Brassica oleracea var. gongylodes (Kohlrabi)

Kohlrabi (Brassica oleracea var. gongylodes) is a cruciferous vegetable rich in glucosinolates, vitamin C, and polyphenols including kaempferol and quercetin. Its primary bioactive compounds exert antioxidant and potential chemopreventive effects through free radical scavenging and modulation of detoxification enzyme activity.

Origin & History

Brassica oleracea var. gongylodes, or kohlrabi, is a cruciferous vegetable native to Northern Europe, cultivated for its enlarged, fleshy stem and leaves.[1][6] It is a member of the Brassica species, rich in sulfur-containing glucosinolates, and is typically prepared from the whole plant without specific extraction methods beyond simple aqueous extracts for analysis.[1][5]

Historical & Cultural Context

Originating in Northern Europe, kohlrabi is traditionally consumed as a cooked vegetable or fermented into dishes like “Mounji Achar” in the Jammu and Kashmir region of India.[1][6] Ground kohlrabi meal has also been used in Taiwan as a fungicidal seed treatment, though no formal medicinal uses in systems like Ayurveda or TCM are documented.[5]

Health Benefits

[{"benefit": "Exhibits Antioxidant Activity (In-Vitro)", "description": "Aqueous extracts from kohlrabi leaves demonstrated up to 50% radical scavenging activity against DPPH and ABTS in laboratory settings, an effect attributed to its phenol and flavonoid content.[1]", "evidence_quality": "Preliminary (in-vitro)"}, {"benefit": "Rich Source of Phenolic Compounds", "description": "Compositional analyses show kohlrabi contains significant levels of phenols (up to 2.14 mg GAE/g dw), which are compounds known for their antioxidant potential.[1]", "evidence_quality": "Compositional Analysis"}, {"benefit": "Contains Potentially Fungicidal Isothiocyanates", "description": "Kohlrabi contains glucosinolates that hydrolyze into isothiocyanates, such as 4-methylthiobutyl isothiocyanate (55.6% of total), which have been investigated for fungicidal properties.[3][5]", "evidence_quality": "Compositional & Functional Analysis"}, {"benefit": "Provides Anthocyanins in Purple Varieties", "description": "Metabolic profiling identified 12 types of anthocyanins, primarily cyanidin derivatives, in purple kohlrabi, which are pigments with known antioxidant capabilities.[2]", "evidence_quality": "Compositional Analysis"}, {"benefit": "Source of Phenylpropanoids", "description": "Purple kohlrabi flesh contains 12.7-fold higher concentrations of phenylpropanoids like trans-cinnamic acid compared to white varieties, which are bioactive plant compounds.[2]", "evidence_quality": "Compositional Analysis"}]

How It Works

Kohlrabi's glucosinolates are hydrolyzed by the enzyme myrosinase upon cell disruption, yielding isothiocyanates such as sulforaphane, which induce Phase II detoxification enzymes including glutathione S-transferase and quinone reductase via Nrf2 pathway activation. Its flavonoids, particularly kaempferol and quercetin, directly scavenge reactive oxygen species (ROS) and chelate pro-oxidant metal ions, reducing oxidative stress at the cellular level. Additionally, vitamin C in kohlrabi regenerates oxidized vitamin E and contributes to collagen biosynthesis by acting as a cofactor for prolyl and lysyl hydroxylase enzymes.

Scientific Research

No human clinical trials, randomized controlled trials (RCTs), or meta-analyses specific to kohlrabi supplementation were identified in the provided research, and therefore no PMIDs are available.[1][2] The existing scientific literature is limited to compositional analyses and in-vitro studies on the plant's chemical and antioxidant properties.

Clinical Summary

Most available evidence for kohlrabi is derived from in-vitro and animal studies rather than controlled human trials. Aqueous leaf extracts demonstrated up to 50% radical scavenging activity against DPPH and ABTS assays, attributed to phenolic and flavonoid concentrations. Epidemiological data on cruciferous vegetables broadly associate higher intake with reduced colorectal and lung cancer risk, though kohlrabi-specific human intervention studies with defined sample sizes and endpoints are lacking. Overall, the evidence base remains preliminary, and clinical efficacy in humans has not been established through rigorous randomized controlled trials.

Nutritional Profile

Kohlrabi (Brassica oleracea var. gongylodes) is a low-calorie, nutrient-dense vegetable. Per 100g raw edible portion (bulb): Energy ~27 kcal, Water ~91g, Carbohydrates ~6.2g (of which sugars ~2.6g), Dietary Fiber ~3.6g, Protein ~1.7g, Fat ~0.1g. Key Vitamins: Vitamin C (ascorbic acid) ~62mg (69% DV) — notably high and well-bioavailable in raw form but significantly reduced by cooking; Vitamin B6 (pyridoxine) ~0.15mg; Folate (B9) ~16µg; Thiamine (B1) ~0.05mg; Riboflavin (B2) ~0.02mg; Vitamin K1 ~0.1µg (bulb; leaves contain substantially more, ~170µg per 100g). Key Minerals: Potassium ~350mg, Phosphorus ~46mg, Calcium ~24mg, Magnesium ~19mg, Manganese ~0.14mg, Copper ~0.13mg, Iron ~0.4mg (non-heme; bioavailability enhanced by co-consumption with Vitamin C). Bioactive Compounds: Glucosinolates — primarily glucoiberin (3-methylsulfinylpropyl glucosinolate) and sinigrin, ranging approximately 1.5–4.5µmol/g dry weight depending on cultivar and growing conditions; these are hydrolyzed by myrosinase upon tissue disruption to bioactive isothiocyanates (e.g., iberin, allyl isothiocyanate) with chemoprotective associations. Phenolic compounds: total phenolics approximately 50–150mg gallic acid equivalents per 100g fresh weight (higher in leaves vs. bulb); predominant phenolics include hydroxycinnamic acids (sinapic acid, ferulic acid), flavonoids (kaempferol glycosides, quercetin derivatives), and anthocyanins in purple-skinned cultivars (primarily cyanidin-3-sophoroside-5-glucoside). Carotenoids: lutein and beta-carotene present in modest quantities (~1–3mg/100g combined), concentrated predominantly in the leaves. Fiber composition: mix of cellulose, hemicellulose, and pectin; supports gut motility. Bioavailability notes: Glucosinolate hydrolysis is optimal in raw or lightly steamed kohlrabi; boiling significantly leaches water-soluble Vitamin C and glucosinolates (up to 40–60% loss). Chopping or chewing before cooking activates myrosinase. Oxalate content is low (~20mg/100g), posing minimal concern for calcium absorption interference.

Preparation & Dosage

No clinically studied dosage ranges for kohlrabi or its extracts have been established due to a lack of human trials.[1] Consult a healthcare provider before starting any new supplement.

Synergy & Pairings

Sulforaphane, Turmeric (Curcumin), Green Tea Extract (EGCG), Vitamin C, Resveratrol

Safety & Interactions

Kohlrabi is generally recognized as safe when consumed in typical dietary amounts, with no established upper intake limit. Individuals taking warfarin (Coumadin) should moderate intake, as its vitamin K content can interfere with anticoagulant therapy and alter INR values. Those with hypothyroidism or taking thyroid hormone medications (e.g., levothyroxine) should be cautious, as raw kohlrabi contains goitrogenic glucosinolates that may inhibit thyroid peroxidase and reduce iodine uptake, though cooking partially deactivates these compounds. Kohlrabi is considered safe during pregnancy as a whole food, but concentrated extracts or supplements have not been evaluated for gestational safety.