EXPERT REACTION: Is popular belief that saturated fats clog up arteries 'plain wrong'?

1. The misleading title of “Saturated fat does not clog the arteries etc.” suggests that it is likely to exacerbate the confusion and distrust that surrounds dietary advice for the prevention of cardiovascular disease.
   
   Science and Medicine have never suggested that saturated fat itself blocks arteries.
   
   The well-proven hypothesis is that saturated fat in the diet is one of the most powerful environmental determinants for the development and progression of the cholesterol-rich inflammatory process in the artery wall that leads to heart attack and stroke.
   
   The article does not present new evidence beyond 2015 but rather expands on views expressed in an opinion piece in 2013.
   
   In addition to the misleading title, the authors ignore the detailed evidence and shift between total and saturated fat to suit their argument.
   
   The PREDIMED and Lyon Diet Heart Study are acknowledged as landmark dietary interventions, and both studies exemplify the benefits of avoiding dietary saturated fat by substitution of healthier unsaturated fat.
   
   In the PREDIMED diet, the intervention group consumed a low saturated fat Mediterranean style diet in which additional mono and polyunsaturated fats were provided in the form of nuts or extra virgin olive oil. The proportion of saturated fat was diluted (pastry, spreads and meat were discouraged).
   
   In the Lyon Diet Heart Study, the intervention group replaced butter and cream with a polyunsaturated (alpha linolenic acid (ALA)-rich) margarine which reduced their saturated fat intake to 8.3% of energy in comparison to 11.7% in the control group.
    
2. The authors’ general scepticism about low-density lipoprotein (LDL) cholesterol has been refuted by several important developments that they failed to mention.
   
   irstly, the problem of insulin resistance to which they refer is indeed an emerging and important additional cause of cardiovascular disease.
   
   Nevertheless, it continues to involve cholesterol, albeit in a different pattern. Blood levels of fat (triglyceride) increase, redistributing cholesterol amongst particles in a way that leads to underestimation of the number of LDL particles.
   
   Consequently, cardiovascular risk is better reflected by “non-high-density lipoprotein” cholesterol levels. It would be instructive to re-evaluate the impact of different diets from this perspective.
   
   Traditional diet advice has long recognised that replacing simple and processed carbohydrates with healthy fats reduces insulin resistance.
   
   Recent sophisticated analyses from Harvard and elsewhere have examined the way that foods displace each other in these substitutions. They demonstrate that replacing anything with trans fats is detrimental, and that replacing simple and processed carbohydrate with saturated fat is borderline, whilst replacement with mono or particularly polyunsaturated fats is beneficial. This is consistent with the findings of the PREDIMED and Lyon Diet Heart studies.
   
   Furthermore, these studies of nutrients have been re-interpreted in terms of “real food”, such that fruit, whole grain, vegetables, nuts and fish are regarded positively in terms of coronary disease, stroke and diabetes, whilst some potential sources of saturated fat such as dairy are neutral and others, particularly processed meats, are detrimental.
    
3. The importance of blood cholesterol has also been re-affirmed by two recent randomised controlled trials (providing the highest form of evidence in over 40,000 patients) in which 2 non-statin cholesterol-lowering drugs significantly reduced cardiovascular events.
   
   Unlike statins, neither of these drugs had any anti-inflammatory effect, so the benefit must be attributed to reduced levels of non-HDL (harmful) cholesterol-carrying particles.
   
   This is consistent with “Mendelian Randomisation” studies which demonstrate that genetically determined low cholesterol levels are associated with 50 – 90% reduction in cardiovascular risk in the setting of otherwise good health.
   
   Insulin resistance, on the other hand, may arise in utero as a consequence of antenatal factors leading to so-called “epi-genetic” effects.
   
   The dietary determinants of a favourable outcome from pregnancy require further study, but current evidence favours highly polyunsaturated fats over saturated and trans fats.
    
4. The issue of insulin resistance is particularly important in the developing world where children who were deprived of adequate maternal nutrition in utero are thought to have been metabolically re-programmed to cope with future deprivation.
   
   If their food environment alters to provide excess carbohydrate or inappropriate fats, insulin resistance and its consequences can ensue.
   
   A previous opinion piece by the lead author in 2013 was widely publicised at a time when discussion about taxes on “junk foods” was gathering pace.
   
   Ironically, an article in the same edition of the British Medical Journal estimated that a 20 per cent tax on palm oil (a major source of saturated fat) would save over one third of a million lives in India in the coming decade.
   
   Debate as to the advantages and disadvantages of dietary taxes is another issue, but clearly primary producers, the drivers of the cost and availability of the materials for human nutrition, need to remain sensitive to the health consequences of their produce.
   
   Saturated palm oil use has increased 5-fold since 1992 and this includes diversion from non-food uses (cosmetics etc) to food.
    
5. The authors and proponents for dietary saturated fat are not satisfied with current advice that foods with a high saturated fat content should be limited to occasional “treats”.
   
