We previously reported that a 4-6 week low-fat fish oil (LFFO) diet did not affect serum IGF-1 levels (primary outcome) but resulted in lower omega-6 to omega-3 fatty acid ratios in prostate tissue and lower prostate cancer proliferation (Ki67) as compared to a Western diet (WD).

In this post-hoc analysis, the effect of the LFFO intervention on serum pro-inflammatory eicosanoids, LTB4 and 15(S)-HETE, and the cell cycle progression (CCP) score were investigated. Serum fatty acids and eicosanoids were measured by gas chromatography and ELISA. CCP score was determined by RT-PCR. Associations between serum eicosanoids, Ki67, and CCP score were evaluated using partial correlation analyses. BLT1 (LTB4 receptor) expression was determined in prostate cancer cell lines and prostatectomy specimens.

Serum omega-6 fatty acids and 15(S)-HETE levels were significantly reduced, and serum omega-3 levels were increased in the LFFO group relative to the WD group, whereas there was no change in LTB4 levels. The CCP score was significantly lower in the LFFO compared to the WD group. The 15(S)-HETE change correlated with tissue Ki67 (R=0.48; p<0.01) but not with CCP score. The LTB4 change correlated with the CCP score (r=0.4; p=0.02) but not with Ki67. The LTB4 receptor BLT1 was detected in prostate cancer cell lines and human prostate cancer specimens.

In conclusion, a LFFO diet resulted in decreased 15(S)-HETE levels and lower CCP score relative to a WD. Further studies are warranted to determine whether the LFFO diet anti-proliferative effects are mediated through the LTB4/BLT1 and 15(S)-HETE pathways.