Supermarket Cooking Oil Secrets: Are Refined Vegetable Oils Really That Good?
Let’s start with a test: does anyone remember what happened on 2nd July 2024? Don’t check your phone; try to think back.
I guarantee the vast majority have forgotten. I searched the internet for this date in 2025, and not a soul mentioned the oil tanker incident from a year ago. The correct answer: on that day, *The Beijing News* exposed the practice of using the same oil tankers to transport both edible oil and chemical liquids without any cleaning in between.
After the exposure, the government rectified the poor supervision, the involved companies expressed regret for their oversight, and the immoral “oil pots” were condemned by all. Then, people returned to their happy, peaceful lives; all’s well that ends well. The foodies, however, felt a lingering sense of dissatisfaction, and thus this article was written.
I.An “Oil Pot”, or a Chamber Pot?
After the tanker incident, a scathing critique went viral: “Essentially, it’s not a question of whether the tank was washed, but that mineral oil and food oil should never share the same tank. No matter how clean a chamber pot is, would you use it as a teapot?”
Every household has an oil pot. In the modern kitchen, these are often dainty and refined, with a focus on drip-free spouts and aesthetic harmony with the décor. A larger version is the oil bottle brought home from the supermarket. The vegetable oils in supermarkets come from major brands, produced by massive edible oil enterprises with annual outputs in the thousands or tens of thousands of tonnes. Storage and transport are as vital as processing; they are essential links in the long, globalised chain from plant to table. In this sense, the tanker is simply a giant oil pot.
People were outraged by those mixed-use tankers carrying edible oil. As a foodie concerned with food health and food sovereignty, I was completely bewildered. While the incident was indeed egregious and deserved condemnation, I hope we can use this opportunity to look deeper and consider the substance known as “oil” inside these pots.
When it comes to the “oil” in the pot, there is one piece of bad news, and then another. Both are depressing.
First, the supermarket vegetable oil we buy is no longer “oil” in the traditional sense. The “mixed loading” of edible oil and non-edible chemical liquids has actually been happening for a long time; it is happening now, and it will continue in the future.
In terms of food, during the agricultural era, oil was either animal fat rendered through heat or seed oil obtained through pressing. Long before the mastery of rendering and pressing, animal fats and plant seeds have ebbed and flowed through human dietary history for millennia. Fats are essential nutrients for life and played a pivotal role in helping humans prevail in the struggle for natural selection. Countless species were eliminated in the river of evolution for failing to obtain sufficient fats; I should probably bow in gratitude to fats for saving my own skin.
I will set aside animal fats for now, as almost all “edible oils” on the market today are vegetable oils—but they are no longer the “oils” that nourished human life throughout evolution.
Why is this? Let’s look at the process.
As humans entered the agricultural era and cultivated more oilseed crops, both East and West developed pressing methods, using external force to squeeze oil from plant seeds. However, in 1843, humans first used carbon disulfide to extract olive oil, and France took the lead in research into solvent extraction. Germany soon overtook them, first establishing the first battery-type extraction plant for industrial production, and then developing the basket-type continuous extractor, which vastly improved efficiency. Then came the United States, which developed the more efficient flat-rotating extractor in 1949, which eventually dominated the market. In 1955, China’s first continuous extraction oil plant was built in Jilin.
The 1950s were an era of rapid progress for the food industry and globalisation, and a time when sugar and refined vegetable oils took up an ever-increasing share of the human diet. Food giants were the driving force. There is a book titled *Salt Sugar Fat: How the Food Giants Manipulate Us*, which provides numerous real-life cases exposing how these giants used everything from massive advertising budgets to bribing scientists to fake academic research.
Before solvent-extracted seed oil reaches the supermarket shelf, it undergoes two high-temperature stages in the factory. There are three types of extraction—pre-pressing extraction, single extraction, and double extraction—which are broadly similar. n-hexane is used to dissolve the oil from the raw materials to obtain a mixed oil. The first high-temperature stage removes the solvent, and the second is used for bleaching, deodorising, and removing impurities. The result is the pure, tasteless, transparent, and clear refined vegetable oil that reaches the supermarket shelves and the kitchens of the people.
