A recently published report shows that high intake of the dietary omega-6 polyunsaturated fatty acid (PUFA) arachidonic acid could increase your risk for colorectal adenoma (precancerous polyps that can develop into cancer).
Colorectal cancer is the second most common type of cancer, accounting for 13% of all cancers.1 With improved endoscopic screening for adenomas, the incidence of colorectal cancer in older adults has declined marginally; however, its incidence in adults under 50 years of age is increasing in Canada and the United States. Notably, modifiable lifestyle factors, such as physical activity, obesity, smoking, and processed and red meat consumption, can increase your risk for colorectal cancer.
It has been shown in animal models that intake of the omega-6 PUFA arachidonic acid is associated with a higher risk for colorectal cancer, whereas omega-3 PUFAs protect against the disease.2,3 However, observational studies about the role of omega-3 PUFAs in cutting colorectal adenoma risk have produced inconsistent results. Importantly, many of these studies used questionnaires and participant reported data to assess omega-3 PUFA intake, which could have resulted in these inconsistencies.
However, a recent study assessed omega-3 PUFA intake by determining the content of these fatty acids in the red blood cell (RBC) membranes of the study participants.4 The results of this study were published in the British Journal of Nutrition in June 2017. The study was designed to assess links between RBC PUFA content and non-advanced or advanced adenomas in participants who were in the 40–75 year age group and had either single small adenomas, multiple small adenomas, or advanced adenomas. A total of 681 individuals with tubular adenomas, 223 with advanced adenomas and 835 polyp-free controls were analyzed.
Data analysis showed that individuals with adenoma were more likely to be older, more likely to drink alcohol and smoke, more likely to be menopausal, and more likely to have lower educational levels than controls. Higher RBC membrane levels of the omega-6 PUFAs linoleic acid and di-homo-γ-linolenic acid were not associated with a higher risk for adenoma. Adenoma risk increased, however, with increasing amounts of arachidonic acid in the RBC membrane; the risk was even higher for advanced adenomas.
By contrast, individuals with the highest membrane levels of the omega-3 PUFA docosapentaenoic acid were at a significantly lower risk for adenoma compared to individuals who had the lowest levels. A reduction in the risk for advanced adenoma was seen with increasing levels of the omega-3 PUFA eicosapentaenoic acid.
A notable limitation of the study was that although determining the PUFA content of the RBC membranes gave the researchers a window to access to dietary information of the preceding few months, the initiation and development of the adenomas themselves probably took several years. Another notable limitation was the focus on adenomas, less than 5% of which progress to cancer.
Overall, the study’s findings suggest that moderating the consumption of arachidonic acid (found in poultry, red meat, fish, and eggs) and increasing the consumption of long chain omega-3 PUFAs (found in fatty fish, krill, and microalgae) could cut your risk for colorectal adenoma and cancer. Meanwhile, the results of other controlled trials examining the role of eicosapentaenoic acid in colorectal adenoma prevention are awaited.5 These could provide new biomarkers for determining the efficacy of eicosapentaenoic acid intervention in colorectal adenoma prevention as well as provide fresh insights into its mechanism of action.
Written by Usha B. Nair, Ph.D.
- Colorectal Canada Canada. 2016 Canadian Cancer statistics. http://www.colorectal-cancer.ca/en/just-the-facts/colorectal/. Accessed July 10, 2017.
- Reddy BS. Omega-3 fatty acids in colorectal cancer prevention. Int J Cancer.2004 Oct 20;112(1):1-7. Review. PubMed PMID: 15305369.
- Cockbain AJ, Toogood GJ, Hull MA. Omega-3 polyunsaturated fatty acids for the treatment and prevention of colorectal cancer. Gut. 2012 Jan;61(1):135-49. doi:10.1136/gut.2010.233718. Epub 2011 Apr 13. Review. PubMed PMID: 21490374.
- Rifkin SB, Shrubsole MJ, Cai Q, Smalley WE, Ness RM, Swift LL, Zheng W, Murff HJ. PUFA levels in erythrocyte membrane phospholipids are differentially associated with colorectal adenoma risk. Br J Nutr. 2017 Jun 29:1-8. doi:10.1017/S0007114517001490. [Epub ahead of print] PubMed PMID: 28660850.
- Hull MA, Sandell AC, Montgomery AA, Logan RF, Clifford GM, Rees CJ, Loadman PM, Whitham D. A randomized controlled trial of eicosapentaenoic acid and/or aspirin for colorectal adenoma prevention during colonoscopic surveillance in the NHS Bowel Cancer Screening Programme (The seAFOod Polyp Prevention Trial): study protocol for a randomized controlled trial. Trials. 2013 Jul 29;14:237. doi:10.1186/1745-6215-14-237. PubMed PMID: 23895505; PubMed Central PMCID: PMC3733694.