BBC – Future – The truth about nitrates in your food


"Nitrates" can make you think of school chemistry courses or fertilizers. They are probably less likely to be associated with a dinner.

If you think of nitrates in the context of food, it's probably a negative image that comes to your mind – in particular, perhaps, the recent call to ban the preservatives of nitrates and nitrites at bacon and ham because of their potential carcinogenic effects.

But the relationship between dietary nitrates / nitrites and health is much more nuanced than simply saying "they are bad for us". For example, the high natural nitrate content of beet juice has been attributed to a drop in blood pressure and an improvement in physical performance. Nitrates are also the active ingredient in some angina pectoris medicines, a condition in which a decrease in blood flow causes chest pain.

Are nitrates and nitrites really bad for us?

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Nitrates and nitrites, such as potassium nitrate and sodium nitrite, are natural chemical compounds that contain nitrogen and oxygen. In nitrates, nitrogen is bound with three oxygen atoms, while in nitrites, nitrogen is bound with two oxygen atoms. Both are legal preservatives that suppress harmful bacteria found in bacon, ham, salami and some cheeses. (Learn more about how dried meats protect us from food poisoning).

In the average European diet, only about 5% of nitrates come from processed meat, while more than 80% comes from vegetables.

Of all the turmoil around processed meat, you can imagine that it is the main source of nitrates in our diet. But in reality, only about 5% of the nitrates in the average European diet come from this source, while more than 80% comes from vegetables. Vegetables acquire nitrates and nitrites from the soil in which they grow – nitrates are part of natural mineral deposits, while nitrite is formed by soil micro-organisms that break down animal matter.

Leafy green vegetables such as spinach and rocket tend to rank high for nitrate content, with other rich sources such as celery and beetroot juice and carrots. Vegetables from organic agriculture may have lower levels than non-organic vegetables because they do not contain synthetic nitrate fertilizers.

However, there is a significant difference between the way nitrates and nitrites are packaged in meat and vegetables – and this also depends on their carcinogenicity.

Link with cancer

Nitrates are quite inert by themselves, which means that they are not likely to be involved in chemical reactions in the body. But the nitrites and the chemical substances that result are much more reactive.

Most of the nitrites we encounter are not consumed directly, but are processed from nitrates by the action of bacteria present in our mouths. Interestingly, research shows that the use of an antibacterial mouthwash can significantly reduce this oral production of nitrites.

When nitrites made in our mouth are swallowed, one of the things that can happen is that they react in the strongly acidic environment of the stomach to form nitrosamines – some of which are carcinogenic and have been associated with cancer. 'intestine.

But for that, you need a source of amines, ammonia-related chemicals, which are found in abundance in protein foods. Nitrosamines can also be created directly in foods when cooked at high temperatures, such as for fried bacon.

It's not so much nitrates / nitrites that are carcinogenic as their cooking and local environment – Kate Allen

"It's not so much nitrates / nitrite per se [that are carcinogenic]but the way they are cooked and their local environment are important factors, "said Kate Allen, executive director of science and public affairs at the World Cancer Research Fund. "For example, nitrites in processed meats are close to proteins (especially amino acids). When they are cooked at high temperatures, it makes it easier for them to form nitrosamines, the carcinogenic compound ".

But Allen adds that nitrites are just one of the reasons that processed meats contribute to bowel cancer and their relative importance is uncertain. Other contributing factors include iron; PAHs (polycyclic aromatic hydrocarbons) that form in smoked meats; and HCAs (heterocyclic amines), which are created when the meat is fired by open flame – and which also promote the formation of tumors.

It is also important to keep the dangers of processed meat in context. While the International Agency for Research on Cancer categorizes processed meat as a "probable carcinogen", the risk is quite low.

In the UK, for example, six in every 100 people will have bowel cancer in their lives. Of those who consume 50 grams of processed meat (about three slices of bacon) a day, the odds are seven out of 100.

