Not all oils are the same. And some oils you're eating could be killing you.
This is the latest revelation from Australian health researcher David Gillespie. The "recovering corporate lawyer" is known for his crusade against sugar.
In his latest book, Toxic Oil, Gillespie issues a warning about vegetable oils - we're talking about canola, sunflower, soybean, grapeseed or rice bran.
These kinds of oils are used in 90 to 100 per cent of the processed foods available to us on the supermarket shelves, he says. And they're at the root of modern epidemics like cancer and heart disease.
"The reason that they're the problem is that they're very, very high in a highly oxidisable fat, called Omega 6 fat," he explains.
But before we get stuck in to the fatal facts, I ask Gillespie for a bit of background about oils.
Firstly, remember, we do need some fat. We make some ourselves ("the wobbly bits") and we consume some in everything we eat. We use some of it for energy, and we need some Omega 6 fats for immunity.
But the teaspoon our bodies require for smooth operation is obtained in all the other things we eat - including fruit, veggies, meat and fish.
We also need fats for building cells. But I'll get in to this after a bit of a history lesson.
Since 1920 the world's population has exploded, making it hard to feed everybody, meaning the price of foods had to increase, Gillespie explains.
"And that's what happened to animal based fats like lard. The processed food industry came to the rescue and invented ways to extract oil from waste products like cotton seeds.
"That would have been a happy ending if these seeds that they extract had the same chemical make-up as the animal fats that they were replacing.
"But they didn't. They performed the same when you cooked with them, they were treated the same by our bodies when we ate them, but the results are disastrous."
See, all fats get taken in to our cell membrane. The cell membrane makers can't tell the different between the good stuff and the bad stuff. So, unlike the fats that we produce (animal fats) and the fats that we've traditionally eaten (animal fats and fruit fats that mimic the fat profile of animal fat) these Omega 6 packed fats react quickly with oxygen and break down fast with oxygen.
"That's bad news when what we're doing with them is building every cell membrane in our body out of them," Gillespie says.
"What happens inside a cell membrane is we burn oxygen. So it's like building a fire place out of balsa wood instead of bricks."
Humans are built to handle some oxidation, we run on the stuff, but when we over-load those systems by putting in something which is too easily oxidised we go to a state called "oxidative stress".
"Which leads down a path straight to cancer.
"Oxidative stress causes cellular decay, it causes DNA mutations and ultimately that's well known to be an environment perfect for a whole range of cancers."
In Toxic Oil, Gillespie refers to human studies which show people eating diets filled with these kind of fats have twice the rate of cancer than those who are eating diets high in animal fats.
So why are only just hearing all about cancer-causing oils now? Gillespie says it's partly because the science is evolving, but also because of the strong commercial interests against letting the cat out of the bag.
"The people making money out of embedding seed oils in every processed food in the supermarket are making far more money than the sugar industry ever has," he says.
The Australian Heart Foundation recently issued a release advising people to ignore Gillespie's analysis. But he's passionate about spreading the word.
"This (vegetable oil) is literally in every item in the supermarket.
"That shows the complete replacement of animal fats in our diet. And this has all occurred in the last 80 years. In the same time span that we've seen massive epidemics in heart disease and cancer."
The damage this oil is doing to our cells is setting us up for a cumulative effect of long-term chronic diseases, he says. Not only cancer and heart disease, but rhumatoid arthristis and children's allergies.
"Children's allergies in the last 15 years have quintupled in the zero to four age group. Is there a possibility that's because we've got pregnant mothers and babies consuming a diet extremely high in these pro-inflammatory fats?
"It's irrational to blame modern disease epidemics like heart disease and cancer on ancient foods which is what I'm recommending people eat.
"Which is essentially what we ate for the entire rest of the history of human kind."
Gillespie cops plenty of flak for the controversial claims he makes. (Have a listen to this oil debate from Australia's ABC radio to hear the other side of the story.) He is clear in stating that he doesn't have any formal health qualifications, the skill he brings to the table is his ability to analyse evidence.
"I get a lot of people who criticise my right to say what I'm saying, but I get no body who has managed to prove that what I'm saying is wrong."
"To me that's a suspicious argument.
"The reason I'm doing it is because if somebody knew what I know and didn't tell me and my family, I'd be furious."
* Toxic Oil, by David Gillespie, published by Penguin, is available now. RRP $37.