In the United States, the Food and Drug Administration recently announced that partially hydrogenated oils (containing trans fats) were no longer ‘Generally Regarded as Safe’ and gave the fats and oils industry three years to get them out of the food supply. So, begrudgingly, the US industry will be forced to adopt a position that companies in the rest of the developed world adopted 20 years ago.

A brief history of trans fats

Health reviews of trans fats conducted in the 1970s and 1980s found little to be concerned about. The food-health relationship considered important at the time was the effect on the level of total cholesterol in the blood and trans fats seemed to be okay – the effect was similar to that of olive oil.

This all changed in 1990 when researchers broadened their investigations to consider the effects of trans fats on LDL-cholesterol and HDL-cholesterol. Unlike any other class of fatty acids, trans fats raised the ‘bad’ LDL-cholesterol and lowered the ‘good’ HDL-cholesterol – a double negative effect. Trans fats had a worse effect on blood lipids than any other fat or carbohydrate.

Soon afterwards researchers at Harvard found trans fats to be associated with increased risk for coronary heart disease in their large population studies. In Australia, both the National Health and Medical Research Council (1992) and the Heart Foundation (1994) flagged a potential problem with trans fats.

The industry response

To their credit, major fats and oils companies in Europe, the United Kingdom and Australia didn’t wait for their governments to tell them what to do. These companies were abreast of the science, took the initiative, made the necessary investment and began to remove trans fats from their products. In Australia, the process to remove trans fats from margarines began in 1995 and by 1998 almost all of the top brands of margarine in the country were virtually free of trans fats. During the 2000s a second wave of trans fat reduction ensued as major food companies combed through their ingredients lists tracking down any sources of trans fat. As a consequence trans fats now comprise just 0.5% of the calories in the Australian diet, most of which comes from dairy fat and meat fat. This is well below the maximum intake recommended by the World Health Organisation (1.0% of calories).

In Denmark, the trans fat content of the diet has fallen about 85% since the 1970s. Sometimes this fall is wrongly attributed to a regulation imposing a limit on the content of trans fats in food ingredients, which was introduced in Denmark in 2003. By far the majority of the fall in the trans fat content of the Danish diet occurred prior to 2000 as the fats and oils companies fulfilled their social responsibility. Interestingly, the trans fat content of the Danish and Australian diets, one subject to regulation of trans fats and one unregulated, are similar. The Danish diet is actually a little higher, presumably due to the Danes’ love of dairy products.

Ignoring all this, fats and oils companies in the United States maintained their love affair with trans fats. This is hard to comprehend as much of the observational data showing that trans fats were a problem was being generated in United States by American researchers. What were these companies thinking? So, two decades on and many premature deaths from coronary heart disease later, the FDA has had to step in and force the industry’s hand.

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Butter: an interesting anomaly

While the FDA will now expect manufacturers of coffee creamers, crackers, biscuits, cakes and stick margarines to virtually eliminate trans fats from their products there remains an interesting anomaly – butter. The FDA’s consumer information sheet on trans fats states in big letters ‘Selecting foods with even small amounts of trans fat can add up to a significant intake’. Butter has about 3-5% of its fatty acids and therefore 3-5% of its calories as trans fats. Once partially hydrogenated oils are removed from the food supply butter becomes one of the richest sources of trans fats.

The dairy industry likes to tell us that these trans fats are ‘natural’ and therefore not a problem. But the facts of the matter are that at least 10 of the trans fats in butter are the same as those found in partially hydrogenated oils. Not surprisingly, dairy trans fats have similar adverse effects on blood lipids to those in partially hydrogenated oils. Butter is actually made of partially hydrogenated oils – cows eat lots of unsaturated fats from grass and seeds; these fats are then partially hydrogenated in the rumen of the cow to yield lots of saturated fat plus some trans fats, which end up in the meat and milk of the cow. Although this bio-hydrogenation may be considered ‘natural’ its consequences are not good and no amount of public relations spin can make it so.

So will butter’s ‘Generally Regarded as Safe’ status be withdrawn by the FDA in the near future? Not likely. The dairy lobby is the best in the business. But what will the regulators do when biscuit manufacturers replace their current baking fats (with trans fats) with butter (with trans fats)?

