Read the words nitrate and nitrite, and your mind may conjure thoughts of fertilizers, or supposedly carcinogenic compounds in processed meats that predispose people to cancer. But there’s now a strong body of evidence that consuming nitrates in vegetables confers many favorable effects on health, and we’ve known for over a decade that nitrates often enhance exercise performance. In this blog, I’ll highlight much of what we currently know about dietary nitrate and exercise. In the next post, I’ll explore other health-promoting effects of dietary nitrate and discuss why I don’t think you should have any reservations about increasing your consumption of nitrate from whole fruits and vegetables.
- Nitrate is a precursor to nitric oxide (NO), a gas that promotes blood flow and improves mitochondrial energy production.
- NO is used more quickly when cells are stressed by diminished blood flow, reduced oxygen availability (as occurs at altitude), and a fall in pH – all of which often occur during exercise.
- Nitrate supplementation reduces how much energy is needed to perform a given amount of exercise and may enhance endurance exercise performance, intermittent exercise performance, sprint performance, and power production.
- Nitrate supplementation may mitigate some adverse effects of reduced oxygen availability on exercise metabolism and performance.
- Effects of dietary nitrate on exercise performance may be lower in people with high cardiorespiratory fitness, particularly those who compete in sports (such as cycling) that rely heavily on lower-body musculature.
- To reap the benefits of supplemental dietary nitrate, try consuming 3 to 6 mg of nitrate per lb of body mass, 1 to 3 hours pre-exercise.
- The bacteria on your tongue are required to maximize conversion of nitrate to NO, so avoid using mouthwash on days on which you seek the effects of nitrate-rich foods on exercise.
Much of this blog series was shaped by an excellent recent review of the scientific literature on nitrate and exercise, so those of you interested in the nitty-gritty details should read this paper by the preeminent authority on this subject, Andy Jones. Anyway, let’s begin by exploring what NO is, how it’s made, and why this matters.
Nitric Oxide Synthases and Nitric Oxide
NO is a gas that’s important to the development of blood vessels, brain cells, and more. NO in your cells is continually and rapidly turned over (its half-life is just 1 to 2 ms), so your body needs a reservoir of compounds from which to make NO to support this flux. Much of the NO in your body is produced from the amino acid L-arginine and oxygen, with help from three enzymes:
- Endothelial nitric oxide synthase. This acts in blood vessels, where NO stimulates relaxation and hence increased blood flow. This is one way by which exercise affects cardiovascular function.
- Neuronal nitric oxide synthase: This enzyme provides neurons with the NO they need. (NO is sometimes referred to as a “gasotransmitter”.)
- Inducible nitric oxide synthase: This is important to the ability of the brach of your immune system that you’re born with (the innate immune system) to mount challenges to pathogens.
Nitrate, Nitrite, and Nitric Oxide
But your body also produces NO from dietary nitrate and nitrite, which typically contribute about half of total NO production. Vegetables such as beetroot and spinach are naturally abundant in nitrates. Dietary nitrates are relatively inert before they’re converted (reduced) to nitrite. Nitrite, on the other hand, does exert some signals in cells that are independent of NO. Anyway, nitrite can then be reduced to NO, and your body uses two systems to carry out this conversion process:
The oral cavity and stomach
The nitrates you consume are quickly absorbed by the first part of the digestive tract. These enter the blood, and about a quarter of plasma nitrate is then taken up by the salivary glands. Next, this nitrate is secreted in your saliva. Anaerobic bacteria on the top of your tongue then convert about a fifth of this to nitrite. This is why antibacterial mouthwash reduces the conversion of nitrate to nitrite. Some swallowed nitrite is then converted to NO in the stomach. Certain chemicals in plants (such as vitamin C and several polyphenols) help this conversion. Much of the remaining nitrite is taken up by the kidneys and excreted in urine.
Now, your body’s NO requirements continually fluctuate, and reductions in blood flow (ischemia), oxygen availability (hypoxia), and local pH all increase NO turnover.
Isn’t it interesting that all of these often occur during exercise?
The implication is that raising your body’s pool of nitrites should support its function under such duress.
