Researchers have published a review in the journal Open Heart, into the evidence around dietary fat, cholesterol and coronary heart disease published before 1983. They conclude that based on the studies which they analysed, dietary recommendations which were introduced in the UK in 1983 were not supported by the evidence.
Prof. Christine Williams, Professor of Human Nutrition, University of Reading, said:
“The claim that guidelines on dietary fat introduced in the 1970s and 80s were not based on good scientific evidence is misguided and potentially dangerous. Whilst it is important to ensure we continue to interrogate the evidence on diet and heart disease, this must be approached through an holistic assessment of the evidence base and recognition of the clear improvements in population cholesterol levels that have taken place over the past 30 years. There are justifiable concerns regarding evidence that saturated fats have been replaced in the diet by sugars and this requires a reasoned assessment of alternative approaches for the future.
“In their assessment of the meta-analysis of randomised controlled trial (RCT) evidence for saturated fat intake and heart disease mortality, Harcombe et al have taken a classical pharmaceutical approach to the evidence, with the assumption that RCTs also provide the gold standard for diet, representing the pinnacle of the evidence hierarchy against which other types of study are inevitably weaker. In fact such an approach would be inappropriate for most population based recommendations (as was also argued in the accompanying editorial by Bahi). Most dietary guidelines have been developed using an approach which takes the degree of consistency of a number of lines of evidence as the gold standard for risk assessment. This approach uses RCTs where such data is available, with caution for the relevance of the population in the study, many of whom are high risk individuals or those with existing disease. At the time of the introduction of the guidelines in UK and USA, consistent evidence for cholesterol raising effects of saturated fats was available from animal studies, cross country comparisons, retrospective and prospective cohort studies. In addition strong evidence was available from trials conducted in metabolic ward and semi-free-living settings in volunteer subjects. These showed effects of saturated fats on cholesterol to be so consistent that the investigators were able to develop a predictive algorithm which would estimate the cholesterol outcome based on the saturated fat content of the diet being fed. The RCT studies discussed in the Harcombe et al paper, were available to the expert committees at the time the guidelines were drawn up and these findings were, in part, responsible for the decisions not to recommend complete replacement of dietary saturated fats with polyunsaturated fats due to possible adverse effects of higher intakes of these fats.
“It is intriguing to note the concerns being raised in recent meta-analyses concerning the decision to reduce levels of saturated fats, since exactly similar types and quality of evidence is available for trans fatty acids, with limited RCT data available to support reduction in these fats. In support of their findings Harcombe et al highlight the recent meta-analyses of the cohort data which argued that more recent cohort data have shown lower relative risk ratios for saturated fat than earlier studies. It is astonishing that none of these experienced epidemiologists have taken account of change in population diet as a confounding factor in long term cohort studies. In the UK since the 1960s, dietary fat intake has fallen by 50% -from around 125g/d to less than 83g/d today. Saturated fat intakes have fallen even more dramatically – from around 55g/d to around 30g/d today with most of this change occurring between 1975 and 1995. For the early cohorts the baseline diet bears no resemblance to the diet actually eaten by the cohort under continuing investigation. Those studies which have undertaken repeat diet assessments have confirmed that the risk ratio has reduced as population diet has changed, thereby providing real life evidence of the benefits of the recommended diet. Exactly similar changes are seen for trans fats; where repeat dietary assessment data are available within cohort studies the risk ratio for the population study has fallen as levels of trans fats in the background diet has reduced. In cohorts established since 1995 it follows that there will be a narrower population range in fat intakes than was the case in the 1960s and 1970s.
“A significant proportion of the UK population are now eating levels of saturated fats that do not elevate LDL cholesterol and lead to risk of heart disease. It should be expected that outcomes from such studies will be less likely to observe significant effects of either trans or saturated fat on heart disease precisely, because the diets have been beneficial to heart health. It should also be noted that just as there is an absence of robust RCTs investigating effects of reducing dietary saturated fats, there are no RCTs investigating effects of increasing dietary saturated fats – a number of European experimental studies have shown that people who increase the proportion of saturated fats in their diets from ~10% to 12-13% do have increased cholesterol. If it was suggested that increasing dietary fats in the diet was advisable, this would therefore seem questionable.”
