Fennel and Fennel Seeds: Benefits, Uses, and More

Brittany Lubeck, RD, is a nutrition writer and registered dietitian with a master's degree in clinical nutrition.

Elizabeth Barnes, RDN, is a registered dietitian nutritionist who specializes in eating disorders, type 2 diabetes, and heart health.

Fennel (Foeniculum vulgare) is a flowering plant native to the Mediterranean region. It is a member of the Apiaceae (carrot) family and grows throughout Asia, North America, and Europe.

Fennel dates back centuries and is thought to be one of the oldest medicinal herbs in the world. It is prevalent in parts of Asia, where many people consume fennel after meals to aid in digestion and freshen their breath.

Fennel and fennel seeds are commonly used to flavor foods. The herb is also thought to possess various health benefits and may be helpful as a digestive aid or diuretic (rids the body of extra water and salt). Fennel has also been traditionally used as a food to boost breast milk supple (a galactagogue).

As with many herbs, though, the science behind the medicinal uses of fennel is weak overall.

This article will provide an overview of the potential health benefits of fennel. It will also discuss side effects, precautions, dosage, and how to use fennel and its seeds.

Getty Images / DR NEIL OVERY

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Along with its nutritional benefits, fennel and fennel seeds may provide additional health benefits.

Fennel is known to contain a long list of nutrients and active ingredients. It is especially rich in antioxidants that are thought to help strengthen eyesight, treat glaucoma, reduce inflammation, and prevent such conditions as cancer and heart disease.

However, few of the alleged health benefits of fennel are supported by scientific evidence.

What follows is an overview of some of the potential benefits of fennel.

Fennel and fennel seeds are a rich source of various nutrients, including antioxidants, unsaturated fatty acids, and amino acids.

Fennel seeds provide:

Many of the nutrients found in fennel are essential nutrients, which means you need to consume them in varying amounts daily to maintain proper health. As such, fennel and fennel seeds are commonly used in cooking and baking.

The fruit or seeds of fennel may be dried before use and are described as both sweet and savory. Other parts of the fennel plant, including the shoots, leaves, and stems, may be eaten raw or in other ways and provide nutritional benefits. Interestingly, fennel leaves contain the highest amount of omega-3 fatty acids.

Research shows that fennel may be a galactagogue, a substance that increases breast milk supply.

The volatile oil of fennel seeds has been found to contain anethole (a phytoestrogen) and other bioactive ingredients that may improve certain aspects of lactation.

Some studies have linked fennel use to increased breast milk volume and fat content. Fennel supplementation while breastfeeding may also lead to infant weight gain.

Although fennel shows promise as a galactagogue, it's important to note that many of the studies on this subject have been very small, of poor design, or performed on animals, not in humans. More research should be conducted for conclusions to be reached.

Due to its anti-inflammatory properties, fennel has been used as a digestive aid for thousands of years.

Laboratory research has shown fennel may indeed have a positive effect on digestive disorders like inflammatory bowel disease (IBD).

In one such study, fennel seed extract strengthened the intestinal epithelium (outer layer of tissue). These findings led researchers to believe that fennel could be a useful complementary and alternative medicine (CAM) therapy for IBD.

A noteworthy study out of China found that heating 500 grams (g) of fennel in the microwave, wrapping it in a towel, and placing it on the abdomen of postsurgical patients improved outcomes.

Compared to a control group, patients who received the heated fennel experienced significantly shorter times to the first bowel movement and passing gas, two important milestones in the recovery process following surgery.

Overall, however, there is a lack of research in this area, and more should be conducted to determine fennel's potential role in digestive disorders.

Along with other herbs, fennel is thought to have a positive effect on various side effects of menopause, although some research results are mixed.

A small clinical trial found that topical fennel cream delayed vaginal atrophy (thinning, drying, and inflammation of the vaginal walls) in postmenopausal women.

In the study, participants used either a placebo (an intentionally ineffective treatment to act as a control group) or 5% fennel vaginal cream once a day for eight weeks. By the end of the study, those who used the fennel cream had significant increases in the number of vaginal superficial cells as well as improvements in vaginal pH, two factors that may cause dryness.

In another study, postmenopausal women who used 2 grams of fennel seed powder daily for eight weeks reported significant improvements in overall menopausal symptoms compared to a placebo.

Researchers from a third small study wanted to determine if fennel played a role in body composition changes that may occur along with menopause. However, no significant results were found, and fennel did not seem to affect body composition, including weight and body mass index (BMI), of postmenopausal women.

It has been suggested that fennel decreases pain and reduces inflammation, which may help with dysmenorrhea (painful menstruation).

According to one review, fennel was found to reduce the pain intensity of period cramps significantly compared to a placebo. This may be due to spasm-reducing (antispasmodic) and pain-reducing effects associated with the herb.

Another review concluded that fennel may be as effective as conventional drugs in reducing dysmenorrhea. However, the review had several limitations, including a wide variation in the severity of reported period pain among study participants and the duration and dosage of fennel treatment.

Additional research on this topic is needed before fennel can be recommended as a treatment option for dysmenorrhea.

Per the Food and Drug Administration (FDA), fennel is "generally recognized as safe" (GRAS). Although rare, using fennel as an herbal supplement may lead to side effects.

Some people have experienced nausea and vomiting after using fennel. Stomach cramps and photosensitivity have also been reported as possible side effects of fennel.

