Thirty two relevant studies were identified: nine RCTs with a placebo or control arm (n=416, range 18 to 90); and 23 other studies that were non-randomised and uncontrolled (n=650, range 9 to 71). The nine RCTs were the focus of the review (further details of all included studies available in the paper). Four of the nine RCTs were double-blind. Two of the double-blind RCTs were of cross-over design. Loss to follow-up (where reported) ranged from 0 to 22%.
Dietary interventions:
Low fat diet (one RCT). A low fat vegan diet gave a significant 4% decrease in PSA compared to a 6% increase in PSA in controls (p=0.02).
Fortified margarine (one RCT). A diet that contained margarine fortified with vitamin E gave no difference in total PSADT, but a significant increase in free PSADT based on a doubling time of 68 weeks in the intervention group and a half-life of 13 weeks in controls (p=0.02), which signified a reduction in risk.
Phytoestrogen-rich diets (four RCTs). The four dietary intervention RCTs that used phytoestrogens included the low fat vegan diet study discussed above. Only one RCT, where the diet was supplemented with soy grits, had a significant result, a 12.7% decrease in PSA compared to a 40% increase in wheat controls (p=0.02).
Dietary supplement interventions:
Lycopene (three RCTs). One RCT that used 4mg lycopene appeared to give a significantly higher mean PSA in the intervention group compared to controls, although it was unclear whether this comparison was carried out within or between groups. This RCT was the only study with a survival outcome and found a reduction in mortality associated with lycopene supplementation in men with metastatic prostate cancer and orchiectomy. Another study used a supplement of 30mg lycopene per day and found no significant result. A crossover RCT that used 15mg lycopene plus numerous other dietary supplements found a significant increase in free PSADT based on 1,150 versus 445 days (2.6 fold, p<0.04) for the supplemented versus placebo-controlled periods.
Phytoestrogens (two RCTs). Studies that used soy isoflavones of 100mg or less included an RCT of fortified margarine, which gave a significant increase in free PSADT compared to controls, and a cross-over RCT of multiple supplements, which also gave a significant increase in free PSADT ( p<0.04) over the supplemented period.