# Welsh Onion (Allium fistulosum)

**Canonical URL:** https://ingredients.hermeticasuperfoods.com/ingredients/welsh-onion
**Data Source:** Hermetica Superfoods Ingredient Encyclopedia
**Updated:** 2026-03-24
**Evidence Score:** 2 / 10
**Category:** Vegetable
**Also Known As:** Allium fistulosum, Japanese bunching onion, scallion, green onion, spring onion, negi, cong bai, bunching onion

## Overview

Welsh onion (Allium fistulosum) contains quercetin and other flavonoid compounds that provide [antioxidant activity](/ingredients/condition/antioxidant) and may support weight management. Preclinical studies show its ethanolic and aqueous extracts can reduce body weight and serum cholesterol through antioxidant mechanisms.

## Health Benefits

• Weight management support in preclinical models - ethanolic and aqueous extracts reduced body weight and serum cholesterol in obese mice (animal study evidence only)
• [Antioxidant activity](/ingredients/condition/antioxidant) through flavonoid content - quercetin (2.22 mg/g in ethanolic extract) and other polyphenols demonstrated radical-scavenging properties (in vitro evidence)
• [Anti-inflammatory](/ingredients/condition/inflammation) effects - onionin A1 inhibited IL-10-induced CD163 expression and boosted iNOS/IFN-γ in macrophages (cell line studies only)
• Anti-glycation potential - inhibited 27.9% fluorescent AGEs formation in laboratory tests (in vitro evidence only)
• Traditional [antimicrobial](/ingredients/condition/immune-support) properties - attributed to sulfur compounds like allicin (20 µg/mL in leaves), though no clinical validation exists

## Mechanism of Action

Welsh onion's primary bioactive compounds include quercetin (2.22 mg/g in ethanolic extract) and other polyphenolic flavonoids that scavenge free radicals and reduce [oxidative stress](/ingredients/condition/antioxidant). These antioxidant compounds appear to modulate lipid [metabolism](/ingredients/condition/weight-management) pathways, potentially influencing cholesterol synthesis and fat accumulation. The weight management effects may result from enhanced antioxidant enzyme activity and reduced [inflammatory](/ingredients/condition/inflammation) signaling.

## Clinical Summary

Current evidence for Welsh onion is limited to preclinical animal studies. Research in obese mice demonstrated that both ethanolic and aqueous extracts reduced body weight and serum cholesterol levels compared to controls. The studies identified quercetin content and measured [antioxidant activity](/ingredients/condition/antioxidant) in laboratory assays. No human clinical trials have been conducted to validate these preliminary findings or establish effective dosages for people.

## Nutritional Profile

Welsh onion (Allium fistulosum) is a low-calorie vegetable (~32 kcal/100g fresh weight) with high water content (~90-92%). Macronutrients per 100g fresh weight: carbohydrates ~7g (primarily fructooligosaccharides and fructans acting as [prebiotic](/ingredients/condition/gut-health)s), protein ~1.8g, fat ~0.2g, dietary fiber ~2.6g. Key micronutrients: Vitamin C (~18-20mg/100g, though values vary by cultivar and plant part - green leaves contain significantly more than white bulb portions), Vitamin K1 (~207mcg/100g in green parts, contributing substantially to daily requirements), Folate (~64mcg/100g), Vitamin A precursors (beta-carotene ~1000mcg/100g in green leaves), Potassium (~276mg/100g), Calcium (~72mg/100g), Phosphorus (~37mg/100g), Magnesium (~20mg/100g), Iron (~1.2mg/100g, non-heme form with moderate bioavailability enhanced by co-consumed Vitamin C). Bioactive compounds: Quercetin quantified at 2.22mg/g in ethanolic extract; kaempferol and isorhamnetin also present; onionin A1 (sulfur-containing compound unique to Allium species); thiosulfinates and volatile sulfur compounds including propyl disulfide; fructooligosaccharides (~2-6% dry weight) with established prebiotic function. Green leaf portions are nutritionally denser than white basal sections. Bioavailability note: fat-soluble carotenoids require dietary fat for absorption; quercetin bioavailability is moderate and enhanced when consumed with other polyphenol-rich foods; sulfur compounds are partially lost during high-heat cooking.

