Sunday, 29 June 2014

A big saturated fat question

This is not the first meta-analysis that has found no link between saturated fat and heart disease. – AFP

This is not the first meta-analysis that has found no link between saturated fat and heart disease. – AFP

The long-held belief that saturated fat is linked with cardiovascular disease is coming under close scrutiny.

It has just been a few months since the headline in the Daily Telegraph announced: “No link found between saturated fat and heart disease”.

This was in response to a study published in the March issue of the Annals of Internal Medicine where researchers said they found no significant link between saturated fat and heart disease.

Since then, there has been much analysis and soul-searching, with some writing that (the study) puts the final nail in the “saturated fat causes heart disease” coffin, whilst others caution against taking the study too literally, arguing that more evidence needs to be unearthed before any definitive conclusion (if any) could be reached.

According to the United Kingdom National Health Service, the study in question was carried out by researchers from the University of Cambridge and Medical Research Council, University of Oxford, Imperial College London, University of Bristol, Erasmus University Medical Centre, the Netherlands, and Harvard School of Public Health, United States.

In essence, it was a meta-analysis of 72 separate studies (45 cohort studies and 27 randomised controlled trials) that included over 600,000 participants in 18 different countries, looking at various components of total saturated fatty acid, both as a component in participants’ diets, as well as levels in the bloodstream.

A cohort study is a form of observational study, while a randomised controlled trial is a study in which people are allocated at random (by chance alone) to receive one of several clinical interventions. It is one of the simplest and most powerful tools in clinical research.

The main buzz generated by the findings were that “total saturated fatty acid was not linked to coronary disease risk”, and there was “insufficient evidence to support guidelines that advise eating more foods containing polyunsaturated fats to reduce heart risk”.

The restaurant's very own seafood soup filled with crab, prawns and mussels cooked with fresh tomatoes, bay leaves, fennel, celery and leek.
Palm oil is actually the most stable of the cooking oils available. – Filepic

According to reports, associate medical director of The British Heart Foundation (which partly funded the study), Prof Jeremy Pearson, said in response to the study: “This analysis of existing data suggests there isn’t enough evidence to say that a diet rich in polyunsaturated fats but low in saturated fats reduces the risk of cardiovascular disease.”

In addition, it was reported that the University of Cambridge’s Dr Rajiv Chowdhury, who was lead author of the study, said that the study “could open new lines of enquiry that carefully question our current dietary guidelines. Cardiovascular disease, in which the principal manifestation is coronary heart disease, remains the single leading cause of death and disability worldwide. In 2008, more than 17 million people died from a cardiovascular cause globally. With so many affected by this illness, it is critical to have appropriate prevention guidelines which are informed by the best available scientific evidence.”

With such a cloud cast over what was once an iron-clad belief that “saturated fat leads to heart disease”, it’s no wonder that there are calls for further studies to clarify the situation.

Perhaps, the results of this meta-analysis shouldn’t come as too much of a surprise.

International Medical Universi-ty’s nutrition and dietetics Associate Professor Dr Tony Ng Kock Wai, in a previous interview with Fit For Life, had pointed to a meta-analysis of 21 studies carried out by researcher Dr Patty W. Siri-Tarino and colleagues at the Children’s Hospital Oakland Research Institute in California, US, looking at the association between saturated fat intake and cardiovascular disease.

The results of the meta-analysis was published in the American Journal of Clinical Nutrition in 2010, and it also found no association between dietary saturated fat and increased risk of cardiovascular disease.

”Saturated fat intake, in fact, lowered the risk of stroke by some 19%,” said Assoc Prof Ng.

He pointed out that while saturated fats do raise low-density lipoprotein (LDL, or “bad”) cholesterol, they also raise the high-density lipoprotein (HDL, or “good”) cholesterol.

Hence, he pointed out that we need to get the record straight about saturated fats.

Assoc Prof Ng had revealed that not all saturated fats are created equal, and only three raised serum cholesterol – lauric acid, myristic acid and palmitic acid.

And then there is the fourth type of fatty acid that raises cholesterol – trans-fat. This, according to Assoc Prof Ng, is the worst type of fat as they raise blood lipid and lipoprotein(a) levels, which are risk factors for cardiovascular disease.

In fact, the US Food and Drug Administration is moving towards banning the use of partially-hydrogenated vegetable cooking oils, which are the main source of trans-fat in our diets.

Assoc Prof Ng had spoken on palm oil as a major fat in our diet at last year’s International Palm Oil Congress held in Kuala Lumpur.

He shared that palm oil is actually the most stable of the cooking oils available. This means that it can withstand the very high temperatures of deep frying for longer periods of time, compared to unsaturated vegetable oils, which degrade more easily under similar conditions.

Though many people may be reluctant to use palm oil as it contains one of the highest saturated fat content among vegetable oils, Assoc Prof Ng pointed out that research has shown that palm oil does not exhibit quite the cholesterol-raising effects expected from its high saturated fat content.

He cited a study in Maastricht, the Netherlands, where 40 healthy male volunteers were fed a controlled diet where their usual sources of saturated fat – typically animal fats and partially-hydrogenated vegetable oils – were replaced with palm oil.

The 1992 paper, published in the British Journal of Nutrition, reported that the participants showed no change in their total cholesterol or LDL-cholesterol levels during the trial.

However, their HDL-cholesterol and apolipoprotein A1 levels had increased, while their apolipoprotein B levels had decreased, providing a protective effect against coronary artery disease.

Another study, carried out in 1997 in China, compared the effects of four diets, enriched with palm oil, soyabean oil, peanut oil and lard respectively, in 120 healthy males.

It found that the palm oil-enriched diet showed the most decrease in total cholesterol and LDL-cholesterol levels.

The same study, published in the Journal of Nutrition, also compared diets enriched with palm oil and peanut oil, in participants with high cholesterol levels.

Those consuming the palm oil-enriched diet showed significant reduction in their total cholesterol and LDL-cholesterol levels, while no changes were seen in the peanut oil-enriched diet, which approximated the volunteers’ usual intake.

This, Assoc Prof Ng concluded, indicates that palm oil is neutral, i.e. it does not raise cholesterol levels, in healthy humans.

All in all, he advised that we keep to the recommended dietary guidelines of keeping fat consumption to less than 10% of your total daily calorie intake.

“The message is, we do not need to fear dietary cholesterol unless we’re having a very high dietary intake, meaning more than 400mg per day.

“We have to remember that the main source of body cholesterol comes from our liver.

“Our liver manufactures 1,000mg of cholesterol a day, and we need cholesterol or we will die,” he says, adding that cholesterol is essential to many bodily functions.

The main source of fats in our diet comes from the oils we use to cook.

“It forms one-third to half of our dietary fat,” said Assoc Prof Ng. “So, choose your cooking oil wisely, I would say.”

Tags / Keywords: Health , saturated fats , link with cardiovascular disease , unproven


Most Viewed

Powered by