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


METHODS
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.
Spentzos
Dimitrios
D
Divisions of Hematology/Oncology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.
Mantzoros
Christos
C
Regan
Meredith M
MM
Morrissey
Mary Ellen
ME
Duggan
Stephen
S
Flickner-Garvey
Stacy
S
McCormick
Heather
H
DeWolf
William
W
Balk
Steve
S
Bubley
Glenn J
GJ
D000368:Aged; D050260:Carbohydrate Metabolism; D004032:Diet; D004041:Dietary Fats / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D017430:Prostate-Specific Antigen / Q000096:biosynthesis* / Q000097:blood; D011471:Prostatic Neoplasms / Q000178:diet therapy*; D030262:Soybean Proteins / Q000494:pharmacology*; D013739:Testosterone / Q000097:blood; D013942:Thymine Nucleotides; D016896:Treatment Outcome
D004041:Dietary Fats; D030262:Soybean Proteins; D013942:Thymine Nucleotides; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D017430:Prostate-Specific Antigen; C024157:thymidine 5'-triphosphate