We do not add any extra salt to the Miso soup. The sodium comes from the seaweed and the bone broth base.
Miso is typically considered to be a high-sodium food since one teaspoon of Miso often contains 200-300 milligrams of sodium. However, recent research has shown that in spite of its high-sodium content, Miso does not appear to affect our cardiovascular system in the way that other high-sodium foods sometimes can.
In recent animal studies, for example, identical concentrations of salt (sodium chloride) obtained from Miso versus table salt were discovered to have very different impacts on blood pressure. High-salt diets that derived their high salt level from table salt raised blood pressure in these animal studies, but high-salt diets that derived their high salt from Miso did not.
Recent human studies on Miso intake among Japanese adults have also shown that Miso-containing diets tend to lower the risk of cardiovascular problems, despite the high-salt content of Miso.
Reasons for this unique relationship between Miso and our cardiovascular system are not yet clear. However, some researchers have speculated that the unique soy protein composition of Miso (including peptide building-blocks of protein that get formed from soy proteins when the beans are fermented) is one of the key reasons for the cardiovascular support provided by Miso. If you are on a low-sodium diet, you should always consult with your healthcare provider before incorporating new foods.