Good chemicals

Nitrites are not all bad. There is growing evidence that they can deliver cardiovascular and other benefits through a molecule called nitric oxide.

In 1998, three American scientists were awarded the Nobel Prize for their discoveries about the role of nitric oxide – a gas – in the cardiovascular system. We now know that it dilates the blood vessels, lowers the blood pressure and is part of the body's weapons against infections. The limited ability to produce nitric oxide is associated with heart disease, diabetes and erectile dysfunction.

One of the ways in which the body makes nitric oxide comes from an amino acid (a building block of the protein) called arginine. But it is now known that dietary nitrates can also contribute significantly to the formation of nitric oxide. We also know that this can be especially important in the elderly, because the natural production of nitric oxide via arginine tends to decrease with aging.

If the nitrates present in ham are chemically identical to those of a salad, it is those based on vegetables on which you should shoot.

However, although the nitrates present in ham are chemically identical to those of the salad you will eat with it, these are the vegetable-based ones you should shoot at.

"We have observed an increase in the risks associated with nitrates and nitrites in meat for some cancers, but we have not observed any risks associated with nitrates or nitrites in vegetables – at least in large observational studies where Absorption is estimated from self-reported questionnaires, "says Amanda Cross, a cancer epidemiologist at Imperial College London.

Cross adds that it is "a reasonable assumption" that nitrates in leafy vegetables are less likely to be harmful (ie to form nitrosamines). They do not contain protein-rich foods and also contain protective components such as vitamin C, polyphenols and fiber, all of which have been shown to reduce nitrosamine formation.

When most of the nitrates in our diet come from vegetables – and in turn encourage the formation of nitric oxide – they are probably good for us.

So when most of the nitrates in our diet come from vegetables – and in turn encourage the formation of nitric oxide – they are probably good for us.

An expert in nitric oxide went further, saying that many of us lacked nitrates / nitrites and that they should be classified as essential nutrients that can help prevent conditions such as heart attacks and heart attacks. stroke.

The right amount

It is virtually impossible to reliably estimate dietary intake of nitrates because the content of food varies widely. "Levels can vary up to 10,000 times for lettuce, and nitrates in drinking water can also vary considerably within legal limits (50 mg / liter)," says nutrition epidemiologist Gunter Kuhlne, from the British University of Reading, UK.

"This means that studies of the effects of nitrates on health should be interpreted very carefully, as" nitrates "could simply be a marker of vegetable consumption.

A report published in 2017 by the European Food Safety Authority (EFSA) recommended an acceptable daily intake (ADI) (quantity that can be consumed throughout life without appreciable health risk) equivalent to 235 mg nitrate for a person weighing 10 stones (63.5 kg / 140 lb). But the report also noted that people of all age groups can overtake this ADI quite easily.

Nitrite intakes are generally much lower (an estimate of the average intake in the UK being 1.5 mg per day), and EFSA indicates that exposure to nitrite preservatives is within safe limits for all population groups in Europe, with the exception of a slight overflow in children with high diets in additives.

Some experts argue that the nitrate / nitrite ADIs are outdated anyway and that higher levels are not only safe but also beneficial – as long as they come from vegetables and not from processed meats.

Having 300-400 mg of nitrates at one time – potentially provided by a big salad of rockets and spinach, or a beetroot juice – is the amount that has been linked to falls in blood pressure, for example.

As always, the dose makes the poison and concentrations of 2 to 9 grams (2,000 to 9,000 mg) of nitrate can be extremely toxic, resulting in changes in hemoglobin that manifest as a bluish hue of the lips and skin. But it would be difficult to achieve this level in a single session and it is very unlikely that it comes from the food itself – it is rather a risk due, for example, to water contaminated with feritliser.

The result? If you want to eat the right types of nitrates and nitrites and avoid those that are potentially carcinogenic, opt for a very varied diet including at least five servings of fruits and vegetables a day, and avoid too much munching on processed meats. In this way, the benefits of nitrates and nitrates will almost certainly outweigh the disadvantages.

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