April 25, 2017

expert reaction to editorial on saturated fat and heart disease

In an editorial published in the British Journal of Sports Medicine, researchers report that saturated fat does not increase the risk of a heart attack by clogging up arteries and the risk of coronary heart disease can be reduced by healthy lifestyle interventions.

Dr David Nunan, Senior Researcher at the Centre for Evidence Based Medicine, University of Oxford, said:

“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. This latest opinion editorial published in the BJSM advocates a similar call and highlights selected evidence in support. However, the authors do not address concerns with 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 trial 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 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.”

Dr Amitava Banerjee, Senior Clinical Lecturer in Clinical Data Science and Honorary Consultant Cardiologist at University College London, said:

“This is an editorial, which does not present any new data or research. Unfortunately the authors have reported evidence simplistically and selectively. They failed to cite a rigorous Cochrane systematic review which concluded that cutting down dietary saturated fat was associated with a 17% reduction in cardiovascular events including coronary heart disease on the basis of 15 randomised trials¹. A lot of the evidence the authors quote about saturated fats, including the systematic review by de Souza and colleagues in the BMJ, is based on observational data, making it harder to draw conclusions, due to confounding factors.

“There is no dispute over the key role of a healthy diet and a healthy lifestyle (including more exercise) in good heart health and the authors are right to re-emphasise these issues. Health professionals, patients and public all need to focus more on the importance of diet and exercise when it comes to preventing heart attacks. However, an individual’s risk of coronary heart disease is based on the interplay of many factors, including diet, physical activity and clinical factors such as diabetes, high blood pressure and high cholesterol. Other important contributors are social (e.g. education, socioeconomic status and stress), environmental (e.g. availability of open spaces to take exercise) and genetic. In order to tackle heart disease, a multi-pronged approach which addresses these different factors will be necessary, whether at individual or population level. Therefore physical activity and dietary change alone are necessary but not sufficient to prevent coronary disease.

“There is often an unhelpful tendency to pit treatment versus prevention as competition and exclusive approaches. As a health system, it is possible – and essential – to treat heart attacks and prevent them. Therefore, medicines (including blood thinners such as aspirin or cholesterol-lowering strategies such as statins) and more invasive strategies (e.g. angioplasty or coronary artery bypass surgery) have an important role alongside a healthy lifestyle.”

¹  https://www.ncbi.nlm.nih.gov/pubmed/26068959

Prof. Christine Williams, Professor of Human Nutrition at the University of Reading, said:

“Snappy editorials recently published in the British Journal of Sports Medicine and the British Medical Journal by a well-known cardiologist continue to argue the case for saturated fats as an innocent bystander in cardiovascular disease.  It is unclear what the motivation for publishing these incomplete and limited accounts of the evidence might be at this particular point, since no new research has emerged in the past year or so.

“The editorials fail to cover the extensive literature on effects of saturated fats on cardiovascular health, including adverse effects on  LDL cholesterol, vascular function and susceptibility to clot formation. In particular there is no mention of the largest meta-analysis of randomised controlled trials (RCTs) of saturated fat reduction on coronary heart disease, published in 2015, which showed replacing saturated fats with polyunsaturated fats reduced cardiovascular events by 27%. This may be because this highly cautious, well received study reported that the degree of reduction in events was related to the reduction of serum total cholesterol.

“The authors of the editorials rather focus on positive findings from an intervention study in a Mediterranean population from which they conclude that there is no need for people to avoid or replace saturated fats in their diets. Whilst data from the PREDIMED study  are a welcome addition to the literature – as is the focus on whole diets and physical activity – the findings  are not consistent with the conclusion that ‘saturated fats are innocent’.

“Furthermore the nature of their public health advice appears to be one of  ‘Let them eat nuts and olive oil’ with no consideration of how this might be successfully achieved in the UK general population and in people of different ages, socio-economic backgrounds or dietary preferences.  The authors point out that ‘There is no business model or market to help spread this simple yet powerful intervention.’  Some would argue the journals have a very credible business model – based on attracting controversy in an area of great importance to public health where clarity, not confusion, is required?”

Dr Gunter Kuhnle, Associate Professor in Nutrition and Health, University of Reading, said:

“The authors claim that ‘real food’ is the best advice to prevent cardio-vascular diseases – but neither they nor anyone else explains what ‘real food’ is. Indeed, ‘real food’ is nothing more than a fashionable term similar to ‘clean eating’.

“The evidence cited to support that saturated fat does not increase the risk of CVD does not really support the claim: the PREDIMED study did not investigate differences in fat or saturated fat intake, the Lyon Heart study actually showed a beneficial effect.

