The WHO has classified processed meat as a group 1 carcinogen. One of the reasons is the high nitrate and nitrite content of cured meat. But what about nitrates in vegetables? Vegetables are the richest dietary sources of nitrates.  Could it be that nitrates from vegetables are as bad as bacon? Turns out the answer is not quite what you expect.

I was quite conflicted while researching for this article. After reading several studies I had to face the facts. I thought the salad I usually eat for lunch with a little bit of olive oil was a healthy choice. But it turns out this meal has a dark side too. It’s because of the nitrates often found in dark green leafy vegetables. Under certain circumstances, they can be harmful, even carcinogenic. But is this a reason to stop eating dark green leafy vegetables, the healthiest foods on the planet? Here is some background on the subject to put my decision at the end in more context.

Where nitrates come from

Sources of nitrate rich vegetables

Nitrates are present in all vegetables. They originate from nitrogen in the soil that provides food for the plants. Nitrogen is a common substance added to fertilizers to make vegetables grow better. The highest concentration of nitrates in vegetables are found in greens like rocket salad, swiss chard, lettuce, beet greens, rhubarb, spinach, …
Nitrates from food don’t seem to be the problem though. It’s the conversion of nitrates to nitrites and nitrosamines that’s a concern. This conversion happens in your body after we eat nitrate or nitrite-rich foods.
Nitrosamines are genotoxic carcinogens linked to various cancers including colorectal cancer. They are the reason the WHO classified cured meat as a group 1 carcinogenic. According to the data from 10 studies for every 50 gr of processed meat you eat (about 1 middle sized hot dog) your risk for colorectal cancer rises by about 18%.

How the body processes nitrates

How the body processes nitrate

To get clear about the subject it’s important to understand how the body metabolizes nitrates. About 60-70% of the nitrates we eat get absorbed from the stomach and small intestines into the bloodstream. They are then excreted by the kidneys through urine in the first 24 hours. The rest of the nitrates are reduced to nitrites in the presence of bacteria on the tongue. That’s why salvia has a high amount of nitrite which ends up in the stomach after we swallow it. In the acid environment of the stomach, nitrites can convert into two forms. They either form the health-boosting nitric oxide gas or genotoxic nitrosamines. In which form will they end up? The answer is it depends on the conditions in the stomach environment.

Nitric oxide – Why is it important to eat nitrates

Nitric oxide is known to have many health benefits. It is a vasodilator that can lower blood pressure and improve blood circulation. Once nitric oxide (NO) is formed from nitrites in the stomach it enters the intestines. It then reaches the liver through the portal vein. There it is oxidized again into nitrite. The nitrite enters the bloodstream and reaches resistance blood vessels where it is once more converted to nitric oxide. Now nitric oxide enters the smooth muscle cells of the blood vessels. It makes them dilate which leads to an immediate decrease in blood pressure and heart rate. The drug nitroglycerin uses the same mechanism in people who need to lower blood pressure spikes.

Nitric oxide dilates blood vessels

Nitric oxide has been studied because of these beneficial vasodilator properties. It seems that the blood flow in the dilated blood vessels is improved. One of the benefits is that this increased blood flow can lead to better athletic performance. That’s why many athletes drink beetroot juice, which is rich in nitrates. The athletes’ blood vessels get dilated from the nitric oxide and have increased blood flow. That makes athletes perform better and longer.

Nitrosamines – When nitrites go bad

Nitrosamines are the other compounds that can originate from nitrites. In the acid environment of the stomach, nitrites combine with free amines originating from amino acids of protein chains. There are several different nitrosamines which are all considered carcinogenic for humans. Urine samples of people who eat meat and processed meat have shown the presence of nitrosamines.

nitrites and nitrates in food

Cured meat is problematic because nitrates and nitrites are added directly into the meat. There are several reasons the meat industry uses these additives. First nitrates and nitrites prevent botulism which can develop in packaged meat. Also, these additives keep the meat nice and pink and enhance flavor. During the production process, the added nitrates and nitrites bind to the proteins in the meat and form nitrosamines. So the problematic thing with meats like hams, hot dogs, bacon, salami, prosciutto… is that you’re eating already formed nitrosamines. That increases your load of carcinogenic factors significantly. In comparison, nitrates from vegetables first, need to be converted into nitrosamines in your body. That will happen if specific conditions are met.

How to eat veggies to be safe?

Turns out our body is very resourceful and has various mechanisms in place to protect us from serious cell damage. There are certain inhibitors that prevent the formation of nitrosamines. These include various phytonutrients, vitamins like vitamin C, phytic acid, …

The great thing is that these compounds usually, come packaged with the food itself. For example, rocket salad is a great source of nitrates. But it’s also rich in vitamin C. So if you eat nitrate-rich vegetables without fat your body will prevent nitrosamine formation. To get this effect you only need a small amount of the inhibitor. You’ll get enough vitamin C if you eat e.g. a slice of paprika, half a kiwi or one small stem of broccoli.

Vitamin C inhibits the formation of nitrosamines.

But if you consume nitrate-rich food with fat nitrosamines will be formed. An in vitro study showed that nitrosamine formation from nitrates was decreased by vitamin C. In the absence of lipids vitamin C converts nitrites to nitric oxide. But when researchers added 10 % fat to the mix vitamin C promoted the formation of nitrosamines severalfold.

Does that mean you shouldn’t eat a salad with nuts, chicken or olive oil dressing? Well, according to this study you shouldn’t. But you have to weigh the risks and benefits of your food choices. You can’t only look at one aspect because potential carcinogens are all around us. It’s impossible to avoid all. Even normal metabolism produces damage to your DNA. A vegetable-rich salad with dressing is maybe going to form some nitrosamines. But it is also going to arm your body with, vitamins, minerals, and phytonutrients that can repair the damage done to your DNA.

I eat most of my dark green leafy veggies in a vegetable packed green smoothie. That could be the middle ground to eating more vegetables, getting more nitric oxide, and experiencing all the other health benefits dark green vegetables have been linked with. What about you? Tell me how do you eat your vegetables?

Photo credit: Swiss Chard,Blood vessels by KelvinSong (Own Work)