Soy sauce is a popular condiment in the Asian diet and many commercial soy sauces have been shown to have a high antioxidant activity, though so far this had not been demonstrated in humans consuming soy sauce. A recent study by scientists from the National University of Singapore (NUS) has shown that indeed the antioxidant properties of dark soy sauce apparent in the test-tube are also occurring in humans who consume it.
Led by Professor Barry Halliwell, Head of Department of Biochemistry, Yong Loo Lin School of Medicine at NUS, the research group found that dark soy sauce is a potent antioxidant that counters damage to human cells and tissues caused by free radicals.
Free radicals are constantly produced in the body and are associated with the etiology of major chronic diseases; for instance, cancer, diabetes and heart diseases. However these detrimental effects of free radicals can be prevented by antioxidants. Many foods have been shown to have antioxidant properties and it is thought that a diet rich in these foods has significant health benefits, but so far this has been very difficult to prove in practice.
The NUS study recruited 24 healthy volunteers (14 males and 10 females with average age of 23 yrs old) who were non-smokers to take part in the study. After a period of fasting, the volunteers were fed either a single dose of 30 ml dark soy sauce mixed with 200g plain boiled rice or 200g plain boiled rice mixed with food colouring (placebo). No other foods were taken over the experimental period. Blood and urine sample were taken before giving the meals to the volunteers and hourly up to 4 hours post-meal for measurements of two accurate biomarkers of antioxidant activity.
The study found that dark soy sauce has a rapid antioxidant effect (3-4 hours after dark soy sauce meal) against lipid peroxidation in the human volunteers. Going forward, the research group hopes to investigate the antioxidant responsible in dark soy sauce.