Buy or Bye: Miso

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Salty, earthy and funky, miso is finding its way into more American kitchens. Its popularity is soaring as the interest in fermented foods continues to rise. Though several varieties exist, the miso we most often see on store shelves is made from cooked whole soybeans which are combined with koji (a bacteria starter), salt and rice or barley. Over months, the enzymes in the koji work together with microorganisms in the environment to break down the structure of the beans and grains to produce a paste that is similar in consistency to nut butter. Owing to its high levels of the amino acid glutamate, miso is a source of umami, the much sought-after “fifth flavor” that, roughly translated, means savoriness.

The Upside: Since miso is considered a fermented “live” food, it is not too far of a stretch to say that, similarly to items like yogurt and sauerkraut, it can boost the population of friendly bacteria in your gut thereby helping to contribute to improved immune and digestive health. But, to date, we have very little data to show that the strains of bacteria found in miso in the quantities normally eaten can lead to better health measures. Another question that remains to be properly answered is what impact heating miso has on its probiotics. While soy can be hard to digest for some people and bring on unpleasant GI issues like gas, the fermentation process used to make miso breaks down the structure of the beans into easier digesting amino acids and carbs. Miso is a source of several important micronutrients, including manganese, copper and vitamin K, but at levels that are rather low in relation to other food sources.

The Downside: Most miso contains high amounts of sodium and a tablespoon serving of the soy-based paste provides about 28% of the daily allotment for sodium. Individuals who need to limit the amount of sodium in their diets for health reasons, such as lowering blood pressure numbers, or are prone to sodium-induced bloating, may need to go easy on miso. However, a 2020 research review published in the journal Environmental Health and Preventative Medicine found that a relationship between the frequency of miso soup intake and blood pressure levels or hypertension incidence has not been observed in clinical observational studies. Compounds in miso may lessen sympathetic nerve activity, resulting in less of a blood pressure spike seen with regular salt intake.

The Verdict: We should not expect foods like miso paste that are consumed in small quantities to provide substantial nutrition and health benefits and there is very little quality miso research to go on. But as long as someone is not needing to go easy on sodium, miso could be an ingredient that helps give the microbiome a boost without the gastro concerns. And certainly, miso as a condiment can be a great way to add low-calorie flavor to foods like dressings and sauces, which is helpful if you are looking for ways to add excitement to your meals but in a way that doesn’t pack on the calories.