Ms Catherine Collins, Principal Dietitian at St George’s Hospital NHS Trust, said:
“Harcombe and associates present an interesting review of 30+ year old medical research and early 1980’s population advice on dietary fat and heart disease prevention. They found, using today’s common tools of systematic review and meta-analysis, a paucity of clinical evidence at that time for supporting dietary fat recommendations to reduce cardiovascular disease mortality. This in an era of the traditional ‘meat and two veg’ home cooked meals, socially acceptable smoking and belief in the flawed assumption that dietary cholesterol intake boosted blood cholesterol levels.
“The limitations of the seven studies evaluated are well described by the researchers. Studies had small study numbers (most with a history of heart disease), were highly varied in dietary and lifestyle approach, and reviewed outcomes over a short time scale – around five years on average. All these factors would influence the outcome – whatever dietary changes were made.
“In contrast to that era, today’s population studies review tens of thousands of people over decades before making recommendations on diet or lifestyle factors, improving the accuracy of findings.
“The authors make some errors in their commentary. The 1977 US guidelines did not target a US population of over 220 million people – 65.5m of this number were children, exempt from adult guidelines. UK dietary guidelines from 1991 (COMA Report) recommended a healthful diet providing up to 35% of calories from fat – which is currently our average intake, from current National Diet and Nutrition Survey (NDNS) surveys. This is lower than the average population diet of 40% calories from fat in the late 1970s (National Food Surveys, 1940-2000).
“Current public health guidelines from NHS choices and Change4life continue this overall recommendation as part of a healthy diet, although NICE guidelines (2014) recommend 30% energy from fat specifically for heart disease prevention http://1.usa.gov/1DU1IoG.
“Should the public be concerned that current advice may be pinned on flawed recommendations from three decades ago? Not at all. With medical knowledge doubling every three years, research has moved us far beyond the single nutrient (fat/sugar/salt) vilification of the early 1980s. As a freshly minted dietitian produced the same year as the NACNE ‘healthy eating’ guideline, I personally found it a miserable read and hard to promote with its ‘Eat LESS fat, eat LESS sugar, eat LESS salt, eat MORE fibre’ messages.
“Fast forward to today, and the authors’ key message to readers to ‘question’ low fat dietary advice is anachronistic to the modern ‘whole diet’ approach to health exemplified by the ‘Mediterranean’ style of eating – one rich in plant-based foods, wholegrains, olive and unsaturated oils, with modest intakes of dairy and meat and even alcohol. A ‘whole diet’ approach provides macronutrients, micronutrients and bioactive components inherent in foods that act synergistically to protect the body from diseases of ageing such as heart disease and cancer.
“Modern population healthy eating advice bases recommendations on food, not nutrients, whether we’re talking free primary school meals or cardiac rehab classes. A food-based approach, currently used by the Change4Life programme to help people make practical dietary swaps to improve health, is easier to understand and adopt, compared to a nutrient swap approach used in research for dietary modelling.
“Finally, this review reminds us that like Saturday Night Fever, tartan culottes and bubble perms, the reductionist ‘single nutrient’ dietary recommendations deserve to be left in the early 80’s where they belong. As do doctors and other health professionals who persist in their persecution of single nutrients whilst ignoring a ‘whole diet’ approach.”
Dr Nita Forouhi, MRC Programme Leader in Nutritional Epidemiology and Consultant Public Health Physician, MRC Epidemiology Unit, University of Cambridge, said:
“The authors’ attempt to apply a ‘retroscope’ to the trial-based evidence available at the time of issuing of dietary guidelines on fat intake in 1983 is unhelpful for several reasons including methodological limitations and interpretation of their work. As such, the current dietary guidelines on fat intake should not be influenced by this study.
