When the second atomic bomb fell on Nagasaki in 1945, Dr Akizuki and 20 others were caring for 70 tuberculosis patients in a hospital only 1.4 kilometres away from the epicentre of impact. Despite usual expectations, Dr Akizuki and the others did not have their health destroyed by acute radiation poisoning. He then considered that their consumption of miso soup, with wakame seaweed, every day was the cause of this. Subsequent research on mice found that miso eaten before, but not during or after, irradiation protected against tissue damage and improved survival. The length of fermentation time, from 3 days to 180 days, also had an association with the efficacy of miso against radiation damage, with longer fermentation increasing the effects.
This review also discussed a protective effect against certain cancers such as breast cancer. In a human cohort study involving 21, 852 women, it was found that consumption of miso soup and isoflavones was associated with a reduced risk of breast cancer, but not other soy foods. These findings did not change after adjusting for reproductive or family history, smoking or other dietary factors. Compared with the lowest quartile of soy isoflavone intake, women in the highest quartile had a 54% reduced risk of breast cancer, with a stronger association in post-menopausal women.
The review also mentioned an epidemiologic study where the risk of colon cancer was reduced by soybean consumption. A study on mice was then discussed, where mice fed miso had a decreased number of abberant crypt foci (ACFs) after carcinogen exposure. In another that followed, mice administered 180 day fermented miso and the same carcinogen also saw a significantly lowered number of ACFs, from an average of 87 to an average of 65 ACFs. Mice in the 3-4 and 120 day fermented miso groups had averages of 85 and 83 ACFs respectively, only a few less than the controls.
Additionally, in light of studies showing an inhibition of lung cancer by soy isoflavones, research on rats once again found a reduced number of tumours in rats given miso. Another epidemiological study on humans found that miso soup consumption in women without a history of liver disease is associated with a reduced risk of dying from liver cancer. Despite a high salt content, miso may even lower the risk of stomach cancer too! This may be because of other minerals and compounds present, or salt on its own being harmless in terms of cancer as opposed to the foods that first come to mind upon hearing the words “high salt”.
On top of these health benefits, compounds found in miso soup may be an effective alternative to conventional treatments for osteoporosis. In an animal study, 96 rats with their ovaries removed received either oestrogen replacement therapy, anti-osteoporosis pharmaceuticals of genistein, a phytochemical found in fermented soy products such as miso, for 12 weeks. The genistein turned out to be the most effective, beating all other treatments in improving bone mineral density, bone mineral content and breaking strength, but does this hold up in human studies? A 2007 study on 389 postmenopausal women with osteopenia compared the use of 54mg of genistein daily to a placebo, alongside calcium and vitamin D supplementation. After two years, there was no change in endometrial thickness in comparison to the placebo group. However, bone mineral density increased in the femoral neck and lumbar spine, by 0.035g/cm2 and 0.049g/cm2 respectively, while in the control groups, bone mineral density declined by 0.037g/cm2 and 0.053g/cm2 respectively. These findings show that women do not have to choose between reproductive cancers and osteoporosis, as natural treatments including genistein often have targeted effects.
In conclusion, miso and other fermented soy products can have many health benefits unlike their unfermented or processed cousins. Miso can be taken as a drink, as a base in a light soup or a condiment in other recipes.