   This prevents healthcare workers from effectively managing cardiovascular risk by means of diet.
   
   As a compromise, proponents could acknowledge that their advice to liberalise saturated fat consumption will lead to an increase in the number of individuals who will require cholesterol-lowering therapy (statins and non-statins).
   
   They have eschewed this option by vilifying those treatments in a manner that has been comprehensively refuted by the esteemed medical journal, The Lancet.
   
   The harm done in the process has been documented internationally, including increased mortality rates in Denmark.
   
   By recommending a cholesterol-raising nutrient without providing a counterbalance, the authors want to have their cake and eat it. They justify this high-risk approach with the assertion that one of the most thoroughly researched areas of medical science is an hoax, but this is not the case.

It is fair to say that the role of saturated fat and coronary heart disease has been overstated.

It is simplistic to attribute a complex disease to just one fatty acid and there is increasing evidence that many dietary components in food as well as physical activity and mental health all have an important role to play. 

Diet is always more complex than avoiding one item - be it sugar or saturated fat. We have forgotten about the positive aspects of whole foods.

These are: 

• Higher fat foods such as oily fish, nuts, seeds and olive and other liquid oils. 
• Whole grain breads and cereals that are high in soluble and insoluble fibre and have a low glyceamic response.
• Fruits and vegetables that have consistently been associated with lower cardiovascular mortality.
• Dairy foods - with new research showing that full fat cheese is neutral to plasma cholesterol.
• Lean protein foods including eggs! 

But should we revert back to butter, coconut fat and fatty bacon along with the major sources of saturated fat, salt and refined carbohydrates in our food supply -" junk" or discretionary foods?

You know the ones...we eat 36% of our kilojoules on these each day.

So let's not quibble about which single dietary component we should or should not eat.

Focus on eating more vegetables and less junk food - it's a message no one can dispute. 

In this contextually useful paper, the cardioprotective role of dietary diversity is seen to be superior to individual nutrients such as saturated fatty acids.

The evidence has been going in this direction for some time with studies of dietary patterns in Europe and Asia, even Australia, paving the way.

This is a very difficult paper to comment on as it is a mixture of truths, half truths and misconceptions.

What is rightly stated is that there is more to coronary disease than saturated fat and (low-density lipoprotein) LDL cholesterol.

It is also true that the objective in prevention is to stop the final event before a heart attack or major cardiovascular event. This occurs when a clot or thrombosis forms over a crack or erosion in a diseased artery wall and rapidly occludes an artery.

It is correct that inflammation in the artery wall plays a role. It is also correct that regular physical activity prevents many of the factors leading to that stage.

However it is incorrect to imply that saturated fat and LDL cholesterol are completely blameless. Eating saturated fat increases LDL cholesterol. People with high LDL cholesterol have more heart attacks. There is more to it than this but leaving LDL cholesterol out of the story is misleading.

Where the article is most misleading is the description of the current paradigm. Nobody, least of all authoritative health authorities believes ‘the conceptual model of dietary saturated fat clogging a pipe’. There are a number of poor and discredited studies quoted to support the arguments presented and confusion between high total fat in the diet and high saturated fats.

Furthermore, saturated fats are not a single thing and we eat food, not individual biochemical components.

The Heart Foundation message is: To address diet-related health problems, including heart disease, diabetes and cancer, you should limit foods containing saturated fat, such as biscuits, cakes, pastries, pies, processed meats, commercial burgers, pizza, fried foods, potato chips, crisps and other savoury snacks and sugar-sweetened beverages.

As a whole, this group of foods is the leading contributor to saturated fat and trans fat intake, but also contributes substantial amounts of energy, added sugar, refined carbohydrates and sodium; and takes up space in our diets where core foods should be.

There is no doubt that inflammation is involved in vascular disease and that insulin resistance and diabetes are important contributors, as well as are fruit and vegetables and polpyphenols.

Many interventions with a variety of agents that lower low-density lipoprotein (LDL) cholesterol by different mechanisms clearly show that lowering LDL cholesterol is important.

Saturated fat elevates LDL cholesterol to a small degree so lowering saturated fat and replacing it with unsaturated fat lowers LDL cholesterol and has been shown to reduce events, although not in the two trials they quote.

Saturated fat also enhances insulin resistance and inflammation so replacing it with unsaturated fat has other benefits than just lowering LDL cholesterol.

Food is an important part of our life.

The natural food containing saturated fat has long been an important nutrition source for humans for thousands of years. Unsaturated fat is an important structural component of every single cell in our body and it is also part of the important molecules which are important for cells to talk with each other. Therefore, our body’s function partially depends on saturated fat.

The idea that saturated fat increases cardiovascular disease is only a misconception, because there is no clinical evidence to back it up.

On the contrary, depriving saturated fat from our diet, unsurprisingly, has been shown to increase mortality risk.

