Risks and benefits of omega 3 fats for mortality, cardiovascular disease, and cancer: systematic review

Excess Omega-6 Fats Thwart Health Benefits from Omega-3 Fats

27 March 2006

Conducting a meta-analysis study on the effectiveness of omega-3 fats for mortality, cardiovascular disease and cancer, without considering the impact of excess omega-6 fat in the diet, is akin to reviewing the efficacy of a healthy diet without factoring the effects of smoking.

Excess omega-6 fats interfere with the health benefits of omega-3 fats because they compete for the same rate-limiting enzymes. A high proportion of omega-6 to omega-3 fat in the diet shifts the physiological state of the body toward the pathogenesis of many diseases: prothrombotic, proinflammatory and proconstrictive (1).

Chronic excessive production of omega-6 eicosanoids is associated with heart attacks, thrombotic stroke, arrhythmia, arthritis, osteoporosis, inflammation and cancer. Furthermore, coronary heart disease mortality has been demonstrated to be proportional to plasma levels of long chain omega -6 fat. (2)

Prior to industrialization, no population has been exposed to the current high levels of omega-6 polyunsaturated fats in westernized diets. Today we eat fat that did not exist 100 years ago, such as cottonseed oil (3). Humans evolved on a diet with a balanced ratio of omega-6 to omega-3 fats of about 1:1. Today, that ratio in westernized countries is near 17:1.

The Greenland Inuit Eskimos are famous for their high omega-3 fat diet, but just as importantly, their diet was also low in omega-6 fat. The Lyon Diet Heart study illustrated the significant impact of a Mediterranean diet, with a striking reduction in all-cause mortality and coronary heart disease; this diet was low in omega-6 fat (4).

Cultures that suddenly increase their omega-6 fat intake experience markedly higher mortality rates and health problems. When Okinawans tripled their omega-6 fat intake, they experienced a rise in cancer and cardiovascular disease, which Japanese researchers called “excess linoleic acid syndrome” (5). Notably, this syndrome occurred in the presence of consuming fatty fish.

Israel embraced a high polyunsaturated fat diet (at the expense of saturated fats). Consequently, they now have one of the highest omega-6 fat intakes in the world, along with an unexpected high incidence of chronic western diseases, which researchers term the “Israeli paradox” (6).

Eating an adequate amount of long chain omega-3 fats, whether through regular fish consumption or fish oil supplements is only half of the health picture. Omega-3 fats provide little if any benefit if there are excessive dietary omega-6 fats. It’s puzzling that the authors did not address this issue as a limitation of their study, especially when the international scientific community has published guidelines addressing the need to balance omega -6 and omega-3 fats, by decreasing the former while increasing the latter (7).

1. Simopoulus, AP and Cleland LG. Omega-6/Omega-3 Essential Fatty acid ratio: the scientific evidence. World Review of Nutrition and Dietetics. (2003): 92:1-174.

2. Lands EM. Dietary fat and health: the evidence and the politics of prevention. Annal New York Academy of Sciences (2005). 1055:179-192.

3.Cordain, L et al. Origins and evolution of the Western diet: health implications for the 21st century. American Journal of Clinical Nutrition (2005).81:341-354.

De Lorgeril et al. Mediterranean diet, traditional risk factors, and the rate of cardiovascular complications after myocardial infarction; final report of the Lyon Diet Heart Study. Circulation (1999)99;779-785.

Okuyama, H et al. Dietary fatty acids—the n-6/n-3 balance and chronic elderly diseases: excess linoleic acic and relative n-3 deficiency syndrome seen in Japan. Prog. Lipid. Res (1997); 35(4):409-457.

Dubnov G. and Berry EM. Omega-6/omega-3 fatty acid ratio: The Israeli Paradox. World Review of Nutrition and Dietetics. (2003):92:81-91.

Simopoulos AP, Leaf A, Salem Jr N. Workshop statement on the essentiality of and recommended dietary intakes for omega-6 and omega-3 fatty acids. Prostaglandins, Leukot Essential Fatty Acids (2000) 63:119-121.

Competing interests: None declared

Competing interests: None declared

Evelyn f Tribole, Consulting Nutritionist

15615 Alton Pkwy, Suite 450, Irvine, CA 92618 USA

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