Saturated fats are still the enemy

In recent years, there has been a trend of debunking the relationship between diet and heart disease, and in particular, the relationship between saturated (hard) fat, cholesterol and heart disease. The latest headlines portray sugar as the new enemy and fat as the hero, which can be misleading for the general public. With extensive media coverage on the subject, dietitians and doctors may doubt the advice they would have traditionally given about fat, however, it is important to have confidence in the scientific basis for this advice given to patients.

Cholesterol

Cholesterol is a fat that is essential to life. The problem is that the blood of man contains four times more cholesterol than that of any other animal, and indeed about four times more than we need. 

Most of the cholesterol in our blood is manufactured in the liver, mostly from saturated (hard) fats in the diet. A much smaller amount comes directly from dietary cholesterol, eg. eggs and meat.

It was only in the 20th century that the epidemic of coronary heart disease became obvious. It rapidly became clear that it seemed to relate to a rising standard of living. 

By the 1940s, doctors were beginning to observe that heart attack patients were likely to be smokers, to have high blood cholesterol levels and to have high blood pressure. This led to meticulous research that has continued to this day to establish the causes of atherosclerosis and hence heart attacks, led by giants such as Ancel Keys, Jeremiah Stamler and the Framingham investigators.

But lots of things relate to a rising standard of living – cars, personal computers, television sets, mobile phones, refrigerators, the ability to afford to eat fat and to smoke and so on.

Interestingly, atherosclerosis is confined to man and is not seen in any free-living animal species, unless we interfere with them. This was first shown when Anitschkow induced atherosclerosis by feeding rabbits cholesterol. But rabbits are not really like humans, whereas primates such as chimpanzees are. Left alone they are essentially vegetarian and free of atheroma. They only get hardening of the arteries if a high fat Western-style diet is imposed upon them.

Saturated fat

Worldwide, a diet high in saturated fat is associated with a high blood cholesterol level which in turn is associated with an increased risk of heart attack. To see this you need to look at all countries; the scatter is quite wide but overall the relationship is strong. This is an example of where selective quotation is rife, for example, by selecting one or two countries, one can make the relationship between fat intake and blood cholesterol either stronger or weaker than it really is. The relationship may also not be very strong within a single country, simply because the within person variation in fat intake may be similar to the between person variation. To see the pattern one needs to look at much wider international differences in fat intake.

Causal associations of heart attacks

How do we find out which factors associated with risk of heart attack are causal and which are merely measures of a rising standard of living?

Deciding if an association is causal is easy if there is a single cause such as an infection. It’s more difficult with the atherosclerosis that causes heart attacks because there are hundreds of associations and most are not causal. Smoking, a high fat diet with a consequent high blood cholesterol level, and high blood pressure regularly emerge as causes. 

If there are a variety of factors that relate to heart attacks, how do we find out which are actually causal? It has taken 70 years of grinding research to sort this out. 

We have already mentioned the observations that led to the suspicion that the ‘big three’ (smoking, cholesterol and high blood pressure) were likely candidates, but that wasn’t enough.

In the 1950s, Doll and Hill were very aware of the association between smoking and lung cancer. To establish if the relationship was, beyond any reasonable doubt, one of cause and effect, they established the criteria for causality. Stamler and others subsequently applied these to cholesterol and coronary heart disease. They may be summarised as follows:

• Is it plausible that the association is one of cause and effect? Yes, the relationship between fat consumption, blood cholesterol level and heart attacks may be causal

• Is the relationship strong? Yes, a high blood cholesterol increases the risk of heart attack by approximately three-fold

• Is it graded (eg. the higher the cholesterol level, the higher the risk)? Yes, the risk rises in proportion to the cholesterol level. Hardening of the arteries occurs universally in people with extremely high blood cholesterol levels

• Does the risk factor come before the disease (a ‘temporal relationship’)? Yes, both in studies of people with an inherited high cholesterol level, and in follow- up studies of initially healthy people