The good news for the Australian public is that current advice to replace saturated fats like dairy and meat fat with unsaturated fats is also the best advice for further lowering trans fat intake.

The changing science

The science relating to how much of what we should eat for good health has certainly evolved in recent decades, but it’s not a simple story.

• In the early 1980s, most health authorities recommended that saturated fat in the diet should be limited to lower heart disease risk.

• At that time trans fats were thought to be neutral but by the 1990s they were considered be as bad as saturated fats. And by the 2000s trans fats were thought to be worse than saturated fat.

• Three decades ago carbohydrate was thought to be the ideal replacement for saturated fat, which led to widespread support for low fat diets. But by the late 2000s scientific support for low fat diets had dropped away.

• Although the early science indicated that unsaturated fats may be the best option to replace saturated fat in the diet somehow they were less preferred to carbohydrate. Their time has now come.

The Willett Model

Harvard nutrition guru Professor Walter Willett has developed a simple model for explaining the current state of the science. His model puts saturated fat at the centre of our attention and then shows how heart disease risk is affected when other nutrients replace it in the diet.

Key points to note are:

If trans fats replace saturated fats in the diet, heart disease risk goes up. So trans fats should be minimised in the diet, which has been successfully achieved in Australia.

If unsaturated fats replace saturated fat, heart disease risk goes down. The resulting Mediterranean-type diet is moderate in total fat but enriched in unsaturated fats. This is now the preferred foundation for a heart-healthy diet.

Which brings us to the third point: there is no advantage in replacing saturated fat with carbohydrate, or vice versa. Heart disease risk is unchanged. The big lesson for nutritionists from this was to stop advocating low fat diets for heart disease prevention. The other lesson – for the general public in particular – is to ignore all the rhubarb from low carbohydrate advocates who argue that we should all eat more saturated fat, in general, and more coconut oil in particular. It has no basis in science.

Dubious motives

The motives of the saturated fat enthusiasts are particularly dubious. Not content with pushing the myth that saturated fat is better for health than carbohydrates they further muddy the waters by demonising ‘seed oils’, which is code for unsaturated fats. So we are asked to believe that carbohydrate and unsaturated fats are both evil and therefore the only safe thing for us to eat is saturated fat. Claptrap of the highest order.

Needless to say, all of the world’s leading nutrition authorities do not support these arguments.

If your suspicions were not already fully aroused, ask yourself why these dietary myths are pushed by non-nutritionists via social media. Hmmm, you don’t think it could be a thinly-veiled marketing campaign for coconut oil, do you?

The origins of the low fat diet

The low fat diet had its origins in 1980 with the publication of the first Dietary Guidelines for Americans. The recommendation to ‘Avoid too much fat, saturated fat and cholesterol’ was intended to lower blood cholesterol and reduce the risk for heart disease. Although the focus was really on lowering saturated fat, it was thought that lowering total fat intake may help prevent some cancers and obesity.

In Australia, the simpler guideline ‘Avoid eating too much fat’ was adopted to aid its communication.

Keys versus Yudkin

The low fat diet had a low key launch. Yet these humble origins are now being re-imagined as the disastrous consequences of a fight to the (professional) death of two of the great nutritionists their era – Ancel Keys and John Yudkin. As an epidemic of heart disease raged in the post-war years Yudkin pointed his finger at sugar. But Keys argued that the effect of different fats on blood cholesterol was the key mechanism affecting heart disease risk, and he won the day.

Yet Keys’ victory is now being portrayed as the fateful moment when nutrition science careered off course for four decades. Fortunately for humankind, ‘the truth’ that the problem was sugar all along has now been revealed by various journalists, lawyers, economists and B-list celebrities, all of whom seem to have made a packet in doing so.

Not content with challenging Ancel Keys’s views, the myth-makers have set out to destroy his reputation, arguing that he fudged his data – that Keys was a fraud. In contrast, Yudkin is now portrayed as a prophet, whereas he was discredited in his day.

The mythical fork in the road

Why the myth-makers need to construct this fanciful sugar or fat fork in the road is a mystery. After all, both the Australian and the American dietary guidelines published in the early 1980s discussed fat and sugar. The relevant sugar guideline in Australia was ‘Avoid eating too much sugar’ and the American guideline simply said ‘Avoid too much sugar’. And the advice to limit sugar intake has stayed in place ever since.

