Is It Safe to Consume Vegetable Oil Every Day?
Comparable to virgin cold-pressed Olive oil The plastic-bottled are available in glass bottles. vegetable oil in the supermarket is truly bang-for-your-buck, and it can be found in almost every kitchen. However, how often can vegetable oil be used for frying, boiling, sautéing, and deep-frying? Be careful, as you may be unknowingly ingesting carcinogenic toxins.
Vegetable Oil Refined at High Heat Contains Carcinogenic Toxins
The raw materials of commercially available vegetable oils, such as soybean oil, corn oil, sunflower oil, and grapeseed oil, are not as high in oil content as olives, so the oil is actually obtained from the raw materials by extraction.
The method involves soaking soybeans and other raw materials in an “organic solvent” such as hexane to extract the oil. Then the materials are heated and the evaporation process removes the solvent. The refining process for vegetable oil is very complicated, and the oil has to go through various steps such as degumming, deacidification, decolorization, deodorization, and so on.
Tung Chih-Hong, deputy director and senior research scientist at the Food Industry Research & Development Institute in Taiwan, said that lecithin and other colloids in soybeans, for instance, will be removed during degumming, and lecithin will be processed into soy lecithin health products.
The next step is deacidification, which involves adding alkali (such as sodium hydroxide) to convert free fatty acids, which are not conducive to long-term storage of oil products, into soapstock through a “saponification” reaction, and then removing them. This can increase the stability of the oil.
The step after deacidification is decolorization. There are a lot of impurities, pigments, or soapstock left over from deacidification in the plant body, so activated clay will be added and heated to over 100 degrees under a vacuum. This allows the activated clay to adsorb the substances, thereby clearing the oil.
The final step is deodorization. All the substances remaining in the oil, such as objectionable odors and decomposed peroxides, will be sucked away after being exposed to a high heat of more than 200 degrees under high vacuum pressure. Once all the steps are complete, refined and pure vegetable oils are obtained.
Chih-Hong said that raw materials such as soybeans, corn, and rapeseed will go through a high-temperature refining process unless the product packaging emphasizes that it is cold-pressed. This is to ensure the stability of oil products for mass sales and long-term storage.
However, the high-temperature refining method produces some unhealthy byproducts, such as what follows.
Trans fats
Trans fats cannot be metabolized and utilized by the body and will thus accumulate in the body. Trans fats have been shown to increase the risk of coronary heart disease, have adverse effects on the brain and nervous system, and may play a role in the development of Alzheimer’s disease and cognitive decline with age.
Studies have also proved that trans fats are directly related to breast cancer, colon cancer, diabetes, obesity, and allergies.
Monochloropropanediol, glycidyl fatty acid esters
These two substances will be converted into free monochloropropanediol (MCPD) and glycidol after entering the body. Glycidol is a group 2A carcinogen, which is a substance that is probably carcinogenic to humans and has genotoxicity and carcinogenicity. MCPD is a group 2B carcinogen and is possibly carcinogenic.
4-Hydroxynonenal
Vegetable oil is high in linoleic acid (omega-6), which has a low heat resistance and will produce 4-hydroxynonenal at high temperatures.
4-Hydroxynonenal is toxic and has been linked to a number of conditions, including inflammatory and degenerative diseases such as atherosclerosis, liver damage, Parkinson’s, Alzheimer’s, and cancer.
All oils contain omega-6 fatty acids, just in different proportions. Oils high in omega-6 include safflower oil, grapeseed oil, sunflower oil, corn oil, cottonseed oil, soybean oil, sesame oil, peanut oil, etc.
“All foods processed at high temperatures undergo some reaction and may produce some trace substances. This is a normal phenomenon,” Chih-Hong pointed out. “It will not cause harm to the body if it is kept below a certain amount.”
Is it true that these byproducts can only be controlled and reduced in amount, but cannot be completely avoided?
Chao Ming-Wei, a toxicologist and associate professor in the biotechnology department at Chung Yuan Christian University in Taiwan, answered frankly, “It is really difficult.” Take 4-hydroxynonenal as an example: Vegetable oil will produce oleic acid and linoleic acid during the high-temperature extraction process, and linoleic acid contains 4-hydroxynonenal.
