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The end for PUFAs?

We have had 50 years of advice to substitute vegetable oils rich in polyunsaturated fatty acids (PUFAs) for animal fats, rich in saturated fatty acids (SFAs). The advice originated in the 1960s, when PUFAs were thought to be a uniform molecular category with one relevant biological mechanism - reduction in blood cholesterol. The bestknown PUFA at the time was omega 6 (n-6) linoleic acid (LA), and PUFA and LA were often used interchangeably when reporting clinical trial results and giving advice on diet. However, we now recognise that there are several different categories of PUFA - each with unique biochemical properties and possibly different cardiovascular effects.

The authors of this paper evaluated the effectiveness of replacing dietary SFA with omega 6 linoleic acid for the secondary prevention of coronary heart disease and death. They used recovered data from the Sydney Diet Heart Study, a single blinded, parallel group, randomised controlled trial conducted between 1966 and 1973. They also did an updated meta-analysis including these previously missing data. The participants were 458 men aged 30 - 59 with a recent coronary event.

The intervention was 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 did not get any specific instruction on diet or study foods. All non-dietary aspects were designed to be equivalent in both groups. Outcomes were all-cause mortality (primary outcome), cardiovascular mortality and mortality from coronary heart disease (secondary outcomes).

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 - 2.64), p=0.05; cardiovascular disease 17.2% v. 11.0%, 1.70 (1.03 - 2.80), p=0.04; coronary heart disease 16.3% v. 10.1%, 1.74 (1.04 - 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 - 1.79); p=0.06) and cardiovascular disease (1.27 (0.98 - 1.65); p=0.07).

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.

Ramsden CE, et al. BMJ 2013;346. []

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Title Annotation:Abstracts
Publication:CME: Your SA Journal of CPD
Date:Mar 1, 2013
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