Most of the commercial “soy” sauce sold in the United States is a non-fermented, synthetic product made from defatted soybean meal and grains, mixed with chemicals. It should be noted that a harmful group of chemical contaminants known as chloropropanols (3- monochloropropane-1, 2-diol or 3-MCPD), is produced as a byproduct during the synthetic method of soya sauce manufacture. There are mixed reviews regarding the safety of chloropropanols.
True tamari or shoyu is an aged product, which takes almost a year to ripen and form its characteristic flavor. This natural process does not produce chloropropanols.
Therefore, it is best to select natural soya sauce. Remember that because of its high salt content, soya sauce can cause fluid retention and swelling.