Fennel Bulb: Nutrients, What Research Shows and Safety

Fennel bulb is the swollen, pale-green base of the fennel plant, Foeniculum vulgare, in the carrot family (Apiaceae). People slice it raw in salads or cook it, and enjoy its mild, sweet, aniseed-like flavor. This page is about the bulb as a vegetable. It keeps the food apart from fennel seed, fennel tea and fennel oil, which are different products, and from hype.

Read this first

• Allergy: fennel belongs to the carrot family, and people who react to celery or to mugwort pollen sometimes react to other plants in this group. For trouble breathing or swelling of the face or throat, call 911. See food allergy basics and emergency signs. [5][6]
• Warfarin: the bulb contains vitamin K, which can change how warfarin works. MedlinePlus advises keeping vitamin K foods about the same from day to day. [1][2]
• Kidney disease and some blood pressure medicines: MedlinePlus says people with kidney problems may need to limit potassium-rich foods, and ACE inhibitors, ARBs and potassium-sparing diuretics can raise blood potassium. The bulb has a moderate amount of potassium. Ask your care team. [1][3]
• Evidence in one line: fennel bulb is a low-calorie source of vitamin K, vitamin C, fiber and potassium; we found no trial showing the bulb prevents or treats any disease.

What is in it (USDA values)

Source: USDA FoodData Central, "Fennel, bulb, raw", item 169385, SR Legacy (April 2018 release). [1] USDA household portions: 1 cup, sliced, 87 g; 1 bulb, 234 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.

USDA also lists beta-carotene (578 µg per 100 g) and lutein plus zeaxanthin, which are carotenoids (yellow-orange plant pigments). [1] A 2022 laboratory study measured phenolic acids and flavonoid compounds in fennel bulb, stem and leaf, but the abstract gives no bulb values, so we give none. [11] Those are lab findings, not results in people.

What research says

An association in observational studies is not proof, because people who eat more vegetables often differ in other ways. [8]

Eaten as food vs taken as a supplement or extract. The numbers above are for the vegetable. Fennel seed (the dried fruit), fennel tea and fennel oil are separate products with their own questions about safety and use, covered at fennel (seed and herb). We make no claim here that the bulb has the effects studied for the seed or its preparations.

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. [9]
• The NHS "5 A DAY" guide (last reviewed 9 June 2026) counts 80 g of fresh, canned or frozen fruit or vegetables as one portion. [10]
• The USDA household portion for the bulb is 1 cup sliced (87 g), or one whole bulb (234 g). [1]
• These are official figures for information, not a prescription for you.
• We found no source on how cooking changes the vitamins or carotenoids of fennel bulb, so we make no claim.

Safety, allergy and medicines

• Celery, mugwort and spice allergy. A 2025 review of celeriac allergy says people sensitized to the celeriac allergen Api g 7 are often also sensitized to the major mugwort pollen allergen Art v 1, because the two proteins are structurally similar. [5] A 2023 review proposes the name "defensin-related food allergies" for food reactions linked to mugwort pollen. [6] Fennel is a relative of celery, and our herb page notes that the EU herbal monograph lists cross-reactivity between fennel fruit and mugwort pollen. [12] Proper evidence not found in the sources we read on how often fennel bulb itself causes reactions. If you have reacted to celery, mugwort pollen or spices, ask an allergy clinician. See herbal allergy and cross-reactivity. For trouble breathing or swelling of the face or throat, call 911.
• Vitamin K and warfarin. MedlinePlus (reviewed 21 January 2025) says vitamin K, or foods that contain it, can change how warfarin works, and advises eating about the same amount of vitamin K foods each day. [2] It does not name fennel. USDA lists 54.6 µg in one cup (87 g) of raw sliced bulb, 46% of the Daily Value. [1] The point is steadiness: do not suddenly add or drop a food high in vitamin K without telling the person who manages your warfarin. See foods and medicine interactions.
• Potassium, kidney disease and some heart medicines. MedlinePlus (reviewed 30 April 2026) says people with kidney problems, especially on dialysis, should not eat too many potassium-rich foods, and lists ACE inhibitors, ARBs and the potassium-sparing diuretics spironolactone, triamterene and amiloride among causes of high blood potassium. [3] USDA lists 360 mg per cup of bulb, 8% of the Daily Value. [1] Follow your own team's food list. See foods, kidney disease, potassium and oxalates.
• Estragole. Estragole is a natural compound in fennel that the EU herbal monograph for fennel fruit treats with caution for children and in pregnancy. [12] EFSA's 2023 opinion on fennel essential oils reports estragole up to 6.1% in bitter fennel oil, which is a concentrated oil. [13] We found no estragole measurement for the bulb as a vegetable in the sources we read, so we make no claim about it, and we do not apply the seed and oil limits to the bulb.
• Fennel seed, tea and oil. These have separate safety notes (age limits, pregnancy, treatment length) on the fennel page. Do not assume the bulb behaves the same way.
• Fiber and the gut. The NHS lists benefits of fiber but we did not find a source on fennel-bulb tolerance, so we make no claim about gas or bloating. [7] FODMAP (gut-fermentable carbohydrate) figures for fennel bulb: not found in the sources we read.
• Pregnancy. We did not find a source that singles out the bulb as a vegetable. Ask your prenatal care provider about your whole diet. See foods in pregnancy.
• Pesticide residues. We did not read a fennel-specific source, so we say nothing about residue levels.

Choosing, storing and food safety

• Washing. The FDA says to rinse fresh produce under running water, not with soap, detergent or produce washes, and to dry it with a clean cloth or paper towel. Washing lowers germs but does not remove them all. [14]
• Storing. The FDA says to keep perishable produce in a refrigerator at 40°F or below and to refrigerate cut or packaged produce. [14]
• Cutting boards. Keep raw produce apart from raw meat, poultry and seafood, and wash boards and knives with soap and hot water between tasks. [14]

Related pages

• Fennel (seed and herb)
• Parsnips
• Leeks
• Foods and medicine interactions: vitamin K, grapefruit and others
• Herbal allergy and cross-reactivity
• Fresh, frozen and canned produce