Coronary heart disease (CHD) is the leading cause of death both in the UK and worldwide being responsible for more than 73,000 deaths in the UK each year. About 1 in 6 men and 1 in 10 women die from CHD. It can manifest its self as angina pains or as heart attacks occurring when the heart’s own blood supply (called coronary arteries) is inadequate being clogged up by disease process called atherosclerosis. It is known the clogs (called atheroma plaques) are made up of fat and cholesterol and involves an inflammatory process (likely related to oxidised LDL) but what exactly triggers it is complex and not fully known. The same atherosclerosis process is involved in 85-90% of strokes and in several other illnesses. There are several established risk factors each being independent of the other for CHD with the biggest being tobacco cigarette smoking, diabetes (including pre-diabetes & insulin resistance), high blood pressure, lack of exercise, obesity and abnormal cholesterol profiles. Dietary factors can influence these risk factors we will focus on particular types and the evidence behind them. This is highly relevant and important today as it was 40 years ago due to mixed messages being sent by some experts. The pretend experts (quacks) who want to be seen as the pioneers in health have jumped on the band-wagon taking the contention to a whole new level such that butter and ghee are being viewed as healthy.
Difficulty in Studying Foods compared to Medicines
It is scientifically difficult to attribute disease causation to dietary factors. Relationships (associations) are first made through surveys or observational studies, but recording exactly what people eat is difficult and can involve recall bias. People eat very varied diets, and maybe over time diets change making baseline group difficult to match exactly in an intervention or control groups. Where a change in diet is advised it can have an unreliable effect as several variables can be at play in the diet; reducing one nutrient may increase another or it may affect calories or affect absorption of other nutrients. Diets & illnesses in one region (or even one time period) can be vary greatly such that dietary advice for in one region may not be fully applicable in another region e.g supplementing milk with Vitamin D. In contrast a drug trial, where there will be one variable of where the drug was taken or not taken, is more easier to control and determine the variable factors. Adherence is an important problem in drug trials but a much bigger problem in trials of diets, as people may find it very difficult to follow an unfamiliar diet. Also, the trials are usually short-term and rarely include hard outcomes such as heart attacks or deaths. Finally we need to recognise bias in the forms of overenthusiastic scientists, poor science particularly with how other risks factors have been accounted for or even over-accounted for, massive conflicts of interest and politically driven policy makers can make deeply damaging mistakes. The food world is a large big business industry and much depends on what people are talking about in the media including social media and health magazines, celebrities and more so the views of experts or even those that are perceived as experts as discussed elsewhere.
Saturated Fat, Cholesterol and CHD
Fats consists of several types and from them are
- SFA – Saturated fats – found in foods like fatty cuts of meat, butter, ghee, palm oil, coconut oil, lard, cheese, especially hard cheese, cream, soured cream, ice cream, some savoury snacks and chocolate confectionery, biscuits, cakes and pastries.
- MUFA – Monounsaturated fats – found in foods like olive oil, rapeseed oil including their spreads, avocados and some nuts like almonds, brazil nuts and peanuts.
- PUFA – Polyunsaturated fats – two types omega-3 and omega-6.
- Omega-3 fats – found in oily fish such as mackerel, kippers, herring, trout, sardines, salmon and fresh tuna. Walnuts, flaxseed oil, soybean, and canola oil
- Omega-6 fats – found in vegetable oils such as rapeseed, corn, sunflower, black seed and some nuts.
- Trans fats – partially hydrogenated fats – unsaturated fats that are made more solid. Mostly artificial and previously used for frying or as an ingredient in some processed foods such as biscuits and cakes however in recent years many food manufacturers have abandoned using it as universal agreement to its harm in affecting lipids as proven in trials. Trans fats can also be found naturally in some foods at low levels, such as those from animals, including meat and dairy products.
Falling Incidence but High Prevalence of CHD
Saturated fats have shown to increase the bad type of cholesterol transporters called low density lipoprotein (LDL) cholesterol in the blood with the exception of stearic acid, found in dark chocolate, which has no effect on bad cholesterol. The problem is that some saturated fat subtypes increase the good cholesterol (called high density lipoprotein – HDL) as well as the bad LDL cholesterol and this is the cause for controversy and contention upon the likely net effect.