In contrast, as new scientific evidence about fat became available the cancer link was dismissed and recommendations steadily evolved to have more focus on fat type and less on lowering total fat. All the recent research is ignored by the myth-makers.

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Mistakes were made

Certainly, mistakes were made by some of our health authorities. By the mid-90s the ‘eat less fat’ message should have been disappearing into history. However, it was given a new lease of life when obesity experts latched onto it, based on insufficient evidence which soon fell away.

According to the myth-makers, this wasn’t a policy failure. No, it was the work of the sugar barons conspiring with their operatives in academia to prop up the low fat diet to further their commercial interests!

Fraud? Conspiracy?

Alternatively, maybe nutrition experts have just been gradually refining their dietary recommendations as new scientific evidence becomes available.

About the only thing that all these seed oils have in common is that they are relatively low in saturated fat, which is considered to be a good thing by every reputable nutrition and heart health authority in the world.

Of course, things are very different in the curious world of celebrity-driven nutrition advice where for some reason saturated fat is seen as desirable and coconut oil, one of the most saturated of all oils, is promoted a healthy choice.

What’s the problem with seed oils?

Supposedly the biggest threat that seed oils pose to heart health is inflammation caused by omega 6 polyunsaturated fats. This is a myth, but it is repeated so often that I will happily address it in depth in another post in this series.

It should be remembered that polyunsaturated fat is the only type of fat that is actually essential for human nutrition. Mother Nature would certainly have made a mess of things if the only essential fats in our diet also caused heart disease.

Some critics say we just eat too much polyunsaturated fat. But the amount of polyunsaturated fats in the Australian diet has been falling for 30 years and is now just 4% of daily calories, right at the bottom end of the recommended intake range of 4-10%.

None of the arguments against seed oils stands up to any scrutiny. Critics of seed oils tend not to dwell on the fact that polyunsaturated fats lower the level of cholesterol in the blood, which lowers heart disease risk. Or that saturated fat raises blood cholesterol, which increases heart disease risk. Instead, they argue that the whole cholesterol story is wrong, ignoring the last 60 years of research in the process.

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A natural experiment

So, nutrition experts say eat more seed oils and less saturated fat to promote heart health while the celebrity chefs and book sellers say the exact opposite. Who’s right?

It wasn’t too long ago that a whole country put the idea to the test. During the 1990s a natural experiment occurred in Poland. Following major political changes some government subsidies were removed raising the prices on saturated animal fats; less expensive seed oils like canola and soybean oils flooded into Poland. But was this sudden rush of seed oils bad news for heart health?

On the contrary, between 1990 and 2002 rates of heart disease in Poland fell by about 40% in both men and women, a remarkable change in such a short period.

Maybe nutrition experts know what they are talking about after all.

Part 1 of this series examined claims that omega 6 in vegetable oils causes ill health by increasing the risk for cancer, macular degeneration, Parkinson’s disease and inflammatory conditions, such as rheumatoid arthritis, ulcerative colitis and asthma. These claims, frequently expressed on the internet and in social media, were found to be baseless.

Part 2 will consider whether omega 6 increases or decreases the risk for coronary heart disease. Unlike the wild social media claims about omega 6, this issue is argued in the scientific literature with credible scientists on both sides. Whose argument is stronger?

The conventional wisdom

Leading heart health agencies such as the Heart Foundation, the American Heart Association and the World Health Organisation assert that polyunsaturated fats (mainly omega 6) are heart healthy and that they may be the ideal replacement for saturated and trans fats in the diet. The case appears to be strong:

• Polyunsaturated fat (mainly omega 6) has a beneficial effect on blood lipids. When saturated fat is replaced by polyunsaturated fat the level of serum LDL-cholesterol and the total cholesterol/HDL cholesterol ratio both fall, which is consistent with lower risk for coronary heart disease.

• Epidemiological studies indicate that polyunsaturated fat (mainly omega 6) is heart friendly. A pooled analysis of 11 prospective cohort studies conducted in Europe and the United States shows that replacing saturated fat with polyunsaturated fat lowers coronary risk more than other macronutrients.

• In randomised controlled trials coronary heart disease risk falls when saturated fat is replaced by polyunsaturated fat (mainly omega 6) – see Harvard’s meta-analysis.

