New study challenges benefits of fish oil

CAMBRIDGE, England — A new study published in the March 18 journal Annals of Internal Medicine raises questions about current guidelines which generally restrict the consumption of saturated fats and encourage consumption of polyunsaturated fats, or fish oils, to prevent heart disease. 

"These are interesting results that potentially stimulate new lines of scientific inquiry and encourage careful reappraisal of our current nutritional guidelines," suggested Rajiv Chowdhury, lead author of the research at the University of Cambridge.

"This systematic review and meta-analysis raises an interesting viewpoint, but an unfortunate, and potentially irresponsible one, for consumers who will once again be subject to nutritional guidance whiplash," countered Duffy MacKay, SVP scientific and regulatory affairs for the Council for Responsible Nutrition. “There are thousands of studies and decades of recommendations from government, academic, nutritional and medical organizations and experts supporting the important heart health benefits associated with diets high in polyunsaturated fats, low in saturated fats and avoidance of trans fats."

An international research collaboration led by the University of Cambridge analyzed existing cohort studies and randomized trials on coronary risk and fatty acid intake. They showed that current evidence does not support guidelines which restrict the consumption of saturated fats in order to prevent heart disease. The researchers also found insufficient support for guidelines that advocate the high consumption of polyunsaturated fats, such as omega 3 and omega 6, to reduce the risk of coronary disease.

For the meta-analysis, the researchers analyzed data from 72 unique studies with more than 600,000 participants from 18 nations. The investigators found that total saturated fatty acid, whether measured in the diet or in the bloodstream as a biomarker, was not associated with coronary disease risk in the observational studies. Similarly, when analysing the studies that involved assessments of the consumption of total monounsaturated fatty acids, long-chain omega-3 and omega-6 polyunsaturated fatty acids, there were no significant associations between consumption and cardiovascular risk.

"Their conclusions, if taken to heart, leave consumers to rely on genetics and fate to avoid coronary heart disease, an unacceptable situation given the fact that the scientific literature contains so many studies that point to benefit for omega-3 fatty acids," MacKay said. 

The investigators did find that different subtypes of circulating long-chain omega-3 and omega-6 fatty acids had different associations with coronary risk, with some evidence that circulating levels of eicosapentaenoic and docosahexaenoic acids (i.e., two main types of long-chain omega-3 polyunsaturated fatty acids), and arachidonic acid (i.e, an omega-6 fat) are each associated with lower coronary risk.

"This analysis of existing data suggests there isn't enough evidence to say that a diet rich in polyunsaturated fats but low in saturated fats reduces the risk of cardiovascular disease," noted Jeremy Pearson, associate medical director at the British Heart Foundation, which helped fund the study. "But large scale clinical studies are needed, as these researchers recommend, before making a conclusive judgement."

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