The Air Jintan Manis Grandmothers Gave Colicky Babies Has Randomised Controlled Trials Behind It
Trans-anethole does two separate jobs in the body — one explains why fennel calms a crying baby’s stomach, the other explains why it’s classified as a “women’s herb” across almost every traditional medicine system that has touched it.
This article uses two terms repeatedly, so let’s define them in plain language first.
Trans-anethole is the main aromatic compound in fennel — it’s what gives fennel seeds their sweet, liquorice-like smell and taste, and it makes up more than 80% of fennel’s essential oil. Think of it as fennel’s single most important active ingredient. Almost everything fennel is traditionally used for traces back to what this one compound does in the body.
A receptor is like a lock on the surface of a cell, and a compound that fits it — like a key — can switch a specific process on or off. Trans-anethole fits two different locks in the body: one on gut muscle cells (calming spasms) and one that estrogen normally fits (mild hormone-like effects). Same key, two different locks, two different jobs.
- Fennel seed oil has been tested in multiple randomised controlled trials for infant colic — not just observed anecdotally.
- The same compound responsible for fennel’s digestive effects is also a documented phytoestrogen.
- Fennel and mint both relieve gut cramping, but through two completely different molecular mechanisms.
- Chewing fennel seeds after a meal triggers at least three separate pharmacological effects at once.
- Concentrated fennel essential oil is not the same product as traditional dilute fennel seed water — and the safety profile of the two is very different.
Names You’ll See
Three Thousand Years of People Taking Fennel Very Seriously
Long before anyone ran a randomised trial on it, fennel had already talked its way into battlefields, gladiator arenas, protective charms, church pews, and refugee kitchens. None of what follows is offered as medical evidence — it’s cultural record. But it explains why a small liquorice-scented seed has never quite been treated as “just a spice.”
The Plain of Fennel
The Ancient Greek word for fennel is marathon. The Battle of Marathon was fought on a coastal plain so thick with wild fennel that the Greeks named the place after the plant itself. When the outnumbered Athenians won, the runner Pheidippides carried word of the victory back to Athens — the run modern marathons still commemorate. The Athenians reportedly wove fennel stalks into wreaths as a symbol of that victory, which is how a herb ended up lending its name to a 26.2-mile footrace two and a half thousand years later.
Prometheus’s Torch
Wild giant fennel (a towering relative of the culinary plant, up to four metres tall) has a hollow stalk packed with a dry pith that smoulders slowly without ever bursting into open flame — a natural slow-burning fuse. In Hesiod’s telling, this is exactly what Prometheus used to smuggle a stolen ember out of Olympus and give fire to humanity. Whether or not the myth predates the observation, the botany checks out: giant fennel stalks really do carry embers this way, and were used as portable fire-carriers in the ancient world.
The Gladiator’s Wreath and Pliny’s Snakes
Roman gladiators reportedly mixed fennel into their food before combat for strength, and a victorious fighter could be crowned with a garland of fennel. Separately, the naturalist Pliny the Elder recorded that snakes rubbed themselves against fennel plants after shedding their skin — he concluded they did it to restore their eyesight. That single observation rippled through European herbal medicine for over a thousand years, cementing fennel’s reputation as an eye remedy right through to the 17th-century herbalist Nicholas Culpeper, who published fennel-and-eyebright eye washes.
One of the Nine Sacred Herbs
Fennel is named in the Anglo-Saxon Nine Herbs Charm, a poetic incantation recorded in the medical manuscript Lacnunga around 1000 CE, chanted while preparing a salve against infection and “flying venom.” Fennel is called one of “two very mighty” herbs in the charm, said to have been set into the world to help “the wretched and the fortunate” alike. The folk practice continued for centuries afterward: hanging fennel over the doorway on Midsummer’s Eve, and pushing the seeds into keyholes, to keep spirits from entering the house.
