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Fennel is a member of the Umbelliferae (Apiaceae) family, closely related to carrots, parsley, celery, and dill.
From the large white bulb, multiple bunches of 4–5 long stems extend up to 6–7 feet above the ground. As one of the oldest cultivated plants, fennel has many traditional uses in food and medicine.
This article will review the types, nutritional value, proposed health benefits, cautions, and preparation of fennel.
The nutritional content of 100 g of fennel includes: (1)
- Energy – 31 calories
- Fiber – 3.1 g
- Calcium – 49 mg
The fennel bulb is a good source of fiber, potassium, manganese, and vitamin C. It also contains calcium, iron, folate, and antioxidants lutein and zeaxanthin.
The seeds are typically consumed in small amounts (1–1½ teaspoon per day) in tea or as a spice in prepared food. They also contain potassium, vitamin C, manganese, iron, calcium, and folate.
Additionally, 1 teaspoon of seeds has 33.8 mg of polyunsaturated omega-6 fats and antioxidants kaempferol and quercetin.
Types of Fennel
There are two main types of fennel:
- Herb fennel (Foeniculum vulgare): The long, aromatic stems, leaves, and seeds are usually used as an herb or spice.
- Florence fennel (Foeniculum vulgare var. dulce): With shorter stems, it is usually grown for the large bulb and eaten as a vegetable. Like other root vegetables, it can be eaten raw or prepared in a dish.
Both types of fennel have distinct anise or licorice flavor. Fennel is often mistakenly sold at supermarkets labeled as anise due to their similar flavor and aroma. The only part of the anise plant that is used in foods is the seeds, whereas all parts of the fennel plant are edible.
Proposed Health Benefits
Traditional uses for fennel range from helping the body pass gas to freshening the breath. This section will discuss a few of the proposed benefits and uses of fennel.
1. May reduce menstrual cramps
Increased uterine contractions cause cramps during a woman’s menstrual cycle. Contractions are stimulated by the hormone oxytocin and prostaglandin.
Several human studies suggest that fennel oil may inhibit oxytocin and prostaglandin, reducing uterine contractions and pain during mensuration. (2)(3)
In fact, it has been found almost as effective as 250 mg of mefenamic acid, an NSAID drug that is commonly used to treat menstrual pain. (4) However, further investigation is needed to determine its long-term effects and safety of use.
2. May help in weight management
Fennel is replete with fiber and water, both of which promote satiety by filling up the stomach without adding to the calorie load. Some researchers believe that anethole, a compound found in the oils of fennel seeds, may also contribute to appetite control. (5)
Although fennel is a nutritious and low-fat vegetable, there is no research to support that fennel intake by itself will accelerate fat burning or weight loss. (6) The most you can expect is some degree of appetite suppression when fennel is eaten as part of an overall healthy, well-balanced diet.
3. May improve blood flow
Fennel seeds contain nitrites and nitrates. Some researchers hypothesize that the nitrites and nitrates in fennel could help promote vascular function and improve physical performance. (7)
There is not enough research to support this hypothesis. More research is needed to investigate the effects of fennel on blood flow.
4. May help relieve constipation
Fennel is traditionally used as a laxative in various cultures. Constipation is characterized by decreased water excretion in the colon, causing tough stools that are difficult to pass.
A randomized controlled trial studied the effect of a traditional Brazilian laxative containing fennel on relieving constipation. (8) More rigorous scientific studies are needed to validate the use of fennel as a laxative.
5. Acts as a carminative
Fennel is traditionally used as a carminative due to the anethole in oils, which reduces muscle cramping. These effects have the potential to relieve the symptoms of patients with irritable bowel syndrome (IBS). (9)
More research is needed to determine fennel’s exact mechanism, safety, and dosage for IBS symptom relief.
6. May eliminate the symptoms of colic
Colic is often caused by food intolerances or allergies that lead to intestinal discomfort. Fennel is commonly included in “gripe water” preparations that are rumored to relieve colic.
A study that included 125 infants found colic was eliminated in 65% of infants treated with fennel seed oil compared to 23.7% in the control group. (10) Additionally, no significant side effects were reported among the treatment group.
Although traditional gripe water contained alcohol, it is now known that this ingredient is inappropriate for infants, making fennel-infused gripe water a much safer alternative.
7. Freshens breath
Mukhwas is a mix of seeds, herbs, and spices, including fennel, as well as anise, ginger, dill, coconut, coriander, or sesame. You may encounter mukhwas at your favorite Indian restaurant, served as a sugar-coated candy after the meal to freshen breath.
Processing and Storage of Fennel
The stems of the plant can be trimmed about 3 inches from the bulb, wrapped in a plastic bag, and stored in the fridge.
Alternatively, place them upright in a vase of water. Consume promptly after harvest for the strongest flavor. Dried fennel stalks last longer. The feathery leaves (called fronds) are best used as a fresh herb in salads and soups or as a garnish.
The bulb should be separated from the stems before storage. It can be stored on the countertop in a brown paper bag for 2–3 days, in the fridge for 7–12 days, or in the freezer for 8 months.
The yellow flowers of the fennel plant produce small, comma-shaped, brown seeds. After they are collected from the plant, they should be stored in a cool, dry, dark area of the kitchen or refrigerated.
Fennel oil is created by distilling crushed fennel seeds. The aroma and flavor are powerful in the concentrated oils.