“Diet has an important role in the prevention of heart disease – but such recommendations need to be based on a thorough review of the evidence.”

Dr Gavin Sandercock, Reader in Clinical Physiology (Cardiology) and Director of Research at the University of Essex, said:

“This editorial is not founded on good evidence.  There is no such thing as ‘real food’ – the authors don’t define what it is so it’s meaningless.

“The authors say ‘A high TC to HDL ratio drops rapidly with dietary changes such as replacing refined carbohydrates with healthy high fat foods.’   This is not true.  There is no reference to support this statement and I am not aware of any good supporting evidence.

“It’s true that eating fatty foods does not cause heart disease. Having high cholesterol is linked to heart disease but it has very little to do with what we eat. The authors bemoan the quality of evidence for saturated fats but there is even less (or no evidence) for benefits of ‘real food’ or ‘healthy diet’ as a means to combat heart disease.

“We must continue to research the complex links between fat, cholesterol and heart disease but we must not replace one myth with another. The science linking fatty food and heart disease may have flaws but the science linking ‘real food’ and heart disease is totally non-existent!

“I agree that the links between diet and disease can be weak, and that the risk posed by moderate consumption of saturated fat is sometimes overstated.  In moderation as part of a mixed diet, there is no single food item that is bad for you, and no single nutrient should be thought  of as ‘healthy or unhealthy’ – this is  true for fat, protein and carbohydrates.

“We have to stop searching for dietary silver-bullets too – there is no one food that can make you ‘healthy’.  Confusion arises from such misplaced ideas.

“Unlike diet, there is no question over the evidence that being physically active is beneficial to health – and in more ways than just reducing heart disease.  Walking an extra 22 minutes a day will improve health in less active individuals, and walking more will lead to even greater improvements.  There is no confusion or argument over the benefits of physical activity. As long as you’re not starving or overconsuming calories, diet has very little impact on most people’s health and there is nothing you can do to eat yourself healthy and you certainly cannot eat yourself fit.”

Dr Mary Hannon-Fletcher, Head of School, Health Sciences, Ulster University, said:

“The best dietary and exercise advise I have read in recent years:  Walking 22 min a day and eating REAL food. This is an excellent Public Health message, the modern idea of a healthy diet where we eat low fat and low calorie foods is simply not a healthy option. All of these foods have been so altered they are anything but healthy, the human body is a complex organism and simply changing one thing for example:  eating reduced fat foods, will not have a positive impact on the body’s metabolism as  a whole, we are much too complex for that. It may indeed, have a negative effect on important hormonal production. So eating real foods, in moderation and exercising daily is the answer to keeping fit and healthy, it’s just too simple a message for the public to take on board.”

Prof. Alun Hughes, Professor of Cardiovascular Physiology and Pharmacology & Associate Director of the MRC Unit for Lifelong Health and Ageing at UCL, said:

“This editorial is muddled and adds to confusion on a contentious topic. The authors present no really new evidence, misrepresent some existing evidence, and fail to adequately acknowledge the limitations in the evidence that they use to support their point of view.

“I agree that there is only weak and inconclusive evidence that dietary saturated fats cause coronary heart disease, although the evidence is not as conclusively negative as they claim.¹ Some other assertions made by the authors are specious.  For example they say that emphasis on lowering plasma cholesterol ‘by ‘low-fat’ foods and medication’ is ‘misguided’, but lumping low-fat foods together with medication is highly misleading – the evidence for benefit of cholesterol-lowering medication on cardiovascular disease and total mortality is very convincing².

“Other statements are unsupported by evidence.  What is the evidence that ‘Childhood  trauma can lead to an average decrease in life expectancy of 20 years’?  This is unreferenced.  Some of their statements confuse correlation with causation – e.g. while observational studies demonstrate positive associations between more exercise and more life expectancy this has yet to be demonstrated in randomized clinical trials,³ and a recent randomized lifestyle intervention including physical activity showed no benefit on cardiovascular disease in people with diabetes⁴.”

¹ Hooper L, Martin N, Abdelhamid A, Davey Smith G. Reduction in saturated fat intake for cardiovascular disease. Cochrane Database Syst Rev 2015; (6): Cd011737.

² Chou R, Dana T, Blazina I, Daeges M, Jeanne TL. Statins for Prevention of Cardiovascular Disease in Adults: Evidence Report and Systematic Review for the US Preventive Services Task Force. JAMA 2016; 316(19): 2008-24.

³  Seron P, Lanas F, Pardo Hernandez H, Bonfill Cosp X. Exercise for people with high cardiovascular risk. Cochrane Database Syst Rev 2014; (8): Cd009387.

