Saturated fats are not associated with an increased risk of death, heart disease, stroke, or type 2 diabetes, finds a study published in The BMJ this week. However, the findings show that trans fats are associated with greater risk of death and coronary heart disease. The study confirms previous suggestions that industrially produced trans fats might increase the risk of coronary heart disease and calls for a careful review of dietary guidelines for these nutrients.

Guidelines currently recommend that saturated fats are limited to less than 10%, and trans fats to less than 1% of energy to reduce risk of heart disease and stroke.

Saturated fats come mainly from animal products, such as butter, cows' milk, meat, salmon and egg yolks, and some plant products such as chocolate and palm oils. Trans unsaturated fats (trans fats) are mainly produced industrially from plant oils (a process known as hydrogenation) for use in margarine, snack foods and packaged baked goods.

Contrary to prevailing dietary advice, a recent evidence review found no excess cardiovascular risk associated with intake of saturated fat. In contrast, research suggests that industrial trans fats may increase the risk of coronary heart disease.

To help clarify these controversies, researchers in Canada analysed the results of observational studies assessing the association between saturated and/or trans fats and health outcomes in adults.

Study design and quality were taken into account to minimise bias, and the certainty of associations were assessed using a recognised scoring method.

The team found no clear association between higher intake of saturated fats and all cause mortality, coronary heart disease (CHD), cardiovascular disease (CVD), ischemic stroke or type 2 diabetes, but could not, with confidence, rule out increased risk for CHD death. They did not find evidence that diets higher in saturated fat reduce cardiovascular risk.