Since the 1970’s there have been public health campaigns to try to reduce saturated fats and bad cholesterol in the developed (industrialised) countries and over the past few decades there has been a reducing trend in cholesterol as evidenced by Farzadfar et al. This decline has been mirrored by a decline in heart disease (CHD) in the form of reduced number of heart attacks and more importantly reduced number of deaths from heart disease as reviewed by Tunstall-Pedoe.
This last point is important as many will try to make you believe that CHD is rising in developed countries, saying so for a variety of reasons but mostly trying to convince people with the perception that the public health dietary campaign/strategy is outright failing. However, due to the aging of the population and better survival of those affected, the number of people who suffer with the illness (called prevalence) remains high. These are important concepts to not confuse but unfortunately often do; incidence (rate of new cases) and prevalence (number of known cases).
There have been some recognised problems with the strategy but the principle concept of reduction in cholesterol is being achieved and is being mirrored with a reduction in CHD disease is an overall indication that the strategy has had a partial effect. Matching trends (correlation) do not prove a definite link of causation but this relationship between cholesterol and CHD gives a possible indication particularly more so with large numbers as was seen in a large study (meta-analysis of observational studies) of nearly 900,000 adults in developed countries which showed a linear falling relationship between total cholesterol and CHD death rates. A similar relationship has been demonstrated between cholesterol and non-fatal CHD in many developing regions (particularly Asia) where a worsening trend in both was shown. This is not to say that cholesterol is the only risk factor for heart disease as there are some studies where there is low cholesterol in the blood yet death from heart disease is noted and this is easily explained by not accounting for the other known risk factors such as smoking and other illnesses.
Problem with the Low Saturated Fat strategy
The food industry had to replace the reduction in saturated fats that our governments demanded with something else. Initially this replacement was trans fats which were later shown to adversely raise bad LDL cholesterol and reduce the good HDL cholesterol. This was subsequently replaced by interesterified fats (hydrogenated and molecularly changed) the initial effects of which appear neutral on fasting cholesterol profile but longer studies maybe needed. The food industry in order to provide low-fat or fat-free products have turned to carbohydrates particularly refined carbohydrates. This we will discus more in part 2 where we tackle the issue of sugar.
So we have a link between cholesterol and heart disease (CHD) and likewise we know that a low saturated fat diet reduces bad LDL cholesterol but this does not imply low saturated fat in the diet will achieve the same outcome of lower CHD. The issue however is not straight forward as it appears because when lowering saturated fat in the diet it will naturally be replaced by ‘something else’ and that something else can not also be a risk factor for heart disease otherwise, although we reduce one risk factor we increase another risk factor and the net effect maybe no change. This may explain why we have conflicting studies where some show no association between dietary saturated fat and CHD such as Siri-Tarino et al where reduction in saturated dietary fat was looked at without details as to what replaced it from other nutrients due to a large variation of the individual underlying studies. Likewise the Women Health Initiative found no net effect when saturated fat was replaced with carbohydrates.
In opposition to this, a study by Mozaffarian et al where a reduction in dietary saturated fat had been replaced with polyunsaturated fat resulted in a 19% reduction in CHD events (corresponding to 10% reduced CHD risk for each 5% energy of increased PUFA). The same study also showed replacing saturated fat with carbohydrates did not cause a reduction in CHD events. It is worth noting that the benefit shown was from a meta-analysis of eight blinded randomised control trials (RCTs) which is a much stronger evidence than the meta-analysis of cohorts by Siri-Tarino. We also have other studies that support replacement of saturated fat with polyunsaturated fat rather than carbohydrates. Further support from a 2012 Cochrane systematic review found no effect on deaths from CHD or all causes (as the duration was short) but did find a 14% reduction in cardiovascular events in men (not women) when saturated fat was substituted for either monounsaturated or polyunsaturated fat but it was unclear which of the two was better.