The key lies in the amount. There are now regulations around the world to ensure that the byproducts in these vegetable oils do not exceed a certain number of parts per million or billion (ppm or ppb) to be sold to the public. Hence, legal manufacturers around the world try to reduce these byproducts in the process of refining oil products.
The Inevitable Poison: This Cooking Habit Makes Vegetable Oil More Toxic
There are regulations governing the amount of toxins in vegetable oil, but we still have to be mindful of how we cook it. When cooking, there is one habit that will increase the toxicity of vegetable oil—and that is high-temperature cooking.
What not to do with vegetable oil
Do not use it in high-temperature deep-frying, pan-frying, or sautéing.
Vegetable oil with high omega-6 content is only suitable for stir-frying on medium heat due to its low heat resistance.
Dr. Yen Tzung-Hai, a professor in the department of nephrology in the Clinical Poison Center at Chang Gung Memorial Hospital in Taiwan, pointed out that the frying temperature may reach up to 392 F (200 C). Omega-6-rich oils are prone to peroxidation during frying, resulting in the formation of 4-hydroxynonenal. He mentioned that oils with high smoke points and high saturated fat, such as lard and palm oil, should be used when frying food, but make sure not to fry them repeatedly.
People from East Asia like to sauté at high heat when cooking, which involves pouring oil into a hot pan, and then stir-frying spices such as shallots and garlic to force out the aroma. However, the oil temperature will continue to rise during this process, exceeding the smoke point and emitting oil fumes. Ming-Wei pointed out that during the process of high-temperature sautéing, the toxins in vegetable oil will start to oxidize and volatilize, exposing people to these chemicals. When the cook inhales, these fumes can cause lung damage and increase the risk of lung cancer.
In addition to avoiding high-temperature cooking, we also need to ensure that the vegetable oil is stored in the right way.
Vegetable oil should be kept in a cool place at room temperature to avoid oxidation due to exposure to light or sunlight. Most bottles are made of transparent plastic, but it is best to choose a dark bottle, or better yet, a glass bottle. “This is because oil products are indeed unstable,” Ming-Wei said.
The plastic bottles of vegetable oil sold in supermarkets and retailers are mainly made of type 2 (high-density polyethylene, HDPE) and type 5 (polypropylene, PP) plastics, which are resistant to corrosion, acid and alkali, high temperatures, and have no plasticizer. If you wish to repack oil at home, a glass bottle should be your first choice, followed by type 2 and type 5 plastic bottles. Do not use type 3 plastic bottles (polyvinyl chloride, PVC), as they contain added plasticizers to improve plasticity.
Is Cold-Pressed Oil Safer and Healthier?
In terms of health benefits, pressed oils such as olive oil and tea seed oil are better because they are unrefined and thus retain more of their original nutrients.
Ming-Wei said that, generally speaking, consuming a little vegetable oil every day will not cause too much harm. However, given the choice, he recommends opting for cold-pressed oils like olive oil, which are healthier.
But is cold-pressed oil necessarily better?
Chih-Hong pointed out that cold-pressed oil stored in a poor environment or with poor raw-material quality may also produce some aflatoxin or other problems.
Moreover, cold-pressed oil does not necessarily preserve better than extracted oil. Although cold-pressed oils retain more of the original plant nutrients, they also retain some harmful substances and odors.
Take olive oil, for example. Because it retains its original polyphenols, odor, and pigment, it is not suitable for food processing (i.e., it isn’t as stable and won’t have as long a shelf life). But since most of these substances are removed from vegetable oils, these oils are easy to process and have long shelf lives.
In addition, there are different grades of olive oil. The processes of making extra virgin and virgin olive oils involve washing and crushing the olives and then centrifuging them to separate the oil. Some of the oil remaining on the pomace can be pressed under stronger conditions, or extracted with solvents—that is, through a high-temperature refining process. The refined oil is called pomace oil, and manufacturers will mix it with virgin olive oil to form what is marketed as “pure olive oil.”
If the olive oil is not labeled as cold-pressed virgin or extra-virgin on the package, it is a blend of refined oil and virgin oil. As consumers, we should pay attention to labels when purchasing products.
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