• Is the relationship independent (not explained by another factor)? Yes, you can’t explain the relationship away by statistical adjustment

• Is the evidence consistent? Yes, there is consistent evidence across many studies

• Is there also agreement between different scientific disciplines (basic science, pathology, autopsy studies, clinical observation, feeding experiments, intervention studies etc.)? Overall there is a high degree of concordance in the findings of studies from different disciplines

• Does reducing or removing the factor reduce the occurrence of the disease? In populations that reduce their saturated fat consumption, heart attack death rates go down. It is harder to see such a strong effect in individuals because diet alone has quite a small effect. However statin drugs block the ability of the liver to make cholesterol and trials on hundreds of thousands of people have shown that statin drugs reduce both cholesterol levels and risk of heart attack by at least 30%.

Many studies have confirmed that the relationships between saturated fat consumption, blood cholesterol levels and coronary heart disease fulfill all of the criteria outlined and they are, beyond any reasonable doubt, causal. 

Conventional medicine has made many mistakes over the years, but the evidence that the relationships between saturated fat consumption, blood cholesterol and heart attacks is one of cause and effect is as strong as in any other aspect of medical science, and ample to encourage public health actions to reduce saturated fat consumption at population level and the active management of high blood cholesterol levels in individuals.

Basic, effective dietary advice

In addressing a high blood cholesterol level, it is important to give people basic but effective dietary advice. This includes:

• Making positive food choices such as eating fresh, unprocessed foods including fruit and vegetables, unprocessed cereals and fish. These foods have numerous health benefits, and while they may not impact directly on cholesterol levels, they make it harder to eat too much fat and sugar

• Reducing red meat and processed meat intake as this reduces saturated fat. It is important to remind people that processed meat includes foods cooked at home as well as those bought in fast food restaurants. These foods include rashers, sausages, burgers, pies and chicken nuggets

• Reducing processed food intakes such as sweets and cakes, as this can reduce refined sugar intake, as well as restricting saturated fat and transfat consumption

• Reducing intake of fried foods, especially deep-fried foods such as chips and fried processed meats like burgers and sausages, is another way to reduce saturated and transfat intake. 

In reducing foods which are high in total, saturated and transfats, it’s important that these foods are not replaced by sugar. Lowering sugar intake helps to lower triglyceride levels, as does reducing alcohol intake and body weight. In this regard, priority should be given to reducing both sweet foods and drinks such as cakes, biscuits, sweets, and especially sugar-sweetened beverages like fizzy drinks and alcohol. 

Reducing saturated fat isn’t just about avoiding certain foods, it’s also about positive choices – actively ‘displacing’ fat by choosing vegetables, fruits and cereals and replacing foods high in saturated fat with healthier alternatives like oily fish at mealtimes. 

As well as displacing saturated fat from the diet, oily fish also contain omega three fats which can reduce serum triglyceride levels. For this reason, two to three servings of oily fish (either fresh or tinned) per week should be recommended.

For some people, a further option is to increase the intake of stanol/sterol enriched spreads or yoghurts, as these have been shown to have a direct lowering effect on total and LDL cholesterol. These products have quite a small effect and are expensive, so may not be a viable option for all patients. However, increasing monosaturated fatty acid intake from nuts and olive oil may also reduce LDL, as well as increasing HDL levels. 

Fats and refined sugars are of course not the only causes of coronary heart disease. It can also relate to simple overeating. Excess weight, especially tummy fat, increases blood pressure and blood cholesterol. 

Hardening of the arteries leading to cardiovascular disease usually has several causes. Dietary measures, although important, will be far more effective if combined with other lifestyle interventions. This includes smoking cessation, weight management, regular physical activity and control of high blood pressure.  Athough improving diet is only one piece of the puzzle for good health, it is a good place to start. 

Patient information leaflets are available to download from www.stroke.ie