Credible nutrition scientists have opposing views on whether omega 6 in vegetable oils is good for heart health. But who is right?
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?
Following the publication of the latest national dietary survey it is clear that sugar intake has fallen since 1995. But mere facts are unlikely shake the resolve of the non-nutritionists driving the lucrative sugar scare.
The trend in sugar consumption in Australia has been a contentious issue in recent years, especially as nutritionists and lay people have sought dietary explanations for the obesity epidemic. On one side of the argument is the view that the intake of sugar, or perhaps fructose, has increased in recent decades and that this has been the driving force behind the epidemic. This argument emerged in the United States where sugar intakes are undoubtedly high.
In the Australian context it has been argued that sugar intake hasn’t increased at all and is actually in steady decline. Proponents of this argument include Dr Alan Barclay and Professor Jennie Brand-Miller who published an assessment of trends in intakes of sugars and obesity rates in Australia, the United Kingdom and the United States between 1980 and 2003. In this paper the authors identified an ‘Australian Paradox’ – increased rates of obesity despite an apparent fall in sugar intake.
The recent publication of new data from the Australian Health Survey (AHS) has provided some clarity on this issue.
Sugar data from the Australian Health Survey
The AHS was conducted by the Australian Bureau of Statistics, which also conducted Australia’s last national dietary survey of adults and children in 1995, so now we have insights into how the diet of Australians has changed over the intervening period of approximately 16 years. Here are some of the top-line results relating to sugar.
• Intake of total sugars has fallen in men, women and children.
• The percentage of dietary energy from total sugars has also fallen.
• Carbohydrate intake has fallen, both in absolute terms and as a percentage of energy. Total energy intake has also fallen.
More than six months after it broadcast two misleading Catalyst programs about diet, medication and heart disease the ABC has admitted there were problems with impartiality and has undertaken corrective action. But there is still something fishy about this.
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:
Omega 6 in vegetable oils stands accused of causing ill health by increasing the risk for cancer, macular degeneration, Parkinson’s disease, inflammation and heart disease. Sounds bad, but is any of it true?
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.
Addressing the obesity epidemic by taxing sugary soft drinks sounds good in theory but it appears to fall down in practice. How could a taxation strategy be made to work?
Obesity is proving to be an intractable public health problem demanding innovative solutions and one idea that is attracting attention is the taxation of sugar-sweetened beverages. The theory is simple enough. Basic economics tells us that if the price of sugary soft drinks were to rise, their consumption would fall; lower intake should mean lower calorie intake which would lead to lower body weights. But would it work in practice?
The Ohio experience
A recent research study conducted in the United States provided some interesting insights. Taxing soft drinks has a long history in the US and occurs in many states today, though historically the rates have been low and the purpose has been to raise revenue. But there was an interesting exception. In 1992, the state of Ohio introduced high taxation of sugary soft drinks which was then repealed at the end of 1994. This provided an opportunity to test the effect of taxation of soft drinks on body weights over a period of two years. The researchers compared changes in body weights in Ohio over this period to (1) all other states that had no increased taxation and (2) a bundle of states with the same mean BMI as Ohio. The researchers found:
… very little evidence that the large tax imposed in Ohio had any detectable effect on population weight … our results cast serious doubt on the assumptions that proponents of large soda taxes make on its likely impacts on population weight.
How come? Why didn’t quite high taxation of sugary soft drinks affect body weights?
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.
Public health nutrition is a noble cause but its practitioners are increasingly seeing their role in terms of the left-right political divide. But in doing so have they made public health nutrition a target?
Nobody seems to disagree with the idea that improving the nutritional quality of the national diet is a good idea but getting agreement on the best way of achieving it is another thing.
In the 1980s the approach to public health nutrition was characterised by ‘intersectoral collaboration’ – fostering links and cooperation between the agriculture, food processing, nutrition research and nutrition education sectors. The Heart Foundation’s Tick program was born in this era and was based around an acknowledgement of competing interests – the health experts wanted changes to the food supply; the food industry wanted a marketing advantage for the reformulation being requested; and a means of food approval was devised to consolidate the compromise.
Now it’s war!