## Dosage & Preparation

No clinically studied human dosages are available. Preclinical mouse studies used ethanolic and aqueous extracts over 8 weeks, standardized to contain quercetin (2.22 mg/g and 0.43 mg/g respectively) and ferulic acid (0.17 mg/g and 0.38 mg/g respectively). Consult a healthcare provider before starting any new supplement.

## Safety & Drug Interactions

Welsh onion is generally recognized as safe when consumed as food, but supplement safety data is limited. As with other Allium species, it may interact with anticoagulant medications due to potential blood-thinning properties. Individuals with bleeding disorders should exercise caution. Pregnancy and lactation safety has not been established for concentrated extracts, though culinary use appears safe.

## Scientific Research

No human clinical trials, randomized controlled trials, or meta-analyses have been conducted on Welsh onion supplementation. Current evidence is limited to preclinical studies in cell cultures and animal models, including an 8-week intervention in high-fat diet-induced obese mice showing reductions in body weight and cholesterol parameters.

## Historical & Cultural Context

Welsh onion has been used for centuries in traditional East Asian medicine, particularly in Chinese systems, to treat colds, digestive issues, wounds, and hypertension. Historical applications span [antimicrobial](/ingredients/condition/immune-support), [anti-inflammatory](/ingredients/condition/inflammation), and cardioprotective roles, with cultivation centered in East Asia.

## Synergistic Combinations

Garlic extract, quercetin, green tea extract, turmeric, vitamin C

## Frequently Asked Questions

### How much quercetin is in Welsh onion extract?

Welsh onion ethanolic extract contains approximately 2.22 mg of quercetin per gram of extract. This quercetin content contributes significantly to the plant's antioxidant activity and potential health benefits.

### Can Welsh onion help with weight loss?

Animal studies show Welsh onion extracts reduced body weight and serum cholesterol in obese mice. However, no human studies have confirmed weight loss benefits, so evidence remains preliminary and limited to preclinical research.

### What's the difference between Welsh onion and regular onions?

Welsh onion (Allium fistulosum) is a perennial species with hollow leaves, while regular onions (Allium cepa) form bulbs. Welsh onions have different flavonoid profiles and may contain higher concentrations of certain antioxidant compounds.

### Are there any side effects of Welsh onion supplements?

Welsh onion supplements may cause digestive upset or interact with blood-thinning medications like other Allium species. Limited safety data exists for concentrated extracts, though culinary consumption appears well-tolerated.

### How should Welsh onion extract be taken?

No standardized dosage exists for Welsh onion supplements since human studies are lacking. The animal research used ethanolic and aqueous extracts, but optimal human dosing requires clinical investigation to establish safety and efficacy.

### Is Welsh onion safe to take with blood thinners or anticoagulant medications?

Welsh onion contains quercetin and other polyphenols that may have mild anticoagulant properties, so caution is warranted if you're taking prescription blood thinners like warfarin or aspirin. Consult your healthcare provider before adding Welsh onion supplements to your regimen to avoid potential interactions. Individual risk depends on dose, extract concentration, and your current medication profile.

### What is the difference between Welsh onion extract and whole Welsh onion powder for bioavailability?

Ethanolic extracts concentrate bioactive compounds like quercetin to approximately 2.22 mg/g, providing higher polyphenol density than whole powder preparations. However, whole powder may retain additional fiber and synergistic compounds lost during extraction, and absorption differences between forms have not been directly compared in human studies. The optimal form depends on your intake goals and whether you prioritize potency or whole-food matrix effects.

### Can you get sufficient Welsh onion polyphenols from dietary sources alone, or do you need a supplement?

Welsh onions are nutrient-dense and can be consumed fresh in salads, soups, and stir-fries to obtain natural quercetin and other flavonoids, though precise polyphenol content varies by growing conditions and cultivar. Supplemental extracts provide standardized, concentrated doses that exceed typical dietary consumption, making them more practical for therapeutic research doses studied in weight management and antioxidant contexts. For general health maintenance, whole food sources are sufficient; supplements may be considered for specific therapeutic goals backed by emerging evidence.

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