The science behind the war on seed oils

HostI was at the grocery store recently and noticed that nearly every snack bag had a huge label on it bragging that it was made without seed oils. It feels like these oils, things like canola, corn, and soybean oil, have become the new public enemy number one in the health world.

HostWhy has the mood shifted so fast against these oils that we used to think were better for us than butter?

GuestIt's a massive turnaround. For about fifty years, health groups told us to ditch animal fats and use these vegetable oils instead. They're full of a specific kind of fat called linoleic acid. But lately, people have started to worry that we're eating way too much of it. The big fear is that this fat is like a hidden trigger for swelling and redness inside the body, which doctors call inflammation. The idea is that our bodies weren't built to handle the sheer amount of oil we get from seeds today.

HostBut we have been eating these for a long time. If they were actually making us sick, wouldn't the science be pretty clear on that by now?

GuestYou would think so, but the data is messy. Part of the worry comes from how these oils are made. Unlike an olive, which you can just press to get oil, a seed like a soybean is dry and tough. To get the oil out, factories use really high heat and sometimes even chemicals. People who stay away from these oils argue that this process damages the fat before it even gets to your kitchen. They worry that when these fats hit the heat of your frying pan, they break down into tiny, nasty bits that can mess with your cells.

HostOkay, but if I cook a piece of chicken in canola oil, am I really doing more damage than if I used butter?

GuestWell, that's one of the friction points. When you look at humans in actual health studies, the link to inflammation kind of falls apart. When researchers give people more of these seed oils, they don't usually see an increase in those red flags for swelling in the blood. In fact, in many cases, people's heart health markers actually get better. Their bad cholesterol goes down. So, there's this huge gap between what people see in a lab dish and what actually happens inside a living person who's just eating dinner.

HostSo is the whole movement just based on bad vibes then?

GuestI wouldn't go that far. There's a real tension here about where our food comes from. If you look at a graph of how much seed oil we eat, it has gone up like a rocket ship over the last hundred years. At the same time, we have seen a huge rise in weight gain and heart problems. People look at those two lines going up together and assume one caused the other. But as we know, a lot of things changed in the last century. We sit more, we eat more sugar, and we spend way more time on screens.

HostThat makes me wonder if we're blaming the oil for the crimes of the junk food it lives in. I mean, you don't usually find these oils in a salad you made from scratch. They're in the frozen pizza and the boxed cookies.

GuestThat's a huge part of it. These oils are the backbone of almost every food made in a factory because they're cheap and they stay fresh on a shelf for a long time. If you cut out seed oils, you naturally end up cutting out almost all ultra processed junk food. You start eating more whole foods, like meat, eggs, and vegetables. You probably feel a lot better because you stopped eating corn syrup and food dyes, but you might give all the credit to the fact that you stopped eating soybean oil. It's hard to tease those two things apart.

HostBut what about those old studies from the sixties and seventies? I have heard people say there was evidence against these oils back then that got hidden or ignored.

GuestThere was one famous study in Minnesota where they fed people in a hospital lots of corn oil instead of butter. Their cholesterol went down, but they didn't actually live longer. In some cases, the people eating the vegetable oil fared worse. Critics point to that as the smoking gun. But other experts push back and say that study was flawed because the people weren't on the diet long enough, or they were already quite sick. So even the historical evidence is a bit of a tug of war. There's no one perfect study that proves these oils are the main thing making us sick.

HostIt feels like we're searching for one simple villain to explain why health is getting worse, and seed oils fit that role perfectly because they're everywhere.

GuestThey really do. It's much easier to tell someone to stop eating one kind of fat than it's to tell them to change their entire lifestyle or fix a broken food system. Right now, the strongest science we have still suggests that replacing saturated fats, like the ones in lard or butter, with these oils is generally good for your heart. But the vibes are moving in the other direction because people are craving foods that feel more natural and less like they came out of a lab.

HostEven the most careful tests show that while these oils might lower your cholesterol, they don't seem to be the magic health fix we were promised decades ago.

HostThat pricey bag of chips might be more about how the label makes us feel than what's actually happening in the frying pan.