You may be more likely to experience side effects if you use too much fennel at one time. Therefore, it's important to use fennel only as directed and never exceed a recommended dose.

Despite its apparent safety, fennel may not be right for everyone and some people should take extra precautions when using it.

Fennel contains a substance called estragole that may be carcinogenic (cancer causing) and genotoxic (damaging to genes). However, these effects have only been displayed in animal models and not in humans.

There is not enough information to know if fennel is safe during pregnancy. In fact, there is some concern that fennel may cause preterm birth, but this is not supported by scientific evidence. Talk with a healthcare provider to determine if you should avoid fennel during pregnancy.

Fennel is thought to be safe when used in normal amounts while breastfeeding. However, large doses of fennel while breastfeeding have been associated with toxicity in infants in some cases.

Always consult with a healthcare provider before taking a supplement to ensure that the supplement and dosage are appropriate for your individual needs.

There is no standardized dosage information for fennel. This is because there is not enough scientific evidence to support its use for any health condition.

Fennel used in amounts common in foods is considered safe, but little is known about the safety of using the herb in medicinal doses.

In human, animal, and lab studies, fennel has been used in varying doses, ranging from as little as 30 milligrams per kilogram (mg/kg) to 200 mg/kg or more.

More research is needed before proper dosage information can be confirmed for fennel. Until then, follow dosing directions as listed on the product label of fennel supplements or as recommended by a healthcare provider.

Fennel can be used in various ways in cooking. It is a common flavoring agent in both French and Italian cuisines. Many parts of the fennel plant can be used for cooking, including the seeds and leaves. It is popular for its licorice-like flavor.

Fennel is typically used as a vegetable. It can be consumed raw or cooked and may be added to salads, stews, soups, or grilled with fish. Fennel may also be used in baking, as a preservative, or brewed as an herbal tea.

Fennel may negatively interact with certain medications, supplements, and foods.

Although not fully proven, an old (from 1999) animal study found an interaction between fennel and ciprofloxacin, an antibiotic. Additional research is needed to confirm this potential interaction.

There is some evidence that fennel may interact with tamoxifen, a drug used to treat breast cancer. According to lab research, tamoxifen interacts with beta-sitosterol, an active ingredient in fennel and other herbs. This interaction may make tamoxifen less potent.

Because fennel may act as a phytoestrogen, there is concern that it interacts with both estrogen and birth control pills. As a phytoestrogen, fennel may block the actions of estrogen by binding to various receptors in the body.

More research is needed to determine if additional interactions exist.

It's important to carefully read the ingredients list and nutrition facts panel of a supplement to learn which ingredients and how much of each ingredient is included. Please review supplement labels with a healthcare provider to discuss any potential interactions with foods, other supplements, and medications.

Store fresh fennel in the refrigerator to prolong its shelf life. It is often recommended to wrap fresh fennel in a paper towel or place it in a storage bag before putting it in the refrigerator. Some people separate the parts of the fennel plant before storing it.

Fennel seeds do not require refrigeration. You may keep them in an air-tight container and store it in a cupboard.

Store fennel seeds and supplements in a cool, dry place. They should also be kept out of direct sunlight and out of reach of pets and small children.

Discard fennel once it reaches its expiration date or shows signs of rancidity.

Fennel may be used fresh, as a spice, or in supplement form.

You can purchase fennel seeds, fennel spice, and fresh fennel at many grocery stores. Fennel seeds and spices are also available online.

Fennel supplements may be found in various forms, including capsules and powders. Fennel supplements are not common but can be purchased online.

Fennel is naturally vegan and gluten-free. Some forms are also organic.

Unlike fresh fennel, herbal supplements are largely unregulated in the United States. To be safe, it's best to choose supplements approved by third-party agencies like U.S. Pharmacopeia (USP), ConsumerLab.com, and NSF International. These agencies review supplements for contaminants and ensure the ingredient list is accurate.

Some herbs are similar to fennel in terms of flavor, use, and potential health benefits.

Regarding cooking, other herbs may work similarly to fennel in various recipes. Herbs that are said to provide similar flavors as fennel include:

Many of these herbs are also thought to provide potential health benefits.

Fennel is a flowering plant used for centuries for its potential health benefits. Despite its long-term use, though, few scientific studies exist on fennel, and many of its health claims remain unfounded.

Fennel is generally thought to be safe when used in amounts found in foods, but it may not be suitable for some people, including those who are pregnant or who are taking certain medications.

If you're thinking of using fennel as a dietary supplement, talk with a healthcare provider first to help you decide if it's right for you.

Fennel is said to have a licorice-like flavor. The flavor is also sometimes described as sweet and highly aromatic. This flavor profile makes fennel suitable for both savory and sweet recipes.

Fennel can be consumed in various ways.

Some people consume fennel raw, while others prefer to eat it grilled, boiled, or baked. The herb is also commonly used as a flavoring agent in the form of fennel seeds or ground fennel.

Yes. Fennel contains a long list of nutrients. These include protein, unsaturated fatty acids, calcium, iron, magnesium, potassium, and manganese, among others. Fennel is also a good source of fiber, making it a well-rounded, nutritious vegetable.

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By Brittany Lubeck, RDBrittany Lubeck, RD, is a nutrition writer and registered dietitian with a master's degree in clinical nutrition.