After years of quietly evading justice, sugar has now been outed as the arch-enemy of human health that it is. But hiding in plain sight, and arguably just as harmful, are the refined vegetable oils most people use to cook their food. It’s time they too had their comeuppance.
Odds are that corn, soya, sunflower and sesame seed oils are staples in your store cupboard, and have never come under scrutiny. Why would they? They contain polyunsaturated fats, which you are told are good for you. Perhaps you avoid saturated fats, such as butter, which you are told are bad for you.
It’s time to shed some light on the facts about fats, and those vegetable cooking oils masquerading as healthy options.
The truth is that by the time they have been bottled and put on the shelf, these polyunsaturated oils have been processed beyond recognition. Any goodness they may once have contained has been well and truly dispatched.
Vegetable cooking oils are usually extracted from beans (soya), grains (corn) or seeds (typically sunflower, sesame, safflower). The most common extraction method involves a solvent called hexane, derived from petroleum.
This procedure is followed by a series of refining processes, including degumming, bleaching and deodorization. These are performed at temperatures in excess of 200ºC.
During this refinement process most of the nutrients are removed, including vitamin E — which is present naturally in the oil to protect it from damage. The high temperatures involved during processing create rancid odours that must be neutralised, hence the deodorization process.
Nutrient carnage aside, the most disturbing aspect of all this activity is the generation of high levels of free radicals, trans fatty acids, and chemicals called aldehydes.
Free radicals are unstable molecules that create a good deal of damage in the body, and in excess are associated with cardiovascular disease, cancer, dementia and premature ageing. Polyunsaturated fats — the kind found predominantly in vegetable cooking oils — are highly vulnerable to free radical attack. That vulnerability is made worse by the removal of protective vitamin E.
Then there are those infamous trans fatty acids.
Trans fats are ‘deformed’ fats created when polyunsaturated oils are hydrogenated — made hard with the addition of hydrogen atoms. The point of hydrogenation is to turn liquids into solid fats, such as margarine. The benefit of this (to industry, anyway) is that you now have a highly marketable product.
It is now well known that the process of hydrogenation has serious implications for human health. Trans fatty acids are perhaps most notorious for their link with heart disease. They increase platelet aggregation, which can cause clotting. Trans fats are believed to be carcinogenic, and although there is, to date, no conclusive evidence, studies suggest an association with colon cancer and breast cancer.
The association between trans fats and serious ill health is so strong, and so well documented, that many manufacturers have bowed to pressure and voluntarily stopped using hydrogenated oils in processed foods and ready-meals.
However, in some cases there’s no law to stop them. Different countries have different regulations. In 2003, Denmark became the first country to introduce strict regulations on the use of trans fats in food products. The regulations amounted to an effective ban. In the U.S. where there have been some state bans in place since 2005, a federal ban is due to be implemented by the middle of 2018. In the UK, despite much debate on the subject and calls for similar action, no legal ban is in place.
However, even where there’s a ban, there’s a sting. Because even when the manufacturer has not added trans fats, they are created anyway as a by-product of the refining process. For that reason, you won’t find trans fats on the label, despite their presence.
Now it’s time to create aldehydes
Food fried at home usually reaches average temperatures of 180ºC. That is enough to cause further degradation, whether you deep-fry or shallow-fry. If you reheat the same oil, you exacerbate the degradation, creating more free radicals and trans fats in the process.
Frying polyunsaturated oils also creates toxic aldehydes, which are linked to atherosclerosis (the formation of plaques on artery walls), cancer, inflammatory joint disease and (in animal studies) birth defects. In a study published in the journal Free Radical Research, it was found that when pregnant rats were fed safflower oil that had been heated for twenty minutes, nearly 22% developed embryo malformations, compared to less than 6% of rats fed the same oil, unheated.
You don’t even have to eat fried food to suffer the effects of frying: people working close to fat fryers have been found to be at risk from air-borne breakdown products of heated oils, in particular aldehydes. Women in China frequently exposed to fumes from indoor cooking with woks have one of the highest rates of lung cancer in the world.
