By substituting healthy vegetable fats -- such as olive and canola oils, nuts, seeds and avocados -- for animal fats and carbohydrates, men with the disease had a markedly lower risk of developing lethal prostate cancer and dying from other causes, according to the study.

The research, involving nearly 4,600 men with non-metastatic prostate cancer, could help with the development of dietary guidelines for men with the disease. While prostate cancer affects millions of men around the world, little is known about the relationship between patients' diets following their diagnosis and progression of the disease.

The study was published online on June 10 in JAMA Internal Medicine.

"Consumption of healthy oils and nuts increases plasma antioxidants and reduces insulin and inflammation, which may deter prostate cancer progression," said lead author Erin L. Richman, ScD, a post-doctoral scholar in the UCSF Department of Epidemiology and Biostatistics.

"The beneficial effects of unsaturated fats and harmful effects of saturated and trans fats on cardiovascular health are well known," Richman said. "Now our research has shown additional potential benefits of consuming unsaturated fats among men with prostate cancer."

Analyzing Intake of Fats from Various Sources

Nearly 2.5 million men in the United States currently live with prostate cancer and another quarter-million men are expected to be diagnosed this year. One in six men in the U.S. will be diagnosed with the disease during their lifetime.

In recent years, evidence has indicated that diet might be an important way for men with prostate cancer to take an active role in determining their disease outcome and overall health. Research on advanced prostate cancer has suggested that fat intake may be relevant to disease progression, but this is the first study to examine fat consumption post-diagnosis in relation to risk of lethal prostate cancer and overall survival.

The new paper analyzed intake of saturated, monounsaturated, polyunsaturated and trans fats as well as fats from animal and vegetable sources.

The data were derived from the Health Professionals Follow-up Study, which began in 1986 and is sponsored by the Harvard School of Public Health and is funded by the National Cancer Institute.

The fat intake study involved 4,577 men who had been diagnosed with non-metastatic prostate cancer between 1986 and 2010. During the study timeframe, 1,064 men died, primarily from cardiovascular disease (31 percent), prostate cancer (21 percent) and other cancers (nearly 21 percent).

The authors uncovered a striking benefit: Men who replaced 10 percent of their total daily calories from carbohydrates with healthy vegetable fats had a 29 percent lower risk of developing lethal prostate cancer and a 26 percent lower risk of dying from all causes.

More Study Needed on Potential Benefits of Healthy Fats

Adding a single serving of oil-based dressing a day (one tablespoon) was associated with a 29 percent lower risk of lethal prostate cancer and a 13 percent lower risk of death, the authors found. And adding one serving of nuts a day (one ounce) was associated with an 18 percent lower risk of lethal prostate cancer and an 11 percent lower risk of death.

The study adjusted for factors such as age, types of medical treatment, body mass index, smoking, exercise and other dietary factors, elevated blood pressure, cholesterol at the time of prostate cancer diagnosis and other health conditions.

The researchers say further research is needed on the potential benefits of healthy fats among prostate cancer patients.

"Overall, our findings support counseling men with prostate cancer to follow a heart-healthy diet in which carbohydrate calories are replaced with unsaturated oils and nuts to reduce the risk of all-cause mortality," said Richman.

The senior author is June M. Chan, ScD, a professor in the UCSF Department of Epidemiology and Biostatistics and the Department of Urology. Co-authors include Stacey A. Kenfield, ScD, an assistant adjunct professor in the UCSF urology department. The research was conducted with collaborators at the Harvard School of Public Health, Harvard Medical School, and Brigham and Women's Hospital.