Eating a diet high in saturated fats may not increase your risk of heart disease after all, an international study has revealed.
Contrary to current advice to eat less "unhealthy" fat, researchers found no association between saturated fat consumption and heart disease.
In addition, levels of "healthy" polyunsaturated fats such as omega 3 and omega 6 had no general effect on heart disease risk.
But different specific strains of fat did have some impact. Two kinds of saturated fat found in palm oil and animal products were weakly associated with heart disease, while a dairy fat called margaric acid was significantly protective.
Similarly, two types of omega-3 fatty acid found in oily fish - EPA and DHA - and the omega-6 fat arachidonic acid were linked to a lower risk of heart disease.
However, popular omega-3 and omega-6 supplements appeared to have no benefit.
Lead researcher Dr Rajiv Chowdhury, from Cambridge University, 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."
The team, whose results appear in the journal Annals of Internal Medicine, conducted a "meta-analysis" of data from 72 studies involving more than 600,000 participants from 18 countries.
Pooling study findings in this way is a statistically powerful technique that can reveal previously hidden trends.
A key finding was that total saturated fat, whether measured in the diet or the bloodstream, showed no association with heart disease.
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Professor Jeremy Pearson, associate medical director at the British Heart Foundation - which co-funded 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."