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Clin Cancer Res. 2003 Aug 15;9(9):3282-7.

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

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  • 1Divisions of Hematology/Oncology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.

Abstract

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.

PMID:
12960113
[PubMed - indexed for MEDLINE]
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