Fermented vegetables like kimchi offer the nutritional benefits of veggies plus a probiotic bonus. But some research suggests that they increase the risk of stomach cancer. Should you include fermented vegetables in your diet?
Nutrition Diva listener Brian wants to know:
"Do the benefits of fermented vegetables such as sauerkraut and kimchi outweigh the risk of getting stomach cancer. I understand that Koreans, who eat a lot of kimchi, also have the highest rates of stomach cancer. So, I'm wondering whether increasing our consumption of these products in order to help the beneficial bacteria in our guts is worth the risk."
Brian is right: People in Asian countries, where fermented vegetables make up a large part of the diet, do have higher rates of stomach cancer than elsewhere in the world.
What are the main risk factors for stomach cancer?
Fifty years ago, stomach cancer was the most common type of cancer diagnosed worldwide. And the good news is that the global incidence of stomach cancer has declined significantly over the last decades. This is due in part to declines in smoking, which is a significant risk factor for stomach cancer. It's also due to better detection and treatment of h. Pylori, a bacterium that commonly infects the digestive tract and can cause stomach ulcers as well as stomach cancer. H. Pylori is readily eradicated by antibiotic therapy and now that we know to look for it, and how to get rid of it, ulcers and stomach cancer are far less common.
What's the link between fermented veggies and cancer?
However, the incidence of stomach cancer remains high in Korea and elsewhere in Asia. And, believe it or not, the very high consumption of fermented vegetables is thought to be one contributing factor. This is a little confusing because eating more vegetables is a good way to reduce your risk of cancer. And, as Brian points out, fermented vegetables also contain probiotic bacteria, which foster a healthy gut.
At the same time, fermented vegetables contain nitrosamines. These compounds, which are by-products of the fermentation process, can have carcinogenic effects. Here in the West, the primary source of dietary nitrosamines are cured and processed meats. In Korea, where total nitrosamine intake is much higher, the primary dietary sources are smoked or salted fish and fermented vegetables.
The traditional Korean diet is also much higher in sodium than the typical Western diet (which is not exactly low in sodium), and this may be another contributing factor to the high rates of stomach cancer. Sodium, in high amounts, can irritate the lining of the stomach and perhaps make it more vulnerable to the carcinogenic effects of nitrosamines.
Another thing to keep in mind is that the traditional Korean diet, while high in fermented and pickled vegetables, may be quite low in fresh vegetables. The nutrients in fresh vegetables, especially vitamin C, can neutralize the nitrosamines in the digestive tract. And the epidemiological evidence bears this out: People whose diets are high in pickled vegetables but also high in fresh vegetables appear to be protected against the increase in cancer risk.
This same protective effect also applies to the nitrosamines found in processed meats such as bacon or hot dogs. Western diets that contain a lot of processed meats have been repeatedly linked to increased risk of cancers of the digestive tract. However, this increased risk is not seen in those who eat a lot of processed meat but also eat a lot of vegetables.
How do vegetables protect against cancer?
Although it's clear vegetable consumption is associated with reduced cancer risk, we still don't know all of the mechanisms involved. It could be the antioxidants that vegetables provide. The fiber could also play a role, both by improving digestion and elimination and by fostering a healthy gut microbiome. And perhaps this carcinogen-neutralizing effect is also part of what makes vegetables very so good for us.
So, to answer Brian's question: I think you can safely (and beneficially) incorporate fermented vegetables into your diet, both as a way to get more vegetables and to get some probiotic bacteria. Just make sure your diet also contains plenty of fresh vegetables and not too much salted, smoked, or cured meat and fish. It's fine to enjoy foods from that category on occasion, just not as a dietary staple.