Nowadays, the solvent commonly used in extraction is n-hexane—a non-edible petrochemical product that is harmful to health.
This solvent can remain in the vegetable oil. According to the “National Food Safety Standard for Vegetable Oils”, the solvent residue for edible vegetable oils (including blended oils) produced by the extraction process is ≤20mg/kg. For pressed oils, solvent residue must be undetectable (values below 10mg/kg are considered undetectable). The EU has established even stricter standards for solvent residues in edible oil; the current safety standard is 1mg/kg, which is 10 to 20 times stricter than ours.
II. Industrial Alchemy: Turning Oil into Inflammation
For consumers to use the nutritional profiles of traditional, agricultural-era pressed oils to seek quality in supermarket oils is like trying to find the Monkey King by using his old ID card, unaware that he has long since attained enlightenment and become the Victorious Fighting Buddha.
Then there is the second piece of bad news: supermarket oils may not only contain solvent residues but may also contain trans fats.
Trans fats do not only appear in hydrogenated vegetable oils; they are also produced during the oil refining process and through high-temperature cooking.
When vegetable oil undergoes two stages of high-heat treatment, the first piece of bad news is that the heat-sensitive nutrients originally found in the seeds—such as the natural antioxidant vitamin E and phytosterols—are wiped out. Another piece of bad news is that the monounsaturated fatty acids and polyunsaturated fatty acids, which played a monumental role in the vast sweep of human evolution, are also largely destroyed. The worst news of all is that matter is never truly destroyed; after being forged and transformed in the high-temperature furnace, a portion of these fats is converted into the trans fats that strike fear into the hearts of modern health-conscious people.
If you are like me—possessing only a superficial understanding but a diligent will to learn—you will inevitably encounter contradictory findings during your research. For instance, some literature mentions that finished oils may contain residual solvents, while others suggest that carcinogens such as benzo[a]pyrene may be produced during the process. Conversely, official announcements claim that in products that pass inspection, the levels of harmful substances remain within controllable limits. I choose to believe—to believe that God helps those who have faith.
Vegetable oils have also become pro-inflammatory agents that jeopardise general modern health.
Vegetable oils contain essential fatty acids that the human body cannot synthesise: linoleic acid (ω-6) and α-linolenic acid (ω-3). While vegetable seed oils do contain ω-3, the levels are not high. These are more abundantly found in wild fatty fish, free-range chicken and duck eggs, grass-fed beef and lamb, and full-fat milk. To rely on vegetable seed oils to meet one’s ω-3 requirements is an entirely counterproductive pursuit.
But the worst news is the excess of ω-6. The ideal ratio between ω-3 and ω-6 is between 1:1 and 1:4. In vegetable seed oils, ω-6 is far more prevalent, and it exists widely across the entire food chain; we already have enough of it. Now, as we consume more and more vegetable seed oils, the ratio in our daily diet can reach 1:15 or even higher. This imbalance promotes inflammation, ageing, and oxidative reactions, leading to serious trouble.
Despite these issues, the reason solvent-extracted seed oils remain popular worldwide is straightforward. I grow my own rapeseed and peanuts and have used a small press to extract oil myself. Rapeseed, with an oil content of around 40% (37.5%–46.3%), yields only about 10% oil per jin (500g) of seed. If sent to a small village mill for hot pressing, the yield increases to nearly 30%. With such methods, roughly half of the oil remains in the residue. However, solvent extraction can achieve an oil yield of up to 99%.
III. The clumsy bear dies of stupidity; the “capable” man dies of his own cleverness
Regarding seed oils, modern humans have truly “outdone” themselves. Extraction rates are higher than ever, supermarket oils are cheaper, and highly oil-rich processed or semi-processed products are more accessible than ever. We have become increasingly “capable”, right until the end.
I once read this: “Nature does not make unhealthy food, but factories do.”
