First, let’s talk about numbers. According to WHO’s norms the allowed daily dose of nitrates is 5 mg per kilogram of body weight. With an average weight 70 kg, the daily maximum of nitrates is 350 mg. Consuming 600-650 mg of nitrates in one meal leads to a discernible intoxication in adults.
Table below shows maximum allowed concentration of nitrates in different products. It is worth mentioning that these norms were established by the decision of related authorities and so they can be easily increased or decreased.
Table Maximum allowed concentration of nitrates in different products
Every plant permanently extracts nitrates (nitric acids salts) from the soil and turns them into organic nitrogen-containing compounds (amino acids, proteins and others). This is a unique ability of plants – to produce organic compounds out of mineral salts. Plants basically survive because of that, which is why they always contain nitrates (those that have already been extracted from soil, but have not turned into proteins yet). However, nitrates are distributed in the plants on a not very even basis. Fruits contain least of them, which is why they and beans usually do not cause any concerns in terms of nitrate consumption.
The rate of absorption and transformation of nitrates depends a lot on temperature and time of the day. The rate of transformation is increased in the morning and in the evening, especially when it is hot, and slower in cold weather during the day. The difference is quite significant – up to 3-4 times. Thus, it is worth considering the time of the day when harvesting.
Nitrates on their own are not harmful for our organism. But a part of them turns into nitrites (salts of nitrous acid), that block cells breathing processes. Hemoglobin is tied up and the concentration of cholesterol and lactic acid increases. Therefore, nitrites can be considered poison.
In a healthy body transformation of nitrates into nitrites is significantly slower when compared to a weakened one. Most nitrates are simply removed; some of them are transformed into useful compounds. Protective mechanisms for nitrates were created by the nature itself, and a normal metabolism even relies on the presence of some amount of these salts. After all, it is all about dosage…
High nitrate content in plants is usually due to excessive amount of mineral fertilizers. However, many people today started to understand that problem and are trying to solve it. Fortunately, there are producers who used too much fertilizer in the past and now have changed their methods knowing what an excess of nitrates can cause.
We should note that increased nitrate content is not always caused by excessive use of nitrous fertilizers. Sometimes even in the farms where fertilizers are not used, the harvest still contains a lot of nitrates. This usually happens as a result of breaking some elementary agronomic rules. Say, an owner got a truck full of manure in the spring and happily spread it on the soil right after. By doing this he intended to produce “clean” vegetables, but in the end they will contain much more nitrates than he expected.
An interesting research on defining minimum and maximum content of mineral nitrogen in vegetables was conducted by the Institute of Soil Science and Photosynthesis. The calculated nitrate content data in common products is presented in table below (according to Sokolov “Nitrates under control”).
Table Minimum and maximum nitrate content in vegetables, melons and gourds (mg/kg)
This table is undoubtedly interesting. Though sometimes you can find parsley with nitrate content less than 250 mg/kg (and other products containing much less mineral salts than the above stated minimum), those vegetables usually come from small farms where chemical fertilizers are not used at all. That does not mean I am against using mineral fertilizers. When used moderately, they can unquestionably be useful. However, in supermarkets you often encounter some stuff that can easily cause an acute intoxication. Of course in most cases the nitrate content of vegetables does not exceed the maximum allowed. However, there are still reasons to worry, as there are some exceptions that can lead to sad consequences. It is advised to understand what we are eating and for that you need to learn how to evaluate the quality of food.
You can also measure nitrate content in products using an indicator paper. Of course, it is not very precise, but it can give you a rough idea. Besides, it is very nice to eat parsley or dill knowing that they contain not the allowed 2000 mg/kg of nitrates (what happens in most cases), but just 500. It makes even more sense to check vegetables when you are buying a big pack, like potatoes or cabbage for the whole winter etc. However, some vegetables (for example beetroot) cannot be checked for nitrates using an indicator paper.
There is one more way to do it. Vegetables with high nitrate content usually have an unnatural taste. It does not feel nice to chew and swallow them and they do not bring any pleasure.
Moreover, taste indicates not only nitrates level, but the sum of qualities of what we are chewing at the moment. Such evaluation ability is given to us by nature. Our tongue is an incredibly sensitive organ if you do not dull its sensibility with inappropriate food. Professional tasters can distinguish the most subtle features of tastes even when it is not possible to find out the difference during a laboratory study.
It is probably better to throw away vegetables that obviously contain too much nitrates.
Here are the most popular vegetables high in nitrates.
Beetroot is considered the queen of vegetables, but it is also a champion in nitrate concentration. Some can contain up to 4000 mg/kg. For this reason it has to be thrown away or cut mercilessly much more often than other vegetables.
Nitrates are not distributed in beetroot evenly. Its lower part contains 4 times more nitrates than the middle, while the upper part (closer to leaves) contain 8 (!) times more. Therefore, in suspicious cases it is better to cut the top (approximately one quarter of the taproot) and the bottom part (approximately one eighth of the taproot). By doing this you get rid of three fourths of nitrates contained in beetroot.
Salad leaves, parsley, dill and other greens sometimes contain even more nitrates than beetroot. The content of mineral salts in plants that were not fertilized is usually quite moderate, while in the ones cultivated on nutritive solutions or heavily fertilized soil the nitrate concertation can reach up to 4000-5000 mg/kg.
