The Secret in the Supermarket Oil Bottle: Is Refined Vegetable Oil Really Any Good?
Let me start with a little test: does anyone remember what happened on 2 July 2024? Don’t go searching your phone – just think.
I guarantee the vast majority of people have forgotten. On this very day in 2025 I searched online, and no one mentioned the oil tanker affair from a year ago. The correct answer: that day, The Beijing News exposed tankers carrying edible oil and industrial liquids without ever being washed in between.
Once the story broke, the government cracked down on inadequate oversight, the companies involved issued self-criticisms for their failures, the unscrupulous “oil pots” became the target of universal scorn, and everyone went back to a happy, peaceful life – all was well again. But this foodie was left grumbling and pensive, and so this essay was born.
I. An “Oil Pot”, or a “Chamber Pot”?
After the tanker scandal, a sharp one-liner circulated widely: “The issue isn’t whether the tank gets washed or not – mineral oil and food-grade oil should never share the same tank in the first place. No matter how spotless you make a chamber pot, would you use it as a teapot?”
Every household has an oil pot. The oil dispensers in a modern kitchen are sleek and compact; the priority is a spout that doesn’t drip and a design that matches the kitchen décor. A slightly bigger “oil pot” is the plastic jug you lug home from the supermarket. The vegetable oils on supermarket shelves all bear big brand names, produced by large edible-oil manufacturers churning out thousands or tens of thousands of tonnes a year. Storage and transport, just like processing, are indispensable links in the long, globalised chain that runs from plant to plate. In that sense, a tanker truck is just a giant oil pot.
Those tankers carrying edible oil alongside other liquids set public fury ablaze. As a foodie who cares about food health and food sovereignty, I was completely bewildered throughout. The affair was undeniably outrageous and certainly deserved the outrage, but I had hoped people would seize this chance to dig one layer deeper and care about what’s actually inside those tanks – the stuff we call “oil”.
As for the “oil” in the pot, there is one piece of bad news, and then another – and neither one is easy to stomach.
The first is this: the vegetable oil you buy from the supermarket is no longer “oil” in the traditional sense. The “co-loading” of edible oil and non-food chemical liquids has been happening for a long time, is happening now, and will go on happening in the future.
As food in the agricultural age, oil meant one of two things: animal fat rendered over heat, or plant seed oil obtained by pressing. Long before humans mastered the crafts of rendering and pressing, animal fats and plant seeds had drifted through the vast sweep of human food history for millions of years. Fats and oils are vital nutrients essential to life, and they played an incalculable role in humanity’s triumph in natural selection. Countless species have been swept away by the long river of evolution for failing to secure enough fats and oils – I should bow to fat itself for keeping this little life of mine going.
I’ll set aside animal fats for now, because virtually all “edible oil” sold today is vegetable oil – yet it is no longer the “oil” that sustained human life across the ages of evolution.
Why do I say that? Let’s start with the process.
Once humanity entered the agricultural age and had access to more oilseed crops, both East and West developed the pressing method, using external force to squeeze oil from plant seeds. But in 1843, humans first used carbon disulfide to extract oil from olives, and France took the lead in solvent-extraction research. Germany then overtook France, first building the earliest tank-group extraction plant for industrial-scale production, then developing the basket-type continuous extractor, which dramatically improved efficiency. Then came America, which in 1949 developed the higher-efficiency rotary-type extractor and dominated the entire industry through massive adoption. In 1955, China’s first continuous-extraction oil mill was completed in Jilin.
The 1950s was an era when the food industry and globalisation charged ahead full steam, and also when sugar and refined vegetable oil made up an ever-growing share of the human diet. The food giants were the driving force behind it all. There is a book called Salt Sugar Fat: How the Food Giants Hooked Us, packed with true stories that expose how food conglomerates pull out all the stops – from eye-watering advertising campaigns to buying off scientists and fabricating research.
Before seed oil made by solvent extraction ever reaches a supermarket shelf, it undergoes two rounds of extreme heat in the factory. Solvent-extracted oil production comes in three forms – pre-press solvent extraction, single-stage extraction and two-stage extraction – each broadly similar in principle: n-hexane dissolves the oil in the raw material to form a miscella, which then passes through two stages of high heat. The first stage removes the solvent; the second involves high-temperature decolourisation, deodorisation and removal of impurities. Pure, odourless, crystal-clear refined vegetable oil goes onto supermarket shelves and into kitchens everywhere.
