Possible Causes of Increased Cancer Rates from Fermented Vegetables
Older research out of China described common family fermentation methods that lasted for months. They also described batches frequently developing mold and still being consumed (Yang 1980). Testing also showed high levels of mold or fungal contamination in fermented vegetables. Animal studies that fed rats fermented vegetables, found numerous cancers and precancerous lesions, where control rats were cancer free (Yang 1980).
While fungal contamination could be a problem in some types of fermented vegetables, kimchi is often processed for shorter periods of time or at low temperature, minimizing the risks for fungal growth. And studies on kimchi consumption still appear to be linked to stomach and esophageal cancer. A recent study explored another possible carcinogen: enzymes produced by certain bacteria involved in the fermentation process, including β-glucuronidase and β-glucosidase. In the study, bacteria from kimchi were isolated and grown in culture. The cultures were then evaluated for the presence of the enzymes. Over half of the bacteria found in kimchi produced one or both of the carcinogenic enzymes, raising concerns (Lee 2021).
A separate study also found that stomach cancer patients that consumed fermented vegetables had significant disruptions in their folate biosynthesis pathway (Yang 2020). While the study needs verification, low folate levels are known to increase the risk and severity of gastric cancer (Lee 2014).