So the conventional wisdom is based on three consistent lines of evidence with a rare meta-analysis of randomised controlled dietary trials sitting on top. Impressive. How could you argue against it?

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The alternative view

Although in the minority, credible scientists do argue against it. In relation to mechanism, it is argued that omega 6 antagonises omega 3, offsetting the heart health benefits of the latter. Omega 6 is also said to pro-inflammatory (though this is a dubious claim – see Part 1 of this series). These effects are presumed to overwhelm the beneficial effects of omega 6 on blood lipids.

In the absence of supporting epidemiological evidence, the argument that omega 6 has adverse effects on heart health really rests on a recent meta-analysis of randomised controlled trials that comes to different conclusions to the Harvard meta-analysis mentioned above.

Duelling meta-analyses

How can two meta-analyses of essentially the same data lead to differing conclusions?

Although both meta-analyses considered polyunsaturated fat-for-saturated fat exchanges, the recent meta-analysis sought to separate those trials that used pure omega 6 as a substitute for saturated fat from those that used mixed polyunsaturated fats i.e. omega 6 plus omega 3. But the trouble was there were few studies with pure omega 6 interventions, just the large Minnesota Coronary Survey (men and women) and the tiny Rose Corn Oil Trial. Undeterred, the researchers went looking for more pure omega 6 trials and identified the 40-year old Sydney Diet-Heart Study. The data for this study had to be completely re-analysed in order to be considered in the meta-analysis, an amazing effort in itself.

When the results of the mixed polyunsaturated fat studies were meta-analysed they showed a fall in heart disease risk, essentially the same result as that observed in the Harvard meta-analysis. But the effect of the pure omega 6 studies was a non-significant rise in heart disease risk which led the researchers to conclude that there was ‘a possibility of harm’ associated with omega 6.

A sceptical nutritionist’s view

The conclusion that omega 6 is possibly harmful essentially relies on two studies, both of which are problematic. The Sydney Diet-Heart Study did not employ a pure omega 6-for-saturated fat exchange as claimed. This old trial replaced saturated fat with Miracle polyunsaturated margarine, which in the early 1970s contained about 15% trans fatty acids. So, the intervention was the replacement of saturated fat with omega 6 and trans fats. Given the high risk associated with trans fats is it any wonder that heart disease risk did not fall? But why attribute the lack of benefit to the omega 6 and not to the trans fats?

The Minnesota study was a large well designed trial that was supposed to be conducted in institutionalised subjects over five years. However, a policy of de-institutionalisation brought the study unstuck. Rather than subjects receiving five years of dietary intervention, the average time on the trial was just over a year – too short to see any benefit from a lipid lowering trial of this size. So the observed lack of benefit in this trial is actually the expected result.

Randomised controlled dietary trials are notoriously difficult to conduct and all of the trials included in these meta-analyses have shortcomings, but basing a contrarian position on the non-significant findings of these two trials is drawing a rather long bow.

Following the publication of the recent meta-analysis several experts wrote to the relevant journal encouraging the authors to ‘consider all the evidence’ in coming to conclusions about omega 6. Good advice for us all.

Conclusions

At this stage the evidence that omega 6 in vegetable oils confers a heart health benefit when it replaces saturated fat in the diet is much stronger than the counter argument. However, if you are still sitting on the fence, it is worth remembering that no heart health agency actually recommends that pure omega 6 replace saturated fat. The advice is to replace saturated fat with polyunsaturated fats – both omega 6 and omega 3. Both duelling meta-analyses support this position so maybe the two sides of this argument are not as far apart as it seems.

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In October last year ABC television’s science program Catalyst ran two controversial programs purporting to expose myths about diet, medication and cardiovascular disease. In the first program Catalyst presenter Dr Maryanne Demasi challenged the role of dietary saturated fat in affecting risk for coronary heart disease and in the second she questioned the efficacy of statin medication. Essentially, the Catalyst program argued that the world’s leading nutrition organisations and cardiovascular researchers had got it wrong over the last four decades.

Heart Foundation outraged

In an interview on the ABC radio program PM, Maryanne Demasi even stated that the Heart Foundation was ‘certainly supportive’ of the Catalyst program’s evidence. In fact, the Heart Foundation was livid, took offence and submitted a formal complaint. They weren’t alone – the ABC received a total of 146 complaints. To their credit, journalists within the ABC, such as health reporter Dr Norman Swan and Media Watch front man Paul Barry, challenged the accuracy of the programs and the standard of the journalism on display, respectively. For more of detail see my two posts on the Catalyst programs here and here.

