Fennel Nutrition Calculator — Calories & Nutrition per Serving

Raw fennel bulb (FDC 169385) delivers 414mg potassium per 100g (9% DV) — exceeding banana's 358mg while containing just 31 calories versus banana's 89. On a per-calorie basis, fennel provides 13.4mg of potassium per calorie compared to banana's 4.0mg — a 3.3x advantage that makes fennel one of the most potassium-efficient vegetables available ^[1].

The overall macro profile is lean: 1.24g protein, 0.2g fat, 7.29g carbohydrates, with 3.1g dietary fiber (11% DV) accounting for nearly half the carb content. Water makes up 90.2% of the bulb's weight. One medium fennel bulb (~234g) provides approximately 73 calories, 969mg potassium (21% DV), and 7.3g fiber (26% DV) ^[1].

Beyond potassium, fennel delivers 62.8mcg vitamin K (52% DV), 12mg vitamin C (13% DV), and 0.191mg manganese (8% DV) — a micronutrient combination not typically associated with bulb vegetables. Among common vegetables with similar calorie density, fennel's combined potassium + vitamin K profile is unusually strong ^[1].

Fennel's distinctive anise-like flavor comes from trans-anethole, the dominant volatile compound in its essential oil, typically comprising 50-80% of the total volatile fraction. Secondary compounds include fenchone (contributing bitter notes) and estragole (adding sweet undertones). These compounds are concentrated in the seeds but are also present in the bulb at lower levels ^[2].

The phenolic content of fennel bulb includes rosmarinic acid, chlorogenic acid, and quercetin derivatives — common plant polyphenols found in many vegetables. Fennel also contains 607mcg lutein and zeaxanthin per 100g and 578mcg beta-carotene, giving the fronds their characteristic green color while the white bulb contains lower concentrations ^[2][3].

For nutrition logging purposes, these phytochemicals are not captured in standard macronutrient or micronutrient panels. The USDA's 31-calorie figure reflects the metabolizable energy from protein, fat, and carbohydrate only — volatile oils contribute negligible caloric value at the concentrations found in bulb fennel ^[1].

Fennel and celery are often substituted for each other in recipes — both are crunchy, water-rich, and low in calories. But the nutritional differences are significant: fennel has nearly 2x the fiber (3.1g vs. 1.6g), 60% more potassium (414mg vs. 260mg), and more than 2x the vitamin K (62.8mcg vs. 29.3mcg) per 100g. Celery wins only on calorie count (14 vs. 31 kcal) ^[1].

Vitamin C content favors fennel as well: 12mg vs. 3.1mg for celery — nearly 4x more. Calcium is comparable (49mg fennel vs. 40mg celery). Where celery has a clear advantage is in sodium logging: celery contains 80mg sodium per 100g versus fennel's 52mg, which can matter for sodium-restricted tracking ^[1].

Among the broader comparison group, artichoke leads in fiber (5.4g) and protein (3.27g) but at a higher calorie cost (47 kcal). Kohlrabi dominates vitamin C (62mg) but has negligible vitamin K (0.1mcg). Fennel occupies a unique position: the highest potassium (414mg) and vitamin K (62.8mcg) of the group at a moderate calorie cost ^[1].

Raw fennel preserves the full vitamin C (12mg) and folate (27mcg) content and is the most reliable baseline for nutrition logging. Thinly sliced raw fennel in salads retains all water-soluble vitamins intact. The crisp texture comes from high water content (90.2%) and intact cell walls ^[1].

Roasting at 200°C (400°F) evaporates approximately 25-30% of water, concentrating calories to roughly 44 kcal per 100g and potassium to 470mg. However, vitamin C drops to approximately 6mg (~50% loss) and folate to 18mcg (~33% loss). Roasting also caramelizes fennel's natural sugars (3.93g per 100g raw), intensifying sweetness and producing a softer texture ^[2].

Boiling and draining causes the largest mineral loss due to leaching: potassium drops to approximately 352mg (15% loss) and calcium to 42mg (14% loss). Vitamin C declines to about 7.5mg (38% loss). For nutrient retention, sautéing is a middle ground — the added oil (raising calories to ~52 kcal per 100g) improves absorption of fat-soluble vitamin K and beta-carotene while preserving more potassium than boiling ^[3].

Fennel's 62.8mcg of vitamin K per 100g covers over half the daily value in a single serving — an amount comparable to broccoli (101.6mcg) when adjusted for typical portion sizes. One cup of sliced fennel (~87g) delivers 54.6mcg vitamin K (46% DV) at just 27 calories. One medium bulb (~234g) provides 147mcg vitamin K (123% DV) ^[1].

The mineral profile includes 0.73mg iron (4% DV), 49mg calcium (4% DV), 50mg phosphorus (4% DV), and 17mg magnesium (4% DV). While no single mineral is exceptional in isolation, the breadth across four minerals at 4% DV each means a fennel serving contributes modestly across multiple categories simultaneously — useful for balanced dietary logging ^[1].

Manganese at 0.191mg (8% DV) and selenium at 0.7mcg (1% DV) round out the trace mineral content. Fennel's 27mcg folate (7% DV) is moderate — less than asparagus (52mcg) or endive (142mcg), but meaningful when combined with other folate sources in a mixed meal. The overall micronutrient density — led by vitamin K and potassium — is strong relative to the 31-calorie budget ^[1].