Japanese style fermented soy sauce (shoyu) has many health benefits. It promotes digestion. The consumption of a cup of clear soup containing soy sauce enhances gastric juice secretion in humans. Soy sauce possesses antimicrobial activity against bacteria such as Staphylococcus aureus, Shigella flexneri, Vibrio cholera, Salmonella enteritidis, nonpathogenic Escherichia coli and pathogenic E. coli O157:H7. It also contains an angiotensin I-converting enzyme inhibitor having antihypertensive effects. The active compound is identified as nicotianamine, which comes from soybeans. The high content of salt in soy sauce is a concern for some patients with high blood pressure. Fortunately, low salt soy sauce is not available in grocery stores and some Japanese restaurants.

Soy sauce and cancer prevention
Soy sauce exhibits anti cancer effects. Giving a diet containing it to mice inhibits benzo[a]pyrene -induced neoplasia. The flavor components of Japanese style fermented soy sauce, such as 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone, which is a characteristic flavor component of Japanese style fermented soy sauce and 4-hydroxy-2,5-dimethyl-3(2H)-furanone and 4-hydroxy-5-methyl-3(2H)-furanone exhibit antioxidant activities and anticarcinogenic effects. The feeding of a diet containing 10% soy sauce to male C3H mice for 13 months reduces the frequency and multiplicity of spontaneous liver tumors. Fermented soy sauce contains three tartaric isoflavone derivatives called shoyuflavones. These shoyuflavones inhibit histidine decarboxylase, which produces histamine, a mediator of inflammation, allergy and gastric acid secretion. Soy sauce also has antiplatelet activity. beta-Carbolines were isolated from soy sauce as the active compounds. Soybeans and wheat, which are the main raw materials of soy sauce, are allergenic foods. However, recent studies by enzyme-linked immunosorbent assay showed the absence of soybean and wheat allergens in soy sauce.

Soy sauce healthier than wine?
Dark soya sauce, widely used in east Asia, may prove to be more effective than red wine and vitamin C in combating human cell damage. Scientists found that the sauce -- derived from fermented soya beans -- contains antioxidant properties about 10 times more effective than red wine and 150 times more potent than vitamin C. The National University of Singapore study also found that the sauce improved blood flow by as much as 50 percent in the hours after consumption. However, llarge amounts of dark soya sauce have high salt content, which could lead to high blood pressure in those susceptible to blood pressure problems.

Fortification with iron
Soy sauce could be considered a functional food. Soy sauces are available in different types and grades, which allows them to reach consumers of all socioeconomic groups. Ferric sodium ethylenediaminetetraacetic acid (NaFeEDTA) has been used for iron fortification of soy sauces in some countries, however, its high cost may make it unattractive to policymakers and industry. Both naturally fermented and chemically hydrolyzed soy sauces could be fortified with five iron sources. Five iron sources -- ferrous sulfate, NaFeEDTA, ferric ammonium citrate, ferrous lactate, and ferrous gluconate -- do not significantly affect the sensory qualities of the soy sauce product. Ferrous sulfate is the most appropriate source because of its low cost and acceptable sensory characteristics. Soy sauce is a promising vehicle for iron fortification, however, the bioavailability of iron in the products examined here needs to be evaluated under normal use conditions.

J Agric Food Chem. 2013. Studies on the key aroma compounds in raw (unheated) and heated Japanese soy sauce. An investigation using the aroma extract dilution analysis (AEDA) technique of the aroma concentrate from a raw Japanese soy sauce and the heated soy sauce revealed 40 key aroma compounds including 7 newly identified compounds. Among them, 5(or 2)-ethyl-4-hydroxy-2(or 5)-methyl-3(2H)-furanone and 3-hydroxy-4,5-dimethyl-2(5H)-furanone exhibited the highest flavor dilution (FD) factor of 2048, followed by 3-(methylthio)propanal, 4-ethyl-2-methoxyphenol, and 4-hydroxy-2,5-dimethyl-3(2H)-furanone having FD factors from 128 to 512 in the raw soy sauce. Furthermore, comparative AEDAs, a quantitative analysis, and a sensory analysis demonstrated that whereas most of the key aroma compounds in the raw soy sauce were common in the heated soy sauce, some of the Strecker aldehydes and 4-vinylphenols contributed less to the raw soy sauce aroma. The model decarboxylation reactions of the phenolic acids during heating of the raw soy sauce revealed that although all reactions resulted in low yields, the hydroxycinnamic acid derivatives were much more reactive than the hydroxybenzoic acid derivatives due to the stable reaction intermediates. Besides the quantitative analyses of the soy sauces, the estimation of the reaction yields of the phenolic compounds in the heated soy sauce revealed that although only the 4-vinylphenols increased during heating of the raw soy sauce, they might not mainly be formed as decarboxylation products from the corresponding hydroxycinnamic acids but from the other proposed precursors, such as lignin, shakuchirin, and esters with arabinoxylan.

Toxicity, danger
J Emerg Med. 2013. Survival of acute hypernatremia due to massive soy sauce ingestion. There are a variety of treatment recommendations for hypernatremia, ranging from dialysis to varying rates of correction. We report a case of acute severe hypernatremia corrected with rapid free-water infusions that, to our knowledge, has not been previously reported. A 19-year-old man presented to the Emergency Department in a comatose state with seizure-like activity 2 hours after ingesting a quart of soy sauce. He was administered 6 L of free water over 30 min and survived neurologically intact without clinical sequelae. Corrected for hyperglycemia, the patient's peak serum sodium was 196 mmol/L, which, to our knowledge, is the highest documented level in an adult patient to survive an acute sodium ingestion without neurologic deficits. Emergency physicians should consider rapidly lowering serum sodium with hypotonic intravenous fluids as a potential management strategy for acute severe hypernatremia secondary to massive salt ingestion.