The world is full of dangers. If the poisonous snakes don’t get you, and the deadly wasps stay away from you, and you don’t fall into an arctic crevasse, then maybe you’ll stick around long enough to accumulate a lethal dose of nitrates. Hopefully not! We will all live forever! But also, nitrates can turn into nitrites in the body (primarily in saliva) and that may increase the risk of cancer. (There is some debate about the health benefits of nitrates as well. Scroll to the end of the article for that.)

Maybe you are worried about that. Maybe you didn’t know about that. Maybe you are casually interested in which foods want to kill you fastest.

Well!

We did the work for you this past week, as we bought bags and bags of fruits and vegetables, which we then tested with a portable nitrate testing machine that claims to be 90% accurate. We compared vegetables from our local wet market, conventional vegetables from Hema (they also do organics but we did not buy those) and organic vegetable delivery service Yimishiji.

The results were surprising! Mostly good! Sometimes not so good! We’ll never eat a leafy green again!

What are nitrates and how do they end up in my food?

Nitrates are inorganic chemical compounds made up of nitrogen and oxygen. They naturally occur in soil and drinking water, but are also used in gunpowder, explosives and (more relevant to our topic) synthesized fertilizers and preservatives for processed meats and animal products. Since inorganic fertilizers were introduced into industrialized farming, nitrates have also started to be introduced into our bodies through excessive nitrogen-based fertilizer some farms use to make the vegetables grow bigger, faster and prettier.

Tell us about this science machine you used

Greentest is a scientific test device manufacturer started in Russia by a Chinese national in 1996. In 2016, it moved back to China and is now based in Shenzhen. They manufacture a range of handheld portable devices intended for consumer use that measure nitrate levels in food, the hardness of water and, with the more expensive models, background radiation. The science is based on the electrical conductivity of salts, which is actually what the devices measure. SmartShanghai bought the Greentest Model 0808, which looks like a fake kiddie cellphone. It was 899rmb on Taobao (this is their official shop).

Why should we believe this machine?
Couldn’t these all be random numbers?

Yes. It could. So we asked Anna Korobeinikova, an account manager at Greentest, exactly that question. Her answer ranged from the scientific (they benchmarked their device against expensive lab tests in 2014 which showed they were 90% accurate) to the anecdotal (“Imagine a circle of friends all using it. They definitely want to compare the numbers"). She referred me to their official website for an explanation of how the science behind the machine works. Not buying it? You can ask her directly at sales@greentest.cn.

Do we buy it?

It’s hard to say. There was definitely some correlation between our results and the World Health Organization standards for various fruits and vegetables (which is the standard the Greentest device uses to determine if results are in the green, yellow or red zones).



At the same time, the testing methods are very specific — you can’t just stick the probe into the side of a carrot or into a watermelon, for example. You’re not supposed to measure roots or stems (nitrate accumulates there). You need to take more than one reading (we did three per item and took an average). The clunky design and touchscreen of the device, the weird multiple Greentest websites in typo-ridden English (which Greentest says were produced by dealers, not them) — they don’t inspire confidence.

But for curiosity’s sake, let’s give them the benefit of the doubt.

So what did we find?

Well, this.

To see the complete results, with full test results, click here to download our final Excel sheet with every measurement.

More specifically, we found that these vegetables do, in fact, fall within the World Health Organization’s standards for their type, according to our tests.

VEGETABLES, SAFE LIST

• Cucumber (wet market, Hema, Yimishiji)
• Garlic (wet market, Hema, Yimishiji)
• Ginger (wet market, Hema, Yimishiji)
• Tomato (wet market, Hema, Yimishiji)
• Eggplant (wet market, Hema, Yimishiji)
• Broccoli (wet market, Hema, Yimishiji)
• Cauliflower (wet market, Hema, Yimishiji)
• Carrot (wet market, Hema, Yimishiji)
• Onion (wet market, Hema, Yimishiji)
• Green lettuce (Yimishiji)
• Bell pepper (wet market, Hema, Yimishiji)
• Cai xin (Hema)

Vegetables naturally contain nitrates, sometimes in very high levels. It’s not necessarily a sign of excessive fertilizer use the way it might be in other vegetables (though in some cases, that does seem to be an issue). And the levels of nitrates can vary between seasons. Still, these vegetables are all naturally high in nitrates in general.

VEGETABLES, NATURALLY HIGH

• Broccoli (wet market, Hema, Yimishiji)
• Cauliflower (wet market, Hema, Yimishiji)
• Green lettuce (wet market, Hema, Yimishiji)
• Jie lan (wet market, Hema, Yimishiji)
• Cai xin (wet market, Hema, Yimishiji)
• Baby bok choy (qing cai)(wet market, Hema, Yimishiji)

These vegetables had excessive nitrates, according to the Greentest 0808.

VEGETABLES, EXCESSIVE LIST

• Potatoes (wet market)
• Green lettuce (wet market)
• Green lettuce (Hema)
• Jie lan (Hema)
• Cai xin (wet market)
• Cai xin (Hema organic)
• Baby bok choy (qing cai) (wet market, Hema, Yimishiji)
  
  

FRUIT

Fruits are generally low in nitrates, and that was reflected in our testing.



These were within the WHO standards.

FRUITS, SAFE LIST

• Apple (all vendors)
• Orange (all vendors)
• Mangosteen (all vendors)
• Lychee (Hema)
• Dragonfruit (all vendors)
• Mango (all vendors)
• Banana (all vendors)
• Strawberry (all vendors)
• Avocado (all vendors)

But not all. These three fruits had excessive nitrates compared to WHO standards.

Not necessarily. On their website, Greentest makes clear that even excessive amounts of nitrates in a batch of food don’t mean you should throw them away, only that consuming vegetables with a high nitrate concentration for long periods of time will raise the risk for particular diseases.

They suggest that you can lower the nitrate level in some vegetables by up to 60% by: storing leafy vegetables in the fridge immediately if not using them; cooking them soon after cutting; washing and peeling vegetables before cooking; and putting high-nitrate vegetables in boiling water for one to three minutes and discarding the water.

The basic premise of the Greentest machine is that nitrates may be a health hazard. It's not necessarily that simple. If you are concerned and want to delve deeper into the science, research and literature on it, here are a few places to start.

The BBC wrote a balanced explanation of why dietary nitrates and nitrites may be more beneficial than harmful, quoting several cancer researchers. Find that here.

A small US county, which might have been experiencing nitrate issues caused by people using well water, put out an interesting two-pager explaining nitrate and nitrite consumption issues in clear terms. Find that here (PDF).

A 2017 article in the African Journal of Traditional, Complementary and Alternative Medicines tried to determine "whether there is a significant difference, considering the location and seasonal sampling period, in the level of nitrate in certain types of green vegetables, all in order to be able to assess their intake, and possible impact on human health, especially knowing that exposure to nitrate can be potentially higher for vegetarian population group." Find that here.

A 2018 article in the Journal of Pharmacognosy and Phytochemistry from two Sri Lankan researchers has some useful basic scientific explanations. Find that here (PDF).

Several Chinese researchers did basically the same thing we did, in 2017, except they did it with actual scientific equipment and were looking for nitrites, not nitrates. Their paper "describes the nitrite contents in vegetables of 15 families and 46 genus". Lots of graphs and decimal places involved. For an idea of how rigorous it was, here's their process for nitrite extraction:

Music to our ears. Find that here (PDF).

***

To see the complete results, with full test results, click here to download our final Excel sheet with every measurement.