Natural saturated fats may not be a major threat to heart health, researchers say today.
Instead processed trans fats are a serious threat, raising the risk of death and coronary heart disease, they warn.
Saturated fats in the diet are mainly found in animal products including butter, milk, and meat, and in some fish and egg yolks.
Trans unsaturated fats, or trans fats, are mainly produced industrially from plant oils (a process known as hydrogenation) and found in margarine, snack foods and packaged baked goods. The two have usually been lumped together in studies on diet and the heart.
Dr Russell de Souza of McMaster University, Ontario, Canada and his team explain that a recent review found no excess cardiovascular risk associated with intake of saturated fat, but a raised risk with trans fats.
They investigated further by analysing the findings of results of 50 previous observational studies on saturated and trans fats, and health outcomes. This showed that "saturated fat intake was not associated with all cause mortality, cardiovascular disease mortality or incidence".
On the other hand, trans fat intake was associated with a significantly higher rate of all of these outcomes. Neither type of fat was linked to ischaemic stroke or type 2 diabetes. Full results appear in The BMJ.
A small amount of natural trans fats are found in animal products. These were analysed separately to processed trans fats. Analysis showed: "Industrial, but not ruminant, trans fats were associated with coronary heart disease mortality and incidence".
Dr de Souza says: "For years everyone has been advised to cut out fats. Industrial trans fats have no health benefits and pose a significant risk for heart disease, but the case for saturated fat is less clear."
de Souza, R. J. et al. Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies. BMJ 12 August 2015 doi: 10.1136/bmj.h3978 [abstract]
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