Meta-analysis Reveals “Heart Healthy Omega-6 Fat” Ups Risk of Heart Disease
Bottom Line: The research upon which the American Heart Association based their "eat-your-omega-6-fat" advisory, is fatally flawed, according to the results of a meta-analysis study, which showed that a steady diet of omega-6 polyunsaturated fatty acids increases the risk of heart disease and death, especially for women [1]. British J Nutr. Dec 2010.
Background: ln 2009 the American Heart Association (AHA) published a health advisory touting the benefits of eating a high omega-6 polyunsaturated fatty acids (PUFA), and warned that eating less than 5% of calories from omega-6 PUFA would be hazardous to heart health. [2-3].
The conclusion of AHA's advisory were seriously questioned in part, because of their failure to:
- Distinguish the types of PUFA used in studies, which also substantially increased omega-3 fats, which are a PUFAs.
- Include relevant trials with unfavorable results.
- Exclude poorly designed studies.
Notably, these studies did not provide or differentiate the specific fatty acid content of the intervention diets. (Yet the AHA recommended to specifically increase omega-6 PUFA).
These flaws prompted a team of National Institutes of Health (NIH) scientists to re-evaluate the data, using techniques resembling a scholarly forensic investigation.
Design: Nine randomized controlled trials (the gold standard of study design), were identified, which met the criteria of having an intervention diet high in PUFA at the expense of other fat and also reported clinical outcome data.
Next came the detective work. Most of the studies did not provide omega-3 data--it was just lumped together in the PUFA category. In order to track down the missing fatty acid data, (many of these studies were conducted over 40 years ago), they had to dig through newspaper archives, public records, scientific proceedings from national conferences and correspond with the study investigators (or their colleagues, if deceased).
Once the fatty acid data was collected, they were segregated into two categories:
- Mixed Diet (containing both omega-6 and omega-3 polyunsaturated fatty acids.)
- Omega-6 Specific Diet
Then the data was pooled to evaluate the the effect of the Omega-6 Specific Diet, compared to the effect of the Mixed Diet, on clinical outcomes. They also evaluated the potential confounding role of trans fatty acids.
Results: Here's what they found when evaluating the composition of the intervention diets.
- Only three of the nine so-called PUFA studies were "pure" omega-6 intervention trials, which upped omega-6, without a concurrent rise in dietary omega-3. Combined, these three studies had 9,500 participants.
- Four of the studies increased both the omega-3 PUFA (EPA and DHA) and omega-6 PUFA, which totaled over 1,700 participants. Notably, the researchers discovered that the Oslo Diet-Heart Study provided about 5 grams of EPA and DHA per day to the intervention group. (That's equivalent to about 16 fish oil capsules).
- The control diets had a mean estimated trans fatty acid content of 3% (a significant confounding factor, which unquestionably increases risk of heart disease).
Heart Disease and Death Outcomes
When the effects of the Omega-6 Specific Diet were compared to the Mixed Omega 6/omega-3 PUFA, the following health outcomes were discovered:
Omega-6 Specific Diet:
- Increased risk of heart disease and death, compared to the Mixed Diet intervention studies.
- The relative risk of cardiac death increased by 28%.
- Increased the risks of all relevant cardiovascular outcomes.
- There was only one study with women, which showed significant harm.
The Mixed Omega-6/Omega-3 Diet:
- There was 8% risk reduction of death from all causes.
- There was 22% risk reduction from heart disease death.
Study Quote:"The increased cardiovascular heart disease risks from omega-6 specific PUFA diets in our meta-analysis may be underestimated as omega-6 PUFA also replaced substantial quantities of trans fatty acids." An accompanying editorial applauded the “extensive detective work” by the NIH research team, led by Christopher Ramsden [4]
Commentary: There is more to this story. In my next post, I'll describe what went on behind the scenes, as three NIH scientists from this study, tried to get letters to the editor published in the AHA's scientific journal, Circulation, in response to their omega-6 advisory. (I was actually a participant and witness).
Links to Sources
[1] Christopher E. Ramsden,Joseph R. Hibbeln,Sharon F. Majchrzak and John M. Davis (2010).Omega-6 Fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials. British Journal Nutrition. Dec 2010; 104(11): pp 1586-1600.
[2] Harris WS et al. Omega-6 Fatty Acids and Risk for Cardiovascular Disease. A Science Advisory From the American Heart Association Nutrition Subcommittee of the Council on Nutrition, Physical Activity, and Metabolism; Council on Cardiovascular Nursing; and Council on Epidemiology and Prevention. Circulation published January 26, 2009. [Free Full Text.]
[3] American Heart Asssociation News Release. Omega-6 fatty acids: Make them a part of heart-healthy eating DALLAS, Jan. 27, 2009. [Free full Text]
[4] Philip C. Calder (2010).The American Heart Association advisory on n-6 fatty acids: evidence based or biased evidence? British Journal Nutrition. Dec 2010; 104(11): pp 1575-1576.[Abstact]
Copyright © 2010 by Evelyn Tribole, MS, RD Published at http://www.EvelynTribole.com