“The common use of wok cooking in China might be an important but controllable risk factor in the etiology of lung cancer. In the United States, where cooking oils are usually refined for purity, additional studies should be conducted to further quantify the potential risks of such methods of cooking.”
Grootveld et al (2001).Foodservice Research International 13(1): 41–55
As long ago as 2001 warnings were issued about heating cooking oils. A report was published in Foodservice Research International ‘To alert the foodservice industry, particularly the fast-food industry, of an emerging health issue’. That issue was the amount of evidence that had accumulated over the previous two decades that showed that heating cooking oils, especially polyunsaturated oils, posed serious health hazards to the consumers of fried food.
The authors of the report were perhaps a little naïve. It is hard to believe that the food industry is not already well aware of these health issues, but in the absence of any public health warnings, let alone government regulation, it’s business as usual. Since that report was published there has been little further scientific (or food industry) research into the health hazards of cooking.
Home cooking is currently enjoying a very welcome renaissance, which allows us to combine an interest in wholesome, natural food with a passion for creativity in the kitchen. However a potential dilemma often arises during the first stages of following a recipe, when we are instructed to heat the oil in a pan.
Fortunately, there are alternatives to the perilous polyunsaturated fats which feature regularly on the ingredients list. These alternatives are monounsaturated fats and saturated fats, because the fatty acids they contain are resistant to heat-induced degradation.
Saturated fats, as found in butter and coconut oil are not prone to oxidation and are perfect for cooking.
The next best frying option is monounsaturated oil, such as olive oil. Although not quite as stable as saturated fats, monounsaturates are much less prone to degradation than polyunsaturated oils.
At this point we need to talk about olive oil. There is as much nonsense written and said about olive oil as there is about other fats and oils, so here are the facts.
Olive oil undergoes the same refining process as other vegetable oils, rendering it nutritionally bereft and potentially hazardous, unless it is extra virgin olive oil.
Extra virgin olive oil is more expensive and there is good reason for this. It is subject to strict regulations governing its production and processing, as laid down by the Olive Oil Council and the EU.
The main and most important difference between ordinary and extra virgin olive oil is that the extra virgin variety is extracted by crushing the fruit in a stone mill or metal crushers without the use of heat or solvents. That is why it is sometimes called ‘cold pressed’.
This is the oil that is truly deserving of its reputation. Extra virgin olive oil is your best option, not only for frying but also for dressings.
Extra virgin olive oil still retains its vitamin E content. This vitamin occurs naturally in vegetable oils but is destroyed when oils are refined or exposed to strong sunlight. So leave the cheaper ‘olive oil’ on the shelf and choose ‘extra virgin olive oil’ for both cooking and dressing.
Do not fear the fat
If you’re scared of saturated fat, don’t be. The evidence against saturated fat has always been flimsy, and more speculative than factual.
In November 2008, the World Health Organization and the Food and Agricultural Organization held a joint, four-day expert consultation on the subject of dietary fat and health at the WHO headquarters in Geneva. The aim of this consultation was to review all the most robust, published studies linking the various types of dietary fat to disease. The results of this consultation were published in The Annals of Nutrition and Metabolism. In their interim summary, the WHO and FAO stated that the experts involved in the consultation agreed with previous reports
…“that there is no probable or convincing evidence for significant effects of total dietary fats on coronary heart disease or cancers… There is probable evidence that replacing SFA (saturated fatty acids) with largely refined carbohydrates has no benefit on CHD, (coronary heart disease) and may even increase the risk of CHD.”
Later, in 2015, The British Medical Journal published a review of the most robust studies into the assumed harmful effects of saturated fat, and concluded that there was no association between saturated fat intake and increased risk of death from any cause, including heart disease.
They did however find an association between industrial trans fats and risk of cardiovascular disease.
So ditch the vegetable oils and go back to butter — it was always better.