“Meetin’ Seeds”
Puritan congregations sat through Sunday services that could run most of the day, with eating strictly off-limits. Fennel and dill seeds became the workaround — small enough to chew discreetly, and apparently not considered “eating” in the eyes of the congregation. They became known colloquially as meetin’ seeds, carried to church specifically to get through the sermon without a rumbling stomach — arguably the original fidget snack.
A Recipe That Outlasted an Expulsion
Sicilian Jewish communities cooked heavily with fennel for generations. When the Spanish Inquisition’s expulsion order forced them off the island and onto the Italian mainland, they carried their fennel-forward cooking with them. The dish they became known for — fennel braised in olive oil with garlic — is still called finocchi alla giudia, “fennel, Jewish style,” in Italian kitchens today: a recipe that survived displacement and is still on the table five centuries later.
Battlefield namesake. Stolen fire. Gladiator’s crown. Protective charm. Church-pew snack. Refugee recipe. Unconnected cultures, unconnected centuries, and the same small seed kept showing up. Here’s what happens when you actually test what it does.
Fennel in the Malaysian Kitchen
Jintan manis is one of the four seed spices — alongside jintan putih (cumin), ketumbar (coriander), and halba (fenugreek) — that anchor a Malaysian and Indian rempah. It’s easy to mistake fennel for cumin at a glance; both are elongated seeds sold in similar-looking packets at the pasar. The giveaway is the smell — fennel is sweet and aniseed-like, cumin is warm and earthy. In a biryani or a curry base, fennel contributes sweetness and a distinctive liquorice note that balances the heat of chilli and the earthiness of the other spices.
Outside the curry pot, fennel has a specific and enduring role in Malaysian and Indian households: air jintan manis, a simple infusion of fennel seeds steeped in warm water, given to infants for colic and to adults after a heavy meal for bloating. It’s also the seed most likely to appear at the end of an Indian meal as mukhwas — a small dish of roasted, sometimes sugar-coated seeds chewed as a digestive and breath freshener.
I still remember the gripe water bottle from when I was a small boy — amber glass, that same label, sitting on the shelf in more or less every Malaysian home with a baby in it. Fifty-odd years later, walk into a pharmacy and the bottle still looks almost exactly the same. Products don’t usually survive that long without a redesign. This one never seemed to need one.
Here’s the detail worth being honest about, though: Woodward’s original 1851 formula was built on dill oil, not fennel. Dill and fennel are botanical cousins, and in Malaysian households the two have long been used somewhat interchangeably in gripe-water talk and in air jintan manis at home. They’re close, but not identical — dill’s active carminative compounds are different from fennel’s trans-anethole, even though both relax gut smooth muscle by a related route. Depending on which bottle was in your family’s cupboard, what you were given as a baby may have been dill-based, fennel-based, or a blend of the two.
Either way, the mechanism that generation was quietly relying on, and the one behind the randomised trials cited earlier in this article, are the same family of chemistry. The bottle just never bothered changing.
What the Research Actually Shows
The Grandmothers Were Right Before the Trials Existed
Trans-anethole relaxes intestinal smooth muscle through calcium channel antagonismMuscle cells contract when calcium flows into them. Trans-anethole partially blocks that calcium flow in gut muscle, which means the muscle can’t spasm as hard or as often — the same principle certain blood pressure medications use, just applied to gut muscle instead of blood vessel muscle. — blocking the calcium influx that drives muscle contraction. In a colicky infant’s gut, this translates directly into fewer and weaker intestinal spasms.
Multiple randomised controlled trials on fennel seed oil emulsion for infantile colic have documented a significant reduction in crying time compared to placebo. The mechanism is identical in the infant gut and the adult gut, which is why fennel also shows up in the evidence base for adult irritable bowel syndrome (IBS) cramping.
Trans-anethole calcium channel antagonism in intestinal smooth muscle; multiple RCTs on fennel seed oil emulsion for infantile colic vs. placebo; mechanism consistent across infant and adult IBS-related cramping evidence.
