrate and FODMAPs: Proper evidence not found in the sources we read for lettuce.

Choosing, storing and food safety

• The FDA advises washing produce thoroughly under running water; this reduces bacteria but does not eliminate them. [10]
• Packages marked "pre-washed" or "ready-to-eat" do not need more washing. If you wash them anyway, keep them away from unclean surfaces. [10][7]
• The FDA does not recommend soap, detergent or commercial produce wash. [10]
• Keep perishable and pre-cut produce in a clean fridge at 40 degrees F (4 degrees C) or colder. [10]
• CDC also advises separate cutting boards for produce and raw meat, and washing hands before and after handling produce. [7]

Related pages

• Leafy greens
• Foods and medicine interactions: vitamin K, grapefruit and others
• Dietary nitrate in beets and leafy greens
• Fresh, frozen and canned produce
• Food allergy basics and emergency signs
• Wild lettuce (a different plant)