PSA (prostate-specific antigen) levels are commonly used to screen for prostate cancer and for tracking the disease after its diagnosis. The findings therefore lend support to epidemiologic evidence suggesting that soy may reduce the risk of prostate cancer development and progression.
Prostate cancer is now the second-leading cause of cancer death in men and affects more than 500,000 men worldwide every year.
The study carried out at Australia's Monash University tested the effects of a specially manufactured bread containing 50 g of heat-treated soy grits or 50 g of heat-treated soy grits and 20 g of linseed. Some funding was provided by George Weston Foods.
A group of 29 men diagnosed with prostate cancer and scheduled to undergo a radical prostatectomy were randomized to receive four slices daily of either the soy-rich bread, the bread with both soy and linseed or a normal wheat-based bread.
The daily diet containing soy favourably influenced PSA levels in the patients after just one month, report the researchers in the September issue of Urology (vol 64, issue 3, pp510-5). Adding soy to the diet resulted in a 13 per cent drop in total PSA levels in men with prostate cancer.
"This work provides some evidence to support epidemiologic studies claiming that male populations who consume high phytoestrogen diets have a reduced risk of prostate cancer development and progression," write the authors.
It also highlights the advantages to formulators adding soy to their products. According to Mintel, in the first half of 2004, almost 500 new soy protein products were introduced in the United States. The ingredient is also being used increasingly in Europe.
Earlier this year UK bread maker Allied Bakeries introduced a soy-enriched bread, marketed at consuemrs looking to lower cholesterol and improve heart health.