Should You Gargle Beetroot Juice?

This was a question posed to me recently, and it’s interesting enough that I figure it merits its own blog entry.

We know that beetroot juice seems to be an effective endurance-booster, at least for the average runner. But we also know that it has the potential to trigger, er, digestive distress – not just purple poop, but potential mid-race bathroom breaks. We also know that the active ingredient in beet juice is nitrate, which is converted to nitrite by bacteria in your mouth (and then subsequently to nitric oxide, which is what helps endurance). Strangely enough, using antibacterial mouthwash wipes out the benefits of beet juice.

We also know that you can get some of the benefits of carbohydrate sports drink simply by swishing it around in your mouth. There are carbohydrate sensors in your mouth (independent of your taste buds – it works even with tasteless carbohydrate, but doesn’t work with artificially sweetened drinks) that signal directly to your brain that fuel is on the way. Studies have found that rinsing and spitting sports drinks consistently boosts endurance performance in activities lasting an hour or more, and in some cases also in shorter events. Some elite athletes use this strategy late in long races, where actually drinking might upset their stomachs.

So the question I was asked is this: If the beetroot juice magic happens through its interaction with the saliva in your mouth, and if swallowing leads to potential digestive problems, why not just rinse and spit the beetroot juice?

Unfortunately, it’s not that simple. The beetroot juice magic does happen in your mouth – but not the first time it passes through. Instead, the nitrate is processed through what researchers have dubbed “entero-salivary circulation.” Here are two diagrams of the process (link 1 and link 2); the basic steps are:

(1) You chew and swallow beetroot;

(2) The nitrate from the beetroot is absorbed into the bloodstream from the stomach and (primarily) the small intestine;

(3) Up to 25% of the nitrate in the bloodstream is extracted by the salivary glands and concentrated tenfold in the saliva (much of the rest is excreted in urine);

(4) The nitrate-rich saliva enters the mouth, where friendly bacteria convert it to nitrite;

(5) You swallow the saliva that now contains nitrite, and the acid in your stomach converts part of the nitrite to nitric oxide;

(6) The nitric oxide enters the bloodstream where it works its magic.

So the key point is that gargling beetroot juice won’t have any effect, because you first need to swallow the juice, absorb the nitrate into your bloodstream, and concentrate it in your saliva. Still, it’s an interesting question (and a good excuse to dig deeper into how dietary nitrate actually works!).

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