Reducing saturated fat in favour of “vegetable” oils increases risk of death by 62%
9th February 2013
If you have been following advice to swap butter and other saturated fats for “healthy” margarines and vegetable oils then you ought to take notice of evidence published in the British Medical Journal this week. The new evidence, from a previously missing data, shows replacing saturated fats (found in meat, egg, dairy products and coconut oil) with omega-6 polyunsaturated vegetable fats is linked to an increased risk of death among patients with heart disease.
The researchers say their findings could have important implications for worldwide dietary recommendations. Advice to substitute vegetable oils rich in polyunsaturated fatty acids (PUFAs) for animal fats rich in saturated fats to help reduce the risk of heart disease has been a cornerstone of dietary guidelines for the past half century. The most common dietary PUFA in Western diets is omega-6 linoleic acid (n-6 LA for short).
This advice has long caused controversy, because evidence that linoleic acid lowers the risk of cardiovascular disease is limited. An in-depth analysis of the effects of linoleic acid on deaths from coronary heart disease and cardiovascular disease has not previously been possible because data from the Sydney Diet Heart Study – a randomised controlled trial conducted from 1966 to 1973 – was missing.
But now, a team of researchers from the US and Australia have recovered and analysed the original data from this trial, using modern statistical methods to compare death rates from all causes, cardiovascular, and coronary heart disease.
Their analysis involved 458 men aged 30-59 years who had recently had a coronary event, such as a heart attack or an episode of angina. Participants were randomly divided into two groups. The intervention group was instructed to reduce saturated fats to less than 10% of energy intake and to increase linoleic acid (from safflower oil and safflower oil polyunsaturated margarine) to 15% of energy intake. Safflower oil is a concentrated source of omega-6 linoleic acid and provides no omega-3 PUFAs.
The control group received no specific dietary advice. Both groups had regular assessments and completed food diaries for an average of 39 months. All non-dietary aspects of the study were designed to be equal in both groups.
The results show that the omega-6 linoleic acid group had a higher risk of death from all causes (elevated by 62%), as well as from cardiovascular disease and coronary heart disease (increases of 70 and 74%), compared with the control group.
The authors then used the new data to update an earlier meta-analysis (a review of all the evidence). This also showed no evidence of benefit, and suggested a possible increased risk of cardiovascular disease, emphasizing the need to rethink mechanisms linking diet to heart disease.
The authors’ concluded:
“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.”
In an accompanying editorial, Professor Philip Calder from the University of Southampton says the new analysis of these old data “provides important information about the impact of high intakes of omega 6 PUFAs, in particular linoleic acid, on cardiovascular mortality at a time when there is considerable debate on this question.”
Calder says the findings argue against the “saturated fat bad, omega 6 PUFA good” dogma and suggest that the American Heart Association guidelines on omega-6 PUFAs may be misguided. They also “underscore the need to properly align dietary advice and recommendations with the scientific evidence base.”
Ramsden C E et al. 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. BMJ, 2013; 346 (feb04 3): e8707 DOI: 10.1136/bmj.e8707
Calder P C Old study sheds new light on the fatty acids and cardiovascular health debate. BMJ, 2013; 346 (feb04 3): f493 DOI: 10.1136/bmj.f493
Ramsden C E et al. n-6 fatty acid-specific and mixed polyunsaturate dietary interventions have different effects on CHD risk: a meta-analysis of randomised controlled trials. British Journal of Nutrition, 2010, 104: 1586-600
Categories: Nutritional News, Healthy Aging, Metabolic Health