Seed oils are cooking oils extracted from the seeds of plants, as opposed to oils pressed from the fruit or flesh of a plant (like olive oil or coconut oil). They include some of the most widely used oils in kitchens and food manufacturing worldwide, and they’ve become a lightning rod for health debate in recent years. Here’s what they actually are, how they’re made, and what the evidence says about eating them.
The Most Common Seed Oils
Eight seed oils dominate the conversation: canola, soybean, corn, safflower, cottonseed, grapeseed, rice bran, and peanut oil. Soybean oil alone is the most consumed cooking oil in the United States, appearing in everything from salad dressings to restaurant fryers. These eight get the most scrutiny online, but the category also includes sesame oil, flaxseed oil, sunflower oil, and walnut oil, all of which have been used in cooking for generations.
The distinction that matters is between seed oils and fruit oils. Olive oil comes from pressing the flesh of olives. Avocado oil comes from the fruit’s pulp. Coconut oil comes from coconut meat. Seed oils, by contrast, come from seeds that are generally harder and contain less oil by weight, which means extracting the oil requires more processing.
How Seed Oils Are Made
Most seed oils on grocery store shelves are labeled “RBD” oils, meaning they’ve been refined, bleached, and deodorized. This three-step process is what separates a bottle of refined canola oil from a cold-pressed artisan oil, and it’s central to much of the controversy.
The process starts with crushing the seeds and extracting the oil, typically using a chemical solvent called hexane. Hexane is hazardous in gas form but evaporates during processing, leaving minimal to no residue in the finished product. After extraction, the oil goes through refining, which neutralizes free fatty acids and removes compounds containing phosphorus. Next comes bleaching, where the oil is filtered through special clay that strips out pigments and impurities. Finally, deodorizing removes vitamins, protein fragments, trace pesticides, and other compounds that affect flavor and smell.
The result is an oil that’s consistent in color, neutral in taste, and stable on the shelf. That consistency is precisely why food manufacturers rely on these oils so heavily. It’s also why critics argue that RBD oils are overly processed and stripped of nutritional value. Cold-pressed or expeller-pressed versions of the same oils skip the solvent extraction and some of the refining steps, but they cost more and have shorter shelf lives.
What’s in Seed Oils Nutritionally
Seed oils are composed primarily of unsaturated fats. Canola oil, for example, is roughly 63% monounsaturated fat, 30% polyunsaturated fat, and just 7% saturated fat. That fat profile is quite different from butter, lard, or coconut oil, all of which are high in saturated fat.
The polyunsaturated fat in seed oils includes omega-6 fatty acids, particularly one called linoleic acid. Your body needs linoleic acid (it’s considered essential because you can’t make it yourself), but the concern raised by some researchers and many wellness influencers is that modern diets contain far more omega-6 than omega-3 fatty acids, and that this imbalance could promote inflammation. Canola oil is somewhat of an outlier here, as it also provides alpha-linolenic acid, a plant-based omega-3, along with phytosterols, naturally occurring plant compounds that may help lower cholesterol.
Where Seed Oils Show Up in Your Diet
If you eat packaged or restaurant food, you’re almost certainly consuming seed oils regularly. They’re the default cooking fat in commercial kitchens because they’re inexpensive, have neutral flavors, and hold up well at high temperatures. Refined soybean oil can handle temperatures above 450°F. Refined safflower oil can reach 510°F before it starts to smoke and break down. Refined peanut oil sits around 450°F. For comparison, unrefined versions of these same oils smoke at dramatically lower temperatures (unrefined safflower oil breaks down at just 225°F), which is why refined versions dominate commercial cooking.
Check the ingredient list on chips, crackers, frozen meals, salad dressings, baked goods, and margarine, and you’ll typically find soybean oil, canola oil, or sunflower oil listed. Fast food chains almost universally fry in seed oil blends. Even foods marketed as healthy, like granola bars or plant-based meat alternatives, frequently use canola or sunflower oil.
The Health Debate
Online, seed oils have earned nicknames like “the hateful eight,” and some wellness communities treat them as a root cause of chronic disease. The core argument is that industrial processing damages the fats, that high omega-6 intake drives inflammation, and that the dramatic rise in seed oil consumption over the past century tracks with rising rates of heart disease, obesity, and other conditions.
Major medical organizations see it differently. The American Heart Association’s 2026 dietary guidance specifically recommends nontropical plant oils, including soybean and canola oils, as part of heart-healthy eating patterns. Their position is based on clinical trial evidence showing that replacing saturated fat (from butter, beef tallow, or coconut oil) with polyunsaturated fat consistently lowers LDL cholesterol, which is a direct risk factor for cardiovascular disease. The AHA groups these seed oils right alongside olive oil as healthy fat sources.
Harvard Health has noted that while hexane is used in extraction, it evaporates during processing and leaves limited if any residue in the final product. The concern about hexane exposure from eating seed oils doesn’t have strong evidence behind it.
Where both sides find some common ground is on the question of ultra-processed food. People who consume the most seed oil tend to do so through packaged snacks, fried fast food, and other heavily processed products. It’s genuinely difficult to separate the effects of the oil itself from the effects of an overall diet built around those foods. Someone drizzling a tablespoon of canola oil on roasted vegetables is in a very different dietary situation than someone eating fried food three times a day, even though both are consuming seed oils.
Seed Oils vs. Olive and Coconut Oil
Olive oil, especially extra virgin, is widely considered the gold standard for cooking oil. It’s mechanically pressed from fruit rather than chemically extracted from seeds, which preserves a range of beneficial plant compounds that get stripped out during RBD processing. That said, refined olive oil (the type labeled “light” or simply “olive oil”) also goes through a refining process that removes many of those compounds.
Coconut oil occupies a strange position in this debate. Many seed oil critics recommend it as a replacement, but coconut oil is roughly 82% saturated fat, which is higher than butter. The AHA classifies it as a tropical oil to limit, not a heart-healthy alternative.
The practical tradeoff for most people comes down to cost and cooking needs. Extra virgin olive oil costs significantly more than canola or soybean oil and has a lower smoke point, making it less ideal for deep frying. For high-heat cooking on a budget, refined seed oils perform well. For dressings, finishing dishes, or moderate-heat sautéing, extra virgin olive oil offers a stronger nutritional profile with well-documented health benefits.