Title: Does soy sauce keep cancer at bay?
Key words: anti-cancer compounds, antioxidants, HEMF, neoplasia, DNA, RNA, tumour,
Date: April 2001
Category: Specific conditions
Author: DJE Candlish
Does soy sauce keep cancer at bay?
Some of the compounds that give soy sauce its distinctive flavour and aroma could help protect against tumours, say American researchers. This result reverses the status of soy sauce, which in the past has been suspected of causing cancer and allergic reactions. In the early 1980s, scientists suspected that soy sauce was one cause of the high incidence of stomach cancer in Japan. But experiments failed to show this.
Michael Pariza and colleagues at the Food Research Institute of the University of Wisconsin, Madison, have now shown that mice fed flavour-giving compounds extracted from soy sauce developed far fewer stomach tumours than control animals after being exposed to the potent carcinogen, benzo(a)pyrene. One compound called HEMF, 4-hydroxy-2(or 5)-ethyl-5(or 2)-methyl-3(2H)-furanone was particularly effective in quantities as small as 4 milligrams per kilogram of body weight (Cancer Research, vol 52, p 1754).
In preliminary work, Pariza's team had fed mice on a diet made up of some 20 per cent aged soy sauce. They also added nitrite to the drinking water, expecting it to react with components of the sauce to produce mutagens which damage DNA. But they found instead that this mixture inhibited uncontrolled cell production (neoplasia) in the stomachs of the mice. When they used fresh soy sauce they got the same results even without the nitrite.
Pariza believes that unlike the fresh soy sauce, aged samples in the earlier experiments contained a lot of oxidation products. The nitrite was thought to be simply reducing these and regenerating their antioxidant activity. Antioxidants are thought to inactivate carcinogens, and so protect against tumours.
To find out what compounds in the soy sauce were responsible for its anti-carcinogenic effect the researchers used solvent extraction to separate out the various components. They then tested each component to see if it had any tumour-inhibiting effect.
Pariza's team extracted the soy sauce with the organic solvent ethyl acetate and water. They found the compounds that dissolved in the solvent were those that give the sauce its aroma and flavour. The coloured compounds (amino-carbonyls) were concentrated in the organic insoluble fraction.
The researchers discovered that both the soluble and insoluble fraction inhibited the tumour-promoting effect of benzo(a)pyrene in the mice. One of the main flavour components, HEMF, which is generated during fermentation, was by far the most effective compound against benzo(a)pyrene-induced neoplasia.
Benzo(a)pyrene is a particularly potent carcinogen. It is found in coal tar, cigarette smoke, smoked food and soot. It does not itself cause the uncontrolled cell division that results in tumour growth. In the body it is metabolised to a more reactive positive ion, which can damage negatively charged DNA and RNA - the nucleic acids which carry the genetic code for making proteins. Compounds such as antioxidants can prevent the positive ion from forming or block its action.
Further tests on HEMF revealed that only 25 parts per million in the diet was sufficient to reduce the number of stomach tumours in the mice by 66 per cent. The artificial antioxidant 2-tert-butyl-4-hydroxyanisole is 75 per cent effective at a dose of 5400 ppm. 'HEMF appears to account for a substantial fraction of the antioxidant activity of soy sauce,' says Pariza.
He believes that inhibition takes place at the tumour-production stage. 'This has important implications, since inhibitors of tumour production are likely to be effective against neoplasia induced by a range of carcinogens (not just benzo(a)pyrene),' he says. Such inhibitors might even be used as antitumour drugs.
From New Scientist magazine, vol 136 issue 1848, 21/11/1992, page 14
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