Results of independent review

Yesterday, the results of a review of the Catalyst programs by the ABC’s Audience and Consumer Affairs Unit were made public and included findings that standards of impartiality had been breached. Here are some excerpts from the review:

It is clear from the reaction to the program that many members of the audience believed that in both episodes, one side of two highly contentious issues was unduly favoured …

In relation to the first program on saturated fat and heart disease:

In our judgement, the quality of the program would have been enhanced if it had more clearly communicated why the National Heart Foundation hold their views. Little substantive evidence was presented to support their perspective and the strength of the evidence that was referred to was doubted in the narration and directly challenged – and often emphatically rejected – by other contributors. Although the program did not explicitly endorse the unorthodox view, the language used by the reporter tended to add weight to the contrarian argument.

In relation to the second program on statins:

Furthermore, by omitting a principal relevant view – held by the National Heart Foundation and other experts – that statins are useful in primary prevention if carefully targeted, the program had the effect of unduly favouring the perspective that statins are ineffective in primary prevention.

In relation to Maryanne Demasi’s statement on the PM program that the Heart Foundation had signed off on the Catalyst program’s evidence:

While the comment was made in a live radio interview, it was nonetheless a misleading oversimplification which failed to acknowledge the clear and important areas of disagreement between the National Heart Foundation and the overall proposition being presented in the programs.

In summing up:

For Catalyst, the core problem identified in this investigation was omission of important information.

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Corrective action undertaken

Yesterday, ABC Managing Director Mark Scott announced that corrective action had been taken:

• The two Catalyst programs had been removed from the program’s website
• The PM program had added an Editor’s Note to the transcript of its story ‘Backlash against ABC’s Catalyst program questioning heart disease-cholesterol links’
• An appropriate entry had been made on the ABC Corrections page.

The Heart Foundation provided a polite response.

Unanswered questions

I guess the moral of this story is that when you see some misleading information about nutrition and health in the media, do what the Heart Foundation and others did – complain!

But there are still unanswered questions about these Catalyst programs. When the program about saturated fat went to air I thought it was so biased that I was convinced that a commercial interest must be involved, and suggested that it might be the palm oil industry. However, I have since had assurances that this industry was not behind it.

If it wasn’t commercially driven, the whole thing doesn’t make sense. How did a hitherto reputable science journalist, Maryanne Demasi, come up with a bizarre list of poorly qualified ‘experts’ in the United States to be interviewed for the Catalyst programs? And why would a journalist with a PhD accept recommendations about ‘experts’ who had virtually no scientific publications in the relevant field? Wouldn’t that be the first thing to check?

Who pitched this story to Catalyst?

And then there is the issue of cost. Why would the cash-strapped ABC agree to pay to fly Maryanne Demasi all the way to the United States to interview these ‘experts’? How could any responsible manager sign off on such expense?

The whole thing just doesn’t add up.

What is omega 6?

All fats – animal or vegetable – are made up of building blocks called fatty acids which generally fall into three main groups called saturated, monounsaturated and polyunsaturated. There are two classes of polyunsaturated fatty acids – omega 6 and omega 3. The omega 3 in vegetable oils is called α-linolenic acid and the omega 6 is linoleic acid. The concern about omega 6 relates to linoleic acid which is the most common polyunsaturated fatty acid in the diet.

Do omega 6 fats cause cancer?

In the early 1980s it was thought that fat intake may affect the risk for cancer of the breast and bowel. This hypothesis was based on very basic evidence i.e. different cancer incidence in countries with differing fat intakes, but worth investigating nevertheless.

Several prospective cohort studies were commenced around this time. Data from seven of these studies were pooled in the definitive breast cancer study by Hunter and colleagues. Breast cancer risk was not associated with intake of total fat, animal fat, vegetable fat or polyunsaturated fat. Another pooled analysis of cohort studies published five years later confirmed that polyunsaturated fat was not associated with breast cancer. So omega 6 was off the hook.

