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 Do the Longest Living People Eat?

The dietary guidelines recommend that we choose meals or snacks that are high in nutrients but lower in calories to reduce the risk of chronic disease. By this measure, the healthiest foods on the planet—that is, the most nutrient dense—are vegetables, which contain the most nutrient bang for our caloric buck. What would happen if a population centered their entire diet around vegetables, like the Okinawa Japanese? They end up having among the longest lives in the world.

Of course, any time you hear about long-living populations, you have to make sure it’s validated because it may be hard to find birth certificates from the 1890s. But validation studies suggest that, indeed, Okinawans really did live that long.

As I discuss in my video The Okinawa Diet: Living to 100, the traditional diet in Okinawa is based on vegetables, beans, and other plants. There’s a common misconception that their traditional diet included a substantial contribution from fish or other meat, but if you look at their actual dietary intake that doesn’t seem to be the case. The U.S. military ran Okinawa until it was given back to Japan in 1972, so we have actual data on what Okinawans were eating from the U.S. National Archives.

If you look at the traditional diets of more than 2,000 Okinawans, it breaks down as follows: Only 1% of their diet was fish, less than 1% of their diet was other meats, and less than 1% was dairy and eggs, so it was more than 96% plant-based and more than 90% whole food plant-based as they ate few processed foods. And their diet was not just whole food plant-based; most of their diet was made up of vegetables, one vegetable in particular: sweet potatoes. The Okinawan diet was centered on purple and orange sweet potatoes.

Eating a 90+% whole food plant-based diet makes it a highly anti-inflammatory and highly antioxidant diet. If you measure the level of oxidized fat within their systems, there is compelling evidence of less free radical damage. Maybe Okinawans just have genetically better antioxidant enzymes? No, their antioxidant enzyme activity is the same as other populations. What may be making the difference is all the extra antioxidants they were getting from their mostly vegetable diet.

Okinawa has 8 to 12 times fewer heart disease deaths than the United States, 2 to 3 times fewer colon cancer deaths, 7 times fewer prostate cancer deaths, and 5½ times lower risk of dying from breast cancer.

Some of this protection may be because they were only eating about 1,800 calories a day. They were actually eating a greater mass of food, but whole plant foods are calorically dilute. There’s also a cultural norm not to stuff oneself. The plant-based nature of the diet may trump the caloric restriction, though, because the one population that lives even longer than the Okinawa Japanese doesn’t just eat a 98% meat-free diet, they eat 100% meat-free. The Adventist vegetarians in California have perhaps the highest life expectancy of any formally described population. Adventist vegetarian men and women live to be about 83 and 86, respectively, which is comparable to Okinawan women, but better than Okinawan men. The best of the best were Adventist vegetarians who also had healthy lifestyles, such as being exercising nonsmokers. They live to 87 and nearly 90, on average. That’s 10 to 14 years longer than the general population. They have 10 to 14 extra years on this Earth by making simple lifestyle choices.

And this is happening now, in modern times, whereas Okinawan longevity is now a thing of the past. Okinawa now hosts more than a dozen KFC restaurants. Okinawans’ saturated fat levels have tripled. They went from eating essentially no cholesterol to a few Big Macs’ worth. They tripled their sodium and are now as potassium-deficient as Americans, getting less than half of the recommended minimum daily intake of 4,700 mg a day. In just two generations, Okinawans have gone from the leanest Japanese to the fattest. As a consequence, there has been a resurgence of interest from public health professionals in getting Okinawans to eat the Okinawan diet too.


Why do those eating plant-based diets live longer? For some people the “why” doesn’t matter, but I’m fascinated by all the all the mechanisms. If you are too, check 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: