Minimal effect of a low-fat/high soy diet for asymptomatic, hormonally naive prostate cancer patients.

PURPOSE: The effects of a low-fat diet or a low-fat diet with the addition of a soy supplement were investigated in a pilot Phase II study for asymptomatic, hormonally naive prostate cancer patients with rising prostate-specific antigen (PSA) levels. EXPERIMENTAL DESIGN: A two-step intervention was implemented. During step 1 patients were begun on a low-fat diet with a goal to reduce fat intake to 15% of total daily calories. On PSA progression, a soy protein supplement was added to the diet (step 2). The primary end point was PSA reduction by 50%. Secondary end points were PSA doubling time and time to progression (TTP). Serum was analyzed for changes in the sex hormone and insulin-like growth factor (IGF-I) axes. RESULTS: Among 18 evaluable patients, (median follow-up on study 10.5 months), no patient on either step had a PSA reduction by 50% at any time. There was a trend toward a longer PSA doubling time (P = 0.06) and a prolongation in estimated median TTP of approximately 3 months (P = 0.018) during step 2 compared with step 1 of the study. During step 1, free testosterone levels decreased by 5% (P < 0.01), and during step 2, IGF-I levels increased by 22% (P = 0.02). CONCLUSIONS: A low-fat diet with the subsequent addition of a soy supplement did not result in a significant decline in PSA levels. The addition of soy protein had a modest effect on TTP. A potentially undesirable effect associated with the administration of soy was an increase in IGF-I serum levels.

Serum levels of insulin-like growth factor-1 and insulin-like growth factor-1 binding proteins after radical prostatectomy.

PURPOSE: Elevated serum levels of insulin-like growth factor-1 (IGF-1) have been consistently shown to be a risk factor for prostate cancer. Alterations in serum IGF-1 binding proteins 1 to 3 have also been associated with prostate cancer risk. A potentially important complication in these studies is that prostate tissue, perhaps especially malignant prostate tissue, may secrete IGF-1 and its binding proteins into serum. In fact, it is possible that altered levels of these proteins observed in subjects at risk for prostate cancer are the result of prostate cancer rather than related to its cause. MATERIALS AND METHODS: The contribution of prostate cancer to serum levels of IGF-1 and IGF-1 binding proteins was determined by analyzing serum samples from 86 patients with prostate cancer 2 weeks before and 8 weeks after radical prostatectomy. Preoperative and postoperative values for IGF-1 and its 3 major binding proteins were analyzed using univariate and multivariate analysis models. RESULTS: On univariate analysis significant increases and not decreases in IGF-1, IGF binding protein-1 and 3 were observed after prostatectomy. On multivariate analysis a significant post-prostatectomy increase was observed for IGF-1 binding proteins 1 and 3 but the increase in IGF-1 was not significant. CONCLUSIONS: Increased levels of IGF-1 and IGF-1 binding proteins were unexpected after prostatectomy. This result makes it extremely unlikely that secretion from the prostate, even if it contains cancer, affects serum levels of these proteins. The implication of these findings is that endocrine production of IGF-1 is a factor in prostate cancer risk. Therefore, strategies to lower serum IGF-1 may be potentially useful.