“For public health messages on diet, it is vital to consider the range of available evidence across different study designs, as adherence to diet modifications based on dietary advice is challenging, and trial settings may not always represent the ‘real-world’ practice. If policymakers applied the randomised trial evidence ‘bar’ to all dietary recommendations, we would still be waiting for many important public health messages such as the recommendation on 5-a-day fruit/vegetables, or the current deliberations around reducing free-sugars intake and sugary beverages.
“There is convincing evidence both from the current study and elsewhere that reduction in dietary saturated fat has benefits for reducing the bad (LDL) cholesterol. There is also separate convincing evidence that high LDL cholesterol contributes to heart disease, which this study did not appraise. The inability to demonstrate a direct link between high saturated fat diets and heart disease can be due to many factors, including but not limited to the challenges of doing diet trials, the failure to consider what replaces the reductions in saturated fat intake (such as unsaturated fat or refined carbohydrates), and the multiple risk factors that influence heart disease risk, including other dietary factors and non-dietary factors (smoking, hypertension, diabetes, obesity, physical activity, family history and others), with cholesterol levels being one factor among several.
“Our collective efforts would be better placed going forward in investing in conducting the best research to understand the complex inter-relationships between health outcomes and dietary fat, types of fat, and indeed what food sources those fats come from, as the totality of the foods we consume has a mix of different nutrients. The sole focus on a single macronutrient – e.g. fat – is unhelpful and we must place it in the wider context of what replaces it in the diet and what dietary source it comes from. We should also use and develop objective biomarkers of dietary intake, as a big challenge in dietary research is the reliance on people’s self-report of what they eat, which can be unreliable.”
Further information from Dr Nita Forouhi:
Methodologically, the systematic review was restrictive and did not specify important search terms on types of dietary fat, and by focusing only on death-events it omitted non-fatal heart disease events which are important health outcomes. The appraisal of effects of the low-fat diets on blood cholesterol level was poorly done, but still showed substantial benefits, re-endorsing the other evidence on the cholesterol-lowering effect of low saturated-fat diets.
In interpretation, the authors claim that best practice evidence – from randomised controlled trials – was available at the time, but their review demonstrates that there were many limitations of the trials themselves including small sample size, lack of appropriate trial design with non-balanced groups and lack of achievement of randomisation for several important parameters, therefore the evidence was far from “best practice”. Thus it is all the more important to consider the totality of the evidence including from other study designs other than randomised trials.
Reports and studies such that are observational in nature do have limitations including that they do not prove a cause and effect association, whilst randomised trials, such as drug trials, provide the best evidence. Realistically, for diet, we are often limited to observational studies as it would not be practical or indeed ethical to randomise people to follow a specific diet for many years to see who gets a heart attack, another chronic condition, or dies. We have to take action on the totality of the evidence.
Prof. Kevin McConway, Professor of Applied Statistics, The Open University, said:
“This study does establish what it says it establishes, which is that the introduction of dietary fat guidelines in the US and the UK, well over thirty years ago, could not have been based on evidence from randomised controlled trials. That’s because, using modern methods to look at the trial evidence available at the time, that evidence just doesn’t support the guidelines.
“But this does not mean that the guidelines were not supported by any evidence at the time. Trials are not the only source of evidence for policy changes like this. The new report itself points out that evidence for the guidelines came from other sources as well, in particular from population studies. This new research tells us rather little about what the overall evidence base for the recommendations actually was. So it really doesn’t help us much in deciding whether or not the decisions made all those years ago were properly grounded in evidence.
“More importantly, that’s not the relevant question for today. The relevant question for now is whether all the evidence available up to 2015 supports the dietary guidelines or not. If it does, then we should keep the guidelines even if they were based on inadequate evidence when they were first proposed. If it doesn’t, we should change the guidelines, even if they were supported by the available evidence at the time. The accompanying editorial by Rahul Bahl makes it obvious than the position today still isn’t clear-cut. It’s too complicated to be made clear by a study of just some of the evidence available up to 1983.”