In today’s solvent-extraction process, the solvent most widely used is n-hexane – a petrochemical product that is inedible and harmful to health.
Residues of this solvent remain in the oil. Under the National Food Safety Standard for Vegetable Oils, the permitted solvent residue in edible vegetable oil produced by solvent extraction (including blended oil) is ≤ 20 mg/kg. For pressed oil, solvent residue must be undetectable (any reading below 10 mg/kg is treated as “not detected”). The European Union, by contrast, has set a far stricter limit on solvent residue in edible oil – the current safety standard is 1 mg/kg, ten to twenty times stricter than ours.
II. The Industrial Alchemy Furnace: Turning Oil to Inflammation
It’s like taking a pressed-oil spec sheet from the agricultural age to a supermarket and searching for something that simply isn’t there any more – like clutching the ID card of the Handsome Monkey King from the Eastern Continent of Superior Bodies to hunt for the Great Sage, Equally Heaven, only to discover he’s long since attained full enlightenment and become the Victorious Fighting Buddha.
The second piece of bad news: supermarket oils may contain not only solvent residues but also trans fat.
Trans fat isn’t found only in hydrogenated vegetable oil – oil refining and high-temperature cooking produce it too.
For vegetable oil that has endured two rounds of extreme heat, one piece of bad news is that the heat-sensitive nutrients naturally present in seeds – the antioxidant vitamin E, phytosterols and the like – are lost as surely as a beauty fading. Another piece of bad news is that the monounsaturated fatty acids and polyunsaturated fatty acids that once played an incalculable role across the aeons of human evolution are also largely destroyed. And yet another piece of worse news: matter is never truly annihilated. After passing through the alchemist’s furnace, undergoing nine rounds of transmutation and shedding every last trace of its old form, some of it emerges reborn as trans fat – the very thing modern people dread at the mere mention.
If, like me, you know only half the story but are doggedly curious, you will inevitably stumble across discordant notes during your research: one paper warns that finished oils may contain solvent residues, another says that benzo[a]pyrene and other carcinogens could form during processing, while an authoritative release reassures us that levels of harmful substances in tested products fall within a controllable range. I choose to believe – and believe that God blesses those who have faith.
Vegetable oil has also become a pro-inflammatory agent, undermining the health of modern people on a wide scale.
Seed oils contain essential fatty acids the body cannot synthesise: linoleic acid (omega-6) and alpha-linolenic acid (omega-3). While seed oils do contain some omega-3, the quantities are low. Real omega-3 lives in wild fatty fish, free-range chicken and duck eggs, grass-fed beef and lamb, and whole milk – trying to meet your omega-3 needs by eating seed oils is like trying to head south by driving north.
But the worse news is omega-6 overload. A healthy omega-3 to omega-6 ratio sits somewhere between 1:1 and 1:4. Seed oils are heavy in omega-6, and omega-6 pervades the entire food chain. We never had a shortage in the first place; now that we eat ever more seed oils, the ratio in a typical daily diet can reach 1:15 or even higher. When the two get this far out of balance, they fuel inflammation, ageing and oxidative stress – and that is a very big problem.
Despite all these problems, plant seed oil produced by solvent extraction is still a global phenomenon for one extremely simple reason. I grow my own rapeseed and peanuts and have pressed oil myself on a small-scale machine. From 500 grams of rapeseed with an oil content of around forty per cent (37.5–46.3 per cent) you get barely 50 grams of oil – an oil yield of just over ten per cent. Send it to a village oil mill for hot pressing, and you get just over twenty but barely thirty per cent. Even this way of pressing leaves roughly half the oil in the seed trapped in the residue. But solvent extraction can achieve an oil yield of 99 per cent.
III. The Bear That Died of Stupidity, and the Person Who Will Die of Cleverness
When it comes to plant seed oils, modern people have certainly gone full tilt on cleverness: oil yields ever higher, supermarket oils ever cheaper, high-oil-content finished and semi-finished products ever more convenient and ever more within reach – clever, right up to the grave.
I once came across this line: “Nature does not make unhealthy food, but factory does.” (Nature does not make unhealthy food, but factory does.)
