toxic fennel seeds

Benefits of Fennel Tea & Essential Oil Not Worth Cancer Risk

It’s in the same family as carrots, parsley, dill, and celery (Apiaceae). When chopped, it also looks a lot like celery and crunches just the same.

This root bulb is often used in salads. Cooking it is more popular in the ethnic cuisine of India and the Middle East.

Can you eat fennel seeds? A lot of people do on a daily basis, both during and after meals, in hopes of it helping flatulence and heartburn.

Here in America, the most common way you hear of this plant being consumed is probably as an herbal tea for gas and bloating, or just to freshen breath. Some even allege these teas to be a treatment for digestive diseases like IBS, constipation, small intestinal bacterial overgrowth (SIBO), leaky gut, Candida yeast infections, acid reflux, and others.

More recently, fennel essential oil has been peddled by some bloggers as being good for many of those same digestive issues and other uses too like wound healing, hiccups from gut spasms, and weight loss.

For most of those alleged advantages there is little to no science to support them. But there is science to support the notion that this essential oil may be the most dangerous of them all.

The “potent carcinogen” inside

fresh fennelYou will see all kinds of articles touting the top 10 fennel benefits or uses for it which are claimed to boost your health.

All this supposed good news about the plant, while ignoring elephant in the room.

The “potent carcinogen” is estragole and it’s found in the bulb, seeds, leaves, and extractions made from these parts (1)

No human studies are available to directly measure cancer risk, but a plethora of mice and rat studies – going back as early as the 1970’s – have linked it to liver cancer. That’s why the State of California prioritized it, when they began to evaluate its status for Prop 65 (whether it causes cancer or reproductive harm) (2):

“Estragole was assigned a final priority of ‘high’ carcinogenicity concern…”

And yes, for the record, estragole has been categorized by the State of California since 1999 as being a carcinogen (3).

But setting aside whether or not fennel causes cancer, it has been found to cause transgene mutations in animals. In other words, it’s a genotoxin. That means it has the ability to damage genetic information in the DNA.

Whether or not that damage leads to a mutation that can spur cancer is the unsettled question, at least in humans.

Regardless, intentionally consuming something which has significant genotoxic activity is bad for you.

Which food source is worse?

estragole molecule chemical structureFennel isn’t the only natural food containing estragole, as it’s also found in the following plants:

  • Anise (Pimpinella anisum)
  • Avocado (Persea americana)
  • Clove basil/African basil (Ocimum gratissimum)
  • Frankincense (Boswellia serrata)
  • Korean mint (Agastache rugosa)
  • Licorice (Glycyrrhiza glabra)
  • Oregano (Origanum vulgare)
  • Parsley (Petroselinum crispum)
  • Sweet basil (Ocimum basilicum)
  • Tarragon (Artemisia dracunculus)

So why is fennel not good for you, but most of these other herbs and spices are considered healthy?

Because among these species, the concentrations vary immensely, as well as which parts we typically consume.

And we’re not inferring all of the supposed superfoods on that list are necessarily healthy.

For avocados, there’s a bigger problem to worry about than its estragole content. There might be yet another reason why avocado can cause genotoxicity.

DNA damage after avocado treatment

Above are actual mutations occurring under a microscope when human white blood cells come in contact with the fruit. So yes, avocado is bad for you too possibly.

When it comes to the foods that contain estragole – and the direct effects of that particular poison – the research seems to suggest the two of most concern are fennel and tarragon.

This is why we have already recommended a substitute for tarragon previously, given its estragole content. Since that spice is only used on rare occasion for things like chicken tarragon, its risk is low relative to fennel.

You have people promoting the benefits of drinking fennel tea daily; to help with gas, bloating, and indigestion. At least tea isn’t the worst source, relative to some other uses of the plant. Still though, the tea is a worry…

“…a potential risk for human health and a priority for risk management. However, fennel teas are generally consumed only for short periods of gastrointestinal disorders.”

That’s a quote from research published in a 2016 edition of the International Journal of Food Sciences and Nutrition. A total of 42 fennel tea brands for sale in Austria were tested. (4)

Of course the problem with their assumption is that not everyone is drinking the tea for short periods of time. Thanks to blogosphere hyping benefits, you now have people drinking it daily for months or even years!

