Onion
The millennia-old cornerstone — fructan + quercetin dual matrix in every kitchen.
In 1 minute
What does it provide? Inulin-type fructans (0.1–2 g/100 g) and quercetin glycosides (especially in the skin) — selective bifidogenic effect and polyphenol-mediated anti-inflammatory action.
How much? ½–1 medium onion (≈ 50–100 g)/day; for IBS-sensitive: onion-infused oil (onion soaked in hot oil, then removed — the flavor is fat-soluble, the FODMAP fructan remains water-soluble, so it doesn't enter the oil).
When to avoid? Large amounts during warfarin or DOAC therapy (anticoagulant interaction), IBS elimination phase, 2 weeks before scheduled surgery in large doses, GERD flare.
Onion is one of the oldest cultivated vegetables: it was already known and used in the ancient Near East and Egypt well before written history — archaeological and literary evidence shows that ancient Egyptians viewed it not only as food but also as a symbolic-cultic object: they saw the concentric layers as an artful sign pointing to eternal life, left onions in pharaohs' tombs, and reportedly placed onions in Ramses IV's eye sockets during mummification. According to Herodotus, the pyramid builders received onion, garlic, and radish as rations — this even appeared on the town's inscriptions. (Encyclopedia Britannica, herbsociety.org.uk)
In Greco-Roman medicine, from the Hippocratic Corpus onward it was mentioned for digestive and general health purposes; Dioscorides and Pliny also noted its anti-inflammatory and diuretic power, though the number of medicinal recipes is smaller compared to kitchen uses. In medieval Europe it became one of the staple vegetables alongside cabbage and bean, due to its excellent preservability and versatility — a cornerstone of peasant household winter supplies, a constant element of monastery herbaria. In modern times the Age of Exploration spread it widely, and it became a friend to American settlers; it remained a constant character in culinary arts and folk medicine — the "food–herb" dual status has persisted for millennia, and this set the stage for modern scientific investigations. (ahpa.org, Encyclopedia Britannica)
🔬 Scientific Background
Onion's two main bioactive groups: (1) inulin-type fructans (ITF), particularly short chain-length fractions (kestose, nystose) — not hydrolyzed in the small intestine, they reach the colon and produce a selective bifidogenic effect; (2) quercetin and quercetin glycosides (especially rutin, isoquercitrin) — the richest dietary quercetin source (purple/red onion skin contains 100–600 mg/kg).
Quercetin bioavailability can be enhanced: the glycoside forms are enzymatically hydrolyzed in the small intestine, then the quercetin aglycone enters into complex bidirectional interaction with the microbiota in the colon — being converted on one hand to microbial metabolites (3,4-dihydroxyphenylacetic acid, hippuric acid), and on the other modifying microbial composition (Firmicutes/Bacteroidetes ratio shift).
Onion fructans' prebiotic effect is dose-dependent — in human interventions, 5–10 g/day ITF intake is bifidogenic, and onion is one of the main non-chicory ITF sources in the daily diet. Quercetin is anti-aggregant: 500 mg/day already causes moderate bleeding-time prolongation, which can be additive with warfarin.
- + Extra-virgin olive oil + tomato (sofrito): Mediterranean foundation, polyphenol synergy, lycopene release.
- + Legumes (bean, lentil, chickpea): ITF + GOS dual prebiotic matrix, butyrate-positive.
- + Live cultures (yogurt, kefir): synbiotic principle.
- + Lemon/vinegar (in brief pickling): quercetin stabilization, bioavailability enhancement.
- + Leafy greens (spinach, arugula): additional quercetin/flavonol source, antioxidant synergy.
- + Meat (iron absorption support): quercetin assists non-heme iron utilization.
- Warfarin, DOACs (apixaban, rivaroxaban, dabigatran): quercetin's anti-aggregant effect + occasional vitamin K fluctuation — INR monitoring.
- High-dose aspirin/clopidogrel + large amount of raw onion: additive bleeding risk.
- CYP3A4 substrates (certain statins, cyclosporine): quercetin is a weak CYP3A4 inhibitor; theoretical interaction at large amounts.
- GERD/reflux disease flare + raw onion: can cause severe reflux.
- Long boiling with discarded liquid: fructans and water-soluble polyphenols enter the liquid — should be reincorporated.
- Large amount of raw onion on empty stomach: GI irritation.
- IBS elimination phase: avoid in the first 4–6 weeks; small-dose reintroduction.
- Severe GERD/reflux disease (flare): avoid raw onion.
- Active peptic ulcer: avoid raw onion, moderately cooked.
- Warfarin/DOAC + scheduled surgery in 2 weeks: reduce consumption.
- Infant under 6 months: avoid (flavor, spices).
- Allium allergy (rare, IgE-mediated): complete avoidance.
- Not a trigger for histamine intolerance — safe.
- Severe kidney disease: moderate potassium, normal consumption is safe.
Daily/weekly serving
½–1 medium onion (≈ 50–100 g) daily for cooking. For IBS-sensitive: onion-infused oil (fat-soluble flavor, fructan stays out) or green part of leek as substitute.
Preparation pattern
- Peel, halve between the growth poles.
- Slice thinly or dice (flavor focus: thin slices caramelize better; for bite: dice).
- In oil over medium heat 8–15 min stirring until caramelization (sweeter flavor), or high heat 2-3 min (translucent state).
Classic patterns
Sofrito (Mediterranean): olive oil + finely chopped onion + garlic + tomato — slowly, 15-20 min.
Caramelized onion paste (French): in butter + oil slowly 30-40 min — for pizza, soup, cheese board.
Onion pickling (quick): sliced red onion + vinegar + sugar + salt, 30 min — for tacos, salads.
French onion soup (soupe à l'oignon gratinée): caramelized onion + beef broth + wine + baguette slice + Gruyère + golden brown in oven.
Storage
Whole raw: dry, dark, ventilated place 2-3 months. Cut: refrigerated in airtight container 3-5 days. Cooked onion: refrigerated after quick cooling max 3 days.
What not to do
Don't store with potatoes (ethylene production and moisture → rapid spoilage). Don't cook 30+ min in strong acid (fructan hydrolysis). Don't leave cooked onion at room temperature longer than 2 hours.
References
[1] Slimestad R et al. Onions: a source of unique dietary flavonoids. J Agric Food Chem 2007;55(25):10067–10080.
[2] Galeone C et al. Onion and garlic use and human cancer. Am J Clin Nutr 2006;84(5):1027–1032.
[3] Suleria HAR et al. Onion: nature protection against physiological threats. Crit Rev Food Sci Nutr 2015;55(1):50–66.
[4] Egert S et al. Quercetin reduces systolic blood pressure and plasma oxidised low-density lipoprotein concentrations in overweight subjects: a double-blind, placebo-controlled cross-over study. Br J Nutr 2009;102(7):1065–1074.
[5] Monash University. Onion FODMAP content. Monash FODMAP database.
[6] Kleijnen J, Knipschild P, ter Riet G. Garlic, onions and cardiovascular risk factors: a review of the evidence from human experiments with emphasis on commercially available preparations. Br J Clin Pharmacol 1989;28(5):535–544.
[7] EMA/HMPC. Community herbal monograph on Allium cepa L., bulbus. Assessment report.
[8] Reinhart KM et al. The impact of garlic on lipid parameters: a systematic review. Nutr Res Rev 2009 (context for the Allium family).