The Same Molecule, a Completely Different Job
Trans-anethole also binds to estrogen receptor alpha (ER-alpha)One of the two main receptor types the hormone estrogen normally binds to. When a plant compound can also fit this receptor, even weakly, it’s called a “phytoestrogen” — a plant-derived compound with mild estrogen-like activity in the body., a completely separate mechanism from its gut effects. This is the pharmacological basis for two traditional classifications that show up across Ayurvedic, Islamic, Malay, and Mediterranean herbal traditions: fennel as a galactagogue (a substance that promotes breast milk production) and as an emmenagogue (a substance that helps regulate menstruation).
The lactation connection works through modest promotion of prolactin release, the hormone that drives milk production — some randomised trials document increased milk output in nursing mothers using fennel, though the evidence base is smaller and less consistent than the colic evidence. The menstrual connection works through mild cycle modulation, with some clinical evidence for reduced menstrual pain (dysmenorrhoea), consistent with both the phytoestrogenic and smooth-muscle-relaxant mechanisms acting together.
This same ER-alpha activity is also why fennel carries a specific caution: it isn’t superstition that traditional systems treated fennel as something to be careful with in certain conditions. It’s the same mechanism, cutting both ways.
Trans-anethole ER-alpha binding: documented phytoestrogenic activity. Galactagogue mechanism: prolactin release promotion, mixed-strength RCT evidence. Emmenagogue mechanism: menstrual cycle modulation, modest dysmenorrhoea evidence.
The Post-Meal Seed Was Three Applications in One
The traditional post-meal fennel seed practice — documented across Indian, Middle Eastern, Malay, and Mediterranean cultures — stacks several mechanisms into one small habit. Carminative: anethole’s smooth muscle relaxation reduces post-meal bloating and trapped gas. Antimicrobial: fennel’s essential oil complex acts against oral bacteria linked to breath odour and against certain intestinal pathogens. Antioxidant: fennel’s polyphenol complex (quercetin, kaempferol, rosmarinic acid) supports digestive tissue health at the cellular level over time.
The volatile carminative effect is immediate; the polyphenol antioxidant effect is sustained. That combination — fast relief plus slow-building support — is a large part of why fennel has held a place as a digestive herb in nearly every culinary tradition that had access to it.
Fennel essential oil antimicrobial activity documented against food-borne pathogens, S. mutans (oral/dental), and select Candida species. Polyphenol antioxidant complex: quercetin, kaempferol, rosmarinic acid.
Fennel vs. Mint — Not Interchangeable
Both fennel and mint relieve gastrointestinal cramping, and Malaysian and Indian households often reach for either one — or both — without distinguishing between them. Pharmacologically, they aren’t the same tool. Mint works through TRPM8 and TRPV1 ion channel activation — the “cold receptor” pathways that desensitise sensory nerve signalling in the gut. Fennel works through calcium channel antagonism, directly blocking the calcium influx that drives muscle contraction.
Same clinical outcome — reduced cramping — through two completely independent molecular pathways. That’s why combining them isn’t redundant: it’s two separate mechanisms addressing the same symptom at once, which is a form of multi-target pharmacology that traditional digestive preparations were using long before that term existed.
Traditional Remedies Involving Fennel
These are the fennel-related petua that circulate in Malaysian and regional WhatsApp groups, family kitchens, and oral tradition. For each one: the pharmacological reasoning, and an honest verdict.
“Give baby air jintan manis (fennel seed water) to stop colic and crying.”
Multiple randomised controlled trials on fennel seed oil emulsion for infantile colic document a significant reduction in crying duration compared to placebo. The mechanism — calcium channel antagonism relaxing intestinal smooth muscle — is well established.
Important distinction: concentrated fennel essential oil is not appropriate for infants. The dilute traditional seed-water preparation is the one with a documented safety profile at infant dosing. The grandmothers weren’t just right about using fennel — they were right about the concentration, too.
“Eat or drink fennel to increase breast milk supply.”
Trans-anethole’s ER-alpha binding provides a plausible mechanism: modest promotion of prolactin release, the hormone driving milk production. Some randomised trials document increased milk output with fennel supplementation, but the evidence base is smaller and less consistent than the colic evidence.