As a “simple” person, I take a simple approach: a blanket ban. I don’t just avoid supermarket oils; I don’t eat takeaways, nor any finished or semi-finished products containing oil. My specific methods are as follows:
1. No stir-frying. Vegetables are wonderful, but stir-frying is not; vegetable oils produce trans fats when cooked at high temperatures. Vegetables can be eaten raw in salads, roasted, steamed, or blanched. Electric ovens and air fryers are a modern blessing. For instance, aubergines—which usually soak up oil like a sponge during stir-frying—can be placed in the oven or air fryer with garlic and green chillies for ten minutes, then mashed with salt and seasoning. It makes for a very refreshing side dish with rice. As I cannot eat spicy food, I leave out the chillies; I’ve heard that mashing them with preserved century eggs creates the classic Hunan home-style dish “Lei Cai”.
The electric griddle is another of my daily essentials. I don’t eat meat, so I make fried eggs every day. At first, I used an oil-free version: eggs and various side ingredients with a bit of soft tofu, poured in once the griddle was preheated. Later, for various reasons, I stopped eating commercial tofu; fearing the eggs would stick or burn, I switched to using a tiny amount of oil—just a single drop, so the consumption is minimal. For those who eat meat, you can make minced meat “water-fried” eggs, using water instead of oil (roughly double the volume of oil). Once the pan is hot and the water boils, add marinated shrimp, diced meat, shiitake mushrooms, or wood-ear fungus; once it boils again, pour in the beaten eggs and stir-fry. This is similar to a speciality from Changwu, Shaanxi. You can also refer to previous Foodthink posts on savoury sauces to make a batch that lasts a long time.
2. Choosing trustworthy oils. Although I don’t stir-fry, I still need oil occasionally. I choose walnut oil from Kang Li, a Yi ethnic minority girl and farmer at the Beijing Organic Farmers’ Market. Usually, I buy three jin (six small bottles) after the Spring Festival; I still have three unopened bottles now, meaning I use less than 3 grams a day on average. This year, I harvested about fifty jin of rapeseed and over a hundred jin of peanuts in their shells, so I won’t need to buy oil in the future.
3. Satisfying cravings with homemade treats. Foodthink has already published my guide to homemade mooncakes. That was a water-oil pastry version using walnut oil with additive-free homemade fillings, though the oil content was still a bit high. Later, I developed taro paste and red bean paste egg yolk pastries using oat flour as the main ingredient for the crust, which are oil-free. I can also make oil-free biscuits using crushed red dates, oats, black sesame, and steamed buckwheat with egg yolk. These snacks are delicious, healthy, and guilt-free; I will share the detailed recipes when I have the chance.
I substitute refined vegetable oils with whole nuts and oilseed crops. Fats are an essential nutrient for the human body, and fat-soluble vitamins cannot function without them, so it is important to have enough. Many nutrients cannot be synthesised by the body, particularly omega-3. My method is to eat nuts rich in omega-3, such as walnuts, and some simply processed products like black sesame paste.
4. And then there are my home-grown peanuts. My most common ways of eating them are:
1. Low-temperature roasting in the shell at 130 degrees for one hour. This makes the peanuts perfectly crisp and easy to peel, with a slightly sweet flavour. This can be done in an oven or an air fryer. I prefer the air fryer because I make small batches—usually less than half a jin—and eat them immediately before they lose their crunch.
2. Boiled peanuts, which I also eat daily. This requires pre-soaking; I keep the peanuts in water in the fridge and drop a few in whenever I make soup. They work well in both salty vegetable soups and light rice soups. The resulting texture—slightly sweet, tender, and not crisp—is very unique.
3. Boiling fresh peanuts. Peanuts have a long growing season in Fujian; if you scatter a few seeds in the corners of your land from the Spring Equinox until the Start of Autumn or White Dew, you can dig them up and eat them from the Lesser Heat and Greater Heat through to the Lesser Snow and Greater Snow—a period of up to six months.
Aside from the last point, which is a perk reserved for farmers, city dwellers can also try the other methods.
Some may worry about “experts” warning that “nuts are healthy but harmful in excess,” but my simple logic interprets it this way: that advice is for people whose “daily oil intake for adults is 25–30 grams.” Those of us who consume less than 3 grams of oil a day are not in that category.
