Trans fats are bad news for heart health but what should we do about them? Should we give them top billing in the new Dietary Guidelines, demand trans fats be declared in nutrition information panels on food labels, or regulate them in some other way? Hang on … haven’t we already dealt with trans fats?
All fats in our diet are made of substances called fatty acids. Although there are hundreds of them, fatty acids can be grouped into three broad classes – saturated, monounsaturated and polyunsaturated. By far the majority of mono- and polyunsaturated fatty acids have a characteristic ‘bent’ shape, which the scientists call cis. However, a small proportion of unsaturated fatty acids are ‘straight’ and this trans shape gives them different physical properties, more like saturated fats. Fats with a high proportion of trans fats (or saturated fats) tend to be solid, not liquid like oils rich in cis fatty acids.
Where do trans fats come from?
There are two sources of trans fats in the human diet – animals and factories. Until relatively recently an industrial process called partial hydrogenation was commonly employed to ‘harden’ vegetable oils. This involved converting some of the unsaturated fats in vegetable oils to saturated and trans fats, turning the oil from liquid to solid. These hardened fats were used in the baking industry where solid fats similar to butter were required and could also be blended with liquid vegetable oils to make soft margarines.
Trans fats are also formed in the gut of ruminant animals such as cattle, sheep and goats. Unsaturated fats in an animal’s feed undergo partial hydrogenation in the rumen, increasing the proportion of saturated and trans fats – basically the same process that occurs in a factory. As a result about 3-5% of the fatty acids in the meat and milk of these animals are trans fats. Butter and the fat on a rump steak are solid at room temperature because of the high proportion of saturated plus trans fats they contain.
‘Natural’ versus ‘artificial’ trans fats
Trans fats in meat and dairy foods are sometimes referred to as ‘natural’ trans fats to distinguish them from the ‘artificial’ trans fats made in a factory. This is just a public relations exercise. The majority of the trans fats found in hardened fats are also found in meat fat and dairy fat. So-called ‘natural’ and ‘artificial’ trans fats are basically different combinations of the same substances. And they have the same effect on the human body.
Are trans fats bad for health?
Early studies of the health effects of trans fats found they had a neutral effect on the total level of cholesterol in the blood, similar to olive oil. No worries there. But in 1990 some Dutch researchers took another look at trans fats and discovered their unique double negative effect on heart health: trans fats raise the level of bad LDL-cholesterol in the blood and lower the good HDL-cholesterol. Both effects would be expected to increase the risk for coronary heart disease. Many studies have now confirmed these findings and it is clear that both ‘artificial’ and ‘natural’ trans fats have similar adverse effects on cholesterol. Large population studies have found that trans fats are indeed associated with increased risk for heart disease.
Do Australians eat a lot of trans fats?
Intake of trans fats in Australia is low. In a recent study by the food regulator, FSANZ, the average trans fats intake was about half of one percent of daily calories, which is half the upper limit recommended by the World Health Organization. Nearly three-quarters of the trans fats in the Australian diet now come from so-called ‘natural’ trans fats, primarily from dairy products. ‘Artificial’ trans fats now comprise just one-eighth of one percent of daily calories – a tiny figure.
Trans fats intake has never been particularly high in Australia, partly because much of our commercial frying has traditionally relied on meat fat (low in trans fats) or palm oil (no trans fats). This is in contrast to the United States where partially hydrogenated soybean oil was widely used for commercial frying and consequently intake of trans fats was two or three times that in Australia. Nevertheless, the intake of trans fats by Australians in the early 1990s was 2.0-2.5% of daily calories – four to five times what it is now. So what happened in the meantime?
Two waves of trans fat reduction
Australia’s leading nutrition authorities including the NHMRC and the Heart Foundation were quickly onto the new trans fats developments, making recommendations in expert reviews. In 1996, the Heart Foundation introduced changes to the margarine criteria for its Tick food approval program and the industry quickly responded, minimising the trans fats content of the majority of leading brands of table spreads by late 1997.
In the early 2000s another wave of trans fats reduction commenced as many food manufacturers began combing through their product portfolios weeding out the trans fats. Quick service restaurants, a major donut chain and a leading supermarket chain all played their part. During this phase of trans fats reduction the Commonwealth Government was actively involved and deserves credit. Public health nutrition relies on inter-sectoral collaboration – nutritionists, policy makers and industry working together – and on this occasion it happened and it worked.
Should trans fats be further regulated?
I recently wrote an article on this topic which is now available online as an ‘early view’ paper ahead of publication in the journal Nutrition and Dietetics. My answer was no based on the facts summarised above. As the job of lowering trans fats intake is already done what would be the purpose of further regulation? The amount of trans fats in our diet is less than that in the Danish diet which is often held up as an example of what regulation can achieve. Advocates of regulation do not appear to be aware that by far the majority of the large fall in the trans fats content of the Danish diet occurred before anti-trans regulations were introduced.
Trans fats and the draft Australian Dietary Guidelines
It was surprising to see trans fats introduced into the top line messages of the draft Australian Dietary Guidelines. Firstly, there was no systematic literature review on trans fats so there was no evidence base on which to base a new guideline (there was no review of saturated fats either). Also, there was only passing reference to trans fats in the text of the Guidelines, which basically said trans fats intake is very low in Australia. And there is the issue of practicality. How could the general public implement the advice as the amount of trans fats in most food products is not currently required to be included in nutrition information panels? Why elevate this issue now when in public health terms it’s already done and dusted?
Best dietary advice?
In Australia, the best advice to lower intake of trans fats is to choose lean meats and low fat dairy products, which also lowers intakes of saturated fats. Other than that, don’t worry.