“Among men with nonmetastatic prostate cancer, replacing carbohydrates and animal fat with vegetable fat may reduce the risk of all-cause mortality,” according to a prospective study of 4,577 men with nonmetastatic prostate cancer in the Health Professionals Follow-up Study. Vegetable fat intake after diagnosis of prostate cancer was also associated with a lower risk of lethal prostate cancer, defined as distant metastases or death due to prostate cancer.
“Replacing 10% of calories from carbohydrates with vegetable fat was associated with a 29% lower risk of lethal prostate cancer” (hazard ratio [HR] = 0.71; 95% confidence interval [CI] = 0.51–0.98; P = .04), the researchers reported. “The magnitude of the association was similar, but not statistically significant, when animal fat was replaced with vegetable fat” (HR = 0.76; 95% CI = 0.52–1.10; P = .14). The results were published online by JAMA Internal Medicine.
Men included in the analysis had to be free of cancer (except nonmelanoma skin cancer) when the study was initiated in 1986 and have a diagnosis of nonmetastatic prostate cancer between then and 2010. Study participants reported medical diagnoses, medication, weight, height, smoking, and physical activity at baseline and then every 2 years, and completed food frequency questionnaires at baseline and then every 4 years. The food frequency questionnaire “asked men to report their usual intake of approximately 130 foods and beverages during the previous year. In addition, they were asked to report fried food consumption, type of cooking fat, and whether visible fat on meat was consumed,” the investigators explained.
At a median follow-up of 8.4 years, 315 events of lethal prostate cancer and 1,064 deaths occurred. “The primary causes of death were cardiovascular disease (31.2%), prostate cancer (21.3%), and other cancers (20.6%),” the researchers reported.
“Crude rates of lethal prostate cancer (per 1,000 person years), comparing the highest and lowest quintiles for intake of each of the fats, were 7.6 vs 7.3 for saturated, 6.4 vs 7.2 for monounsaturated, 5.8 vs 8.2 for polyunsaturated, 8.7 vs 6.1 for trans, 8.3 vs 5.7 for animal, and 4.7 vs 8.7 for vegetable fat.” The rates of all-cause mortality were 28.4 vs 21.4 for saturated, 20.0 vs 23.7 for monounsaturated, 17.1 vs 29.4 for polyunsaturated, 32.4 vs 17.1 for trans, 32.0 vs 17.2 for animal, and 15.4 vs 32.7 for vegetable fat.
“Red meat and poultry with skin were major sources of monounsaturated and polyunsaturated fat in our study population,” the authors reported, “and these foods are also sources of heme iron and heterocyclic amines, which may increase the risk of aggressive prostate cancer.” Among the top food sources of vegetable fats in the study population were oils and nuts. “Consumption of these foods increases plasma antioxidants and reduces circulating insulin, low-density lipoprotein cholesterol, inflammatory markers, and markers of oxidative stress, all of which may affect prostate cancer progression,” the investigators noted.
Further Research Needed
“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,” the researchers concluded. “The potential benefit of vegetable fat for prostate cancer–specific outcomes merits further research.”
In an invited commentary, Stephen J. Freedland, MD, of Duke University Medical Center, Durham, North Carolina, noted that “in the absence of randomized trial data, it is impossible to use these data as ‘proof’ that vegetable intake lowers prostate cancer risk, and the authors have carefully avoided such statements.”
Dr. Freedland continued, “When counseling patients, I remind them that obesity is the only known modifiable risk factor linked with prostate cancer mortality to date. Thus, avoiding obesity is essential. Exactly how this should be done remains unclear,” he wrote, although the study data “suggest that substituting healthy foods (ie, vegetable fats) for unhealthy foods (ie, carbohydrates) may have a benefit. Determining whether this benefit is due to reduced consumption of carbohydrates or greater intake of vegetables will require future prospective randomized trials,” he concluded. ■
Richman EL, et al: JAMA Intern Med. June 10, 2013 (early release online).
Freedland SJ: JAMA Intern Med. June 10, 2013 (early release online).