Prof. Richard Mithen, Acting Director, Institute of Food Research, said:
“This study focused only on one form of research, randomised controlled trials (RCTs). The vast majority of dietary advice is based not upon RCTs but on epidemiological data. If data was required from RCTs there would indeed be very little advice, and we would not have observed the population health benefits that are likely to have arisen from reduction in saturated fat and salt over the last few decades, despite the lack of supporting evidence from RCTs. It’s true that epidemiology studies can be tricky to interpret, and that correlation does not always mean causation, but in reality it is very challenging to design and carry out randomised controlled trials that are big enough and powerful enough to determine effects that are relevant at the whole population scale. Food is more complex that drugs.”
Ms Victoria Taylor, Senior Dietitian at the British Heart Foundation, said:
“Understanding the true relationship between diet and our health is not simple. Unlike drug trials, studies on diet and disease are difficult to conduct. It would be all but impossible to carry out a research trial where you controlled the diets of thousands of people over many years.
“That’s why guidance in the UK is based on a consensus of the evidence available not just on randomised controlled trials.
“We continue to recommend switching saturated fat for unsaturated fat. This is consistent with a Mediterranean style diet, which is associated with a lower rate of coronary heart disease, and research that has demonstrated a link between increased consumption of saturated fat and raised cholesterol levels. We know that raised cholesterol is a risk factor for coronary heart disease.
“When so much attention is placed on the role of fats in our diet it’s vital we remember that dietary advice on preventing and managing coronary heart disease doesn’t begin and end with it.
“Coronary heart disease is a multifactorial condition and no single food or nutrient is solely responsible for addressing our risk through diet. As well as the fats we eat we also need to pay attention to our diet as a whole and the balance of foods within it.”
Prof. Iain Broom, Research Professor, Robert Gordon University, said:
“Firstly this is not the only recent paper to criticise the introduction of low fat diets to combat CHD. The EPIC study from the EC-funded, Cambridge MRC Epidemiology Unit led, also arrived at the same conclusions (published in March 2014 in the Annals of Internal Medicine). Indeed they went further and stated that the evidence supported a protective effect of saturated fat from dairy products, whilst the governments in both the US and UK have practically destroyed the dairy industry by suggesting that butter, cheese and full fat milk increased CVD risk, when the contrary is true. Richard Smith’s editorial in the Christmas edition of the BMJ also supports the findings of the Harcombe and the EPIC study and severely criticises Ancil Keyes “7 Countries Study” as being inappropriately designed and poorly undertaken with very few subjects in the study and all being men. This, or rather Ancil Keyes, was the basis of the US Government pushing through the low fat aspect of dietary protection from CVD, despite a later “22 Country Study” demonstrating no relationship between fat intake and prevalence of CVD, known at the time of the new dietary guidelines issued by the US Government.
“Secondly, in order to maintain appropriate energy intake by reducing fat in the diet, carbohydrate (CHO) intake was therefore increased to more than 50% of energy intake. This has the effect of increasing the requirements for increased circulating concentrations of insulin. This in itself will tend to change the nature of the LDL cholesterol particles to a smaller size, increase their number and such particles are actually more atherogenic. Increasing circulating insulin concentrations also has the effect of promoting fat deposition.
“A number of physicians, not the least of whom is Richard Feinman, the Editor of Nutrition and Metabolism, around the world believe this change in increasing the total CHO intake has actually led to the current obesity epidemic and consequent epidemic of Type 2 Diabetes Mellitus, that awaits behind the scenes. Both Governments in the US and UK continue to plough the furrow of low fat, high CHO as healthy eating and use this as the mainstay for the strategic management of obesity. The only developed country in the world to look seriously at the evidence and change their Government’s food policy is Sweden – they have reduced the CHO content to between 26 and 40% of energy intake as CHO with concomitant recommendations to increase both fat and protein as a percentage of energy intake and also make the statement that dairy produce is cardioprotective. To date no Government directive or Public Health Policy on diet has had any effect on obesity prevalence, this is continuing to rise year on year, and more importantly there has been no effect in stopping the rise in childhood and adolescent obesity, the latter, with time, having a major and damaging effect on NHS resource and spend.
