A new review of published evidence challenges current guidelines that suggest in order to reduce heart disease risk, people should generally restrict intake of saturated fats - like those found in butter and dairy foods - in favor of unsaturated fats - such as in margarine and sunflower oil.
The analysis, published in the journal Annals of Internal Medicine by an international group led by a team at the UK's University of Cambridge, included 72 separate studies on heart risk and intake of fatty acids.
They found no evidence to support guidelines that say people should restrict saturated fat consumption to lower their risk of developing heart disease.
They also found insufficient evidence to support guidelines that advise eating more foods containing polyunsaturated fats (such as omega-3 and omega-6) to reduce heart risk.
And when they dug into the detail of specific fatty acids (such as different types of omega-3), the researchers found their impact on heart risk varied even within the same family of fatty acids.
Findings question current guidelines
The researchers say their findings call into question current guidelines that focus mainly on saturated versus unsaturated fat amounts, as opposed to concentrating on the food sources of the types of fatty acid.
The study was part-funded by the British Heart Foundation, whose associate medical director, Prof. Jeremy Pearson, says:
"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."
Lead author Dr. Rajiv Chowdhury of the University of Cambridge, who describes the findings as "interesting," says they could open new lines of enquiry that carefully question our current dietary guidelines, and adds:
"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."
Researchers pooled data from 72 separate studies
To arrive at their conclusions, Dr. Chowdhury and his colleagues pooled and re-analyzed data from 72 separate studies that included over 600,000 participants in 18 different countries.
The studies had assessed total saturated fatty acid in two ways: one as a component in participants' diet, and the other way was by measuring levels in the bloodstream.
The results of the pooled analysis showed that whether measured in the bloodstream or as a component of diet, total saturated fatty acid was not linked to coronary disease risk.
The analysis also found no significant link between heart risk and intake of total monounsaturated fatty acids, long-chain omega-3 and omega-6 polyunsaturated fatty acids.
Individual unsaturated fats have different effects on heart risk
However, when they looked in more detail at bloodstream levels of individual subtypes of polyunsaturated fatty acids, such as long-chain omega-3 and omega-6 fatty acids, the researchers found they linked to heart risk differently.
For example, they found some evidence that bloodstream levels of eicosapentaenoic and docosahexaenoic acids (two main types of long-chain omega-3 polyunsaturated fatty acids), and arachidonic acid (an omega-6 fatty acid) are each linked to lower heart risk.
They also looked in detail at saturated fatty acids. Here, they found some weak links between bloodstream levels of palmitic and stearic acids (predominantly found in palm oil and animal fats, respectively) and heart disease, but blood levels of the dairy fat margaric acid appeared to significantly reduce heart risk.
Lastly, when they looked at results of trials testing the effects of adding omega-3 and omega-6 supplements to diets, they found no benefit in terms of reducing risk of coronary disease.
Prof. Pearson says large-scale clinical studies are now needed before drawing firm conclusions on this new evidence. In the meantime he advises:
"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."
Medical News Today recently published an article on adopting a healthy lifestyle to reduce heart risk. The article explains the difference between heart risk factors that cannot be changed like genes, and those that can, and cites smoking, obesity, diet and exercise as the main modifiable ones.