A low-fat, high-fibre diet heavy in fruits and vegetables has no impact on PSA levels in men over a four-year period, and does not affect the incidence of prostate cancer, according to a study by researchers at Memorial Sloan-Kettering Cancer Center, the National Cancer Institute, and seven other US research centres.
The four-year, randomised study examined whether a short-term dietary intervention would impact serum prostate-specific antigen (PSA) levels in men - an important marker for the onset and development of prostate cancer. Results of previously conducted observational studies have differed on whether a low-fat, high-fibre diet protects against prostate cancer.
"This is a rigorous and randomised study that provides valuable data which previously did not exist," said Dr Moshe Shike, lead author of the study and director of the Memorial Sloan-Kettering Cancer Prevention Program. "Although this study found no protective effect over four years, it is possible that a healthy dietary pattern sustained over many more years will have an inhibitory effect on prostate cancer."
In the study, 1,350 men without prostate cancer were randomly assigned to the dietary intervention or a control group. The 689 men in the intervention arm received intensive nutrition counselling to consume a diet low in fat and high in fruit, vegetables and fibre, while the 661 men assigned to the control arm received a standard brochure detailing healthy dietary recommendations.
To determine the change in PSA levels over time, researchers measured the PSA levels in both groups at the beginning of the study, and then annually for four years.
After four years, there was no marked difference in PSA levels between the two groups, and the proportion of patients with raised PSA levels was equal at each point over the four years. Incidence of prostate cancer during the study was also statistically similar between the two groups: 19 patients in the control arm and 22 in the intervention arm.
According to Dr Shike, the intervention's failure to impact PSA levels should not be viewed as definitive evidence that diet has no preventive impact on prostate cancer.
"The PSA is only a surrogate marker for prostate cancer, and it is possible that diet could impact the occurrence and growth of prostate cancer without drastically affecting PSA levels." The study had too few participants and was too short to determine the impact of diet on the actual incidence of prostate cancer.
According to researchers, limiting calories and eating a fruit- and vegetable-enriched low-fat diet - with fat intake making up 20-25 per cent of a person's daily intake of calories - should continue to be upheld as part of a healthy lifestyle.