A diet rich in omega-3 polyunsaturated fatty acids (PUFAs) could reduce the risk of colorectal cancer by 74 percent, suggests a new study from Japan.
But high consumption of saturated fatty acids (SFAs) could increase the risk by a whopping 700 percent, said the researchers from the Aichi Cancer Center Hospital and Nagoya University Graduate School of Medicine, Nagoya, Japan.
“We could clearly show decreased and increased risks for colorectal cancer related to PUFAs and SFAs compositions in erythrocyte membranes, respectively,” wrote lead author, Kiyonori Kuriki in the journal Cancer Epidemiology, Biomarkers & Prevention.
Omega-3 has been identified based on evidence that it can aid cognitive function and may help protect the heart against cardiovascular disease. But one area in which the evidence is controversial is the fatty acid's role in reducing the risk of cancer.
The new research investigated the link between the fatty acid compositions of red blood cell membranes (erythrocytes) for 74 people with colorectal cancer (cases) and 221 healthy controls free from cancer. The controls were matched by age and sex.
Dietary intakes were assessed for fish, fat and fatty acid intake, and while no link between meat, fish, fat, and fatty acids in general was observed, the researchers do report a significant association between the docosahexaenoic acid (DHA) concentration in the blood cell membranes and a reduced risk of cancer (74 percent reduction between the highest and lowest concentrations).
Similar beneficial associations were observed for arachidonic acid (AA) and PUFA concentrations, as measured by an accelerated solvent extraction and gas-liquid chromatography (GLC) – risk reduction of 68 and 85 percent, respectively, between the highest and lowest concentrations.
Negative associations, indicating an increase in the risk of colorectal cancer, were observed for red blood cell membrane concentrations of SFA (720 percent increase) and palmitic acid (546 percent) and between the highest and lowest ratio of SFA/PUFA concentrations in the cell membrane (845 percent).
The researchers did not study the underlying mechanism, but Kuriki and co-workers suggest that their results challenge the theory that DHA inhibits the arachidonic acid (AA) cascade that has been linked to cancer formation and cell proliferation.
Metabolism of fatty acids produces compounds called prostaglandins, which can be either pro- or anti-inflammatory. The prostaglandins derived from omega-3 fatty acids are said to be anti-inflammatory and may protect against the development of cancer, while prostaglandins derived from omega-6 fatty acids, like AA, are proposed to be pro-inflammatory.
“Further research is needed to investigate the discrepancy between our findings and the generally accepted role of the AA cascade,” said the researchers.
The researchers concluded: "In conclusion, we could clearly show decreased and increased risks for colorectal cancer related to [omega-3 DHA rich] PUFAs and SFAs compositions in erythrocyte membranes, respectively." DHA and EPA are omega-3 fatty acids commonly found in fish and fish oil. Neptune krill oil is another important source of DHA and EPA.
Kuriki K, Wakai K, Hirose K, Matsuo K, Ito H, Suzuki T, Saito T, Kanemitsu Y, Hirai T, Kato T, Tatematsu M, Tajima K. Risk of colorectal cancer is linked to erythrocyte compositions of fatty acids as biomarkers for dietary intakes of fish, fat, and fatty acids. Cancer Epidemiol Biomarkers Prev. 2006 Oct;15(10):1791-8. PMID: 17035384 [PubMed - in process].