Are Seed Oils Bad for You? What You Should Know

Seed oils — or what a lot of us knew growing up as “vegetable oil” — have a bad rap with the TikTok crowd. But if you consult a nutrition scientist — or the American Heart Association — you’ll get a ringing endorsement for including them in your diet. So what gives — are these neutral-tasting, inexpensive oils bad for you?

The short answer is no. But there’s more to the story.

Seed Oils and Fatty Acids

Seed oils generally refer to eight common oils: canola, corn, cottonseed, grapeseed, soy, rice bran, sunflower and safflower. Their alleged toxicity stems from the idea that the linoleic acid in these oils contributes to inflammation in the body.

All cooking oils contain combinations of different fatty acids — the building blocks of fat molecules — that are essential for many bodily functions. You might be more familiar with terms like “unsaturated fat,” “saturated fat” or “trans fat” — these terms all refer to the way these molecules are structured. The differences in their structure cause our bodies to process them in different ways.

Seed oils contain omega-6 fats, cousin to the better-known omega-3 fatty acids. Linoleic acid — the primary dietary omega-6 fatty acid — is converted into arachidonic acid in the body, which in turn can lead to inflammation, increasing our risk for developing certain diseases. Yet only a small amount is converted in this way, and not all effects of arachidonic acid are inflammatory. Criticism of seed oils is based in part on research conducted on animals — studies focused on human subjects show linoleic acid can have a protective effect, especially for the heart.

And what about omega-3 fatty acids? Found in fish, nuts, seeds and more, these are known to be strongly anti-inflammatory. Omega-6 and omega-3 both are unsaturated fats shown to offer protective benefits for the heart, raise “good” HDL cholesterol and lower “bad” LDL cholesterol.

Process This

Many Americans consume a great deal of fat from canola or corn oil for one simple reason: They are the oils most often used in processed or highly processed foods linked to everything from cancer to cardiovascular disease, depression and shortened lifespans. Because Americans are such heavy consumers of processed foods, a larger percentage of our dietary fats come from seed oil — as opposed to olive or avocado oils, seeds or nuts — perhaps 10 times as much.

This is where the conversation about omega-6 vs. omega-3 fatty acids comes in. A highly processed diet — along with most restaurant food — not only delivers megadoses of omega-6 but also sodium, added sugar and saturated fats, which contribute to inflammation in the body. So while the negative effects of a mostly processed diet are well-documented, omega-6 really isn’t the culprit. Since we already get high amounts of omega-6 from processed foods, it’s important to intentionally include omega-3 food sources to create balance between the two.

An Inflammatory Issue

So, seed oils per se are not the problem. But chronic inflammation most definitely is. Seed oil critics are right to be concerned about that — even if they’re focused on the wrong compound.

Acute inflammation — identifiable by things like redness, heat and swelling — occurs when we have an injury or infection. It’s what draws white blood cells and lymphocytes to the place of injury, so cells can heal the tissue or attack the infection. This kind of short-term inflammation is a necessary part of healing.

Chronic inflammation occurs over a long period of time. The immune system produces the same chemicals, even when there isn’t any “outside danger” — instead white blood cells continue to attack healthy tissue and organs. A diet high in processed food can cause a consistent state of inflammation, along with other causes like stress, smoking and alcohol consumption. Over time this can damage cell DNA and increase risk of disease. Signs of chronic inflammation run from low energy or mood to poor sleep, low-level pain, soreness in joints and a general feeling of malaise. Anti-inflammatory diets such as the Mediterranean diet have been shown to help.

The Bottom Line

Think of it this way: A diet that consisted solely of a single otherwise beneficial nutrient would not be considered a healthy or balanced one. Decreasing consumption of highly processed foods — along with those megadoses of omega-6 — and increasing sources of omega-3 like olive and avocado oils can help tilt your diet into better balance, without completely giving up foods you enjoy.