Background: Diet may play a key role in the etiology of prostate cancer (PC). Dietary fat restriction (DFR) and flaxseed supplementation (FS) may reduce risk, though results are mixed. We undertook an RCT to test the comparative effects of these dietary regimens on the biology of the prostate and other biomarkers. Methods: PC patients (N=161) scheduled > 21 days prior to prostatectomy were block randomized on race (black vs non-black) and biopsy Gleason sum (<7 vs 7+) to these diets: 1) control; 2) FS (30 g/day); 2) DFR (<20% total energy); or 4) FS+DFR. Blood was drawn upon accrual and prior to surgery and analyzed for prostate specific antigen (PSA), sex hormone binding globulin (SHBG), total testosterone (T), insulin-like growth factor 1 (IGF1), IGF binding protein 3 (IGFBP3), c- reactive protein (CRP), and total and low density lipoprotein cholesterol (TC & LDL-C). Proliferation (MIB-1) and apoptosis (TUNEL) was assessed in the malignant and benign prostate. Results: Complete data were collected on 93% of the sample; mean length on protocol was 30 days. Median MIB-1 positive (+) cells/total nuclei ratios were: 1=2.38;2=1.71;3=2.93;4=1.58. Primary analyses suggest a significant protective effect (p=0.016) of FS. Secondary analyses of MIB-1 + nuclei (controlling for total cell counts) show increased proliferation with DFR (p=.017), and a significant interaction with FS and DFR (p<.0001). No differences were observed between groups with regard to PC apoptosis, and histology of benign tissue. No differences were observed between arms for PSA, SHBG, T, IGF1, IGFBP3 or CRP. Significant differences were observed between arms for changes in serum lipids and body weight [ΔTC = +9/-26/-46/-37 mg/dL; ΔLDLC = -14/-17/-29/-21 mg/dL and Δ weight = +0.3/-1.3/-1.7/-1.1 kg (p's<.05)]; effects were attributed to DFR and not FS. Side effects did not differ between arms Conclusions: Preliminary findings suggest that FS is safe and exerts a protective effect (main effect or via interaction with DFR) on PC. Data also provide further support of DFR for cardiovascular disease, though its role in PC is less clear.
Further controlled analyses and additional studies are needed to confirm findings.