Fennel Seeds for a Nitrate Boost

Dozens of studies now suggest that the nitrates in vegetables, such as beets and green leafy vegetables, may help not only sick people “as a low-cost prevention and treatment intervention for patients suffering from blood flow disorders” like high blood pressure and peripheral vascular disease, but also healthy people as an effective, natural performance-enhancing aid for athletes. Most of the studies were done with beet juice, though, which is why I was so delighted to see a study on whole beets, which showed the same benefit. But what about studies on whole green leafy vegetables? That’s one of the topics I cover in my video Fennel Seeds to Improve Athletic Performance.

There was a study a while ago suggesting that one of the reasons the Okinawans in Japan looked forward to many more years of good health at the same age at which many Americans and Europeans were dying is all the nitrate in their green leafy vegetables, which tends to bring down blood pressures. The reason I didn’t report on this at the time is because I had never heard of the vegetables in the study. I know what chrysanthemum flowers are, but I didn’t think most of my viewers (or I) would be able to find garland chrisantemum, ta cai, chin gin cai, Osaka shirona, nozavana (or nozawana) pickles, or water dropwort at the local store.

What about less exotic greens, like frozen spinach? Researchers wanted to test the immediate effects on our arteries of a single meal containing a cooked box of frozen spinach, for both arterial stiffness and blood pressure. First, they needed a meal to increase artery stiffness and pressure, so they gave people a chicken and cheese sandwich, which lowered the elasticity of their arteries within hours of eating. But, when they added the spinach, the opposite happened. After chicken and cheese, the force the heart had to pump went up within minutes, but the spinach kept things level. So, a meal with lots of “spinach can lower blood pressure and improve measures of arterial stiffness.”

That’s great for day-to-day cardiovascular health, but what if you want a whole food source that can improve your performance when you’re out hiking, for example? Beets and spinach aren’t the most convenient of foods when you’re out and about. Is there anything we can add easily to our trail mix? Well, if you look at a list of high-nitrate vegetables, you see celery, endive, lettuce, Swiss chard, and the like—not much you can just stick in your pocket. But what about fennel? That’s on the list. Could fennel seeds (which actually aren’t seeds at all, but the whole little fruits of the fennel plant) be the convenient, high-nitrate source we’re looking for?

Fennel seeds are “often used as mouth fresheners after a meal in both the Indian sub-continent and around the world.” You’ll typically see a bowl of fennel seeds, sometimes candy-coated, as you walk out of Indian restaurants. When you chew them, you can get a significant bump in nitric oxide production, which has the predictable vasodilatory effect of opening up blood vessels. This makes them a cheap and easy way to carry a lightweight, nonperishable source of nitrates. Researchers singled out mountaineers, thinking chewing fennel seeds could help maintain oxygen levels at high altitudes and help prevent HAPE—high altitude pulmonary edema—which is one of the leading killers of mountain climbers once you get more than a mile and a half or so over sea level. Don’t confuse HAPE with HAFE, though, which is caused by the expansion of gas at high altitudes—a condition known as high altitude flatus expulsion or “Rocky Mountain barking spiders.”

Fennel seeds may help with that, too, as they’ve been used traditionally as a carminative, meaning a remedy for intestinal gas. “Fennel has also shown antihirsutism activity,” combatting excessive hair growth in women, the so-called bearded woman syndrome. Indeed, applying a little fennel seed cream can significantly reduce it.

If fennel seeds have such a strong hormonal effect, should we be worried about chewing them? There have been cases reported of premature breast development among young girls drinking fennel seed tea a couple times a day for several months. Their estrogen levels were elevated, but, after stopping the tea, their chests and hormone levels went back to normal.

Current guidelines recommend against prolonged use in vulnerable groups—children under 12 and pregnant and breastfeeding women—and perhaps your pet rat, as rodents metabolize a compound in fennel called estragole into a carcinogen, but our cells appear able to detoxify it.


If you’re interested in learning more about using nitrates to improve athletic performance, check out:

Curious about non-nitrate athletic performance tweaks? See:

And what about sports drinks? See: Are Sports Drinks Safe and Effective? and Coconut Water for Athletic Performance vs. Sports Drinks

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Fennel Seeds vs. Ginger for Menstrual Cramps and PMS

Ninety percent of women report having painful menstrual cramps at least some of the time. Around the Mediterranean, fennel seeds have been traditionally used to relieve painful menstruation. We call them seeds, but they’re actually whole little fruits. I discuss their effectiveness in the treatment of menstrual cramps in my video Fennel Seeds for Menstrual Cramps and PMS. It’s hard to create placebo seeds, so researchers used fennel seed extract to put it to the test. The women started out rating their pain as six out of ten, which then went down to a four within an hour after the taking the fennel seed extract. Fifty-two percent of the women rated the fennel seed treatment as excellent, compared with only 8 percent of those in the placebo group who were just unknowingly given placebo capsules just containing flour.

But women don’t take flour for cramps; they take drugs such as ibuprofen. Mefenamic acid is in the same class of nonsteroidal anti-inflammatory (NSAID) drugs and may actually work better than ibuprofen, but it is not available over the counter. How did it do against an extract of fennel seeds? In a head-to-head study, most women started out in severe pain but ended up pain-free after treatment, and the fennel worked just as well as the drug class considered the treatment of choice––but without the drug’s side effects, which include diarrhea, rashes, autoimmune anemia, and kidney toxicity.

The drug also doesn’t help with the other symptoms of bad periods. During menstruation, women can feel nauseated, out of sorts, weak, achy, and diarrheic. But when put to the test, fennel seeds seemed to help; however, the control group wasn’t given a placebo, so we don’t know how much of that was a placebo effect.

One downside of taking fennel is that women bleed about 10 percent more. Menstrual cramps are caused by the uterus contracting so hard its blood supply is compromised, and we think fennel works through muscle relaxation. It also helps with infant colic, which is thought to be due to intestinal spasms. The advantage of fennel there, too, is the lack of side effects, unlike the drug commonly used for colic. Indeed, dicyclomine hydrochloride can work a little too well to get your baby to stop crying––by developing side effects like death.

Ginger is effective for cramps and reduces bleeding when an eighth of a teaspoon of ginger powder is taken three times a day during one’s period. This is important since up to 18 million young women in the United States experience iron deficiency anemia due to heavy menstrual bleeding. In a study, the amount of blood loss was estimated using a scoring system that gave points for level of saturation and clot size. On ginger, they went from half a cup per period down to a quarter cup. Ginger appears to be a highly effective treatment for the reduction of menstrual blood loss. It is cheap, at only about 6 cents a month, easy to use, and may have fewer side effects than medications and invasive approaches, even sometimes fewer than placebo! The researchers used lactose (milk sugar) for the sugar pills, which may have caused the reported flatulence.

Ginger may also work better for premenstrual syndrome (PMS). An eighth of a teaspoon twice a day of ginger powder for a week before one’s period yields a significant drop in PMS mood, physical, and behavioral symptoms, whereas fennel may help with PMS anxiety and depression but not with the emotional or physical symptoms.


Other dietary interventions that may help include a reduction in salt and animal fat consumption, which I address in my video Dietary Treatment for Painful Menstrual Periods.

We should use whatever works––because sometimes, evidently, PMS symptoms can lead to death. Case in point: Christine English who, at that time of the month, ran down her husband. Accepting PMS as a defense, the court released her with one year of probation.

For more on treating menstrual pain and PMS, see:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: