People choose fennel for its licorice-like flavor and health benefits. Ancient practitioners used fennel in natural remedies, and the practice continues. Fennel is a Mediterranean plant that is now popular all over the world.

Fennel has a pale bulb and long green stalks. It can grow almost anywhere. All parts of the fennel plant, including the bulb, stalk, leaves, and seeds, are edible. They add flavor to other foods.

This article is part of a collection of MNT articles on the health benefits of popular foods.

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Fennel has a range of nutritional benefits.

According to the United States Department of Agriculture (USDA) National Nutrient Database, one raw fennel bulb weighing 234 grams (g) contains:

A cup of fennel also provides:

  • 360 milligrams (mg) of potassium
  • 45 mg of sodium
  • 838 international units (IU) of vitamin A
  • 43 mg of calcium
  • 10.4 mg of vitamin C
  • 0.64 mg of iron
  • 0.041 mg of vitamin B-6
  • 15 mg of magnesium

Fennel also contains:

As well as these, fennel provides high levels of dietary nitrates and is a natural source of estrogen.

The nutrients in fennel are linked to a range of health benefits.

Bone health

The vitamin and mineral content in fennel contributes to building and maintaining bone structure and strength in the following ways:

  • Phosphate and calcium are both important in bone structure.
  • Iron and zinc are crucial for the production and maturation of collagen.
  • Bone matrix formation requires the mineral manganese.
  • Low intakes of vitamin K have been associated with a higher risk for bone fracture.

Vitamin K is important for health, as it modifies bone matrix proteins, improves calcium absorption, and may reduce the excretion of calcium in urine.

Blood pressure

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The nitrates in fennel can help moderate blood pressure.

Maintaining a low sodium intake is essential for lowering blood pressure, but increasing potassium intake may be just as important because of its role in vasodilation, the dilation and contraction of blood vessels.

According to the National Health and Nutrition Examination Survey (NHANES), fewer than 2 percent of American adults meet the daily 4,700 mg recommendation for potassium.

In addition, there is evidence that potassium, calcium, and magnesium decrease blood pressure naturally. All of these are present in fennel.

Dietary nitrates present in fennel and other foods have vasodilatory and vasoprotective properties. Because of this, they help lower blood pressure and protect the heart.

One 2014 study found that blood pressure levels were lower after taking nitrate supplements.

Heart health

The fiber, potassium, folate, vitamin C, vitamin B-6, and phytonutrient content in fennel, coupled with its lack of cholesterol, all support heart health.

Fennel contains significant amounts of fiber. Fiber decreases the risk of heart disease as it helps reduce the total amount of cholesterol in the blood.

Potassium appears to promote heart health. In one study, people who consumed 4,069 mg of potassium per day had a 49 percent lower risk of death from ischemic heart disease compared with those who consumed around 1,793 mg per day.

Vitamin B-6 and folate prevent the build-up of a compound called homocysteine by converting it into a different compound, methionine. When excessive amounts of homocysteine build up, it can damage blood vessels and lead to heart problems.

Cancer

Selenium is a mineral in fennel but not most other fruits and vegetables (as it is primarily found in Brazil nuts and animal proteins). It contributes to liver enzyme function and helps detoxify some cancer-causing compounds in the body. Selenium can also prevent inflammation and decrease tumor growth rates.

Fiber intake from fruits and vegetables like fennel are associated with a lower risk of colorectal cancer.

Vitamin C, vitamin A, and beta-carotene are powerful antioxidants that can help protect cells against damage from free radicals.

Fennel contains folate, which plays a role in DNA synthesis and repair. This might help prevent cancer cells from forming because of mutations in the DNA.

Immunity

The selenium found in fennel appears to stimulate production of killer T-cells. This suggests that it can improve the immune response to infection.

Inflammation

Choline is a very important and versatile nutrient in fennel that helps with sleep, muscle movement, learning, and memory.

It also helps to maintain the structure of cellular membranes, aids in the transmission of nerve impulses, assists in the absorption of fat, and reduces chronic inflammation.

Metabolism

Fennel is a source of vitamin B-6, which plays a vital role in energy metabolism by breaking down carbohydrates and proteins into glucose and amino acids. These smaller compounds are more easily used for energy within the body.

Digestion and regularity

The fiber content in fennel helps to prevent constipation and promotes regularity for a healthy digestive tract.

Weight management and satiety

Dietary fiber is an important factor in weight management and works as a "bulking agent" in the digestive system.

These compounds increase satiety and reduce appetite, making an individual feel fuller for longer and so lowering overall calorie intake.

Increasing iron absorption

Iron deficiency is one of the most common nutrient deficiencies in the world, affecting around 2 billion people globally. It is also a leading cause of anemia.

Pairing high-vitamin-C foods, such as fennel, with iron-rich foods can improve the ability of the body to absorb iron.

Estrogen

Estrogen occurs naturally in fennel. It plays a central role in regulating the female reproductive cycle, and it can also determine fertility.

A study on mice conducted by The University of Texas Southwestern Medical Center found that estrogen also plays an important role in controlling factors that contribute to body weight, such as appetite, body fat distribution and energy expenditure.

Menopausal women have lower estrogen levels which are associated with more abdominal weight gain.

Premenstrual syndrome

Some research has suggested that fennel extract may reduce the effects of premenstrual syndrome (PMS).

Skin

Raw fennel is an excellent source of vitamin C. Vitamin C is essential to collagen, the support system of the skin, and also works as an antioxidant to help prevent damage caused by the sun, pollution, and smoke.

Vitamin C also promotes the ability of collagen to smooth wrinkles and improve the overall texture of the skin.

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People can eat fennel in a salad or in other ways.

Fennel has a crunchy texture and mildly sweet flavor, making it a pleasant addition to any dish, whether eaten raw or cooked. A person can eat all parts of the fennel plant or use the seeds as a condiment.

When buying fennel, avoid spotted or bruised bulbs and look for firmness and a white or pale green color. Stalks should be green, and leaves should be straight and bundled together. A fennel plant with flowering buds is overripe.

Fennel will stay fresh in the refrigerator for about 4 days. Eat fennel right after purchase, however, as it loses flavor over time.

Dried fennel seeds can last for about 6 months in an airtight container or a cool, dry area, such as a spice cabinet.

To prepare fennel, cut the stalks off the bulb at the base where they sprout and slice the bulb vertically. Prepare the fennel leaves, stalks, and bulb in a variety of ways, including:

  • using the stalks as a soup base or stock
  • sautéing the leaves and stalks with onions for a quick and easy side
  • mixing sliced fennel with a variety of your favorite fresh vegetables for a light, crisp salad
  • serving roasted fennel bulbs as an entrée

Some spices, including coriander, fennel, and caraway, might cause severe allergic reactions in some individuals. Those who are allergic to these spices should not eat them.

Beta-blockers, a heart disease and anxiety medication, can cause potassium levels to increase in the blood. Consume high-potassium foods, such as fennel, in moderation when taking beta-blockers.

High levels of potassium in the body can pose a serious risk to people with kidney damage or kidneys that are not fully functional. Damaged kidneys may be unable to filter excess potassium from the blood, and this could be fatal.

It is important to remember that a single food cannot prevent disease and improve overall health, but a varied, nutritious diet can help. Eating a range of fresh foods is the key to good health.