BY TAN SHIOW CHIN
Unsaturated cooking oils are deemed the best for our health, but this is not always true.
THE usage of oil in cooking has gotten a really bad reputation in recent decades. Healthcare professionals are constantly telling us to steam, braise, grill, bake, etc, rather than fry.
But this is hardly surprising, considering the concurrent rise in waistlines, cholesterol levels, blood pressure and heart disease over the past several years.
However, the truth is, we cannot do completely without oil, which is basically a form of fat, in our daily diet. A certain amount of fat is crucial to our nutrition, and this includes both saturated and unsaturated fats.
The primary reason for this is the fact that four essential vitamins – A, D, E and K – are only soluble in fat, thus, requiring it as an agent to enter our body’s digestive system.
Fat is also a powerhouse when it comes to providing us with energy, supplying almost twice the amount of calories per gram that carbohydrates do.
And this remains an important nutritional fact to consider when supplying food aid to the many malnourished communities around the world.
However, for the rest of us office-bound, sedentary people, who have much lower energy needs, but still eat like we do hard physical labour, this is a very bad thing, as the unused excess energy just gets stored in fat deposits around our body.
This is especially so as our body preferentially sources energy from carbohydrates, instead of fats and proteins.
This means that when given a choice, our body will break down carbohydrates first for energy, then only fats, which are less efficient to burn than carbohydrates, followed by proteins as a last resort when malnourished.
In addition, fat plays a far more important role in our food than many of us – other than cooking aficionados – might realise.
The usage of fat affects flavour, texture, appearance, and even, how full we feel, i.e. satiety. (See Food and fat)
But one of the most important functions of fat, in the form of oil, is its ability to be heated up to high temperatures without breaking down and transferring this heat to the food immersed in it. This allows food to be cooked quickly, contributes flavour, and helps in forming that delicious crunchy surface of deep-fried foods.
However, when it comes to cooking, not all edible oils are created equally.
Although the general understanding is that unsaturated vegetable oils are healthier than their saturated counterparts and animal oils, which are naturally high in saturated fats, this rule-of-thumb might not be as clear-cut as it seems.
Too much trans fat
In November, the United States Food and Drug Administration (FDA) announced its preliminary determination that partially-hydrogenated cooking oils are no longer “generally recognised as safe” for use in food.
This is because such oils are the main source of artificial trans fats in our diet.
According to the US Institute of Medicine, not only do trans fats have no known function, other than the generic role of energy source, but they also increase the levels of low-density lipoprotein (LDL, also known as “bad”) cholesterol in our bodies. And a rise in LDL cholesterol, as we know, leads to more atherosclerosis and increased risk of heart disease.
In addition, some studies have suggested that, in comparison to their naturally-occurring siblings, artificial trans fats are actually more harmful to humans.
So, what exactly are partially-hydrogenated cooking oils?
Most vegetable oils consist of polyunsaturated fatty acids – the so-called “healthier” type of fat.
However, before they reach our supermarket shelves, these oils typically undergo a chemical process called hydrogenation, which results in the final partially-hydrogenated version.
The advantages of foods cooked with partially-hydrogenated oils is that they stay fresh longer, with a resultant longer shelf life, and have a more desirable texture; hence, their popularity within the food industry.
Partially-hydrogenated oils are also more stable when used at the high temperatures required for commercial frying, and can be reused more times than unsaturated oils.
The disadvantage, however, is that the process of partial hydrogenation also causes the creation of trans fats – a side effect deleterious enough to human health that the FDA is considering subjecting the usage of such oils to strict pre-market regulation and approval.
Suitable for reuse?
Whether it is in fastfood outlets, kopitiams or roadside stalls, cooking oil is usually reused as many times as possible.
Naturally, there are limitations to the number of times the oil can be reused, dependant on the type that it is.
According to the Food and Agriculture Organisation (FAO), an important requirement of a cooking oil is that it remains stable under the “very abusive” conditions of deep frying, i.e. high temperatures and moisture.
The high temperature causes the cooking oil to polymerise, resulting in a viscous oil that is readily absorbed by foods and produces a greasy product.
Meanwhile, the high moisture content encourages the breakdown of fatty acids during heating, resulting in a poor-quality oil that starts to breakdown at subsequently lower temperatures, and becomes progressively darker in colour and more acrid in flavour and smell.
Needless to say, whatever nutritional values the oil might have diminishes under such circumstances, says Malaysian Palm Oil Board (MPOB) senior research officer Dr Azmil Haizam Ahmad Tarmizi.
The more unsaturated the cooking oil, the more vulnerable it is to these changes, which accumulate the more times the oil is reused.
Under such heavy usage, saturated oils like palm oil are actually more stable and able to withstand such changes.
Saturated oils like palm oil can withstand the harsh conditions of deep-frying better than unsaturated vegetable oils, which break down more easily and lose their nutritional value under such circumstances.
Nutrition-wise, Dr Azmil, who recently spoke at the 2013 MPOB International Palm Oil Congress on Novel Frying Approaches for Enhanced Food Quality, has found that palm oil also retains around half the amount of its original vitamin E, even after 24 hours of continuous frying. Palm oil contains the highest amount of tocotrienol – one of the two forms of vitamin E, found in nature.
Research has indicated that tocotrienols potentially have many health benefits, including lowering total and LDL cholesterol levels, protecting our nerve cells from damage and death during incidents like stroke and brain trauma, and helping to heal fatty liver disease.
Dr Azmil adds that palm oil is also cheaper than other alternative oils like genetically-modified high-oleic sunflower oil, making it a more economical option for the food industry.
So, at the end of the day, it is not just about reducing the amount of oil and fat that we consume, but also about choosing the appropriate type of oil that we do use in order to best protect our health and the health of those that we cook for.
