Seed oils are harmful to the body. And here’s why.
Over the past century, the consumption of seed oils—also known as vegetable oils—has dramatically increased. Scientists warn that modern diets are far too high in these fats and that an overreliance on them may be harming overall health.
How harmful are seed oils, and is it necessary to avoid them altogether? This article breaks down the science behind seed oils—examining the good, the bad, and the ugly—so that individuals can determine what role they should play in a balanced diet.
What Are Seed Oils?
"Seed oils" is a broad term used to describe omega-6-rich vegetable oils made from seeds. Soy and canola oils are also referred to as seed oils, despite not technically originating from seeds.
Today, seed oils make up around 10% of calorie intake in the average American diet. These oils are found in a wide range of products, from infant formula to popular salad dressings.
Although many health organizations, such as the American Heart Association, promote seed oils like soybean oil and sunflower oil over animal and plant-based fats high in saturated fats, health experts have identified significant issues with some commonly used vegetable oils.
According to scientists and physicians specializing in lipid research, the following seed oils may present the greatest concerns for health:
Soybean oil: Derived from soybeans (not soy-based foods like tofu or edamame), soybean oil is the most common vegetable oil in U.S. diets. This fat makes up over 60% of vegetable oil consumption in the United States. Around 55% of soybean oil consists of the omega-6 fat linoleic acid.
Canola oil: Canola is the second-largest oil crop in the world, and over 90% of canola crops grown in the U.S. are genetically modified to increase tolerance to herbicides such as glyphosate. Canola oil is composed of 21% linoleic acid.
Corn oil: Corn oil is a major dietary source of linoleic acid, which makes up approximately 34 to 62% of its fats. It is commonly used by the restaurant industry for deep-frying foods.
Cottonseed oil: Cottonseed oil comes from cotton plant seeds and is high in linoleic acid (over 50%). It is used as a cooking oil and in products such as salad dressings.
Safflower oil: Safflower oil is derived from safflower seeds and is one of the richest sources of omega-6 fats, with an omega-6 to omega-3 ratio of 77:1. It appears in salad dressings, butter replacement products, and snack foods like chips.
Sunflower oil: Produced from sunflower seeds, sunflower oil is among the most popular oils for cooking. It contains up to 70% linoleic acid by weight, making it a major dietary source of omega-6 fats.
Most of these oils are used widely in home and restaurant cooking, as well as in food production, meaning they are commonly consumed on a daily basis. Grapeseed and rice bran oils also concern some health experts, but they are not as frequently used in food production.
The Health Concern with Seed Oils
The issue with seed oils stems from their widespread presence in many foods and their status as some of the most common cooking fats. Because of this, they make up a significant portion of fats in many diets.
According to Whitney Crouch, RDN, CLT, "Seed oils have a higher omega-6 content than other, healthier fat options. The evidence isn't conclusive whether or not omega-6 fats are always inflammatory in a 'bad' way. It is clear that they are needed but in lesser amounts than anti-inflammatory omega-3 counterparts."
Although the ideal omega-6 to omega-3 ratio remains uncertain, experts believe it should lie between 1:1 and 4:1 for optimal health. Unfortunately, the average American diet contains up to 20 times more omega-6 fatty acids than omega-3 fatty acids, potentially promoting inflammation in the body and contributing to inflammatory diseases.
They Are Highly Processed
Seed oils like canola oil (also known as rapeseed oil) undergo a refining process that includes bleaching and deodorizing. This process enhances taste, color, and shelf life, but it also removes beneficial compounds such as vitamin E and phenols, making the oils less nutritious than their unrefined counterparts.
They Are Often Genetically Modified
Genetically modified organisms (GMOs) are among the most controversial topics in nutrition and environmental science.
Most crops used to produce seed oils are genetically modified to improve resistance to harmful herbicides like glyphosate and to increase crop yield. Scientists argue that the increased use of herbicides can harm both human health and the environment.
They Are Prone to Oxidation
Many seed oils have a high smoke point, allowing them to be heated to high temperatures without burning. However, some are rich in polyunsaturated fats (PUFAs), making them prone to oxidation—a reaction between fats and oxygen that forms harmful compounds like free radicals.
Free radicals can damage cells and contribute to inflammation. Oils that are repeatedly heated, such as those used for deep frying in restaurants, are particularly susceptible to oxidation.
Science Showcase
Why are fried foods so detrimental to health? Beyond their high calorie content, fried foods contain lipid oxidation products (LOPs) formed when vegetable oils are heated to high temperatures. According to a 2020 article published in Nutrients, LOPs in frying oils are "carried" by fried foods and pose health risks when consumed regularly. LOPs can trigger inflammation, damage cells, and increase the risk of certain cancers. This is why experts recommend limiting fried foods and choosing those cooked in healthier fats at lower temperatures.
Infrequent enjoyment of french fries or a salad dressing made with canola oil is unlikely to cause significant harm. However, regularly consuming omega-6-rich seed oils and the ultra-processed foods commonly made with them, without balancing the diet with adequate amounts of anti-inflammatory, omega-3-rich foods, could contribute to health issues.
Brands such as Roots Farm Fresh are active in eliminating seed oils from all their products https://rootsfarmfresh.com/
