CAMBRIDGE, United KingdomNew research published in the journal Annals of Internal Medicine calls into question current guidelines that generally restrict the consumption of saturated fats and encourage consumption of polyunsaturated fats to prevent heart disease. The study also found insufficient support for guidelines which advocate the high consumption of polyunsaturated fats, such as omega-3 and omega-6, to reduce the risk of coronary disease.
Researchers at the University of Cambridge analyzed existing cohort studies and randomized trials on coronary risk and fatty acid intake. When specific fatty acid subtypes were examined, the effects of the fatty acids on cardiovascular risk varied even within the same broad “family"questioning the existing dietary guidelines that focus principally on the total amount of fat from saturated or unsaturated rather than the food sources of the fatty acid subtypes.
“These are interesting results that potentially stimulate new lines of scientific inquiry and encourage careful reappraisal of our current nutritional guidelines," said lead author Rajiv Chowdhury, Ph.D.
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 analyzing 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.
The researchers found 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 (EPA) and docosahexaenoic acids (DHA), and arachidonic acid (an omega-6 fat) are each associated with lower coronary risk.
Similarly, within saturated fatty acid, the researchers found weak positive associations between circulating palmitic and stearic acids (found largely in palm oil and animal fats, respectively) and cardiovascular disease, whereas circulating margaric acid (a dairy fat) significantly reduced the risk of cardiovascular disease. No significant effects were found when they investigated the effects of omega-3 and omega-6 fatty acid supplementations on reducing coronary disease in the randomized controlled trials.
“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. But large scale clinical studies are needed, as these researchers recommend, before making a conclusive judgment," said Jeremy Pearson, Ph.D., associate medical director at the British Heart Foundation.
The study supports a review published last year in the journal Advances in Nutrition that concluded saturated fats per se may not be responsible for many of the adverse health effects with which they have been associated, and it is time to re-evaluate the dietary recommendations that focus on lowering serum cholesterol and to use a more holistic approach to dietary policy.
Review author Glen D. Lawrence, department of chemistry and biochemistry, Long Island University, wrote “the influence of dietary fats on serum cholesterol has been overstated, and a physiological mechanism for saturated fats causing heart disease is still missing."
A number of studies published in the 1960s and 1970s, including the seminal Framingham Heart Study, linked dietary fatsparticularly saturated fatsto heart disease. In recent years, however, analyses of these older studies, coupled with new findings, have begun to call the purported negative health consequences of dietary fats into question.
The review examined studies of several dietary factors, including saturated fat, polyunsaturated fat, a-linolenic acid, total fat, meat, eggs and milk. None of these studies provided sufficient evidence to support a positive (or negative) association between fat consumption and heart disease.
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