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:

What to Take After Surgery

Medicine is messy. One of reasons researchers experiment on animals is they can create uniform, standardized injuries to test potential remedies. It’s not like you can just cut open 50 people and see if something works better than a sugar pill. But, wait a second, we cut people open all the time. It’s called surgery.

In my video Speeding Recovery from Surgery with Turmeric, I discuss a double-blind, randomized, placebo-controlled study that investigated the efficacy of turmeric curcumin in pain and post-operative fatigue in patients who had their gall bladders removed. Fifty people were cut into and given either curcumin or an identical-looking placebo, along with rescue analgesics—i.e., actual painkillers to take if the pain became unbearable. Even though it’s just laparoscopic surgery, people don’t realize what a toll it can take. (You can be out of commission for a month!) In India, turmeric—found in curry powder—has traditionally been used as a remedy for traumatic pain and fatigue, so the researchers decided to put it to the test.

According to the study, in the weeks following surgery, there was a dramatic drop in pain and fatigue scores in the turmeric curcumin group, with p-values of 0.000. Those are my kind of p-values! The “p-value” refers to a measure of the strength of evidence. The smaller it is, the stronger the evidence is that the result they found didn’t just happen by chance. By convention, a p-value under 0.05 is considered small enough for a result to be considered statistically significant. This means that you’d only expect to find a result that remarkable simply by coincidence 5% of the time, or in 1 out of 20 cases. So a p-value like the one in the study, <0.000, suggests you’d have to run the experiment thousands of times before you’d come up with such a dramatic result just by chance.

It’s hard to come up with objective measures of pain and fatigue, but drug-wise, the curcumin group was still in so much pain they were forced to take 7 of the rescue painkillers. In the same time period, though, the control group had to take 39 pain pills. Of course, it’s better not to get gallstones in the first place, which you can learn more about in my video Cholesterol Gallstones, but the researchers’ conclusion was like no other I’ve ever read in a drug trial.

“Turmeric is a natural food ingredient, palatable, and harmless.” Okay, so far so good. It continued: “It proves to be beneficial as it may be an ecofriendly alternative to synthesized anti-inflammatory drugs which have a definite carbon footprint due to industrial production.” Since when do surgery journals care about the greenhouse gas emissions from drug companies? I just had to look up the reference in the journal Surgical Endoscopy entitled “Journey of the Carbon-Literate and Climate-Conscious Endosurgeon Having a Head, Heart, Hands, And Holistic Sense Of Responsibdlity.” I don’t know what’s stranger, seeing the word “holistic” in a surgical journal or the name of this guy’s practice: “Dr. Agarwal’s Surgery & Yoga.”


The benefits of turmeric are clear—and not just as a remedy for pain. The spice also serves as a potent treatment against cancer, as I explain in these videos:

Turmeric is effective at fighting many other health conditions, too, as is evident in these videos:

Finally, you may be wondering whether turmeric is best taken as a supplement or in whole food form. I invite you to watch Turmeric or Curcumin: Plants vs. Pills and find out.

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: