fennel
A crisp, anise-scented bulb best evidenced for easing menstrual and menopausal symptoms.
Moderate evidence
🥦Vegetables
Evidence tier
Moderate
Research weight
Citations
8 verified / 8
Classification
Vegetables
❝
What the evidence says. Several controlled trials; effects real but modest or context-dependent.
Nutrition per serving 1 cup sliced, raw (87 g)
- Sugars 3.4 g4%
- Fibre 2.7 g3%
- Other carbs 0.2 g0%
- Protein 1.1 g1%
- Other 79.6 g91%
27 kcal1.1 g protein2.7 g fiber3.4 g sugar
| Nutrient | Per serving | % daily value |
|---|---|---|
| Vitamin C | 10 mg | 12% |
| Fiber | 2.7 g | 10% |
| Potassium | 360 mg | 8% |
| Folate | 23 µg | 6% |
| Vitamin A | 42 µg | 5% |
| Vitamin K | 55 µg | 46% |
| Vitamin B6 | 0.04 mg | 2% |
| Manganese | 0.17 mg | 7% |
| Copper | 0.06 mg | 7% |
| Vitamin E | 0.5 mg | 3% |
| Magnesium | 15 mg | 4% |
| Calcium | 43 mg | 3% |
Composition data: USDA FoodData Central ↗
What is fennel?
fennel is a vegetable used for reduces primary dysmenorrhea (menstrual) pain. NutriDex grades the human evidence as Moderate. Fennel bulb is a low-calorie, hydrating vegetable supplying potassium, vitamin C, vitamin K and the phytoestrogenic essential-oil compound trans-anethole. Its strongest human evidence is in gynecologic symptom relief: meta-analyses of randomized trials show fennel meaningfully reduces primary dysmenorrhea pain (comparable to NSAIDs) and improves menopausal symptom scores, though most trials are small, Iran-based and at risk of bias. Cardiometabolic and weight effects remain unproven in controlled trials.
Purported Benefits
✓Reduces primary dysmenorrhea (menstrual) pain
✓Improves menopausal symptom scores
✓May reduce infant colic crying time
✓Hydrating, low-calorie source of potassium and vitamin K
✓Provides vitamin C and antioxidant polyphenols
Dosing & Compounds
Typical Dose
Standard serving: 1 cup sliced, raw (87 g). Eat whole (with skin where edible); favour whole fruit over juice.
Active Compounds
Safety & Cautions
Concentrated fennel essential oil/extract carries higher exposure to estragole (a rodent hepatocarcinogen) than culinary amounts; supplements should be avoided in pregnancy and in estrogen-sensitive conditions given anethole's mild phytoestrogenic activity. Rare IgE allergy occurs, often cross-reacting with celery, carrot and mugwort/birch pollen. Vitamin K content is modest but relevant for those on warfarin. Culinary bulb amounts are considered safe. Educational only — always check with your doctor or pharmacist before combining fennel with any medicine.
Key Studies
Systematic review & meta-analysis of RCTs
Lee 2020 (Nutrients)
✓ Full text
Across 12 RCTs, fennel was as effective as conventional drugs for dysmenorrhea (n=502, SMD 0.07, 95% CI -0.08 to 0.21) and superior to placebo for pain reduction (n=468, SMD -3.27, 95% CI -5.28 to -1.26, p=0.001).
Systematic review & meta-analysis
Nasiri Lari 2021 (J Complement Integr Med)
✓ PubMed
Pooling 12 trials, fennel significantly reduced primary dysmenorrhea pain versus placebo (SMD -0.632) and was comparable to mefenamic acid.
Systematic review & meta-analysis of RCTs
Lee 2021 (Complement Ther Clin Pract)
✓ PubMed
Two placebo-controlled RCTs (n=145) showed fennel significantly improved menopausal symptom scores (SMD -1.32, 95% CI -1.76 to -0.87, p<0.00001).
Systematic review protocol of RCTs
Ghodsi 2018 (PMC5895370, protocol)
✓ Full text
Registered protocol synthesizing RCTs of fennel for menopausal symptoms, establishing the methodological basis for subsequent meta-analyses.
Meta-analysis
Khorshidi 2003 / Lee 2020 SR
✓ Full text
Systematic review and meta-analysis found fennel comparable to conventional drug therapy for pain (n=502, SMD 0.07, 95% CI -0.08 to 0.21) and superior to placebo (n=468, SMD -3.27, 95% CI -5.28 to -1.26), with high heterogeneity (I2=98%).
Double-blind randomized placebo-controlled trial
Yazdani 2017 / J Menopausal Med (Saghafi 2017)
✓ Full text
In 47 overweight postmenopausal women over 12 weeks, fennel (soft capsule) showed no significant effect on body weight, BMI, waist/hip circumference or fat distribution versus placebo.
Randomized placebo-controlled trial
Alexandrovich 2003 (Altern Ther Health Med)
✓ PubMed
Fennel seed oil emulsion eliminated infantile colic in 65% of treated infants versus 23.7% on placebo (p<0.01) by reducing crying time.
Narrative pharmacological review
Rather 2016 / Badgujar 2014 review
✓ PubMed
Reviews Foeniculum vulgare phytochemistry (trans-anethole, fenchone, estragole) and pharmacology, summarizing antioxidant, antispasmodic and estrogenic activities underpinning clinical use.