Fennel essential oil uses might be the worst

essential oil therapyDespite what you may have read elsewhere about its “miraculous” benefits, the facts about the oil don’t live up to the hype.

The one exception is its antioxidant content.

When you look at the ORAC values of essential oils, out of 72 measured, fennel ranks in 5th place. It has a value of 238,400.

That’s 50x more antioxidants than blueberries when equal weights are compared.

The problem? The weight used is about 3.5 ounces (100 grams). That’s 10x more than an entire bottle of Plant Therapy’s essential oil of fennel, which is 10 ml. Doterra isn’t much bigger at 15 ml.

Whatever brand you use, you’re only using a drop or two at a time, not the entire bottle. In turn, the amount of antioxidants you’re getting is merely a tiny fraction of that 100 gram measurement.

Can you ingest fennel essential oil?

Taking it internally is generally not considered safe or recommended by manufacturers. Most sell a therapeutic version, which is designed for aromatherapy and topical skin care uses. Not drinking or eating.

Doterra does list ingestible uses for their product and make the following claims about it:

  • Add 1–2 drops in a veggie capsule to promote digestion.
  • Take internally to support healthy respiratory function.
  • Put a drop of Fennel in water or tea to help fight sweet tooth cravings.

They’re not telling you to guzzle it. Not even a spoonful. For how to use fennel essential oil internally, their instructions say to use only one drop.

Relative to eating a bowl of berries or even a dark chocolate bar, consuming one drop of the oil will offer you very little antioxidant activity.

Health benefits researched

Sure, it’s possible that it might help with asthma, weight loss, and increase milk supply while breastfeeding. Anything is possible, but none of that is proven.

Only 5 clinical studies have been published. Out of those were 3 with animals (no humans) and those topics are of little relevance to the claims you hear.

1. Parasites in chickens

In this trial, the animals were treated with the mixed oils of sweet wormwood and fennel. The effect they had on the chickens’ Eimeria infections was measured. In case you’re wondering, the sweet wormwood helped a lot more. (5)

2. Antibiotic alternative for piglets

In Germany, antibiotics are banned as an additive in livestock feed (the US should do the same!). The essential oils of fennel seed and caraway were tested as alternatives, but they didn’t perform any better than the control diet. However there was an adverse reaction of weight loss noted:

“The diets containing fennel or caraway oils were consumed at less than 50%. If the diet contained 100 mg fennel oil/kg, the decrease of percentual feed intake was significant.”

That side effect might be considered beneficial in humans trying to lose weight. But these were baby pigs, not humans. No one has checked to see if the same happens with us. (6)

3. Egg production in quail

A total of 180 quail were tested with various diets, one of which included a blend of 6 essential oils; oregano, sage, laurel, myrtle, citrus peel, and fennel seed. A fertility benefit was not observed with this diet, since the amount of eggs laid and their weights were comparable. (7)

Here are the two human studies…

1. Arm and leg swelling + well-being

Published in the European Journal of Oncology Nursing, this trial looked at lymphoedema; swelling of the limbs caused by a blockage in the lymphatic system. It’s often a side effect that occurs during cancer treatment.

It was a randomized trial where patients massaged essential oils on their skin and then reported their feelings of “well-being” and nurses checked their limb volumes for improvement. The conclusion isn’t what EO fans want to hear. (8)

“…aromatherapy oils, carefully chosen on the basis that they should benefit this group, did not appear to influence any improvement in these measures.”

2. Irritable Bowel Syndrome

The most relevant and compelling case of it being useful is the trial completed by 116 women and men who had mild to moderate IBS.

During the 30 day test, each person was given a twice daily dosage of capsules containing curcumin and fennel. When compared to placebo, there was a much greater improvement in abdominal pain and the IBS symptom severity score (SSS) as seen below.

graphs showing fennels effect on IBS patients

Looks impressive, but remember this was a combo of two different plant extracts. Although it’s just a theory, we speculate the curcumin component is more likely responsible for the benefits.

