The Seed Oils Question

Seed oils, sometimes called industrial or vegetable oils, are the pale, neutral oils pressed and refined from seeds and grains. The ones people mean are usually the eight below, and they share one defining trait: they are very high in an omega 6 fat called linoleic acid. That single fat is the centre of the entire debate.

A seed is not naturally oily the way an olive or an avocado is. To pull oil out of it at scale, the seeds are crushed, heated, and usually washed with a solvent called hexane to free the last of the oil. The crude oil is then refined, bleached and deodorized, a process the industry calls RBD, to strip out the colour, smell and taste that raw seed oil would otherwise carry.

This is the part that makes people uneasy, and it is worth being precise. Regulators including the European Food Safety Authority consider the trace hexane left in finished oil to be within safe limits, and modern refined oils contain very little trans fat. So the strongest concern is not really the solvent. It is what these fats are, and where they end up.

Seed oils did not take over the food supply by accident. They are pressed from abundant, heavily grown crops, so they are cheap. They are nearly flavourless, so they vanish into any recipe. They pour easily, they resist going rancid in a warehouse, and they survive factory frying. For a company building a product that must last months in a box and taste identical every time, they are close to perfect.

So they went everywhere: fried foods, chips and crackers, dressings, sauces, spreads, baked goods, protein bars, plant milks, restaurant fryers and most of the packaged aisle. If a food has a long ingredient list and a long shelf life, a seed oil is very often in it. Hold on to that fact, because it turns out to matter more than any single lab study.

Here is the fact most people have never heard, and it reframes the whole question. Linoleic acid does not simply pass through you. Your body builds it into the walls of your cells and stores it in your body fat, and it stays there a remarkably long time.

The half life of linoleic acid in human body fat is roughly 680 days, close to two years. The fat you are carrying today is a slow moving record of what you have eaten for years, which is exactly why changing it is a patient climb and not a weekend fix.

Close to a doubling, sitting in the tissue of the average person, and tracking almost perfectly with how much seed oil the food supply added over the same years. Whatever you conclude about cause and effect, this is not a fat that visits. It moves in.

To be fair, and this matters, a large body of mainstream research does not find seed oils harmful, and some of it finds the opposite. This is the case the defenders make, and it is a serious one.

In a 2009 science advisory, the American Heart Association concluded that omega 6 fats are safe and beneficial for the heart, and recommended getting at least five to ten percent of daily calories from them. Pooling six randomized trials, that advisory reported replacing saturated fat with omega 6 fat cut coronary events by about a quarter. It is worth knowing the most recent systematic review lands softer: a 2018 Cochrane review of nineteen trials and more than six thousand people found that increasing omega 6 made little or no clear difference to deaths or cardiovascular events, on low-certainty evidence. Neither the alarm nor the reassurance is as firm as its loudest advocates claim. In a pooled analysis of thirty groups of people, those with the most linoleic acid in their blood had lower rates of heart disease and death, not higher. And contrary to the common claim, feeding people more omega 6 in controlled studies has generally lowered or not changed their inflammation markers.

And yet the story has another half that rarely makes the headline. When researchers recovered the lost data from two large, careful trials run in the 1960s and 70s, the picture grew more complicated.

In the Minnesota Coronary Experiment, more than nine thousand people replaced saturated fat with corn oil. Their cholesterol fell by about fourteen percent, exactly as the theory predicted, yet they did not live longer. In the recovered data, the people whose cholesterol dropped the most tended to die at higher rates rather than lower, and there was no fall in heart attacks or hardened arteries. The Sydney Diet Heart Study, which swapped in safflower oil, pointed the same unsettling direction.

So the honest summary is this. The evidence that these oils lower cholesterol is strong. The evidence that doing so makes people healthier is mixed. And almost no human study can cleanly separate the oil from the ultra processed food it usually arrives in. Careful, well informed scientists still disagree. Anyone who tells you this is completely settled, in either direction, is selling something.

Here is the freeing part. You can hold all of that uncertainty and still know your next move, because the clearest signal in the entire pile of research is not really about the molecule. It is about the company it keeps. Seed oils are the fingerprint of ultra processed food, and when you build meals from whole food, most of them quietly disappear from your plate without you ever counting a gram.

So at Ascent we do not call seed oils poison, and we do not treat them as health food either. We cook with stable, minimally processed fats like butter, ghee, extra virgin olive oil, avocado oil and coconut oil. We steer clear of oils that have been deep fried, reused or overheated. And we spend our attention where the evidence is strongest: whole food first, and the seed oils largely take care of themselves.