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A RE-EVALUATION of a 40-year-old study has cast doubt on the cardioprotective role of omega-6 polyunsaturated acids and underlines the importance of leaving no stone unturned in analysing clinical data, says an Australian expert.
Professor Anthony Keech, deputy director of the NHMRC’s Clinical Trials Centre, said it was important for all data collected in clinical trials to come to light.
Researchers from the US National Institutes of Health recovered unreported data from the Sydney Diet Heart Study, conducted in 1966‒1973, which showed substituting dietary linoleic acid for saturated fats increased the rates of death from all causes (17.6% vs 11.8%); cardiovascular disease (17.2% vs 11.0%); and coronary heart disease (16.3% vs 10.1%). (1)
The single-blinded randomised controlled trial of 458 men aged 30‒59 years who had been hospitalised with a coronary event used safflower oil in the intervention group, which contains high levels of linoleic acid but no other polyunsaturated fatty acids.
The researchers originally reported increased overall mortality in the dietary intervention group compared with the no intervention group, but did not report the primary survival outcomes, such deaths from all causes, cardiovascular disease or coronary heart disease.
“We’ve waited an awfully long time for that to happen with this data set”, Professor Keech told MJA InSight. “Even though a primary end point might not be significant, it’s still important to look at the rest of the data because it might generate important hypotheses about whether things are good or bad for you.”
The researchers said the findings could have important implications for worldwide dietary advice to substitute omega 6 linoleic acid, or polyunsaturated fats in general, for saturated fats.
However, Professor Paul Nestel, cardiovascular nutritionist with the Baker IDI Heart and Diabetes Institute, said the results from the small Sydney study conflicted with the results of more recent, much larger studies.
“We now have evidence over 20‒30 years from very large prospective trials, such as the Nurses’ Health Study and the Physicians’ Health Study, with collectively more than 100 000 people, and there’s no question that substituting linoleic acids for saturated fatty acids is associated with significant reductions in all cardiovascular events”, Professor Nestel told MJA Insight.
He said intervention trials such as the Los Angeles Veterans Administration Diet Study and the Finnish Mental Hospital Study also demonstrated linoleic acid’s cardioprotective properties. (2, 3).
Professor Nestel said the proportion of linoleic acid used in the Sydney study (15% of food energy) was far above the maximum levels of 7%‒10% recommended by health organisations around the world.
“[This is] partly because oils are oils — they’re high-energy foods — not so much because we have other concerns”, he said.
“We all agree that increasing the long-chain omega 3s from fish oils is highly desirable, it’s not a question of either/or, it’s a recognition that both … are healthy and a reasonable ratio, such that is recommended around the world, is probably the way to go.”
Professor Peter Clifton, Baker IDI’s head of nutritional interventions, said the results may have been confounded by the presence of trans fatty acids in the margarine used for the intervention group.
“Although dismissed by the authors, trans fats are likely to be responsible for the lack of benefit. The margarine would have contained at least 20% trans fatty acids,” Professor Clifton said.
However, Professor Keech said the data suggested that all polyunsaturated fats were not alike and that oils with low concentrations of linoleic acid, such as olive oil, might be the better choice from a cardiac-risk perspective.
“Overall, replacement of saturated fats with polyunsaturated fats is still advantageous based on the overall evidence, but those that are rich in linoleic acids don’t seem to share the same benefits based on this [study]”, he said, adding that it would be useful to have more data.
An editorial in the same issue of the BMJ said the findings underscored the need to properly align dietary advice and recommendations with the scientific evidence base. (4)
“These findings argue against the ‘saturated fat bad, omega 6 PUFA good’ dogma”, the editorial said.
– Nicole MacKee
1. BMJ 2013; Online 5 February
2. Lancet 1968; 7577: 1060-1062
3. Lancet 2013; 7782: 835-838
4. BMJ 2013; Online 5 February
Posted 11 February 2011
Given the nature of neuroscience, research in this area may be more rigorously undertaken (perhaps given higher levels of scrutiny and scepticism?) than in areas of diet and CVD. Dr Diamond, a neuroscientist, discovered that research in the latter areas has been fraught with conflicts of interest and incompetence. More pertinent are the alarming consequences given the widespread mis-education of doctors, and thus the general populace, in these health sectors.
This YouTube video posted by the University of South Florida shows David Diamond’s excellent presentation in which he explains how he discovered that his cardiologist was giving him bad – but commonplace – advice regarding weight loss and decreasing his CVD risk.
http://www.youtube.com/watch?v=3vr-c8GeT34
“Misinformation about Fat and Cholesterol”
Prompted by his own health concerns, Dr Diamond learned of the problems with: eating the ubiquitously promoted Low Fat Diet, the cholesterol theory of heart disease, Statins, and avoiding consumption of saturated fat generally.
Most concerning are the allegations about the profits of the drug industry in selling Statin drugs. Ancel Keys appears to be one culprit who helped lead the Western world down the garden path and towards obesity.
You can also download David Diamond’s PowerPoint presentation and get this video as a podcast at http://www.cas.usf.edu/news/s/169/#VIDEO:%20Bad%20science,%20big%20busin…
Thank you, Rosemary, for speaking plain sense. Trans fats are the problem, not saturated fat.
Prof Stanton is spot-on. Our tendency to reduce nutritional research to artificially isolated chemical components only serves to convey the misleading idea that there are “magic bullets” for good nutrition. The community members who take these messages to extreme then lose any faith they might have had in nutrition science, saying “they used to tell us to do this, now they say the opposite”. Nutrition advice needs to be much more about balance – balance of nutrients and balance of energy. There are no magic bullets. One need not eliminate fats, or carbs, or fructose – none of these are “toxic” unless consumed in excess.The best advice that can be given is the principle of “eat food, mostly plants, and not too much.”
Thank you Dr Stanton for highlighting this fact. It’s very difficult to oppose a reductionist approach when our scientific method is the primary means by which we gain new knowledge, but I strongly agree that diet is not so simple. Digestion takes biochemically complex structures (which we call food) and turns it into fuel via myriad co-occurring reactions. This cannot be replicated in any laboratory.
Our advice needs to reflect this in the strongest of language, to avoid messages concerning molecules and ions, and focus instead on fuel and nutrition. The traffic light system recommended for nutritional advice on foods goes some of the way, but it needs to be even simpler, and needs to be imposed upon the food industry even at the expense of their profits, or their profits will continue to come at the expense of our society’s health.
And thank you Rosemary for being such a strong influence on my family when I was growing up, which has ensured that my appreciation and passion for healthy food has continued well into adulthood.
This and other studies show the problems when we try to reduce a food to just one of its component parts. The subjects were not given linoleic acid; they were given safflower oil and also a margarine made with safflower oil. I remember patients from the study at the time complaining to me that they had been advised to pour some of the oil onto their breakfast cereal! They found it easier to use the margarine. This did mean that much of their linoleic acid was accompanied by elaidic acid, a nasty trans fatty acid that resulted from the partial hydrogenation of the oil to turn it into a spread. Australian margarines now contain minimal elaidic acid, but no margarine consists of a single fatty acid.
People eat foods so we should look at diet in terms of foods and eating patterns rather than taking a reductionist approach and concentrating on a single nutrient that is almost never consumed on its own.