So, what are the effects of nitrate supplementation during exercise?
Dietary Nitrate and Exercise Efficiency
The first study on this topic showed that three days of sodium nitrate supplementation reduced oxygen consumption during cycling at fixed work rates. We consume oxygen to make energy by aerobic respiration, so this means that these healthy young men needed less energy to complete a given amount of cycling. Subsequent work showed that consuming nitrates naturally present in food (500 ml of beetroot juice, in this case) had similar effects. (To your body, nitrate is nitrate, so I’ll use the catch-all term “nitrate supplementation” from now on.)
Whereas these studies assessed effects on cycling, others have shown that nitrate supplementation reduces oxygen consumption activities such as walking, running, kayaking, and knee extensor exercise (in which people sit in a chair and rhythmically and alternately straighten their knees against resistance).
Systematic assessments of all studies on dietary nitrate and exercise have shown that supplementing with nitrates tends to reduce oxygen consumption during moderate- and vigorous-intensity exercise (but perhaps not in people with chronic disease), and increase how long people can endure a given intensity of exercise. (Overall, it seems that nitrates may not help people complete a given amount of work faster though.)
You may be wondering whether consuming supplemental nitrate daily over many days has additive beneficial effects on exercise. This doesn’t seem to be the case. But at least people don’t seem to build tolerance to nitrate supplementation – its effects are simply sustained with repeated ingestion.
Dietary Nitrate and Exercise: Single- and Repeated-bouts of Brief, Maximal Exercise
The studies I discussed above largely focused on fixed-rate exercise (how long someone can maintain a given exercise intensity), incremental-intensity exercise to exhaustion (VO2 max tests, for instance), or time trial performance (how fast somebody can cycle 16 km, for example). But what about power performance?
First, dietary nitrate supplementation may increase knee extension power at high velocities. This isn’t a type of exercise that many do inside or outside the gym, but it’s useful in making precise measures of neuromuscular performance.
Next, when team sport athletes supplement with dietary nitrate for several days in a row, their 5-, 10-, and 20-metre sprints times tend to improve a little, as do their performances in intermittent sprint running tests. The same is true of repeated 6-s cycle sprints, and nitrate supplementation may increase the highest power output people can achieve during 3- to 4-s cycle sprints.
This said, not all studies have found that nitrate supplementation improves performance in a series of short cycle sprints (1, 2), and nitrate supplementation may not boost performance in repeated 30- or 60-s sprints.
This kind of inconsistency between study findings is quite common. At first blush it can seem baffling, but stratifying the studies gives clues as to what determines who will respond well to nitrate supplementation.
Trained Athletes May not Benefit so Much
Consuming extra dietary nitrate may not help well-trained endurance cyclists or runners as much as their less aerobically fit peers. Interestingly, elite kayakers (1, 2) and rowers (1, 2) may still gain some advantages from nitrate supplementation though, and it’s plausible this is because the upper body tends to contain proportionally more type-II muscle fibers than the lower body. (Type-II fibers are well suited to producing lots of force quickly, at the expense of limited endurance.)
Dietary Nitrate and Exercise: Which Biological Mechanisms Are at Play?
Nitrate supplementation tends to enhance blood flow to highly active muscles, especially those that are dense with type-II fibers. This may be especially important as more of these fibers are recruited during very strenuous exercise. Nitrate supplementation also reduces oxygen consumption exercise by enhancing how efficiently mitochondria produce ATP. This is one way by which nitrate supplementation reduces how much oxygen is needed to support skeletal muscle contractions.
Finally, nitrate and nitrite may activate signaling pathways that are important to endurance exercise training adaptations, perhaps stimulating the formation of new mitochondria and shifting some muscle fibers towards a profile that more efficiently uses oxygen for energy. This has been shown when recreationally active people undergo training involving repeated 30-s cycle sprints over four weeks. During this time, daily nitrate supplementation also led to greater improvements in the highest work rate achieved in increasingly intense exercise.
But these adaptations don’t explain the performance-enhancing effects of nitrate supplementation on power and sprint performance. So, what might explain these?