This is a complement, not a fix. It doesn’t replace addressing the actual drivers of low supply — latch issues, feeding frequency, hydration. Use dietary amounts (tea, culinary use) rather than high-dose supplements while nursing, since the same phytoestrogenic activity that helps also introduces hormone-like compounds at whatever dose is taken.
“Chew fennel seeds after a meal to help digestion and freshen breath.”
This is one of the most efficient traditional practices in this collection. Chewing fennel seeds after a meal simultaneously delivers: smooth muscle relaxation (reducing bloating and gas), antimicrobial activity against the oral bacteria behind post-meal breath odour, phytoestrogenic exposure at low dietary levels, and antioxidant polyphenols.
Three to four pharmacological effects from one seed, chewed for thirty seconds. The traditional Indian mukhwas — a post-meal digestive seed mix typically built around fennel — was a sophisticated multi-target intervention dressed up as a pleasant habit.
“Drink fennel tea to regulate periods and ease menstrual discomfort.”
Anethole’s phytoestrogenic ER-alpha binding gives this petua a real mechanistic basis, and some clinical evidence supports fennel for reduced menstrual pain — consistent with both the hormone-like and the smooth-muscle-relaxant effects working together.
The rationale is sound; the evidence isn’t yet at colic-trial strength. Menstrual irregularity has many possible causes — thyroid, PCOS, stress, nutrition — and fennel’s mild activity only touches one of them. Persistent irregularity deserves medical evaluation, not just tea.
“Air jintan manis or fennel seeds relieve bloating and trapped gas better than any medicine.”
Carminative activity — relief of trapped gas and bloating — is the most consistently documented pharmacological property of fennel across study types. Calcium channel antagonism relaxes intestinal smooth muscle so trapped gas can move, and the volatile compounds also directly reduce gas-producing bacterial fermentation.
“Better than any medicine” overstates it — pharmaceutical carminatives like simethicone have stronger documented effects for acute relief. But the underlying claim, that fennel water reliably reduces bloating and gas, is well supported.
Preparation Methods
Air Jintan Manis (Traditional Seed Water)
1 teaspoon fennel seeds steeped in a cup of warm water for 10–15 minutes, strained. The traditional infant-safe preparation — dilute, not concentrated oil.
Post-Meal Chewing
½ to 1 teaspoon whole seeds, chewed slowly after a meal. Roasted seeds have a milder, nuttier flavour than raw.
Fennel Tea for Adults
1–2 teaspoons crushed seeds (crushing releases more essential oil) steeped 10 minutes in hot water. Crush just before steeping for maximum potency.
In the Rempah
Whole or ground, fennel toasts well in dry-roasted spice blends before grinding — toasting deepens the sweetness and rounds out the liquorice edge.
Honest Limitations
The infant colic evidence is genuinely strong — multiple RCTs, consistent direction, plausible and well-characterised mechanism. That’s the exception here, not the rule.
The lactation and menstrual applications sit in a weaker evidence tier: real mechanism, smaller and less consistent trial bases, and multiple confounding causes for the conditions they’re meant to help. “Pharmacologically plausible” is not the same claim as “clinically proven at scale,” and this article has tried to keep that distinction visible rather than blur it into one confident verdict.
Fennel is also not a substitute for medical evaluation of persistent digestive issues, low milk supply, or menstrual irregularity — it’s a well-evidenced complement in some of those areas, and a weaker one in others.
⚠ Caution
Fennel’s phytoestrogenic activity means high-dose supplementation is not appropriate for individuals with estrogen receptor-positive cancers — this is a documented contraindication, not an abundance-of-caution footnote.
Concentrated fennel essential oil is not the same product as dilute seed-water infusion, and should not be used at infant or high adult doses without professional guidance. Dietary and culinary amounts of fennel are widely considered safe; therapeutic-dose supplementation is a different risk category and warrants a conversation with a healthcare provider, particularly during pregnancy, while nursing, or alongside hormone-sensitive conditions.