Fast forward to 2014 and the environment is very different – the notion of collaboration is gone. Now, it’s war! Listen to the rallying cry from none other than Margaret Chan, Director-General of the World Health Organization, at a health promotion conference in Finland last year:
It’s not just Big Tobacco any more. Public health must also contend with Big Food, Big Soda and Big Alcohol. All of these industries fear regulation … This is formidable opposition … [There] is a failure of political will to take on big business … When industry is involved in policy-making, rest assured that the most effective control measures will be downplayed or left out entirely. This, too, is well documented, and dangerous.
Sugar-sweetened beverages are in the sights of public health nutritionists, especially in relation to obesity. But there is some good news: a fundamental shift from sugar-sweetened to non-sugar soft drinks is underway and the amount of sugar entering the national diet from these beverages is in long-term decline.
Despite all the interest in sugar in recent years Australian nutritionists don’t really know for sure whether sugar intake in Australia is going up, going down or staying the same. Unlike American nutritionists who have the findings from the ongoing NHANES series of nutrition surveys to go on, we have been hamstrung by the poor quality of our nutrition data. There are few national nutrition surveys to guide us.
In 2011, Dr Alan Barclay and Professor Jennie Brand-Miller collated the available Australian data and concluded that per capita consumption of sugar had decreased by 16% in Australia between 1980 and 2003. Their work was attacked with uncommon vigour. Apparently, this was not a message that some people wanted to hear. One concern expressed about their work was that Barclay and Brand-Miller had partly relied on ‘apparent consumption’ data, which the Australian Bureau of Statistics ceased publishing in 1998/99.
In a subsequent analysis by the commodity firm Green Pool, the apparent consumption data were updated and analysed, and again suggested a long-term fall in sugar consumption in Australia was underway. There were more howls of protest. Unfortunately, when the quality of the available data is ordinary this sort of debate ensues and we end up with lots of heat but little light.
Fructose has been accused of being the root of all dietary evil but at a symposium in Sydney this week Canadian researcher John Sievenpiper argued that fructose has been misjudged.
John Sievenpiper knows a fair bit about dietary carbohydrates and health. His team in Toronto recently conducted systematic reviews and meta-analyses evaluating the effects of fructose on body weight, blood pressure and glycemic control in humans. He discussed some of the findings at the ‘Sweet Symposium’ on 2 December.
The fructose-centric view
Sievenpiper reviewed the rapid evolution of what he called the ‘fructose-centric view’ in modern nutrition, which positions fructose as a central driver of the obesity epidemic and cardiometabolic risk. Certainly several lines of evidence had raised suspicions about fructose – apparent increases in fructose consumption were associated with increases in obesity in population studies; animal studies showed fructose had adverse metabolic effects; there were similar findings in some human studies; and an articulate anti-fructose champion, Robert Lustig, emerged and took his simple ‘fructose is toxic’ message to the general public. And the media loved it – even the ABC’s ‘science’ program Catalyst jumped on the bandwagon and pushed the idea around. In less than a decade the fructose hypothesis became an anti-fructose doctrine with a chanting chorus of true believers.
Media Watch, Australia’s leading forum for media analysis and comment, has lambasted the journalism behind the ABC’s recent Catalyst programs on cholesterol describing them as ‘sensationalist and grossly unbalanced’.
Giving up on the search for truth was the title of an article about declining standards of journalism penned by Nick Cater, the Editor of the Weekend Australian, on 2 November. Cater wrote By abandoning the pursuit of truth, modern journalism appears to have fallen for the philosophical error that blights modern academe … The empirical route to knowledge through investigation, observation and reason is rarely respected. Instead, journalists have come to believe knowledge comes through revelation … Cater was primarily talking about political journalism but his comments rang true in the light of the recent Catalyst programs on cholesterol.
Assessment by Media Watch
Fortunately, some journalists take their profession seriously. MediaWatch was scathing of the quality of the journalism behind the ABC’s Catalyst programs. For those who are unfamiliar with Media Watch, it is an ABC television program that analyses the media for Conflicts of interest, … deceit, misrepresentation, manipulation, plagiarism, abuse of power, technical lies and straight out fraud … Media Watch turns the spotlight onto those who literally ‘make the news’. We also keep an eye on those who try to manipulate the media: the PR consultants, spin-doctors, lobbyists and “news makers” who set the agenda’.
In commenting on the Catalyst programs, Media Watch presenter Paul Barry said Now, Media Watch is not going to take sides in this scientific debate. But looking at the journalism we’re almost as shocked as the doctors. Both episodes of Catalyst struck us as sensationalist and grossly unbalanced; and some of their so-called ‘experts’ had questionable qualifications.