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by tan shiow chin
Around one-third to half of our fat intake comes from the cooking oil used to cook our foods. – Filepic
Saturated fat is often seen as public enemy number one in the war against cholesterol, but it may be less fearsome than it seems.
COMMON knowledge says that eating saturated fat raises your cholesterol levels. And as we also know, high cholesterol levels are a risk factor for coronary artery disease and stroke.
However, not all saturated fats are created equal.
International Medical University nutrition and dietetics associate professor Dr Tony Ng Kock Wai says that people need to get the record straight about saturated fats.
Fats, he explains, are made up of a glycerol backbone and three fatty acids, which are the components that actually cause concern.
“The fatty acids that raise serum cholesterol are limited to four types. The saturated fatty acid types are lauric acid, myristic acid and palmitic acid.
“So, these three saturated fatty acids raise cholesterol; all the other saturated fatty acids do not.”
In fact, Assoc Prof Ng says that if we were to take away all saturated fats from our diet, and only consumed a diet of proteins, carbohydrates, polyunsaturated fats and monounsaturated fats, we would get sick in a matter of weeks.
“Why? Because we are victims to oxidative stress.
“Unsaturated fats are susceptible to attack by reactive oxygen species. The antioxidants in our body tend to counter this effect, but the bad always wins.
“So, in the end, we grow old, we die of old age, we have chronic diseases. Therefore, we need saturated fats to be in there to balance things. Too much of anything is never good,” he explains.
And then there is the fourth type of fatty acid that raises our cholesterol – trans-fat. This, according to Assoc Prof Ng, is the worst type of fat to have in the diet.
“They are not saturated, but they have the trans configuration. They are really bad because they raise blood lipid levels and they raise lipoprotein(a), which is a risk factor (for cardiovascular disease),” he says.
Trans-fat is deemed so harmful that the United States 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.
The fear of saturated fats started in the early 1950s when American physiologist Dr Ancel Keys reported the results of what came to be known as the Seven Countries Study.
According to Assoc Prof Ng, Dr Keys’ study purportedly showed that the intake of saturated fats was directly related to serum cholesterol levels, and thus, to the increased risk of dying from cardiovascular disease.
“And then came this phobia of saturated fats and cholesterol, and this lasted one generation – 50 years or more,” he says.
“But in fact, we do not have to fear saturated fats or dietary cholesterol.”
He points to a meta-analysis of 21 studies done by Children’s Hospital Oakland Research Institute, California, United States, researcher Dr Patty W. Siri-Tarino and colleagues, looking at the association between saturated fat intake and cardiovascular disease.
Published in the American Journal of Clinical Nutrition in 2010, the comparative study 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%,” says Assoc Prof Ng, adding this is a powerful paper as it is a summary of several clinical trials.
He points 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.
Conversely, polyunsaturated fats do decrease LDL-cholesterol, but they also decrease HDL-cholesterol.
The key, he says, is to 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 effects of palm oil
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,” says Assoc Prof Ng. “So, choose your cooking oil wisely, I would say.”
The nutritionist, who spoke on Palm Oil as a Major Fat in the Diet: Nutritional and Health Issues at the 2013 MPOB International Palm Oil Congress in November, shares 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.
Many people fear to use palm oil, as it contains one of the highest saturated fat content among vegetable oils.
However, Assoc Prof Ng points out that research has shown that palm oil does not exhibit quite the cholesterol-raising effects expected from its high saturated fat content.
In a study in Maastricht, the Netherlands, 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.
Meanwhile, a 1997 Chinese study comparing the effects of four diets, enriched with palm oil, soyabean oil, peanut oil and lard respectively, in 120 healthy males, 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 concludes, indicates that palm oil is neutral, i.e. it does not raise cholesterol levels, in healthy humans.
Research has suggested that the reason behind this might be the specific distribution of palmitic acid in the palm oil molecule.
Over 90% of the palmitic acid chains sit in position one and three on the molecule’s glycerol backbone, with only 9% occupying the middle position.
“This unique positioning apparently prevents cholesterol raising in the blood, and this has been demonstrated in rabbits,” he says.
The theory behind this is that pancreatic lipase, which is the main enzyme that helps us digest fats, preferentially cuts off the fatty acid chains at positions one and three.
These palmitic acid chains then form calcium compounds and are excreted in the faeces, resulting in their being less well-absorbed, compared to other fatty acids.
However, the story changes when it comes to overweight, and otherwise, unhealthy people.
In such people, the LDL-cholesterol receptors on their cells, which help capture and clear LDL-cholesterol from the bloodstream, become less active, causing an increase in blood LDL-cholesterol levels.
Another factor, he adds, is genetic. People with a certain type of gene, coding for their apolipoprotein E, are prone to having higher levels of blood LDL-cholesterol.
Such people need to be more wary over the overall fat, as well as saturated fat, content of their diets.
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