“The paper itself is a well conducted systematic review of the literature available at the time of the introduction of new National Dietary Guidelines in both Countries, but does only include RCT’s. RCT’s of dietary intake are notoriously difficult to carry out and were not designed for such studies but to test the efficacy of new drugs. Such studies do, however, remain the mainstay of National Guidelines and it is now time for the UK Government to grasp the nettle and stop an uncontrolled experiment, which has gone global and may have had bad outcomes in terms of the obesity explosion and creating a more unhealthy nation with the current idea of “healthy eating”. Apart from this paper and that of Chowdhury’s EPIC study, Public Health officials across the country and appropriate members of Government advisory panels should also read Nina Teicholz’s “The Big Fat Surprise” where there is a forensic destruction of the fat hypothesis relative to a healthy diet.”
Prof. Simon Capewell, Professor of Clinical Epidemiology, University of Liverpool, said:
“This study is right about one interesting thing. The early US and UK Dietary fat recommendations were indeed introduced in the absence of supporting evidence from the randomised controlled trials (RCTs) then available.
“However, Rahul Bahl’s editorial is also right. This study is wrong about many important things. Firstly, it ignores the historical, political and scientific context. Even back then, the totality of evidence had generated a solid and useful coronary heart disease risk factor ‘paradigm’.
“Clear causal associations had been demonstrated for smoking, elevated blood pressure and elevated cholesterol (the latter particularly reflecting dietary saturated fats).
“The Discussion also ignores the subsequent large, positive RCTs including Omni-Heart, DASH and PrediMed; and it ignores the large positive PSC meta-analyses, and it ignores the large positive natural experiments, including Finland, Poland, Cuba, and China. All powerfully linking dietary sat fat trends with coronary mortality trends.
“The paper relies heavily on a much-criticised BMJ opinion piece. And it then misinterprets the Choudhury meta-analysis as being negative. In fact, that showed large coronary heart disease mortality increases associated with stearic and palmitic acids (the most common dietary sat fats).
“But perhaps the greatest crime is embodied within the penultimate sentence in the Discussion: “questioning the alleged relationship between saturated fat and coronary heart disease”. Why say “alleged”? It is surely monstrous to suggest that the scientific evidence linking sat fats and coronary heart disease has not increased hugely since 1983. OMG!”
Prof. Tom Sanders, Emeritus Professor of Nutrition and Dietetics, King’s College London, said:
“This report summarises six small trials conducted more than 30 years ago, which were of short duration and lacking sufficient statistical power to show any effect on mortality rates.
“In my view, the authors are wrong to suggest that advice to decrease total and saturated fat should not have been introduced. Their conclusion fails to take into account the totality of the evidence. Public health guidelines do not belong in the same arena as a drug trial where benefit can be weighed against side-effects. Different types of evidence are available such as variations in the rates of cardiovascular disease between different populations, changes in disease prevalence over time, as well as an understanding of the disease process itself.
“As atherosclerosis, which is the process that eventually leads to cardiovascular disease, develops over a period of 30 years or more, guidelines were made for the whole population. It was also recognised that it was not feasible to conduct sufficiently large dietary trials with cardiovascular disease mortality as an endpoint because it would involve studying tens or hundreds of thousands of people over periods of up to 10 years as well as having a control group whose diet would need to remain unchanged. It was well established that high blood cholesterol and being overweight or obese played a major role in causing atherosclerosis. The disease could also be produced in animals including primates by feeding them a diet high in saturated fat and cholesterol.
