Men with prostate cancer had a lower risk of dying of the disease as consumption of vegetable fat increased, data from a large prospective study suggested.

Prostate cancer mortality was almost 50% lower in men who consumed the most vegetable fat versus those who consumed the least. Intake of vegetable fat also had an inverse association with all-cause mortality during a median follow-up 8.4 years, as reported online in JAMA Internal Medicine.

"Among men with nonmetastatic prostate cancer, replacing carbohydrates and animal fat with vegetable fat may reduce the risk of all-cause mortality," Erin L. Richman, ScD, of the University of California San Francisco, and co-authors concluded. "The potential benefit of vegetable fat consumption for prostate cancer-specific outcomes merits further research."

Studies of the relationship between dietary fat and prostate cancer have produced mixed results. More consistent findings have come from studies of fat intake and advanced prostate cancer, suggesting more relevance to disease progression, the authors noted in their review of background information.

The relationship of post-diagnostic fat intake to prostate cancer progression and overall survival has attracted little attention in the literature. Three prospective case-only studies showed that saturated fats are associated with an increased risk of prostate cancer death, and marine fatty acids and monounsaturated fat are associated with lower risk. However, all three studies involved only a small number of cancers, were based on self-reported dietary intake, and involved unscreened patient populations.

In an effort to gain more insight into the relationship of fat intake to fatal prostate cancer and all-cause mortality, Richman and colleagues searched the database of the Health Professionals Follow-up Study, which has enrolled 51,529 male healthcare professionals ages 40 to 75 since 1986.

At baseline, study participants provided information about diet, medication, height, weight, smoking, and physical activity and updated the information in follow-up surveys every 2 years. In 1994, investigators added prostate-specific antigen (PSA) screening behaviors to the survey.

Richman and colleagues limited their search to men who were cancer free at baseline and were diagnosed with nonmetastatic prostate cancer during 1986 to 2010. They excluded men who reported consuming <800 or >4,200 kcal/d, had incomplete data on the baseline questionnaire, or whose prostate cancer records did not include clinical stage or treatment. The final analysis involved 4,577 men.

The investigators grouped the men into quintiles of fat intake, further separated into animal fat, vegetable fat, saturated fat, monounsaturated fat, polyunsaturated fat, and trans fat ."Men who consumed more vegetable fat after diagnosis had a lower risk of lethal prostate cancer," the authors said. "Replacing 10% of calories from carbohydrates with vegetable fat was associated with a 29% lower risk of lethal prostate cancer. The magnitude of the association was similar, but not statistically significant, when animal fat was replaced with vegetable fat.

Again comparing highest and lowest quintiles of fat intake, the investigators found that unadjusted all-cause mortality had a lower risk of all-cause mortality," the authors said. "Replacing 10% of calories from carbohydrates with vegetable fat was associated with a 26% lower risk of death.

The only known modifiable risk factor associated with prostate cancer mortality: obesity. Avoiding obesity is essential," Stephen J. Freedland, MD, of Duke University, said in an accompanying editorial. "Exactly how this should be done remains unclear, although the data by Richman et al. suggest that substituting healthy foods (i.e., vegetable fats) for unhealthy foods (i.e., carbohydrates) may have a benefit.