It seems that hardly a week goes by where we see or hear another story about diet and health. Today it’s the return of saturated fat, which it turns out may not be a problem for our health after all. Here I provide my commentary to the Science Media Centre (SMC) on the evidence-base underpinning the saturated fat story in today’s news.
A number of recently published articles have concluded that associations between high cholesterol and premature death are lacking and call for current public health guidance advocating low saturated fat consumption to be revised. The latest opinion editorial published in the BJSM advocates a similar call and highlights selected evidence in support. However, the authors do not address concerns about the quality of the evidence presented and fail to highlight contradictory evidence.
Much of the evidence the editorial authors cite for a lack of association between self-reported saturated fat intake and coronary heart disease is observational, which is considered low-quality evidence according to best practice evidence-based methods due to the increased potential for bias in these types of studies. Indeed, one of the studies cited in the editorial noted the quality of evidence to be ‘very low’, indicating that the results are very uncertain.
A high-quality meta-analysis of available randomised controlled trials (which provide the highest level of evidence for cause and effect associations) found moderate quality evidence that reducing dietary saturated fat lowered the risk of cardiovascular events (for every 100 people on a lower saturated fat diet 7 of them had fewer cardiovascular events). However, there was no statistical effect on all-cause and cardiovascular mortality, risk of myocardial infarction, and stroke, compared to usual diet. The reduction in cardiovascular events was observed in the studies replacing saturated fat with polyunsaturated fat.
The editorial also highlights evidence from randomised controlled trials suggesting diets high in mono- and poly-unsaturated fats and reduced saturated fat are better for preventing cardiovascular disease and supports the current consensus of a beneficial effect of reduced dietary saturated fat and replacement with mono- and poly-unsaturated fat in the general population.
An encouraging element of the editorial is the repetition of the current consensus for healthy lifestyle interventions including physical activity and management of stress, though the source and quality of evidence for the specific recommendation of 22 minutes of walking is not given.
Whilst an open and honest discourse of the evidence-base underpinning our understanding of the relationship between dietary fat and human health is much needed, such discourse must consider the totality of the evidence-base and the inherent uncertainty with nutritional epidemiological studies and trials. The latest opinion editorial overlooks this complexity and uncertainty.
There is also growing consensus for a balanced discussion of dietary patterns and behaviours away from individual macronutrients that considers collaborative efforts for improving the evidence-base and our understanding of the complex relationship between diet and health.
This commentary was also picked up the Guardian.
Other comments provided to the SMC are worth a read.
The main message: “Nothing new here (yet); eat nuts and olive oil (if you like them)”.
Dr. David Nunan – Departmental Lecturer in Evidence-Based Medicine
Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford.
This response will be posted on www.cebm.net
Dr. David Nunan is a member of the Royal College of General Practitioners (RCGP) steering committee to support the new Physical Activity and Lifestyle clinical priority. He has received funding for research from the NHS National Institute for Health Research School for Primary Care Research (NIHR SPCR) and the RCGP for independent research projects related to physical activity and dietary interventions. The views expressed are those of the author and not necessarily those of the NHS, the NIHR, the RCGP or the Department of Health.
He declares no other relevant conflicts of interest.