(For the sake of completion there has been a meta-analysis study of both RCTs and cohorts by Chowdhury et al which did not support that PUFA replacing SFA however this has been strongly criticised for a variety of reasons, mainly by the addition of a single RCT study which widened the confidence intervals and discussing it here will get a bit too lengthy and dry for some.)
The traditional Mediterranean diet overall is a moderate-fat diet but low in saturated fat and high in monounsaturated fat and moderate in polyunsaturated fat. It is rich in legumes, fruit, vegetables, whole grains (including pasta and couscous), fish & olive oil while low in consumption of red meat, milk, refined grains, and sweets. Many studies already suggested (but not prove) that a Mediterranean diet is protective against heart disease but what specific factors within the diet that may help remained controversial. An interesting Spanish study called PREDIMED randomly assigned participants who were at high cardiovascular risk but not established heart disease to one of three diets;
- a Mediterranean diet supplemented with extra virgin olive oil (1 litre/week, 4 table spoons daily),
- a Mediterranean diet supplemented with 30 grams of mixed nuts per day (walnuts, hazelnuts and almonds), or
- a control Mediterranean diet who were advised to reduce dietary fat without calorie restriction.
Both the intervention groups had a significant 30% reduction major cardiovascular events which included heart attacks, strokes and deaths from cardiovascular causes. Here the nuts are a mixture of polyunsaturated & monounsaturated fat and various other minerals and antioxidants while the extra virgin olive oil is predominately high in monounsaturated fat. A meta-analysis study by Nordmann et al that included the aforementioned study (first 2 year only) along with five other RCT trials in overweight individuals (one trial was in those with established CHD disease and the rest primary prevention). Here Mediterranean diets compared to a low total fat diet were more beneficial in reducing weight and blood pressure when the heart is relaxed (called diastolic BP), total cholesterol and inflammatory markers (high sensitivity CRP) at the two years mark. Importantly this meta-analysis lacks the duration of the original PREDIMED study and had insufficient data on heart disease events and deaths. Lyons-heart study showed a benefit of Mediterranean diet in those after their first heart attack.
So bottom line so far is that determining the best diet is something difficult. Regional and time period variation of diets & illnesses can be vary greatly requiring specific dietary advice to a particular region or time period. Despite this there is very good support (overwhelming but not conclusive) demonstrating the link between bad LDL cholesterol and heart disease (CHD) with both having reduced over the past few decades in the western world and increase together elsewhere in Asia. Likewise there is good support (overwhelming but not conclusive) that the traditional Mediterranean diet is better than the typical western diet. The Mediterranean diet is characterised by high consumption of legumes, fruit, vegetables, whole grains (including pasta and couscous), fish & olive oil while low in consumption of red meat, milk, refined grains and sweets.
There is clear evidence that replacing saturated fats with carbohydrates does not benefit heart disease. However replacing saturated fat with polyunsaturates does benefit heart disease. Mediterranean diets supplemented with further extra-virgin olive oil (4 table spoons daily) or mixed nuts (30 grams daily) particularly hazelnuts, almond and brazil nuts gives an additional benefit where a 30% reduction from cardiovascular events in primary prevention (those without established heart disease) has been established. Likewise the Mediterranean diet is beneficial in those with previous heart attacks.
More importantly eating oodles of saturated fatty foods like butter, ghee and cream is not established to be beneficial in this time of ours and in the western climate. It is possible they may have a role to play in times where undernourishment or anorexia were a problem in times gone by. Replacing them with extra-virgin olive oil is a more sensible option with the current medical evidence strongly supporting that.
There is some mixed messages from one or two young experts regarding butter & ghee as neutral upon the heart. But as they have a proven negative effect on the fats and cholesterol in the blood then this view is premature and needs more evidence to establish it.
As for the pretend experts (quacks) and those duped by them, who say saturated fat like butter & ghee are good for you have no credible evidence that shows increasing saturated fat reduces heart disease relative to a control. They can be safely ignored as they have no evidence and little understanding.
The blessings of olive oil and the tree producing it are established in the Qur’an and Prophetic Sunnah, which is a separate discussion in itself.
In part 2 we will move on to discussing sugar and where it stands in the controversy of heart disease.