Therefore, to improve our health, we need to stop unfruitful attempts to reduce saturated fat intake; rather, we should focus on some more useful, enjoyable and much cheaper ways to do it. These better choices including walking, other moderate exercises, meditation, etc.

However, regarding the fat - frequent consumption of deep fried food using fat (both saturated and unsaturated) has been reported to be linked with worse health outcomes, including coronary artery disease, heart failure, diabetes, and hypertension, etc.

Therefore, it is advisable to avoid frequent intake of deep-fried food.

What’s really important for your heart health? Is it simply a balanced diet, exercise and reducing stress?

A recent review is highlighting the benefits of a healthy lifestyle as the key way to reduce your risk of a heart attack – advocating a healthy diet, exercise and stress reduction.

Controversially, the authors argue that surgery to unclog blood vessels, and drugs and restrictive diets that reduce “bad” cholesterol are of no significant benefit in preventing heart attacks or reducing death. They instead provide a review of studies to support instead the adoption of a diet typical of Mediterranean cultures, being high in good fats such as those found in nuts, olive oil, vegetables and fish, stating that the benefit is derived not from lowering of bad cholesterol (LDLs) but fixing the balance of "good" cholesterol (HDL) to overall (or total) cholesterol in the blood. Another readily accessible and highly successful lifestyle intervention they are promoting improves heart health is exercise – with the authors quoting studies showing that 30 minutes of moderate activity more than 3 times a week improves insulin sensitivity, and therefore reducing the risk of heart disease. The authors also talk about the impact of chronic stress causing increased levels of stress hormones that have a negative effect on our heart health. 

While our individual risk of heart disease is influenced by genetics, environmental factors and other disease states, and advances in medical treatments, be they surgical or drug-based, have evidence both for and against their effectiveness, this article does highlight the data showing the powerful effects of a healthy diet and exercise, and that this can be readily achieved by each of us through simple lifestyle interventions.

Saturated fat is an essential element in our diet. Our body uses saturated fat for energy, hormone production, facilitating vitamin absorption and most importantly, for coating and padding to protect our cellular membranes and organs. 

In the last two decades, saturated fat has been demonised as the main culprit leading to fatty deposits in the coronary artery and causing heart attacks (myocardio-infarction) when the deposits block up the artery.

The truth is that myocardio-infarction is not directly caused by deposition of saturated fat called ‘plaque’ in our coronary arteries.  The main cause of myocardio-infarction is the rupture of the plaque [1]. The main cause of rupture is inflammation [2-4]. There are many factors which will trigger an inflammation response in our body. These include: infection, stress, allergy, and injury…etc. Other genetic factors and social and environment factors also play an important role.

I salute the authors of this paper for their strong spirit of science, identifying new evidence which challenges previous views.  “The important thing is not to stop questioning. Curiosity has its own reason for existing.” - Albert Einstein

As an epidemiologist, public health practitioner and an educator, I concur with the author’s suggestion of the non-pharmaceutical approach to maintain good health.  This simple approach involves an easy short daily walking exercise and eating a good balanced diet with everything consumed in moderation.

References:

1.            Hansson , G.K., Inflammation, Atherosclerosis, and Coronary Artery Disease. New England Journal of Medicine, 2005. 352(16): p. 1685-1695.

2.            Kovanen, P.T., M. Kaartinen, and T. Paavonen, Infiltrates of Activated Mast Cells at the Site of Coronary Atheromatous Erosion or Rupture in Myocardial Infarction. Circulation, 1995. 92(5): p. 1084-1088.

3.            van der Wal, A.C., et al., Site of intimal rupture or erosion of thrombosed coronary atherosclerotic plaques is characterized by an inflammatory process irrespective of the dominant plaque morphology. Circulation, 1994. 89(1): p. 36-44.

4.            Moreno, P.R., et al., Macrophage infiltration in acute coronary syndromes. Implications for plaque rupture. Circulation, 1994. 90(2): p. 775-8.

I’m not a cardiologist, but I know the argument raised in this article will be highly controversial amongst the cognescenti. I think their argument has been overstated, and that the evidence that lowering LDL (or LDL/HDL ratio) reduces coronary mortality is watertight. However  I agree that the common mantra- attributing elevated LDL  to overconsumption of saturated fats - is also overdone.

I should also say that for me the authors lose some credibility when they don’t appear to understand the detail of the arguments about fat consumption. The detail is important because that seems central to their argument. They  misunderstand, or overlook, the distinction between two very different kinds of unsaturated oils that figure in their argument : Linoleic acid (omega 6- maybe bad) and alpha linolenic acid (omega 3 – good). They make this mistake in the  first page, top para of the last column, where they wrongly refer to "alpha linoleic acid” as a better dietary component along with polyphenols etc (they should get it right- linoleic is probably a “bad?” oil, and this is the main constituent of many so-called preferred polyunsaturated oil foods such as margarine or cooking oil). I also suspect their suggestion that walking just 22 minutes a day is a better way to prevent coronary disease than eliminating saturated fats from the diet, is also an overstatement of the evidence