Introduction: Why All the Controversy About Seed Oils?
Have you ever wondered why seed oils have become the bad guys of the nutrition world? Oils like soybean, corn, and sunflower—staples in kitchens everywhere—have been vilified in a growing trend by influencers on YouTube. Certain health gurus have sparked a movement against these oils, claiming they’re packed with linoleic acid (an omega-6 fatty acid) that they claim causes inflammation, heart disease, and a laundry list of other health woes. This anti-seed oil narrative has become increasingly influential, leaving many people questioning a common ingredient in their diets. While many of you, our faithful readers, don’t eat grocery store vegetable oils, we get concerned that even grapeseed oil, organic expeller-pressed canola oil, and unrefined sunflower seed oil and other “healthy” oils in our organic salad dressings are also bad for us.
But is this backlash based on solid science, or is it just the latest health fad? In this article, we’ll cut through the noise and look at what large, long-term studies—backed by biological evidence—actually say about seed oils. Spoiler alert: the data might surprise you.
What Is the Best Way to Answer the Question “Are Seed Oils Bad for You?”
To figure out if seed oils are harmful, we need evidence we can trust. You can’t do randomized trials with hundreds of thousands of people for decades. That level of evidence is impossible. And that’s where prospective cohort studies shine. These studies follow massive groups of people—sometimes hundreds of thousands—over decades, tracking what they eat and how it affects their health. Food-related chronic diseases take a long time to develop, so these long-term studies of dietary patterns are the best we have for figuring out links between diet and disease.
One knock against these studies is that they often rely on questionnaires, which can be shaky since people don’t always remember what they ate. Another problem is that subjects subconsciously under-report “bad” behaviors and over-estimate “preferred” behaviors. But modern research has a fix: biomarkers. By analyzing blood or adipose (fat) tissue samples, scientists can confirm exactly how much linoleic acid or other fats someone’s consuming. This makes the findings far more reliable than self-reported data alone.
Compare that to randomized, controlled studies from the 1960s, which critics of seed oils sometimes choose as their “gold standard.” Those older studies were small, short, and messy—often muddled by abnormally high intake of oils (probably trying to get results faster), high trans fat intake from margarines and processed foods common back then. Trans fats are now known to be harmful, but they were used liberally in margarines at the time, confounding the results. Those 60-year old randomized studies are not the gold standard for this question. Today’s cohort studies, with their scale and precision, leave those outdated experiments in the dust.
What Do the Long-Term Mortality Studies Say?
So, what does the best evidence tell us about seed oils and linoleic acid? Let’s break it down by key health outcomes, drawing from large prospective cohort studies that use biomarkers to verify dietary intake. First, linoleic acid is the principal fat in polyunsaturated plant oils, and it only comes from our diet. Our bodies do not make it. So, it makes a great biomarker for measuring how much of these plant oils we have eaten.
All-Cause Mortality
A systematic review and meta-analysis of 44 prospective cohorts published in 2020 looked at a total of 811,000 people, with over 170,000 deaths. When the results were all pooled together, they found that higher linoleic acid intake was linked to a 13% lower risk of dying from any cause. A Danish study of 4,663 people with linoleic biomarker data backed this up, showing that people with more omega-6 fatty acids (like linoleic acid) in their adipose tissue had a 24% lower all-cause mortality rates.
Another review looked at changes in fat intake. They found that if 5 percent of the energy from saturated fat was replaced with polyunsaturated oils there was a 19% lower rate of all-cause mortality. One very recent study examined butter and plant-based oils specifically. They found that if you replaced 10 grams of butter a day with 10 grams of plant-based oils there was a 17% drop in total mortality.
Cardiovascular Mortality
Heart health is a big concern when it comes to fats, but the news here is good. The large meta-analysis of 44 cohorts mentioned above also found a 13% decrease in cardiovascular mortality. In a review of 15 randomized controlled studies that tried to reduce saturated fat intake it was found that reducing dietary saturate fat resulted in 17% fewer cardiovascular events, but not fewer deaths. And the more saturated fat was reduced, the greater the reduction in events.
Cancer Mortality
Worried about cancer? A study comparing butter and plant-based oils found a protective link between plant oils, including seed oils, and cancer mortality. If 10 grams of butter a day were exchanged for 10 grams of plant-based oils there would be a 17% reduction in cancer mortality. The evidence simply doesn’t support the idea that seed oils fuel cancer risk. There may be some laboratory studies that might indicate the linoleic acid could cause inflammation, but the results in people don’t bear out a real world risk. Seed oils don’t fuel cancer. It simply isn’t true.
Incidence of Type 2 Diabetes
Even metabolic health gets a boost. A pooled analysis of 20 cohort studies with nearly 40,000 adults with biomarkers of linoleic acid showed that higher omega-6 biomarker levels were tied to a 35% lower risk of developing type 2 diabetes.
These studies, grounded in decades of data and biomarker precision, show that seed oils aren’t tied to poor health—they actually help.
How Much Linoleic Acid Do I Need?
If seed oils aren’t the enemy, how much linoleic acid should you aim for? Bill Harris, a research scientist with expertise in omega 3 and omega 6 oils, suggests that 15-18 grams per day is plenty. You don’t need to chug oil to hit that mark—here’s how it adds up:
- Nuts and seeds: 3 tablespoons each of flaxseeds and sunflower seeds, and a ¼ cup of almonds gives you about 10 grams. That is a significant, but achievable amount. Nuts and seeds are very good for you.
- Avocados: This creamy fruit chips in a couple more grams.
- Oils: A tablespoon of grapeseed oil in cooking or salad dressing fills the gap.
For perspective, my analysis of the Hallelujah Diet—a plant-based plan heavy on whole foods—clocked in at about 20 grams of linoleic acid daily. That’s totally doable without leaning on processed junk.
Conclusion and Takeaway
The most robust science we have—decades-long prospective cohort studies with biomarkers—tells a clear story: seed oils don’t increase your risk of dying from heart disease, cancer, or anything else. If anything, linoleic acid might protect your health, from your heart to your blood sugar.
Does this mean you should drown your food in highly processed seed oils, which are refined, bleached and deodorized? Not at all. And you absolutely should also stay away from highly processed and fried foods. But you can choose plant-based oils that have been produced with health in mind. Some good choices are extra virgin olive oil, unrefined sesame seed oil, pumpkin seed oil, grapeseed oil, and expeller pressed oils, and avocado oil. You can make a healthy salad dressing with these oils without a guilty conscience. The bottom line is this: seed oils aren’t the dietary villains they’ve been painted as by some influencers on the internet. Enjoy them in moderation, focus on a whole foods, plant-based diet rich in fruits, vegetables, nuts, seeds, legumes and organic whole grains. And let the science put your mind at ease.