A
new study raises questions about current guidelines which generally restrict
the consumption of saturated fats and encourage consumption of polyunsaturated
fats to prevent heart disease. The research was published 18 March, in
the journal Annals of Internal Medicine.
An
international research collaboration led by the University of Cambridge
analysed existing cohort studies and randomised 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
which advocate the high consumption of polyunsaturated fats (such as omega 3 and
omega 6) to reduce the risk of coronary disease.
Furthermore,
when specific fatty acid subtypes (such as different types of omega 3) 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.
Dr
Rajiv Chowdhury, the lead author of the research at the University of Cambridge,
said: "These are interesting results that potentially stimulate new lines
of scientific inquiry and encourage careful reappraisal of our current
nutritional guidelines.
"Cardiovascular
disease, in which the principal manifestation is coronary heart disease,
remains the single leading cause of death and disability worldwide. In 2008,
more than 17 million people died from a cardiovascular cause globally. With so
many affected by this illness, it is critical to have appropriate prevention
guidelines which are informed by the best available scientific evidence."
For
the meta-analysis, the researchers analysed data from 72 unique studies with
over 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.
Interestingly,
the investigators 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 and
docosahexaenoic acids (two main types of long-chain omega-3 polyunsaturated
fatty acids), 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.
Additionally,
when the authors investigated the effects of omega-3 and omega-6 fatty acid
supplementations on reducing coronary disease in the randomised controlled
trials, they did not find any significant effects – indicating a lack of
benefit from these nutrients.
Professor
Jeremy Pearson, Associate Medical Director at the British Heart Foundation,
which helped fund the study, said: "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 judgement.
"Alongside
taking any necessary medication, the best way to stay heart healthy is to stop
smoking, stay active, and ensure our whole diet is healthy – and this means
considering not only the fats in our diet but also our intake of salt, sugar
and fruit and vegetables."
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