Susan Allport

February 19, 2013

For those who have been following the valiant attempts of certain scientists to clarify the differing health effects of Omega-3s and Omega-6s, here's an important development: the publication by NIH researchers of new data from the Sydney Diet Heart Study.

Here's the abstract:

Use of dietary linoleic acid for secondary prevention
of coronary heart disease and death: evaluation of
recovered data from the Sydney Diet Heart Study and
updated meta-analysis
OPEN ACCESS
Christopher E Ramsden clinical investigator 1 2, Daisy Zamora epidemiologist 2, Boonseng
Leelarthaepin retired, original study investigator 3, Sharon F Majchrzak-Hong research chemist 1,
Keturah R Faurot epidemiology doctoral candidate2, Chirayath M Suchindran senior biostatistician4,
Amit Ringel guest researcher 1, John M Davis professor 5, Joseph R Hibbeln senior clinical
investigator 1
1Laboratory of Membrane Biophysics and Biochemistry, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda,
MD 20892, USA; 2Department of Physical Medicine and Rehabilitation, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill,
NC, USA; 3University of New South Wales, Sydney, Australia; 4Department of Biostatistics, School of Public Health, University of North Carolina at
Chapel Hill, Chapel Hill, USA; 5Department of Psychiatry, University of Illinois at Chicago, Chicago, IL, USA
Abstract
Objective To evaluate the effectiveness of replacing dietary saturated
fat with omega 6 linoleic acid, for the secondary prevention of coronary
heart disease and death.
Design Evaluation of recovered data from the Sydney Diet Heart Study,
a single blinded, parallel group, randomized controlled trial conducted
in 1966-73; and an updated meta-analysis including these previously
missing data.
Setting Ambulatory, coronary care clinic in Sydney, Australia.
Participants 458 men aged 30-59 years with a recent coronary event.
Interventions Replacement of dietary saturated fats (from animal fats,
common margarines, and shortenings) with omega 6 linoleic acid (from
safflower oil and safflower oil polyunsaturated margarine). Controls
received no specific dietary instruction or study foods. All non-dietary
aspects were designed to be equivalent in both groups.
Outcome measures All cause mortality (primary outcome),
cardiovascular mortality, and mortality from coronary heart disease
(secondary outcomes). We used an intention to treat, survival analysis
approach to compare mortality outcomes by group.
Results The intervention group (n=221) had higher rates of death than
controls (n=237) (all cause 17.6% v 11.8%, hazard ratio 1.62 (95%
confidence interval 1.00 to 2.64), P=0.05; cardiovascular disease 17.2%
v 11.0%, 1.70 (1.03 to 2.80), P=0.04; coronary heart disease 16.3% v
10.1%, 1.74 (1.04 to 2.92), P=0.04). Inclusion of these recovered data
in an updated meta-analysis of linoleic acid intervention trials showed
non-significant trends toward increased risks of death from coronary
heart disease (hazard ratio 1.33 (0.99 to 1.79); P=0.06) and
cardiovascular disease (1.27 (0.98 to 1.65); P=0.07).
Conclusions Advice to substitute polyunsaturated fats for saturated
fats is a key component of worldwide dietary guidelines for coronary
heart disease risk reduction. However, clinical benefits of the most
abundant polyunsaturated fatty acid, omega 6 linoleic acid, have not
been established. In this cohort, substituting dietary linoleic acid in place
of saturated fats increased the rates of death from all causes, coronary
heart disease, and cardiovascular disease. An updated meta-analysis
of linoleic acid intervention trials showed no evidence of cardiovascular
benefit. These findings could have important implications for worldwide
dietary advice to substitute omega 6 linoleic acid, or polyunsaturated
fats in general, for saturated fats.
Trial registration Clinical trials NCT01621087.
Introduction
Advice to substitute vegetable oils rich in polyunsaturated fatty
acids (PUFAs) for animal fats rich in saturated fatty acids
(SFAs) has been a cornerstone of worldwide dietary guidelines
Correspondence to: C E Ramsden Chris.Ramsden@nih.gov
Extra material supplied by the author (see http://www.bmj.com/content/346/bmj.e8707?tab=related#webextra)
Web appendix: Supplementary material
No commercial reuse: See rights and reprints http://www.bmj.com/permissions Subscribe: http://www.bmj.com/subscribe
BMJ 2013;346:e8707 doi: 10.1136/bmj.e8707 Page 1 of 18
Research
RESEARCH

What makes this new data so important is that safflower oil was used as the intervention in this study. And the polyunsaturates in safflower oil are all omega-6s, no omega-3s. The vegetable oils in most interventions have a mix of the two essential fats, thereby making it difficult to tease out their differing health effects. But the new data from this old study shows a clear increase in mortality from switching to this high omega-6 oil.

How is the old guard reacting to this new information? By attributing the increase in mortality to the trans fats in the safflower magarines that some of the participants switched to during the study. Ramsden et al have no way of analyzing the levels of trans fats in those earlier diets, and trans fats could possibly have had a harmful effect. But it would be foolish, even criminal, not to listen to the alarm bells that this paper is setting off re: the very real dangers of a diet too high in omega-6s.