A small amount can be used to flavor tea, soups, or dressings. Usually, just a drop or two is needed. The oils are also used in cosmetics and fragrances.
The scent is touted for its rejuvenating and energizing effects. Of note, these oils should not be ingested as they also contain other ingredients that may not be edible.
Cautions to Keep in Mind
Fennel is completely non-toxic in food amounts, but larger doses in tea or capsules may have harmful side effects. Please consider the following cautions:
1. Skin sensitivity
Fennel may increase skin sensitivity and the risk of sunburn. Avoid tanning beds and reduce exposure to direct sunlight. The most common side effects of using fennel are abnormal skin reactions, including rashes and itching.
2. Birth control pills
Fennel contains phytoestrogens and may reduce the effectiveness of some forms of birth control. Discuss birth control with your doctor before taking high doses of fennel.
Do not take fennel if you have an allergy. People with an allergy to other members of the Apiaceae family, such as celery, carrots, parsley, dill, and anise, can also have reactions to fennel. Symptoms of allergies include difficulty breathing, rashes, hives, and swelling.
4. Abnormal breast development
There has been one report of a one-year-old girl developing breasts related to consuming 2–3 teaspoons of fennel in tea daily to prevent restlessness. After discontinuing the tea, her breasts gradually reduced to normal size within 1 year. (11)
5. Breast milk
Two cases of fennel toxicity have been reported in breastfeeding infants. Mothers drinking 2 liters of tea infused with anise, fennel, and goat’s rue per day reported weakness and pain in their infants. (12)
6. Drug interactions
Fennel interacts with seizure medications and may decrease their effectiveness, thereby increasing the risk of seizures.
Always consult with your doctor before taking supplements, especially if you are on any of the following seizure medications:
- Phenytoin (Dilantin)
- Oxcarbazepine (Trileptal)
- Gabapentin (Neurontin)
Expert Answers (Q&A)
Answered by Evelyn Fuller, CDN (Registered Dietitian)
Information on the web is that fennel seeds aid in weight loss by curbing hunger and reducing cravings. However, the research to support this claim is not enough. No current studies are available to support that fennel seeds are beneficial for weight loss.
A balanced diet that includes different fruits and vegetables is good for reducing hunger and cravings. As fruits and vegetables are low in calories and high in fiber, vitamins, and minerals, they help maintain a healthy weight.
It appears safe for healthy adults to eat fennel seeds regularly when consuming them in food form (vs. oil). Fennel seeds are likely safe when used in appropriate doses over a short duration. However, there is no evidence for their long-term medicinal use.
Pregnant and lactating women should avoid the use of fennel seeds as there is not enough evidence that supports their safety during these times.
There were documented incidences, in an old study, of two breastfeeding infants who experienced damage to their nervous systems after their mothers drank an herbal tea that contained fennel. (13)
Side effects are rare, but gastrointestinal upset and seizures are related to ingesting fennel essential oil by mouth. Those who have allergies to celery, carrots, and mugwort are more likely to be allergic also to fennel.
If you are using fennel seeds as a supplement, apply sunblock on sunny days. Fennel is known to increase skin sensitivity. (14)
While fennel has estrogen-like activity, research has not been able to determine that it increases estrogen levels.
Fennel oil was found to have significantly reduced the frequency of uterine contractions by inhibiting the effect of prostaglandin E2, which induces contractions. It was also reported that fennel oil could promote menstruation, alleviate the symptoms of female climacteric, and increase libido. (15)
Fennel has also been studied for its claim to increase lactation in breastfeeding mothers and infant weight gain. However, many of the studies conducted were not randomized or blinded. Thus, there is no significant evidence that fennel does indeed increase lactation or promote weight gain in breastfeeding infants. (16)
Fennel seeds should not be used as a treatment for asthma. Those who have asthma should regularly follow up with their physician and consult them when beginning a new dietary supplement.
One study found that fennel seeds may provide bronchodilator effects. Although the result was promising, the subjects were animals, and, thus, evidence from this particular study cannot be applied or generalized to humans. (17)
It is suggested that fennel seeds have anti-inflammatory properties. One study found that the anti-inflammatory activity of the methanol extract of fennel seeds significantly reduced the inflammation symptoms in acute inflammatory disease. However, the study was conducted on animals; hence, the results are subject to interpretation. (18)
While fennel seeds may be considered thermogenic (food that increases metabolism and burned calories), it is unlikely that these seeds actually increase your internal body temperature.
Thermogenesis is a process that takes place after digestion when your body burns the calories from your last meal.
The calories are then converted to heat. About 10% of the total calories burned are via diet-induced thermogenesis.
The fennel plant, including its seeds and oil, has been used for a wide array of conditions for a very long period. No adverse effects have been reported or documented to indicate any harm to the kidneys.
Roasted fennel seeds are not less beneficial for health. Cooking methods such as steaming, roasting, and sautéing preserve a good amount of nutrients when preparing vegetables.
Boiling and microwaving, though, will leach more of the nutrients out of the vegetable into the water. However, the water can then be preserved by freezing and used at a later date in soups and sauces for an added nutrient boost.
Fennel is a versatile ingredient that adds a unique flavor to many dishes. Cultures around the world use fennel in their most iconic dishes and to treat various health ailments.
Fennel is a healthy vegetable that provides vitamins, fiber, and phytochemicals that contribute to overall health.
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