Although the headlines have got it wrong the science relating to saturated fat and heart disease has evolved considerably. But Australia’s public health nutrition policy makers are blissfully unaware and are implementing science that’s out of date.
In March yet another headline appeared in the mainstream media stating ‘No link found between saturated fat and heart disease’. The media delights in stories about diet that appear to contradict the status quo and, of course, relevant industry groups always put their public relations firms into action whenever an opportunity presents itself. Hence the misleading headlines.
Certainly there have been recent developments in how the coronary risk associated with dietary saturated fat is understood but it has to be said that the significance of these findings has still not fully registered with many nutritionists and policy makers in Australia, let alone the media. So let’s recap.
The way things were
Prior to 2009 many dietary guidelines around the world included a recommendation to eat less saturated fat on the grounds that it increased the risk for coronary heart disease. But there was always an unstated corollary to ‘eat less saturated fat’ i.e. eat more of something else. If your body weight is stable and you just eat less saturated fat you will start to lose weight, because saturated fat contains calories. To maintain weight while eating less saturated fat you have to eat more of other calorie-containing nutrients, such as carbohydrate, monounsaturated fat or polyunsaturated fat. So ‘eat less saturated fat’ really meant replace saturated fat with a healthier macronutrient.
The assumption of the old dietary guidelines was that it didn’t really matter what you replaced saturated fat with – it was thought that all replacements would lower the risk for heart disease. However, we now know that this assumption was wrong.
The Jakobsen pooled analysis
By 2005, evidence was emerging from observational studies indicating that replacing saturated fat with carbohydrate had no effect on coronary risk. This prompted the seminal study by Jakobsen et al, a pooled analysis of 11 cohort studies with a third of a million subjects. This high quality study confirmed that replacing saturated fat with polyunsaturated fat lowered the risk for heart disease, consistent with the findings from randomised controlled trials. However, replacing saturated fat with carbohydrate was not associated with a fall in risk, but a small rise.
So the effects of saturated fat on heart disease risk were found to be modulated by the nutrient that replaced it, which had profound implications for public health nutrition. Until this point there had been two generally accepted dietary models for heart disease prevention – the Mediterranean-type diet (low in saturated fat and high in unsaturated fat) and the low fat diet (low in saturated fat and high in carbohydrate). The pooled analysis showed that the low fat diet didn’t work.
Extensive debate fuelled by further studies followed. Siri-Tarino and colleagues published a meta-analysis confirming that replacing dietary saturated fat with carbohydrate had a negligible effect on coronary risk. The title of a review by several key researchers highlighted the new reality: “Saturated Fatty Acids and Risk of Coronary Heart Disease: Modulation by Replacement Nutrients”. A review by Micha and Mozaffarian in 2010 summed up the evidence:
Based on consistent evidence from human studies, replacing [saturated fatty acids] with polyunsaturated fat modestly lowers coronary heart disease risk … whereas replacing [saturated fatty acids] with carbohydrate has no benefit …
One of the more interesting studies compared the risk associated with carbohydrates of differing quality with that of saturated fat and found that high glycaemic index carbohydrates actually conferred more risk for heart disease than saturated fat, which prompted an editorial by Professor Frank Hu from Harvard who asked “Are refined carbohydrates worse than saturated fat?” Among nutrition scientists a debate followed about how to define carbohydrate quality but this was lost on the mainstream media which was only interested in the sugar scare driven by non-nutritionist activists.
Nevertheless, the outcome of all of this was not that the experts had changed their minds about saturated fat; they had changed their minds about carbohydrate.
The policy response
In the United States there was a substantial shift in nutrition policy in response to these new scientific findings. All reference to low fat diets was dropped from the Dietary Guidelines for Americans (2010) and advice about fats became to replace saturated fats with unsaturated fats. In addition, lower intake of refined carbohydrates (starch as well as sugars) was recommended. Last year a joint report from American College of Cardiology and the American Heart Association recommended the restriction of saturated fats, sweets and sugar-sweetened beverages in heart healthy diets and the inclusion of unsaturated vegetable oils.
In the United Kingdom, the Joint British Societies have just released their Consensus Recommendations on the prevention of cardiovascular disease and recommended:
• The restriction of saturated fat, being replaced by polyunsaturated fat where possible
• Reduced intakes of refined carbohydrates, such as white bread, processed cereals and sugary drinks.
Contrary to the media reports we have been reading, all of these guidelines retain a focus on lowering saturated fat intake. The change from older advice relates to the emphasis on the replacement nutrients, with unsaturated fats being encouraged and refined carbohydrates (both starch and sugars) being discouraged.
Australia makes a mess of it
While the rest of the world has been busily responding to the latest science about saturated fats, carbohydrates and heart disease Australian authorities have been asleep at the wheel. Inexplicably, the National Health and Medical Research Council chose not to conduct a systematic literature review of saturated fat and heart disease for the latest Australian Dietary Guidelines, relying instead on a review conducted 12 years ago. So the substantial shift in the emphasis in diets for the prevention of heart disease was not built into the latest guidelines or the revised Australian Guide to Healthy Eating, thereby ensuring that the next decade of nutrition education in Australia is aligned with an outdated evidence base.
Another unfortunate consequence of this policy failure is the naive use of saturated fat in the algorithm being applied to assess foods as part of the proposed star food labelling system. While saturated fat remains a useful measure of the quality of a fat-rich food, no one involved in the food labelling process seems to understand that rewarding a carbohydrate-rich food for being low in saturated fat is nonsense.
At a recent presentation on the new star food labelling system in Sydney an experienced and highly respected dietitian sitting next to me sighed “God, what a mess”.