What explains the Achilles’ heel in certain Asian diets?
For decades, Japan has had the longest life expectancy in the world, while spending just a fraction on healthcare compared to other high-income countries. This longevity has been attributed in part to Japanese dietary patterns, which are thought to have contributed to their comparatively low rates of coronary artery disease. Japan has historically had among the lowest rates of colon, breast, ovarian, prostate, bladder, and blood cancers. Japan, however, has among the highest rates of stomach cancer, as you can see below and at 0:42 in my video The Role of Kimchi and H. Pylori in Stomach Cancer.
Japanese men may have had seven times less prostate cancer than Americans, but they had six times more stomach cancer. Is there some Achilles’ heel in the Japanese diet?
One of the first theories, proposed in the 1970s, was that it was the talc used to polish white rice to give it a glossy sheen. That was the case with ovarian cancer, which led to billions in damages against Johnson & Johnson’s baby powder, as I detailed in one of my videos, but that did not appear to be the case with stomach cancer. Could it be just genetics? No. Studies on Japanese migrants show that as they and their children westernize their diets and lifestyles, their stomach cancer rates drop accordingly.
The most well-established risk factor for stomach cancer is H. pylori, a bacteria that infects the lining of the stomach and causes the chronic inflammation that can lead to cancer. H. pylori infection is considered a Group 1 carcinogen, indicating the highest level of certainty that it indeed causes cancer. Korea and Japan have the highest rates of stomach cancer and among the highest incidence of H. pylori infection, as you can see below and at 1:52 in my video.
Case closed, then, right? The mystery seemed to have been solved.
But then came the “African enigma.” Countries such as Nigeria had even more H. pylori infections, but only a fraction of Japan’s stomach cancer rates. Then came the “Indian enigma.” H. pylori is twice as prevalent in India than Japan, yet Indians get ten times less stomach cancer, as you can see below and at 2:19 in my video.
Obviously, H. pylori alone can’t explain Japan’s epidemic.
Though most cases of stomach cancer are thought to be caused by H. pylori, most people with H. pylori don’t get cancer. H. pylori is one of the most common human infections. It has been estimated that half of the world’s adult population is infected with H. pylori, yet half of us don’t get stomach cancer. There must be some kind of co-factor in countries like Korea and Japan that explains their elevated cancer rates. The inflammation caused by H. pylori may just set the stage for cancer formation, increasing the susceptibility of the stomach lining to dietary carcinogens. But what’s so carcinogenic about Korean and Japanese diets?
Studies that have compared the dietary components of different Asian populations with similar H. pylori rates but dramatically different stomach cancer rates have suggested preserved, salted foods—both fish and vegetables—as the culprits. Fresh vegetables and fruits, on the other hand, were associated with an 85% reduction in stomach cancer odds, whereas consumption of fresh fish doesn’t appear associated with stomach cancer either way.
A review of 60 studies found that the consumption of pickled foods was associated with significantly higher rates of stomach cancer, though more so in Korea than Japan, perhaps because per-capita Korean consumption of salt-fermented vegetables, like kimchi, is five to eight times greater. You can’t know for sure though, until you put it to the test.
Pickled vegetable extracts can cause DNA damage in cells in a petri dish, but what about in people? Over a three-day period, researchers in Vancouver fed people 30 ounces of fukujinzuke (assorted vegetables pickled in soy sauce) or pickled cucumbers. Biopsies taken from their stomach lining before the experiment started were normal, as were the biopsies taken after eating fresh carrots or cucumbers. But after just a few days of consuming pickled vegetables, moderate to severe tissue abnormalities were found, suggestive of stomach irritation.
The consumption of non-fermented soy foods, such as tofu, edamame, and soymilk, is linked to a lower risk of stomach cancer in Japan, whereas no association was found with fermented soy foods—even highly salted miso. The protection afforded by soy foods was attributed to the anti-inflammatory and antioxidant effects of the isoflavone compounds in soybeans.
Salt itself isn’t considered a direct carcinogen, but it may damage the stomach lining, thin the protective mucus layer, enhance H. pylori colonization, enhance the penetration of carcinogens, and enhance the formation of carcinogens. Even moderately high salt intake is associated with significantly increased risk of stomach cancer, though in Japan this effect may be limited to those already suffering from H. pylori-induced inflammation.
H. pylori infection is typically treated with a cocktail of multiple antibiotics. Is there any way to eradicate it naturally through diet? We’ll find out in the next blog.
Doctor’s Note
Stay tuned for the follow-up blog: The Best Foods to Fight H. Pylori.
The talc video I mentioned was Talcum Powder and Fibroids.
I previously talked about Japan’s stomach cancer rates in Vegetarians and Stroke Risk Factors: Saturated Fat, and Is Miso Healthy? has more on salt consumption and cancer.
