Fennel Seeds Health Benefits, Side Effects & How To Enjoy Them

Scientifically known as Foeniculum vulgare, fennel seeds are a popular spice that comes from flowering plants in the carrot family.

They are renowned for their distinct licorice-like flavor and aroma, often used to enhance the taste and fragrance of a variety of dishes around the globe.

"Fennel seed is a highly nutritious herb rich in nutrients like calcium, vitamin C, potassium, manganese, and magnesium," Jen Scheinman, M.S., RDN, registered dietitian, explains. She adds that "they are loaded with potent antioxidants and healthy plant compounds called polyphenols that can lower the risk of chronic health conditions such as heart disease, some types of cancer, and Type 2 diabetes."

Some evidence suggests that fennel seeds may support intestinal health in various ways, although more well-designed clinical trials are needed to confirm this.

A recent study published in PLoS One evaluated the effects of fennel seed extract on certain effects people may experience when they have inflammatory bowel disease (IBD). Results showed that fennel seed extract was linked to improved barrier function4 of the gastrointestinal tract. Additionally, mice treated with fennel seed showed significantly lower ulcer indexes than control mice.

"The problem with substantiating fennel claims [and intestinal health benefits] is that it's usually combined with other nutrients, like curcumin," Michael A. Smith, M.D., director of education at Life Extension, cautions.

While there is very little in the medical literature that suggests fennel seed impacts weight loss, according to Scheinman, there is some evidence "showing that drinking fennel seeds can suppress appetite, so that may play a role in weight loss and reducing belly fat." 

One very small study published in Clinical Nutrition Research showed that after people were provided with fennel tea, fenugreek tea, or a tea void of these ingredients and then provided with a food buffet, those who consumed the fennel tea experienced less hunger6 and consumed less food at the mealtime vs. those who did not consume this tea.

Cognitive health refers to our ability to think, learn, and remember. Our cognitive health can decline naturally as we age, and it can be affected by many factors, including our diet. 

While more human studies are needed to confirm this link, preliminary data suggests that fennel seed extract may offer unique benefits among rodents with Alzheimer's disease symptoms9. 

Among the many factors that may negatively impact heart health, consuming too much sodium is one culprit. Excessive sodium consumption has been linked to high blood pressure11, which can increase the risk of heart disease and stroke12. 

It is recommended that most Americans limit their sodium intake to less than 2,300 mg of the mineral every day13. One serving of fennel seeds contains a nominal 5 mg of sodium, yet it is incredibly flavorful, making it a fantastic addition to recipes instead of table salt (which is a major contributor to our sodium intake). 

In certain areas of the world, like India, it is common to chew on fennel seeds after a meal to help combat bad breath. These tiny seeds may help keep halitosis at bay thanks to their antimicrobial properties15.

Like many other seeds and spices, fennel seeds can indeed go rancid if not stored properly. Exposure to heat, light, and moisture can degrade the seeds over time, leading to a loss of flavor and nutritional value. However, when stored in a cool, dark, and dry place, fennel seeds can maintain their quality for up to six months. For longer storage periods, refrigeration or freezing in an airtight container can further preserve the seeds' freshness and potency.

Despite their numerous health benefits, fennel seed side effects need to be recognized. Consumption of fennel seeds may lead to allergic reactions16 in some individuals. These reactions can range from mild to severe, including symptoms such as skin rashes, itching, swelling of the mouth or throat, difficulty breathing, and digestive issues.

In rare cases, a severe allergic reaction known as anaphylaxis may occur, which is a medical emergency. It's important to note that if you have a known allergy to plants in the carrot family, which includes fennel, you may be more likely to be allergic to fennel seeds. Always consult with a health care professional before including fennel seeds in your diet if you have food allergies or sensitivities.

Pregnant people are advised to avoid consumption of fennel seeds, as ingestion may stimulate uterine contractions, potentially increasing the risk of premature labor. Those with bleeding disorders or who are on blood-thinning medications should also be wary, as fennel may slow blood clotting17.

When comparing fennel seeds and chia seeds, it's clear that both possess their unique health benefits. While fennel seeds have digestive, anti-cancer, and cognitive support benefits, chia seeds are a rich source of omega-3 fatty acids, fiber, and essential minerals—features that may support heart health, digestion, and bone health.

Hemp seeds, also known as hemp hearts, are the seeds of the hemp plant, Cannabis sativa. Renowned for their nutritional profile, hemp seeds are packed with essential fatty acids like omega-3 and omega-6, fiber, and plant-based protein. They also contain vitamins and minerals such as vitamin E, potassium, magnesium, calcium, iron, and zinc. 

Fennel seeds are a relatively low-cost addition to your diet, selling for around $6 per 3.5-ounce bag.

"Fennel seed can have a mild licorice-like flavor, but its distinctive taste makes it perfect for marinades, dressings, and rubs," Scheinman shares, adding that "many Indian and Middle Eastern dishes use fennel seed as one of their key spices, and it tastes amazing in curries and sauces."

Fennel seeds can add a unique flavor profile to dishes and drinks. And while these seeds provide some nutrients and antioxidants without being high in calories, unhealthy fats, or sodium, the data surrounding the health benefits associated with consuming fennel seeds is not incredibly strong.