As a plain, simple-minded sort, I adopt a plain, simple-minded approach: a blanket rule – no exceptions. I don’t buy supermarket oil, I don’t order takeaway, and I avoid any finished or semi-finished food product involving oil. In practice, this means:
1. No stir-frying. Vegetables are wonderful, but stir-frying them isn’t – heating vegetable oil to high temperatures produces trans fat all the same. Vegetables can be dressed raw, roasted, steamed or blanched. An electric oven or air fryer is a modern gift: take aubergine, that notorious sponge for stir-frying oil, throw it in the oven or air fryer for ten minutes alongside a few chillies and a head of garlic, mash it with salt and seasoning, and you have a beautifully refreshing side for rice. I can’t handle chilli, so I skip it – but apparently if you add a century egg to the mix and pound it all together, you’ve made the Hunan classic home dish “lei cai” – pounded vegetables.
The electric griddle is another beloved daily fixture. I don’t eat meat, so I cook a griddle-fried egg every single day. The earliest version was completely oil-free: eggs with whatever extra ingredients I had, a little water tofu, poured straight onto the pre-heated griddle and done. Later, when the tofu from the shop was no longer in my repertoire, I worried about the pan sticking and the bottom scorching, so I switched to a micro-oil fry – a single drop is all it takes, using a vanishingly small amount of oil. For my friends who do eat meat, try a water-fried egg with minced meat: use water instead of oil, at double the volume. Get the griddle hot and the water simmering, first add your seasoned prawns, diced pork, shiitake mushrooms and wood-ear fungus, then once it bubbles again, pour in the beaten egg and stir. It comes close to a traditional way of eating from Changwu in Shaanxi. You could also refer to Foodthink’s previous issue of stir-fried sauce – make one batch and it keeps for a good while.
2. Choose trustworthy oil. Even though I don’t stir-fry, I still use oil from time to time. I pick walnut oil from Kang Li, a young Yi woman who sells at the Beijing Organic Farmers’ Market. I typically buy three jin (six small bottles) after Chinese New Year each year, and to this day I still have three unopened – averaging under three grams a day. This year I harvested roughly fifty jin of rapeseed and over a hundred jin of unshelled peanuts, so there’ll be no need to buy oil any more.
3. Scratch your own itch by cooking from scratch. Foodthink has already published a piece of mine on homemade mooncakes – that was the water-and-oil puff pastry version, made with walnut oil and all-natural fillings, though it still had a touch too much oil. Since then I’ve developed taro paste and egg-yolk puff pastries and red bean paste and egg-yolk puff pastries, with oat flour as the main pastry ingredient – no oil at all. You can also make oil-free biscuits by blending crushed dates, oat flakes, black sesame and steamed buckwheat with egg yolk. These snacks are tasty, healthy and guilt-free – I’ll share the method in detail when I get the chance.
Replace refined vegetable oil with whole nuts and oilseed crops. Fats are an essential nutrient – without them the body simply cannot absorb fat-soluble vitamins, so you must eat enough. Many nutrients the body cannot make on its own, omega-3 in particular. My solution is to eat nuts rich in omega-3, walnuts especially, along with a few lightly processed items such as black sesame paste.
4. Then there are home-grown peanuts. My most common ways to eat them:
1. Roast peanuts in their shells at a low temperature – 130 °C for one hour. Roasted this way, they come out perfectly crisp and easy to peel, with a gentle sweetness. An oven or an air fryer both do the job. I prefer the air fryer because I make small batches – no more than 250 grams at a time – and I can shell a handful whenever I fancy, finishing them before they have a chance to go soft.
2. Boiled peanuts – another daily staple. This method requires pre-soaking: place shelled peanuts in water and leave them in the fridge. When you make soup, toss in a few. They work beautifully in both a hearty, salty vegetable soup and a plain, mild rice water. Peanuts cooked this way are faintly sweet, smooth yet not crisp – a really distinctive texture.
3. Boiled fresh peanuts dug straight from the ground. In Fujian, peanuts have a long growing season: tuck a few seeds into any spare patch of ground and you can plant from the Vernal Equinox all the way through to the Start of Autumn and White Dew. Dug fresh, peanuts can keep coming from Minor Heat and Major Heat right through to Minor Snow and Major Snow – a span of half a year.
Apart from the last tip being a farmer-exclusive perk, city friends can copy this homework too.
Some people fret over the so-called “experts” who warn that “nuts are good, but eating too many does no good”. My simple-minded logic goes like this, though: that warning is aimed at people whose recommended daily edible-oil intake is 25–30 grams. Those of us who consume barely 3 grams of oil a day are hardly the ones being addressed.