“In the 1970-80s the UK and other Western countries were facing an epidemic of coronary heart disease and there was overwhelming evidence that this was caused by cigarette smoking especially in the presence of high blood cholesterol. It was effectively a policy choice between sitting on the fence and doing nothing or opting to follow what the evidence suggested – that cutting total fat intake would help prevent obesity and reducing saturated fat would lower blood cholesterol. Anyway it seems to have turned out okay, as cardiovascular disease rates have fallen in the UK and other countries that adopted the policy of reducing total fat and partially replacing saturated with polyunsaturated fatty acids: in the UK total fat has fallen from 42% to 35% energy and saturated fat from 20% to 12% energy; between 1997 and 2007/8 cardiovascular disease mortality under the age of 75 years fell by 55%.
“The advice did not encourage replacing fat with sugar or refined carbohydrates. It advised selecting lean cuts of meat or poultry and fish in place of red meat, removing fat from meat before consumption, choosing reduced fat milk and using vegetables oils such as olive oil, rapeseed oil and sunflower oil in place of animal fats. This still remains sensible advice because it lowers calorie intake, which causes some weight to be lost, and the reduction in saturated fat lowers low density lipoprotein cholesterol by about 10% compared to a traditional British diet. The change in low density lipoprotein alone would predict a 6% lower risk of incident cardiovascular disease and a 3% lower risk of fatal cardiovascular disease.
“There are now more effective means of lowering blood cholesterol than diet alone (e.g. statins) for those at high risk. However, lowering the population average body mass index and blood cholesterol remain valid targets for preventing cardiovascular disease, which are helped by moderating total and saturated fat intakes.”
Dr Ian Johnson, Emeritus Fellow, Institute of Food Research, said:
“The authors of this review highlight the negative results of relatively short-term intervention trials used to test dietary strategies for the treatment of patients with existing heart disease. They then use these findings to criticise long-term dietary guidelines developed for the very different purpose of minimising the risk of heart disease in healthy populations. National dietary guidelines of this type are based upon many different types of evidence. Whilst it is important to keep both the evidence and the advice under review, this paper does not, in my opinion, add anything important to that process.”
Dr Tim Chico, Reader in Cardiovascular Medicine / consultant cardiologist, University of Sheffield, said:
“The authors take an unusual approach; to go back over 40 years and re-examine the available evidence from randomized controlled trials (RCTs, where patients are randomly assigned to a particular diet) to “second-guess” the panel drawing up dietary guidelines.
“The authors of the current study are correct that RCT evidence is usually most reliable, but there are few such studies, their design is sometimes not perfect, and there are other forms of evidence (such as observational studies). RCTs that try to test which diet is healthiest have their own difficulties; it is notoriously hard to make someone stick to the diet to which they have been assigned. I do not think that the diet recommended by the guidelines is definitely the healthiest diet possible. However, I am sure it is healthier than many other diets. It would be wrong therefore to conclude that drawing up such dietary guidelines has harmed people.
“It is worth noting that the present study used a technique to combine the results of multiple studies called meta-analysis that was not applied to medical studies when the guidelines were first drawn up. It is also worth noting that RCT evidence does not exist for many medical recommendations and practices. In the absence of a clear answer, it seems reasonable that doctors and scientists try to produce the best advice they can with the totality of evidence available. Almost always, this advice will change, sometimes completely, with the addition of new knowledge.
“Sometimes the most important health questions are the hardest to address scientifically, often for rather mundane or practical reasons like cost or the difficulty in getting people to alter their diet. For these reasons, I do not expect that we will ever be able to say for certain what the best diet is for long-term health.”
‘Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis’ by Zoë Harcombe et al. published in Open Heart on Monday 9 January 2015.
Ms Catherine Collins: “commissioned co-author of cholesterol lowering book 2007. No royalties.”
Prof Simon Capewell: “I am a Trustee of the UK Faculty of Public Health, a Trustee of the UK Health Forum, and a Trustee for Heart of Mersey. I am also a founder member of Action on Sugar, and would therefore usually be biased in favour of some of the authors.”
Prof Tom Sanders is honorary nutritional director of the HEART UK, the charity for people with high blood cholesterol, and a scientific governor of the British Nutrition Foundation.
Dr Ian Johnson is an Emeritus Fellow at the Institute of Food Research, and an honorary research fellow in the School of Medicine at the University of East Anglia.