When mice consume additional nitrate for an extended period of time, their type-II muscle fibers can produce force more quickly – an adaptation that should benefit power athletes. This same effect wasn’t seen in type-I muscle fibers, suggesting that nitrate supplementation has distinct effects on different types of muscle fibres.
And why do highly trained endurance athletes have blunted responses to nitrate supplementation?
Endurance athletes already typically have higher plasma nitrate and nitrite concentrations, greater NO synthesis, more capillaries to deliver blood to muscles, and a lower proportion of type-II muscle fibers. All of these factors help them expend less energy to accomplish a given exercise task. Basically, trained endurance athletes are closer to the biological ceilings of each of the factors by which nitrate boosts exercise performance. It’s also possible that those people who are blessed with high cardiorespiratory fitness without ever having done much exercise may not respond as well to nitrate supplementation.
Dietary Nitrate and Exercise in Simulated Altitude
I mentioned earlier that nitrate supplementation should theoretically be more beneficial during hypoxia, as occurs at altitude. Sure enough, nitrate supplementation apparently offsets the negative effects of hypoxia on skeletal muscle metabolism and energy substrate recovery, which may reflect improved oxygen delivery to the most taxed musculature.
Some (1, 2) but not all (1, 2) studies have found that nitrate supplementation improves cycling performance in hypoxia, and it may take multiple days of nitrate supplementation to gain these effects. As in “normal” oxygen conditions (normoxia), nitrate supplementation may not boost performance in trained cyclists exercising in hypoxic environments.
How to Get These Benefits
I’ll address the nitrate contents of foods in the next blog. I don’t want to leave you hanging though, so I’ll make a couple of recommendations here.
The review article I mentioned suggests that to improve both exercise economy and performance, you should aim to consume at least 527 mg nitrate each day. In general, I find it useful to consider doses relative to body mass, and a dose of 3 to 6 mg nitrate per lb of body mass is probably a good rule of thumb.
It might take several weeks of supplemental dietary nitrate to see endurance exercise performance improvements, and you may be less likely to experience supplementation benefits if you already have a high endurance exercise capacity (say, a VO2 max ≥ 60 ml/kg/min) and/or habitually have a high nitrate intake (you eat lots of certain vegetables).
I love nitrate-rich vegetables like beetroot and spinach, and these typically have over 250 mg nitrate per 100 g. Even after washing and gently cooking them, you probably won’t need more than 300 g or so of these vegetables to reach a dose of nitrate proven to affect exercise.
If you prefer, you can supplement with beetroot products. Dan’s preference is to consume Beet It beetroot products, as he detailed in this podcast. You can also throw some nitrate-rich vegetables in a smoothie (Pro users should check out Ginny’s smoothie recipes.)
Blood nitrate concentration peaks about an hour after consuming nitrates, and nitrite levels peak an hour or two thereafter. So, consuming nitrate within three hours or so of starting exercise makes sense. Just skip the mouthwash on the days that you seek these effects, and maybe avoid brushing your teeth within a few hours of consuming the nitrate-rich food (I use 3 hours before and after consumption as an arbitrary cutoff).
There’s clearly far more to learn about dietary nitrate and exercise. It’s currently difficult to give precise dosing and timing recommendations, and we don’t know much about how dietary nitrate interacts with other dietary compounds.
Can we support NO synthesis in multiple ways to amplify the effects of dietary nitrate? Might combining dietary nitrate with other performance-enhancing compounds (caffeine, creatine, and so on) have additive effects? Does nitrate supplementation have especially potent performance-enhancing effects in exercise modalities that compromise muscle blood flow and oxygen delivery (such as isometric exercise and/or blood-flow restriction exercise)? And how does chronic nitrate supplementation affect adaptations to exercise training?
Even with many unanswered questions, for most people I see no harm in increasing intake of nitrate-rich vegetables. And if you’re an elite athlete and don’t expect noticeable improvements, nitrate supplementation is unlikely to hurt your health and performance.
That’s all for now. I’m off to make a beetroot and spinach salad. (Doused in nitrate-rich processed meat, obviously.)
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