If you've been paying attention to the 2016 Rio Olympics, you're well aware of the Russian Doping Scandal. The global media has a tendency to pick on the Russians, but as John Oliver pointed out (see video below), almost every country has had a doping scandal.
The reason for why athletes go to such lengths is simple, they want to win. But you don't need to graft chimp testicles, stab yourself with HGH, or eat the genitals or other animals to gain an athletic advantage.
In 2009, a study titled "Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans” showed that simply consuming beetroot juice can significantly increase the oxygen carrying capacity of human blood. But why is this important?
Like a car runs on petrol, the human body runs of oxygen. In cars higher octane fuels lead to greater performance, in humans it is more highly oxygenated blood. This is one of the reasons that athletes train at high altitudes and sleep in hypobaric chambers before competitions. In the study scientists put 8 men on bikes, measured their oxygen consumption, and then got them to sip beetroot juice for a couple of days and repeated the experiment.
The study found that the group which was supplementing with beetroot juice could complete the exact same amount of work with less oxygen. To be precise the same amount of work, with 19% less oxygen. The study also looked at endurance and found that, with beetroot supplementation, the men increased their time to exhaustion during "severe cycling,” from 9:43 to 11:15. That is a 16% improvement in endurance with 4/5 of the oxygen requirement! It should be noted that before these experiments there was no known method of increasing the efficiency of energy extraction from oxygen. No steroids, no supplements, and no drugs can do what beetroot can do.
ATP, Nitrates, and Priming the Proton Pump
If you paid attention in high school biology, you'll remember that our bodies use oxygen to make ATP. ATP is essentially the BitCoin of our bodies (that is to say the currency), we use it every time we run, jump, move, and groove. Everything uses ATP, and it needs to be continually replaced or we cease to live. So how do beets (and greens) influence this?
The enzyme which makes ATP is called ATP synthase and it has been likened to a microscopic motor; a proton pump. Like all motors, ATP synthase isn't 100% efficient and there is a small amount of lost energy (in the form of lost protons). Beets offer one of the most concentrated sources of dietary nitrate, which through a complex system is converted into nitric oxide which is then in turn used to "plug up" the leaks in the proton pump. The patched up ATP synthase enzyme is then more efficient, loses less protons, and overall leads to the greater efficiency in energy extraction from oxygen.
Sources of Nitrates
If you want to benefit from this, the first thing to remember is that you need to consume nitrates. Not nitrites and not nitric oxide. Nitrites are commonly used as a preservative on processed meats and are thought to be a carcinogen, not what you look for in your performance enhancing foods. Meanwhile, although nitric oxide is the end product that leads to greater oxygen efficiency, supplements are expensive and there is no proof that they actually offer any benefits. The highest sources of nitrates all come from the plant kingdom. While beetroot offers a high concentration of nitrates, the highest known concentrations can be found in arugula (also known as rocket).
You also have to keep in mind that in order for you body to convert nitrates into nitric oxide, your body relies on bacteria in your mouth. So if you eat beetroot or arugula and then use mouthwash, you won't benefit. Similarly, if you eat the arugula with a source of fat (olive oil, cheese, etc) the conversion is inhibited and you're more likely to end up with nitrites. All in all you're best off eating your nitrate sources fat free, and if you want added points add some lemon juice.
For more info, see the links below.
Sources:
http://jap.physiology.org/content/107/4/1144.full.pdf+html
http://jap.physiology.org/content/107/4/1144.full.pdf+html
http://www.ncbi.nlm.nih.gov/pubmed/21284982