Researchers from UCSF and the Preventive Medicine Research Institute in Sausalito were able to modify major cancer genes with exercise, stress reduction and a very low-fat diet.
Men with early prostate cancer ate a vegetarian diet with tofu, protein supplements and 10 percent fat for three months.
The DNA changes could benefit many kinds of cancer patients, including those with breast cancer, the authors said.
Most doctors, however, want to see a larger study before they sign off on the restrictive diet.
The study is published in the proceedings of the National Academy of Sciences.