When the early results of studies into fats and bowel cancer were published there were hints that animal fat or saturated fat may increase risk, but not polyunsaturated fats or omega 6. Soon it became clear that the problem wasn’t even animal fat; it was red meat. In their review Giovannucci and Goldin concluded:

Intake of red meat or beef has been related to colon cancer risk in most case-control and cohort studies, whereas dietary fat from sources other than red meat, including dairy, poultry, and vegetable oils, does not increase risk of colon cancer.

No smoking gun for omega 6 there.

In fact, there is simply negligible evidence that omega 6 increases cancer risk in humans. Today no credible scientific organisation anywhere in the world recommends restricting omega 6 intake to lower cancer risk.

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Do omega 6 fats cause macular degeneration?

Over a decade ago a case-control study suggested that different types of fatty acids may be linked to the risk for age-related macular degeneration, a condition that can lead to loss of clear vision in older people. A small cohort study (261 subjects) then found that total fat and all major classes of fatty acids were linked to progression of the disease.

However, these findings were not confirmed by two larger cohort studies conducted in Australia. The Melbourne Collaborative Cohort Study and the Blue Mountains Eye Study found no associations between macular degeneration and intakes of total fat, total polyunsaturated fats or omega 6.

Do omega 6 fats cause Parkinson’s disease?

There is a hypothesis that eating lots of omega 6 leads to lots of these polyunsaturated fats in the membranes of brain cells, which in turn leads to oxidative stress, which may then lead to Parkinson’s disease. Okay, it’s a long shot but does the evidence support it?

The question was addressed by Harvard researchers using data from two large cohorts. This study found that replacing saturated fat with polyunsaturated fat was associated with lower risk of Parkinson’s disease. In the Rotterdam Study, intake of polyunsaturated was associated with lower risk for Parkinson’s disease. And that’s all the cohort data we have to go on. Neither of these studies supports the hypothesis that high omega 6 intake increases the risk for Parkinson’s disease.

Do omega 6 fats cause inflammation?

It is often said that too much omega 6 in the diet causes inflammation and therefore may worsen inflammatory conditions, such as rheumatoid arthritis, ulcerative colitis and asthma. However, epidemiological studies do not find higher omega 6 intakes to be associated with higher levels of inflammatory markers. In fact, studies in the United States and Japan find the opposite.

Let’s dig into this. It’s complicated so stay with me.

Inflammation is not a bad thing per se as it is part of the body’s response to infection or injury. But when it occurs in an uncontrolled way the body’s tissues may be damaged. At the cellular level inflammation is governed by long-chain omega 6 and omega 3 fatty acids in cell membranes. The more potent of these is the long-chain omega 6 which is called arachidonic acid (AA). AA can be made in the body from the common omega 6 in the diet, linoleic acid. So the argument is that too much omega 6 in the diet leads to too much AA in the cell membranes, which in turn leads to too much inflammation.

It makes sense, so why doesn’t it happen in real life?

Just because the body can turn omega 6 from the diet into AA doesn’t mean that it automatically happens. The rate of conversion of omega 6 to AA varies depending on the circumstances. If the amount of AA in cell membranes is too low (essential fatty acid deficiency), the rate of conversion of omega 6 to AA is very high. However, if AA in cell membranes is normal the rate of conversion of omega 6 to AA is tiny, about 0.2%. Once the desirable level of AA in cell membranes is achieved it is tightly controlled and stays constant even if omega 6 intake is increased to high levels. Rather than feeding the inflammation process most of the excess omega 6 is burned off for energy.

For a good review on omega 6 and inflammation take a look at the American Heart Association’s Science Advisory on omega 6.

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Summing up

None of these arguments against omega 6 stacks up which is why we hear most of them via the internet and social media rather than from expert scientific organisations.

In my next post I’ll consider omega 6 and coronary heart disease, a topic that is actively debated in the scientific literature.

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.

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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.

Wider debate

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.

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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”.

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Among vegetable oils, coconut oil is one of the richest in saturated fat – about 86-87% of all its fatty acids are saturated. Given the latest advice to replace saturated fat with unsaturated fat it would appear that coconut oil is the last vegetable oil a credible nutritionist would recommend. Wouldn’t all that saturated fat just raise blood cholesterol and increase heart disease risk?

The case for coconut oil

Coconut oil advocates argue that not all saturated fat is the same and that the health effects of coconut oil are better than might be expected. It is true that saturated fat is not a single entity – it’s a collection of different saturated fatty acids, each with its own effect on blood lipids. Medium-chain length saturated fatty acids (6-10 carbons) appear to have little effect, whereas the longer-chain saturated fatty acids (12-16 carbons) all raise total blood cholesterol. Stearic acid, which has 18 carbons, is cholesterol neutral but continues to be treated with suspicion (see below).

By far, the major saturated fatty acid in coconut oil is lauric acid (12 carbons), which the coconut oil lobby conveniently re-badges as medium-chain length and therefore a ‘good’ saturated fatty acid.

This is hard to justify – lauric acid strongly raises total blood cholesterol, which places it with the other longer-chain saturated fats. But this is where it gets interesting. Most of the rise in blood cholesterol with lauric acid comes from an increase in HDL-cholesterol, thought to be the protective fraction, and the effect lauric acid on the total/HDL-cholesterol ratio is more like that of unsaturated fatty acids. So does the coconut oil lobby have a case?

The case against coconut oil

The observational evidence tells a different story about coconut oil and lauric acid. Hu and colleagues investigated the effects of individual saturated fatty acids on the risk for coronary heart disease in a large cohort of women. They found that short- and medium-chain saturated fatty acids were not associated with heart disease risk, consistent with their neutral effect on blood lipids. In contrast, each of the longer-chain saturated fatty acids, including lauric acid, was associated with increased risk.

Another Harvard study also found that intake of all the longer-chain saturated fatty acids was associated with increased risk for heart disease.

Interestingly, in both studies intake of stearic acid was also associated with increased coronary risk. As stearic acid is cholesterol neutral we have to assume that it may have adverse effects on heart health via other mechanisms, perhaps an effect on blood clotting or blood vessel function (CSIRO study).

Countries that use coconut oil as the predominant fat don’t stand out as pillars of heart health. On the surface the Sri Lankan diet may look pretty good, just 25% of energy from fat, yet heart disease rates are much higher than would be expected. Not much support for coconut oil from this quarter.

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HDL functionality

How can we explain these conflicting lines of evidence? The key may be lauric acid’s effect on HDL-cholesterol – the assumed strength may actually be a weakness. We have all learned that HDL-cholesterol is protective against heart disease yet recent research is showing that the reality is much more nuanced.

HDL is complicated. When researchers put a new class of HDL-raising drugs to the test in recent trials the results were perplexing. HDL-cholesterol levels in the blood rose markedly yet the risk for heart disease did not fall and was even increased in one study. There was plenty of HDL but apparently it wasn’t ‘functional’. As discussed in a recent review on HDL functionality, the question about HDL is not simply how much is present but also how effective the HDL is.

Lauric acid and the other longer-chain saturated fatty acids all raise HDL levels but is it giving rise to ‘good’ HDL that lowers heart disease risk or non-functional HDL that does nothing? A study conducted in Sydney was the first to show that the quality of HDL could be changed by the food we eat. It showed that feeding saturated fat impaired the anti-inflammatory effects of HDL i.e. it lowered HDL functionality.

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The marketing push

With a variety of good unsaturated vegetable oils available I would certainly not recommend coconut oil for inclusion in a healthy diet.

But it’s all a bit academic because the coconut oil marketing machine is already in overdrive. The claims are totally over-the-top with coconut oil being positioned as some sort of wonder drug that lowers the risk for just about everything. Here’s a taste:

The health benefits of coconut oil include hair care, skin care, stress relief, maintaining cholesterol levels, weight loss, increased immunity, proper digestion and metabolism, relief from kidney problems, heart diseases, high blood pressure, diabetes, HIV and cancer, dental care, and bone strength.

Don’t you love it? Eat coconut oil to treat HIV! If it wasn’t so cruel it would be funny.

The carriers of the coconut oil message are primarily alternative practitioners, presumably because scientifically trained dietitians and nutritionists would run the risk of being barred from their professional associations if they carried on like this.

The problem for us is that the general public is now hearing dietary advice that’s not supported by good science and, if implemented, would probably damage public health.

So what are you going to do about it?

