Review links high fish and omega-3 intakes to prevention; high omega-6 intakes blunt the benefits
Omega-6 overload fuels cancer
We've covered many studies that highlight the health risks of America's “omega imbalance”.
For example, see:
You'll find these and more in the Omega-3 / Omega-6 Balance section of our news archive.
Most of the huge excess of omega-6 fats in the American diet comes from cheap vegetable oils (corn, soy, safflower, cottonseed, sunflower) and prepared/packaged foods containing them.
Choices low in omega-6s include olive oil, macadamia nut oil, hi-oleic sunflower oil, hi-oleic safflower oil, and canola oil.
Fish consumption in many of the populations studied was too low to produce the body levels of omega-3s needed for cancer prevention.
The kind of fish consumed – and how it is preserved or cooked – can have a major impact on its potential to lower cancer risk.
- Relatively Low Fish Intake: This was often true even among the “high-intake” part of the studied population. The average American's daily intake of the two key omega-3s in fish – DHA and EPA – is only about 100 mg. However, the authors say that it likely requires omega-3 intakes 10 times higher than that (1000mg daily) to impact COX-2 activity. In most studies, even the heavier fish consumers were unlikely to achieve those omega-3 intake levels.
- Lean, not Fatty Fish. Most participants ate lean fish low in omega-3s. Some studies examined by the authors linked intake of fatty fish with cancer protection, whereas no such link is seen with intake of lean fish. This is consistent with other evidence that the omega-3 fats in fish (DHA and EPA) are primarily responsible for the cancer protection afforded by fish consumption.
- High Vegetable Oil Intake: In many studies, the participant's diets were high in omega-6-rich oils (soy, safflower, corn, sunflower, cottonseed). Omega-6 fats promote COX-2 activity and compete with omega-3s. Thus, a high intake of omega-6 fats raises the intake of omega-3 required for cancer protection. As the authors note, Mediterranean peoples who use olive oil (low in omega-6s) almost exclusively are more likely to show a protective effect from frequent fish consumption.
- Farmed Fish. Some study participants ate lots of farmed tilapia, catfish, or salmon. Because they are fed grains, farmed fish have much higher omega-6 levels, lower omega-3 levels, and a higher omega-6/omega-3 ratio than wild fish.
- Participants often ate breaded, deep-fried fish. Frying breaded fish in omega-6-rich vegetable oils sharply raises its omega-6 content and omega-6/omega-3 ratio, and the oil can contain cancer-promoting compounds created by high frying temperatures. This also explains why diets high in fried fish are linked to higher stroke risk, versus diets high in non-fried fish (e.g., poached, sautéed, baked, broiled, roasted) … see “Fried Fish Seen to Raise Stroke Risk”.)
- Salt-Preserved Fish: In some studies – particularly Asian and Nordic ones – salt-preserved fish was the predominant type consumed, and it commonly contains mutagens that promote cancer.
Agency for Healthcare Research and Quality (AHRQ). Diet High in Omega-3 Fatty Acids Unlikely to Reduce Risk of Cancer. January 24, 2006. Accessed at http://archive.ahrq.gov/news/press/pr2006/o3cancerpr.htm
Agency for Healthcare Research and Quality (AHRQ). Effects of Omega-3 Fatty Acids on Cancer Summary Evidence Report/Technology Assessment: Number 113. Accessed at http://archive.ahrq.gov/clinic/epcsums/o3cansum.htm
Bell GA, Kantor ED, Lampe JW, Kristal AR, Heckbert SR, White E. Intake of long-chain ω-3 fatty acids from diet and supplements in relation to mortality. Am J Epidemiol. 2014 Mar 15;179(6):710-20. doi: 10.1093/aje/kwt326. Epub 2014 Feb 3.
DiNicolantonio JJ, McCarty MF, Chatterjee S, Lavie CJ, O'Keefe JH. A Higher Dietary Ratio of Long-Chain Omega-3 to Total Omega-6 Fatty Acids for Prevention of COX-2-Dependent Adenocarcinomas. Nutr Cancer. 2014 Oct 30:1-6. [Epub ahead of print]
MacLean CH, Newberry SJ, Mojica WA, Khanna P, Issa AM, Suttorp MJ, Lim YW, Traina SB, Hilton L, Garland R, Morton SC. Effects of omega-3 fatty acids on cancer risk: a systematic review. JAMA. 2006 Jan 25;295(4):403-15. Review. Erratum in: JAMA. 2006 Apr 26;295(16):1900.
McCarty MF. Minimizing the cancer-promotional activity of cox-2 as a central strategy in cancer prevention. Med Hypotheses. 2012 Jan;78(1):45-57. doi: 10.1016/j.mehy.2011.09.039. Epub 2011 Oct 15.
Papanikolaou Y, Brooks J, Reider C, Fulgoni VL 3rd. U.S. adults are not meeting recommended levels for fish and omega-3 fatty acid intake: results of an analysis using observational data from NHANES 2003-2008. Nutr J. 2014 Apr 2;13:31. doi: 10.1186/1475-2891-13-31. Erratum in: Nutr J. 2014;13:64.
Saint Luke's Mid America Heart Institute (SLMAHI). Diets High in Long-chain Omega-3 Fatty Acids Shown to Help Prevent Cox-2 Dependent Adenocarcinomas. November 06, 2014. Accessed at http://www.prweb.com/releases/2014/11/prweb12301879.htm