However, the concentration of salts can vary in different parts of plants. The nutrition processes start in the earth, so the nitrate levels are especially high in stems and leafstalks. Here is comparative data from O. Sokolov (according to Sokolov “Nitrates under control”).
Table Nitrate content in greens (mg/kg)
Thus cutting stems (if they are bitter) makes even suspicious greens edible. Moreover, fresh greens contain a lot of vitamins impeding transformation of nitrates into nitrites.
However, after the greens are cut, under the effect of microorganisms and oxygen, nitrates turn into nitrites very fast. In just 10 minutes products can suddenly become much more poisonous. The wisest way (if you do not like to eat whole leaves) is to cut greens right before you put them in your plate.
When buying greens, check if there are no broken, damaged or rotten parts, as that is where different processes occur, and when you bring a bunch of such greens home, your meal can contain much more nitrites than vitamins.
In cabbage most nitrates are concentrated in the outer leaves. There (and in the cabbage-stump) are twice as many nitrates as in the middle part of the cabbage head. That is why sometimes people start chewing the outer leaf and then leave it without swallowing. Also, after taking off three or four layers of leaves the taste changes a lot.
When stored, fresh cabbage keeps its nitrate level high till February, in March the concentration of salts decreases almost three times.
In sauerkraut for the first 3-4 days nitrates are actively transformed into nitrites. So it is recommended to start eating freshly made sauerkraut at least in one week after it was made. Afterwards, most nitrates, as well as half of all useful substances, move into the brine. So if you get rid of the brine and wash sauerkraut, what is the point of making it?
No, once you have decided to make sauerkraut, it is better to choose some good cabbage, verified by using taste, pendulum, intuition etc. Then you can eat as much of it as you want, together with brine, carrot and everything. (If it is homemade you can make it not very salty).
Recently there were some recommendations published in magazines saying that you should not use dill and parsley when making sauerkraut, as these greens are very high in nitrates and will pass it all to the brine. In fact, the proportion of cabbage and greens is not comparable in mass and in moderate quantity greens will not do any harm. Moreover, you can also choose good parsley and dill.
There is also cauliflower, which often contains lots of nitrates and its spoiled parts can be high in nitrites. It can be cooked on steam.
Sometimes radish contains up to 2500 mg/kg of nitrates. Nitrate concentration around 500 mg/kg can be considered great (for early types). Round radish contains significantly less nitrates than the prolonged one (“Red giant” type).
You can decrease its nitrate content almost twice by cutting 1/8 from the top and the bottom of a radish.
If potatoes are stored correctly, their nitrate content rapidly decreases in the beginning of March – up to 4 times. Until February the nitrate concentration almost does not change.
Most salts in a tuber are concentrated in its middle part (and the valuable substances closer to skin!), but their concentration does not vary much. Therefore, it is useless to peel it, especially because vitamins and enzymes contained under its skin limit the transformation of nitrates into nitrites.
The best way of cooking potatoes with high nitrate content is on steam and without peeling. Small tubers are cooked whole; bigger ones can be cut into 2, 4 or 6 parts. This way 60-70% of nitrates is removed. (Normal cooking removes up to 40%, while frying removes around 15%). The water left from cooking should be thrown away, of course.
Carrots, especially the early ones, can store up to 1000 mg/kg of nitrates. There are more of them in the top, closer to leaves, and also in the very bottom. It was also noticed that medium-sized carrots contain least nitrates. By the way, this is true for all the vegetables – it is always better to buy medium-sized beetroot, turnip, squashes etc. (and not only because of nitrate content).
After carrot is cut, nitrates rapidly turn into nitrites (just as in greens, beetroot and others). In salads, these processes are intensified by sour cream and even more by mayonnaise (mayo is a poison on its own!), which make up a perfect environment for microorganisms development. Sunflower oil, on the opposite, stops bacteria growth.
Squashes can contain up to 700 mg/kg of nitrates. Most of them are concentrated in the thin layer right under the skin and also in the bottom. Therefore, the bottom part and a thick layer of skin should be removed.
Squashes, especially the ripe ones, are usually cooked, what decreases their nitrate content more than twice. But of course no one wants to throw away the broth. So if you really need to get rid of nitrates, you can cook squashes on steam, using a sauce pan. This way you will lose less precious juice.
When growing in unpleasant conditions cucumbers can store up to 600 mg/kg of nitrates. There are much more of them right under the skin than in the middle. If the skin is bitter and not nice, you can peel it. It is also recommended to cut the least tasty part in the bottom.
Of course, you should keep the information about nitrates in mind, but overall they are not as bad. In most cases their content is within the norms and when a product is not edible, your tongue can always help you understand it, you just need to trust it. Consequently there are no crucial problems here.
However, some people, after learning about “nitrate nightmares”, stopped eating vegetables at all. This is absurd, as nitrates have always been there and will always be, as their permanent presence is absolutely normal. Vegetarians live perfectly fine, though people use much more fertilizers, but they also have very high sanitary control standards. Anyway, you can eat vegetables without worrying, moreover you can eat a lot of them if you want, but it is always good to be a little cautious.
Text: from the book A.Eddar “Treatise of nutrition”. Interpreter: Liza Dukhova