Research Update: Miso Health Benefits

Dayna Dye

Do you order miso soup with your sushi? Turns out, this may be a healthful habit. Blog readers may recall a 2015 post that we published titled the “Magic of Miso” which reported the various benefits of this Japanese staple. Miso continues to reveal its benefits in both popular and scientific literature. Here is More on Miso!


What is Miso?

Miso, a fermented paste of soybeans, has a long history of culinary use among the Japanese, who are known for their longevity. The beans are fermented with koji (Aspergillus oryzae) that has been cultivated on rice or barley. Miso’s best-known usage is as the base of a soup that can be found on the menus of many Asian-themed restaurants in the U.S.

While many foods become more oxidized with time, fermented soy’s antioxidant capacity has been found to increase after eight to nine weeks, while lipid peroxidation levels remained low.1 Indeed, one can find miso on the market that has been aged from one to three years.

Miso Health Benefits

A review of bioactive peptides in soy enumerated their activities against oxidative stress, undesirable microbes, cancer, hypertension and immune dysfunction.2 A 2019 review of fermented soy products’ health benefits noted, “Several previous researches proved that soy products rich in protein can reduce the serum concentrations of total cholesterol, low-density lipoproteins (LDLs) and triglycerides if consumed instead of animal protein. Apart from these lipid-lowering effects, fermented soy products also proved to be effective in attenuating the effects of diabetes mellitus, blood pressure, cardiac disorders and cancer-related issues.”3

New research has found evidence of potential effects for fermented soy foods or miso against hepatitis A, hypertension, gastroesophageal reflux (GERD) and heart rate elevation in humans.4-8 In pre-clinical studies, miso appeared to be protective against stroke and visceral fat accumulation.9,10

Results from a meta-analysis of 330,826 participants in 23 studies, reported in the September 2019 issue of the Journal of the Academy of Nutrition and Dietetics, found that people who were among the highest consumers of soy had a 10% lower average risk of mortality during follow-up in comparison with subjects whose intake was among the lowest.11 A 10 milligram per day increase in soy isoflavones (which are contained in miso) was associated with a 7% decrease in the risk of dying from any cancer and a 9% lower risk of dying specifically from breast cancer. “Our findings may support the current recommendations to increase intake of soy for greater longevity,” S.M. Nachvak and colleagues concluded.

The fact that miso, despite its salt content, is associated with lower blood pressure is of interest. A study that examined the effects of soy foods on blood pressure among 4,165 Japanese men and women found no effects for non-fermented soy foods on the development of hypertension. However, subjects whose intake of fermented soy products (defined as miso and natto) was among the top one-third of participants had a 28% lower risk of developing high blood pressure than those whose intake was among the lowest third.6 A trial that compared the effects of consuming miso soup to a control soy food for eight weeks in participants with high-normal or stage 1 hypertension found that miso lowered nighttime blood pressure.5 In rats with salt-induced hypertension that were given miso, systolic blood pressure was reduced, which the researchers suggested was due to an increase in salt and water excretion.12

In an investigation that evaluated the effects of soy foods among 1,053 men and 373 women, total fermented soy food intake and miso intake in men were associated with a reduction in serum concentrations of interleukin-6 (IL-6), a marker of inflammation. “Some inflammatory biomarkers including [IL-6], IL-18 and C-reactive protein (CRP) have been shown to be associated with increased risk of type 2 diabetes, cardiovascular disease and many types of cancer,” Xiaolin Yang and colleagues explain. They note that “Fermented soy foods have been shown to contain greater amounts of polyamines including spermidine than the amounts in nonfermented soy products, and polyamines have been shown to be associated with cardioprotection and lifespan extension.”13

In human liver cells, miso inhibited replication of the hepatitis A virus (HAV) and increased the expression of a heat shock protein known as glucose-regulated protein 78 (GRP78), which had previously been shown to inhibit hepatitis A virus replication. Authors N. N. Win and colleagues concluded that “Japanese miso extracts can be used as effective dietary supplements for severe hepatitis A.”4

It was reported this year that the U.S. Food & Drug Administration (FDA) is considering revocation of approval of a permitted claim that diets low in saturated fat and cholesterol that include soy might reduce the risk of heart disease. However, the results of a meta-analysis of 43 of the 46 trials identified by the FDA that compared the effects of soy protein to non-soy protein on cholesterol levels concluded that at least 75% of the trials revealed a reduction in LDL cholesterol and that soy protein reduced LDL by an average of 3% to 4% in adults.14 Final action on the FDA proposal has been scheduled for December, 2019.

Benefits of Miso Soup When Sick

A study published last year that included 9,364 men and women enrolled in the ongoing Nagahama Study in Japan revealed a reduction in esophageal reflux and stomach upset in association with miso soup intake.7 Authors Fumika Mano and colleagues note that several amino acids contained in miso soup may promote gastric emptying.

But the most popular use of miso soup remains as a remedy for colds and flu. Although its benefits in seasonal illnesses have yet to be reported in published trials or studies, there have been a few investigations into its effects on immunity.15,16 In addition to the immune-balancing effects of soy peptides and isoflavones, miso contains the bacterium Tetragenococcus halophilus.17One strain of T. halophilus was recently found to have strong immunomodulatory effects that led the investigators to conclude that it has potential as a probiotic.17 So, when making miso soup, be sure to mix in the miso at the end of the process rather than boiling it in hot water or broth, to ensure that its beneficial bacteria remain viable.

Although chicken soup is the traditional Western go-to cold and flu remedy, miso may prove to be a worthy contender. Try it the next time you notice the malaise that can precede an illness. People have reported feeling better immediately.

References
  1. Tonolo F et al. Plant Foods Hum Nutr. 2019 Sep;74(3):287-292.
  2. Agyei D. Recent Pat Food Nutr Agric. 2015;7(2):100-7.
  3. Jayachandran M et al. Food Chem. 2019 Jan 15;271:362-371.
  4. Win NN et al. Int J Med Sci. 2018 Jul 30;15(11):1153-1159.
  5. Kondo H et al. Hypertens Res. 2019 Nov;42(11):1757-1767.
  6. Nozue M et al. J Nutr. 2017 Sep;147(9):1749-1756.
  7. Mano F et al. J Nutr Sci Vitaminol (Tokyo). 2018;64(5):367-373.
  8. Ito K et al. Intern Med. 2017;56(1):23-29.
  9. Watanabe H et al. Am J Hypertens. 2017 Dec 8;31(1):43-47.
  10. Okouchi R et al. Nutrients. 2019 Mar 6;11(3). pii: E560.
  11. Nachvak SM et al. J Acad Nutr Diet. 2019 Sep;119(9):1483-1500.
  12. Du DD et al. Clin Exp Hypertens. 2014;36(5):359-66.
  13. Yang X et al. J Med Invest. 2018;65(1.2):74-80.
  14. Blanco Mejia S et al. J Nutr. 2019 Jun 1;149(6):968-981.
  15. Yimit D et al. Nutrition. 2012 Feb;28(2):154-9.
  16. Zhang R et al. Nutr Cancer. 1997;29(1):24-8.
  17. Kumazawa T et al. PLoS One. 2018 Dec 26;13(12):e0208821.

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