New research at the University of California, Berkeley, may add yet another boost to the healthy reputation of the soybean.
A recent study shows that mice with the soy protein lunasin applied to their skin had significantly lower rates of skin cancer than mice without the lunasin treatment.
More than two years ago, the same UC Berkeley researchers discovered that injecting the lunasin gene into cancer cells in a culture stopped cell division.
In their latest work, they tested whether the lunasin protein could prevent normal cells from becoming cancerous in both cell cultures and in mice.
In the study, varying doses of lunasin were applied to groups of mice over a period of 19 weeks.
They were compared with a control group that had received no lunasin treatments.
After the mice were exposed to chemical carcinogens, the group that had received the highest lunasin dose of 125 micrograms twice a week had a 70 per cent lower incidence of tumours than the control group.
"In the high dose group, some mice did develop some tumours, but there were fewer tumours per mouse and there was a two-week delay in their appearance compared with the control group," said Ben O. de Lumen, nutritional sciences professor in UC Berkeley's College of Natural Resources and principal investigator of the study.
De Lumen is a member of UC Berkeley's Health Sciences Initiative, a partnership among biomedical sciences and technology programs geared towards advancing research into today's major health problems.
The researchers got clues on how lunasin works through tests in cell cultures.
They showed that lunasin binds to deacetylated histones, a specific form of protein in a cell that helps package the long strands of DNA into tight coils.
Lunasin seems to target cells before these histones undergo acetylation, a crucial step recently linked to cell proliferation and the formation of cancer.
In one of the tests, the cells from a lunasin culture showed an 80 percent lower incidence of transformation into cancer cells compared with non-lunasin cultures after exposure to carcinogens.
"The chemical changes that occur in normal cells before and during cancer formation signal lunasin," said de Lumen.
"We believe lunasin is like a watchdog; it's out there sniffing.
When it sees a normal cell transforming, it gets in there and attacks the cell."
Studies on the health effects of soy products have been increasing over the years.
In 1999, the U.S. Food and Drug Administration allowed manufacturers to use food labels stating that eating 25 grams of soy protein a day may help reduce the risk of heart disease.
Foods must contain at least 6.5 grams of soy protein per serving to qualify for the label.
Full findings are published in the October 15 journal of Cancer Research.