Why do we say that? Numerous human studies have suggested that curcuminoids are a potent anti-inflammatory agent and may offer relief for inflammatory bowel diseases like Crohn’s disease and ulcerative colitis. (9) (10) (11)

Our curcumin reviews dive into the research more.

Now for the worst part…

mother breastfeedingAs you see, there’s very little evidence for the things people are saying about fennel essential oil. Being that it hasn’t even been studied during pregnancy, the idea of using fennel oil for lactation seems to be more of an old wives’ tale.

Many say you should drink fennel tea while breastfeeding and a nearly 70 year old paper out of Russia is still being claimed as validation for that practice (12).

In high amounts, fennel seeds aren’t safe in humans. Shouldn’t that be a red flag for mothers?

But like we said, tea may be the lesser issue. The really bad thing is the essential oil because of how much estragole it contains.

Research has found the oil contains anywhere from 2.2 to 2.5%, all the way up to “not more than 10% estragole.” A study using three organic fennel essential oils from Egypt said it was “highly abundant.” (13) (14) (15)

Fresh fennel bulbs and foliage (leaves) are said to only have 0.05% essential oil content (volume/fresh weight). (16)

That’s why they press the seeds to make the oil, not the root which is what most people eat.

How much oil there is in seeds has been measured as being anywhere from 10.7 to 19.0%. That’s total oil composition, not the percentage of oil which is estragole. (17)

In short, chewing seeds is the 2nd highest source of estragole but the number one is purified essential oil. Even if you don’t eat the oil, remember your skin will absorb it.

Here in California, Prop 65 warnings are required when things contain a certain concentration of a carcinogen. We checked the following brands to see if they had it; Young Living, Rocky Mountain Oils, Doterra, Edens Garden, Earthroma, Youngevity, Aura Cacia, Now Foods, Plant Therapy, and Plant Guru. None carried the warning and we suspect they probably should be.

Uses for tea

What are the benefits of drinking fennel tea? There are 3 human clinical trials which have been published so far:

1. Intestinal function after surgery

Postoperative gut recovery was measured in 159 patients who underwent operations for gynecological cancers. For those drinking the tea made from dried fennel, their bowel movements were said to improve versus the control group who drank water. (18)

2. Chronic constipation (Brazil study)

This Brazilian study only involved 20 patients. It’s loosely related at best because the tea also contained senna (Senna alexandrina), anise (Pimpinella anisum), and other herbs. Frequency of bowel movements and patient perception of function improved, but this is not surprising given that senna is perhaps the best natural laxative. (19)

3. Chronic constipation (nursing home study)

A total of 86 patients at a Pennsylvania nursing home were given either placebo or Traditional Medicinals Smooth Move® brand of organic fennel containing tea. The uses for it, according to its packaging, are for occasional constipation and gas relief. (20).

“The Smooth Move group, compared with the placebo group, experienced an average of 4.14 more bowel movements during the 28-day study period…”

Customer reviews of Smooth Move are generally quite favorable and coincidentally, one person on the Superfoodly team happens to have some in the cupboard right now…

tea for constipation

It was purchased for someone post-surgery, as constipation will go hand in hand with narcotics. Since the post-op pain meds never had to be used, neither did the tea.

Even if Smooth Move works, you can’t really extrapolate from that. Their blend of herbs is “proprietary” and it’s unknown how much fennel there is inside.

Smooth Move tea ingredients and nutrition facts

The advantages of fennel tea for short term usage may outweigh the potential side effects of estragole. However using it as a long term remedy for constipation, gas relief, and indigestion warrants extreme caution. For the essential oil of fennel, given the lack of benefits research, it’s hard to justify usage of it in any capacity.

A safer alternative for digestive issues may be another flavor from Traditional Medicinals. Their gas relief tea is made with caraway, coriander, chamomile, lemon balm, and peppermint. You can get it on Amazon.

For other digestive issues, skip Stomach Ease from Yogi tea. Organic fennel seed is a main ingredient in it. Traditional Medicinal’s Belly Comfort is a bad choice for that same reason. For healthy digestion, many seem to like organic dandelion root tea. That’s probably a wiser choice.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.