Trans fats, but not saturated fats, have been linked to greater risk of death and heart disease
'For years everyone has been advised to cut out fats,' said lead author Russell de Souza, an assistant professor in the Department of Clinical Epidemiology and Biostatistics with the Michael G. DeGroote School of Medicine. But there are different 'fats'
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.
Trans fats have no health benefits and pose a significant risk for heart disease, but the case for saturated fat is less clear,” said de Souza. “That said, we aren’t advocating an increase of the allowance for saturated fats in dietary guidelines, as we don’t see evidence that higher limits would be specifically beneficial to health.”
Saturated fats are limited to less than 10 per cent of energy, and trans fats to less than one per cent of energy, to reduce risk of heart disease and stroke, guidelines cited in the BMJ paper (citations 14 to 19) currently recommend.
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, de Souza and colleagues analyzed the results of 50 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 minimize bias, and the certainty of associations were assessed using a recognized scoring method developed at McMaster.
The team found no clear association between higher intake of saturated fats and death for any reason, coronary heart disease (CHD), cardiovascular disease (CVD), ischemic stroke or type 2 diabetes.
However, consumption of industrial trans fats was associated with a 34 per cent increase in death for any reason, a 28 per cent increased risk of CHD mortality, and a 21 per cent increase in the risk of CHD.
Inconsistencies in the studies analyzed meant that the researchers could not confirm an association between trans fats and type 2 diabetes. And, they found no clear association between trans fats and ischemic stroke.
The researchers stress that their results are based on observational studies, so no definitive conclusions can be drawn about cause and effect. However, the authors write that their analysis “confirms the findings of five previous systematic reviews of saturated and trans fats and CHD.”