Although advice to eat less saturated fat has been a fixture in Dietary Guidelines for three decades, the last four years have seen a spirited debate about what should take its place in healthy diets. As saturated fat is a macronutrient, one can’t just ‘eat less saturated fat’ and maintain energy balance. Saturated fat needs to be replaced by something else, such as carbohydrate or unsaturated fats. Carbohydrate is now considered a poor replacement for saturated fat as these two macronutrients confer the same risk for heart disease. This leaves mono- and polyunsaturated fats as the better options to replace saturated fat, but which of these should be preferred?

Until recently, the evidence for polyunsaturates was stronger than that for monounsaturates. Both classes of unsaturated fats have beneficial effects on blood lipids and both appear to be protective against heart disease in observational studies. But the big difference in the evidence bases was that there have been many trials involving the replacement of saturated fat with polyunsaturated fat for the primary prevention of cardiovascular disease and the better trials have recently been subject to meta-analysis, providing a rare degree of confidence in this dietary recommendation.

In contrast, there had not been a single primary prevention trial of mono-rich diets, until now.

The PREDIMED Study

February this year saw the publication of the results of the PREDIMED Study, a randomised controlled trial for the primary prevention of cardiovascular disease using Mediterranean diets. This multi-centre trial conducted in Spain assigned subjects who were at high risk of cardiovascular disease to one of three diets – a control diet low in fat, or one of two Mediterranean diets enriched with either extra virgin olive oil or nuts. Energy intake was not restricted and exercise was not advocated.

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After 4.8 years, both Mediterranean diets significantly lowered the rate of the primary end point (myocardial infarction, stroke and death from cardiovascular causes) by about 30 per cent relative to the low fat control diet. In those following the Mediterranean diets, favourable trends were seen for both myocardial infarction and stroke. No adverse diet-related effects were reported.

These exciting findings stand in contrast to those of the Women’s Health Initiative, a huge US randomised controlled trial for the primary prevention of cardiovascular disease using a low fat diet which showed no benefit whatsoever. Thus PREDIMED provides a strong endorsement of the Mediterranean diet as the basis for healthy diets for the prevention of cardiovascular disease. The Mediterranean diets were also associated with lower risk for diabetes (see my earlier post).

Monos or polys?

In relation to the polys or monos question, the olive oil arm of PREDIMED was richer in monounsaturates than the nuts arm, which included poly-rich walnuts. The key point is that both diets were protective and equally so. Based on these findings it would appear that there is little to be gained from choosing polys over monos or vice versa – both appear to be good substitutes for saturated fat (and carbohydrate for that matter). Let’s confine the monos versus polys argument to history.

In considering the results of PREDIMED it’s important to bear in mind that this is a whole-diet study and that it is difficult to attribute the benefit to just one aspect of the diet. The foods consumed as part of the Mediterranean diets differed from the control diet in several ways – legume and fish intake, as well as nuts and olive oil intake, were higher in the Mediterranean diets. So it’s a package deal – the benefit is associated with the whole diet.

The challenge for nutritionists

A generation of nutritionists (including me) was educated to think that a healthy diet is a low fat diet and the results of PREDIMED, and the Women’s Health Initiative before it, provide further evidence that this is not the case. The PREDIMED investigators provided high fat foods to their subjects to provide benefit. A litre of olive oil per week was given to those in the olive oil arm of the study, an amount that may cause many dietitians to draw breath. And 210g per week of nuts were provided to those in the nuts arm.

The interventions were designed to enrich diets with foods high in unsaturated fats. How many of us think this way when we educate people about healthy eating?

There are only a few opportunities to build unsaturated fats into people’s diets – vegetable oils, unsaturated spreads, salad dressings, mayonnaise, nuts, seeds and avocado come to mind. Yet much of our ‘healthy eating’ advice in recent years has actively discouraged use of some of these foods: ‘avoid fried foods; use just a scrape of margarine on bread; and choose low-fat salad dressing and mayonnaise’. All of this advice has had the effect of withdrawing protective unsaturated fats from the diet. If body weight management is required the targets for energy reduction should be saturated fat and poor quality carbohydrates, not unsaturated fats. You know, baby, bathwater, etc.

But the low fat dogma runs deep. A challenge for nutritionists is to finally shake it off, relax about percent energy from total fat and undo some of the damage we have done over 30 years with poor advice to the general public about the role of unsaturated fats in healthy diets. The public will love us for it – Mediterranean diets actually taste good.

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