This week, though, a British Medical Journal article by cardiologist Dr Aseem Malhotra which urges us to choose butter every time hit the headlines. So, are our beliefs about the 'heart-healthy' properties of margarine built on solid scientific foundations, or just the result of slick marketing and misinformation? Is it time we got our fats straight?
Butter
While the saturated fat that makes up the bulk of butter might boost cholesterol levels in our blood, any effect here is actually irrelevant: it's the impact it has on health that counts. All the most recent, major scientific reviews of the evidence simply fail to find any link between intakes of saturated fat and risk of heart disease.
These 'epidemiological' studies fail to impugn saturated fat, but cannot be used to determine 'causality' (whether or not saturated fat causes heart disease). More enlightening are studies in which the health outcomes of individuals who cut back on saturated fat or replace it with supposedly healthier fats are compared with those who do not make these changes.
A comprehensive review of the literature encompassing almost 50 such studies was published by researchers from the respected Cochrane Collaboration in 2012. Reducing and/or modifying fat in the diet did not reduce the risk of heart disease (or stroke, or any other chronic disease) at all. Life expectancy was not extended by a single day either. The evidence as a whole strongly suggests that our belief that saturated fat causes heart disease and has broadly harmful effects on health is a myth.
The next most plentiful fat in butter is monounsaturated in nature. This type of fat is found in foods such as olives, olive oil, nuts, seeds and avocado, and is associated with improved heart health.
Butter also contains small amounts of what are known as 'trans fats'. Trans fats can be formed during the processing of fats, and are said to cause heart disease. However, the trans fats found in butter have a different chemical nature to those found in industrially-produced fats (such as those found in some margarines). Crucially, there is evidence that while industrially-produced trans fats do indeed have links with heart disease, those that occur naturally in the diet do not.
Margarine
The original health claims for margarine centred on its lower saturated fat content compared to butter. But, seeing as the evidence essentially exonerates saturated fat, this claim has no legs.
Margarine's principal ingredient comes in the form of 'vegetable' oils such as sunflower, corn or safflower oil. These oils are rich in so-called omega-6 fats - one of the two main forms of 'polyunsaturated' fats. Omega-6 fats are vigorously promoted as 'healthy', but in general terms promote inflammation and blood clotting - two things that would be expected to raise heart disease risk. In recent years, many researchers have raised concerns about the considerable glut of this type of fat in the diet, including from processed foods.
Some margarines also contain omega-3 fats (the other major type of polyunsaturated fats) that have generally beneficial anti-inflammatory and anti-clotting properties. However, this will generally be in small amounts and in a form (alpha linolenic acid) that may not confer the health benefits ascribed to the omega-3 fats found in oily fish (EPA and DHA).
Vegetable oils are liquid at room temperature, and need to be solidified to make them suitable for spreading. This can be done through chemical processing such as 'hydrogenation' or 'interesterification'. The end result will be at least some fats that are unknown in nature - a quality that is likely to bring with it some none-too-healthy properties. For me, adding processed fats to butter to make them 'lite' or spreadable simply risks adulterating it from both a nutritional and taste perspective.
Certain spreads have supposed added value for health by being based on monounsaturated fat-rich olive oil. However, liquid olive oil requires solidification through processing, and this likely detracts from any healthy properties it may have and, again, stands to impart some unhealthy characteristics too. Plus, like other margarines, olive oil-based spreads will generally have other processes inflicted on it including bleaching, deodorising, colouring and flavouring. An olive oil spread is a very far cry indeed from the extra virgin olive oil we may use for roasting vegetables or as the basis for a salad dressing.
Whatever the base ingredients in margarine, the end product is always a highly processed and chemicalised foodstuff - in stark contrast to the relatively natural nature of butter (made by the churning or milk or cream).
Bearing in mind the fact that margarine is so often assumed to be the hands-down winner in the battle with butter, you might expect there to be plenty of evidence for its superior health effects. Actually, the evidence in the area is scant, and what exists should give us cause for concern, I think.
There are, for instance, two epidemiological studies in which the relationship between butter and margarine consumption and risk of cardiovascular disease was assessed. In neither study was butter consumption found to be associated with increased risk. However, it was a different story for margarine: both studies linked its consumption with worsened health outcomes.
Again, this sort of evidence cannot prove causality. However, even more concerning are the findings of what is known as the Sydney Diet Heart Study. Here, men were split into two groups. In one, men ate their normal diet, while in the other the men were instructed to eat a diet rich in safflower oil, including safflower oil-based margarine. The men on this 'heart-healthy' diet actually ended up being 74 per cent more likely to die of heart disease.
Cholesterol-reducing margarines
Recent years have seen the emergence of cholesterol-reducing spreads into the market. It's often assumed that cholesterol reduction is beneficial to heart health. However, several cholesterol-modifying drugs have not been found to deliver on their promise, and some have been found to actually harm heart health. Plus, overall, taking dietary steps to reduce cholesterol has not been found to have broad benefits for health.
Again, the effect that a foodstuff has on cholesterol levels should not be our focus, but the impact it has on health. What evidence do we have that cholesterol-reducing margarines reduce the risk of heart disease, heart attack or overall risk of death? Not one single study of this nature exists in the scientific literature.
Some cholesterol-reducing margarines contain 'plant sterols' that partially block absorption of cholesterol from the gut. However, sterols may make their way into the bloodstream too, and evidence links higher levels of sterols in the blood with increased risk of cardiovascular disease. Perhaps worse still, there are several studies that show sterols have the ability to damage tissue and induce worse health outcomes in animals.
While the British Heart Foundation and many doctors heartily support the use of sterols, the National Institute of Health and Care Excellence (NICE) explicitly advises against their routine use.
In the final analysis, I find it impossible to reconcile margarine's heart-healthy image with the facts. The fat-phobia that drove our broad switch from butter to margarine in recent decades never did have any meaningful scientific support, and I believe has been a huge retrograde step in terms of our health.
I am a practising doctor and the author of several books on nutrition, and in over 20 years I have not bought a single tub of margarine, nor have consciouslylimited butter in my diet. There's little doubt in my mind that butter is better, and not just in terms of how it tastes. To my mind, butter need not be a guilty pleasure at all, but just a pleasure.
Its like arguing whats deadlier a 1000m free fall drop onto concrete or 100m drop.
There is no reason to add fat of any kind in a pure form to food.
Olive oil is also not healthy even though it is compared to butter.
Eat whole foods. Not processed crap.