Should You Really Avoid Seed Oils?

A look into the science behind one of nutrition’s most heated controversies.

Photo by jonathan ocampo on Unsplash

If you spend any time around internet health gurus, you’re likely to hear them mention seed oils. Guys like Gary Brecka and even RFK Jr. have spoken out against them.

These critics often point to the industrial processing of oils like canola and soybean, suggesting their omega-6 content promotes systemic inflammation.

But what does science say? Despite the viral warnings, major medical institutions like the Cleveland Clinic and the American Heart Association argue that seed oils are not inherently toxic.

Unfortunately for peddlers of pseudoscience, the literature is pretty clear. Seed oils are, at worst, neutral for your health, and more likely than not, beneficial.

A Brief Overview

Before we get started, let’s define some terms.

Seed oils are vegetable oils extracted from the seeds of plants such as soybeans, sunflowers, canola, corn, and cottonseed. Like all dietary fats, they are made up of molecules called fatty acids, which the body has many uses for. Everything from energy, hormone production, cell membranes, and nutrient absorption relies on dietary fats.

These fats are generally divided into saturated and unsaturated fats based on their chemical structure.

Saturated fats have no double bonds between carbon atoms, making them more rigid and typically solid at room temperature, as seen in butter or lard.

Unsaturated fats contain one or more double bonds, giving them a looser structure that is usually liquid at room temperature, like olive oil or sunflower oil. Seed oils are especially rich in polyunsaturated fats, including omega-6 fatty acids such as linoleic acid.

Cholesterol, meanwhile, is a waxy fat-like substance made primarily by the liver and used to build cell membranes and hormones.

Although cholesterol is essential in the body, high levels of low-density lipoprotein (LDL) cholesterol in the bloodstream are associated with plaque buildup in arteries and increased cardiovascular disease risk.

This is why nutrition research often focuses not just on how much fat people eat, but on the specific types of fat replacing one another in the diet.

Cleveland Clinic and the American Heart Association

Both the Cleveland Clinic and the American Heart Association push back against the popular internet claim that seed oils are inherently “toxic,” though they acknowledge why concerns arose.

The articles explain that critics often point to the heavy processing of oils such as canola, soybean, sunflower, and corn oil, along with their omega-6 fatty acid content and frequent presence in ultra-processed foods.

However, both sources argue that current scientific evidence does not support the idea that seed oils themselves are major drivers of inflammation or chronic disease when consumed in normal dietary amounts.

Instead, they emphasize that many negative health associations likely come from the broader dietary patterns in which these oils are commonly consumed, particularly fast food and ultra-processed products.

The American Heart Association specifically notes that replacing saturated fats with polyunsaturated fats from seed oils is associated with lower LDL cholesterol and reduced cardiovascular risk, while the Cleveland Clinic article frames moderation and overall diet quality as more meaningful than completely avoiding seed oils.

Primary Literature

In case the consensus put forward by large medical institutions is not good enough for you, as some people are skeptical, let’s take a look at the primary literature.

When scientists look at seed oils and other plant oils high in unsaturated fat, the data often look positive. Large reviews of population studies and clinical trials find that when people eat more polyunsaturated and monounsaturated fats from plant oils rather than saturated fats from butter, lard, palm oil, or coconut oil, their risk of cardiovascular disease and type 2 diabetes tends to go down.

Blood tests in these studies show lower levels of “bad” LDL cholesterol and other atherogenic lipids, without increases in inflammation or oxidative stress when linoleic acid–rich omega‑6 oils are used.

Controlled feeding trials where people cook with soybean, olive, or camellia seed oil for months show no weight gain differences between oils and only small, generally favorable shifts in cholesterol and liver enzymes, suggesting these commonly used oils are metabolically neutral to mildly beneficial in realistic amounts.

In older adults with obesity, adding flaxseed, olive, or sunflower oil improved artery function and markers linked to clotting and inflammation, pointing again toward a cardioprotective role for unsaturated plant oils when they displace more harmful fats.

Wider umbrella reviews of many vegetable oils conclude that canola, olive, rice bran, and other unsaturated‑rich oils consistently lower LDL cholesterol, while very saturated tropical oils raise LDL but also raise HDL, likely making their overall effect less clearly harmful but not beneficial either.

Animal and Mechanistic Work

Animal and mechanistic work provides further explanation, as epidemiological research does not explain the ‘how’.

Rat and mouse studies show that oils or blends with a balanced omega‑6 to omega‑3 ratio and a mix of mono‑ and polyunsaturated fats can improve lipids, inflammation, oxidative stress, fatty liver, and even gut microbiota, whereas extremely skewed fatty acid ratios can worsen these markers.

Overall, across human and experimental research, plant oils rich in unsaturated fats look more “good” than bad, especially as replacements for saturated and trans fats, while the details of which oil is best and in what context remain an active area of study.

Take Home

At present, the scientific evidence does not support the idea that seed oils are uniquely dangerous or “toxic.”

While they are often found in unhealthy ultra-processed foods, the oils themselves appear neutral to beneficial when consumed in reasonable amounts, particularly when replacing saturated and trans fats.

Like most areas of nutrition science, nuance matters, but the current literature suggests that overall dietary patterns matter far more than demonizing a single ingredient.