⁴ Wing RR, Bolin P, Brancati FL, et al. Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes. N Engl J Med 2013; 369(2): 145-54.

Prof. Naveed Sattar, Professor of Metabolic Medicine at the University of Glasgow, said:

“Malhotra and colleagues question saturated fat and suggest the LDL-cholesterol hypothesis is over emphasised.  They could not be more wrong.

“To make their arguments they cite observational data – which is bizarre, since not only are such findings prone to many biases such that the results can often be incorrect, but more importantly plentiful randomised trial data (gold standard evidence) show lowered saturated fats lower cholesterol and risk of heart attacks.  So the evidence to lower saturated fat is robust.

“Likewise, the evidence for LDL-cholesterol as a risk factor for heart disease is also robust and supported by over 20 randomised trial worldwide which show statins and now other agents with lower LDL-cholesterol also lower heart attacks and strokes.  It is also supported by genetic data, since many individuals with high cholesterol as a result of their genes have substantially elevated heart attack risks.  In a bigger context, around half of the reductions seen in heart attack rates over the last 2-3 decades is due to better treatment of risk factors – cholesterol, blood pressure and smoking being the three dominant ones.

“The authors should concentrate on the best evidence and be more rigorous in their appraisals. To not do so is misleading to the public and creates confusion for those who are less able to access or understand such evidence.  Simply because they have the title of doctors does not mean they are correct and the public need to be wary of advice which seems to contradict national guidelines in areas of relevance since such guidelines accumulate the best evidence to make recommendations on areas related to health.

“Malhotra and colleagues are correct however to point out new trial findings on Mediterranean diets; but this is one trial set against many for lowering cholesterol.   So yes we have ways beyond cholesterol control to lessen risks, but these should not replace advice on cholesterol and saturated fats – rather they should be used together.  The same is true for lifestyle changes which work in tandem with other advice and cholesterol lowering.”

Gaynor Bussell, Dietitian and member of the British Dietetic Association, said:

“As a dietitian I still feel saturated fat should be kept to 11% of total calories or less, for heart health sake.  Yet many of us now feel that a predominantly Med style diet can be healthy with slightly more fats and fewer carbs, provided the fats are ‘good’ – such as in olive oil, nuts or avocados.

“I still feel there should be carbs with each meal but, like the authors, dietitians note the importance of carb quality, especially if there is insulin resistance; so low GI/GL/high fibre/wholegrain carbs should be the norm.  Physical activity is also important.”

Dr Mike Knapton, Associate Medical Director at the British Heart Foundation (BHF), said:

“The Mediterranean diet and daily exercise can help reduce heart disease risk, but I’m afraid the claims about saturated fat made in this opinion piece are unhelpful and misleading.

“Decades of research have proved that a diet rich in saturated fat increases ‘bad’ LDL cholesterol in your blood, which puts you at greater risk of a heart attack or stroke.

“When it comes to reducing your risk of heart disease the lower your cholesterol is the better. This can be achieved through a healthy, balanced diet or medication for some.

“A coronary artery blocked with fatty plaque causes heart muscle to die as it becomes starved of oxygen.  A stent keeps the artery open so blood can flow through unimpeded. This practice is used by leading cardiologists around the world and has helped save countless lives and improve quality of life.”

* ‘Saturated fat does not clog the arteries: coronary heart disease is a chronic inflammatory condition, the risk of which can be effectively reduced from healthy lifestyle interventions’ by Aseem Malhotra et al. published in the British Journal of Sports Medicine on Tuesday 25 April 2017.

Declared interests

Christine Williams: Member of Governing bodies of the Institute of Food Research and Scottish Rural University College; Member of the British Nutrition Foundation Council and Chair of the Board of Trustees; Chair of the BBSRC Agriculture and Food Security Strategy Advisory Panel; Member of the Science Advisory Council for Wales; Member of EUFIC Scientific Advisory Board; Member Supervisory Board of EIT Food

Naveed Sattar: has consulted for Amgen and Sanofi, and has research support from AstraZeneca.  He has also conducted charity and government funded trials of statins and lifestyle.

Gunter Kuhnle: “Associate Professor at the University of Reading.  Grant funding: Investigation of links between polyphenol intake and health – EU, Mars, Horizon.  Appointments: EFSA Working group – risk assessment of soy isoflavones.  Memberships: British Mass Spectrometry Society, British Nutrition Society, Registered Nutritionist (Reg. Nr. 8236); 2011 to 2012 member of ‘Biomarker group’ at ILSI Europe.”

Gaynor Bussell: “I am a freelance and weight management dietitian in the NHS.  I have no conflict of interests.”

Dr David Nunan: is a lead 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 Department of Health, or the RCGP.