It's a sad, sad truth: processed meats, like delicious cured ham, salami, and the pepperoni dotting your pizza, are unhealthy. A meta-analysis from the World Health Organization estimated that every 50 gram portion of processed meat eaten daily increases the risk of colorectal cancer by about 18%.
The most commonly blamed culprits for this are a couple of related molecules called nitrites and nitrates, which are used in the meat preservation process.
But nitrites and nitrates aren't just present in cured meats. They're also found in a lot of vegetables, like beets and spinach. In some cases, there's higher levels in vegetables than in cured meats!
So why are vegetables considered healthy, while cured meat is carcinogenic (cancer causing)?
The path from nitrate to nitrite
Nitrates and nitrites differ by a single oxygen atom. Nitrate is NO3, while nitrite is NO2. Both nitrate and nitrite have a negative charge, so they're usually bonded to a positively charged atom like sodium, to make sodium nitrate/nitrite, or potassium.
(Both sodium nitrate and potassium nitrate are found widely in nature; they are commonly described as two variants of saltpeter — yes, the stuff used in gunpowder!)
In order to preserve meat, butchers have traditionally added sodium nitrate. In the meat, one oxygen atom is stripped away, leaving nitrite, which suppresses bacteria by damaging them and inhibiting their growth. Thus, the meat is preserved against bacteria!
The big issue is what happens to that nitrite — how it continues to break down.
It's not the nitrite, it's the NOCs
Both nitrate and nitrite merge with certain types of protein fragments, creating N-nitroso compounds (NOCs). It's these NOCs, not the nitrate and nitrite precursors, that have been shown to cause cancer (at least in animal models — ethics boards don't let us feed a bunch of NOCs to people to see if stomach or colon cancer develops).
But nitrates and nitrites don't transform into NOCs on their own. Some molecules help transform nitrites/nitrates into NOCs. Others inhibit it, blocking NOC formation.
- Meat contains an iron-rich molecule called heme, which gives meat its red color — and increases NOC formation.
- Vitamins C and E, as well as other antioxidants, in vegetables help prevent NOC formation.
Nitrite and nitrate are the precursors to cancer-causing compounds, but other molecules drive — or prevent — the cancer-causing NOCs from forming.
What about meat with no added nitrates?
Unfortunately, even if a meat product proudly touts that it contains "no added nitrates" on the label, this doesn't guarantee that it's NOC free.
Added nitrates are typically sodium nitrate, as mentioned above. But because many plants contain high levels of nitrate, food manufacturers can add nitrate-rich plant extracts to meat instead of sodium nitrate. Celery powder is the most commonly used "alternative" addition.
The ingredients label no long has the scary sodium nitrate, but nitrates are still being added to the meat product; the end result is still similar.
Furthermore, meat, especially meat that is cooked at high temperatures (frying, searing, or broiling), contains other carcinogenic (cancer-causing) molecules formed during the cooking process. So even avoiding preserved meat doesn't fully eliminate cancer risk.
In the end, we cannot fully avoid cancer; cancer is the result of progressive cell damage that is our reward for surviving everything else. There is no diet or set of lifestyle choices that will fully prevent cancer from occurring.
But we can make informed choices to balance the immediate reward (mmm, delicious salami) against the long-term cost (increased stomach and colon cancer risk). Cancer is complex, and no single molecule or ingredient causes cancer on its own.
Whether they're added in mineral form or from plant extracts like celery powder, nitrates and nitrites are a necessary part of preserving meat, but also lead to cancer-causing NOC molecules — when reacting with certain other compounds, which are present in meat but not in vegetables.
Perhaps it's time to give that tofu-based recipe another try?