Each decade seems to introduce a new nutritional adversary. First, fat was cast as the villain, then sugar, and now, seed oils have taken center stage in the debate over diet and health. These oils are being blamed for contributing to obesity, chronic diseases, and overall declining health. Yet, avoiding them is nearly impossible. They are found in countless everyday products—from fast food and salad dressings to protein bars and even infant formula. While some argue that seed oils are harmful, others maintain they are a cost-effective, safe, and even beneficial component of modern diets.

The reality is far more complex than a simple good-or-bad verdict. Discussions surrounding seed oils are often oversimplified, reducing a nuanced issue to polarized viewpoints. Even the term “seed oil” itself is misleading, as it encompasses both traditional oils that have been staples in diets for centuries and those engineered for mass food production. To fully grasp the debate, it’s necessary to examine how these oils are processed, how they are consumed, and what impact they may have on overall health.

At their core, seed oils are extracted from seeds, much like olive oil comes from olives or coconut oil from coconuts. However, not all seed oils are created equal. Some, like sesame and flaxseed oil, have been consumed for generations and are extracted using traditional cold-press methods, which help retain their nutritional value and antioxidant content. Others, particularly industrial seed oils—such as soybean, corn, canola, sunflower, safflower, cottonseed, grapeseed, and rice bran—are heavily processed through high-heat extraction and chemical solvents like hexane to maximize output. These oils undergo refining, bleaching, and deodorizing, making them neutral in taste and extending their shelf life, but at the cost of losing beneficial compounds like vitamin E and natural antioxidants.

Many of these oils were originally never meant for human consumption. Canola oil, for example, was initially known as rapeseed oil and primarily used as an industrial lubricant before being modified by Canadian scientists in the 1970s to make it edible. Even its name—”canola”—was a marketing creation derived from “Canada” and “oil.” Similarly, the term “vegetable oil,” though it sounds wholesome, often refers to a mix of industrially processed seed oils that bear little resemblance to actual vegetables.

Experts like Dr. Cate Shanahan, a Cornell-trained physician-scientist specializing in dietary fats, argue that these industrial seed oils were not developed with human nutrition in mind. (Read Dr. Shanahan’s best-selling book “Deep Nutrition”). The crude oil extracted from these seeds is inedible in its raw form, and the crops used for these oils were primarily bred for high yield and industrial applications rather than their dietary benefits. The vast majority of soybeans grown in the United States, for instance, are not meant for human consumption at all. According to USDA data, over 70% of U.S. soybeans are processed into animal feed, and another portion is used to produce biodiesel. What remains is refined into soybean oil, a highly processed product that retains little of the original soy plant’s nutritional profile.

Another concern lies in the fact that over 90% of American soy is genetically modified to resist herbicides like glyphosate, allowing farmers to spray entire fields without harming the crops. The combination of large-scale farming methods and heavy industrial processing results in an oil that is significantly altered from its natural state. Unlike traditional oils such as olive or sesame, which retain their antioxidant properties, industrial seed oils must undergo extensive refining to become shelf-stable. Critics argue that this process removes vital nutrients and increases the oil’s susceptibility to oxidation and degradation, which can raise health concerns.

The question of whether seed oils are beneficial or harmful remains contentious. Supporters argue that replacing saturated fats—like those found in butter and red meat—with polyunsaturated fats (PUFAs) from seed oils can lower the risk of heart disease. Some studies suggest that swapping saturated fats for PUFAs results in improved cardiovascular health. A large-scale 2021 study involving over 500,000 participants found that those who substituted saturated fats with oils like canola, corn, and olive oil experienced lower rates of heart disease and early mortality. Additional research published in JAMA Internal Medicine in 2025 reinforced these findings, showing that individuals who incorporated more plant-based oils into their diets tended to live longer and had lower rates of heart disease and cancer.

Because of this body of research, organizations such as the American Heart Association continue to promote seed oils as part of a heart-healthy diet. However, not all experts agree. Some critics argue that many of the studies supporting seed oil consumption fail to differentiate between highly refined oils and healthier options like extra virgin olive oil. Dr. Vinay Prasad, a hematologist-oncologist and professor at UCSF, has criticized the methodologies of some of these studies, claiming they rely on imprecise measurements and fail to distinguish between different types of fats.

Beyond concerns over research methods, one of the major criticisms of seed oils is their tendency to oxidize. While refining processes make these oils resistant to spoilage, exposure to heat, air, or light—especially during cooking—causes their chemical structures to degrade. Unlike naturally antioxidant-rich oils like olive or sesame, industrial seed oils lose their protective compounds during processing, making them more susceptible to oxidation. This oxidation process generates harmful byproducts such as aldehydes and free radicals, which have been linked to inflammation, cellular damage, and chronic illnesses like cardiovascular disease and neurodegenerative disorders.

Repeated heating of seed oils, as commonly occurs in restaurant fryers, compounds the problem. Research has shown that when vegetable oils are heated multiple times, they produce oxidative byproducts that contribute to cholesterol imbalances and tissue damage. Some studies have even found degraded omega-6 fats accumulating in human fat tissue and artery plaques, raising concerns about their long-term impact on health.

Even those who advocate for the use of seed oils acknowledge that refining has both advantages and disadvantages. While refining removes impurities, it also strips away beneficial antioxidants. However, one point that is often overlooked is that the high consumption of industrially processed seed oils is a relatively recent phenomenon. Dr. Shanahan estimates that these oils now account for 20-30% of the average American’s daily caloric intake—levels that are unprecedented in human history. Historically, diets relied more on animal fats and minimally processed oils rather than the highly refined PUFAs that now dominate modern food supply chains.

One indisputable fact is that seed oils have become a fundamental component of the modern food industry. Their low cost, high yield, and government subsidies have made them a key ingredient in processed foods. In 2016, the U.S. soybean industry alone received $1.6 billion in subsidies, ensuring that production remained high and costs remained low. As a result, seed oils have become a cornerstone of ultra-processed foods, which now account for nearly 60% of the American diet. Alongside refined grains and added sugars, seed oils help improve texture, extend shelf life, and enhance flavor at a fraction of the cost of healthier alternatives.

For consumers looking to make healthier choices, eliminating seed oils from the diet is no simple task—it requires a conscious shift away from processed foods altogether. Experts recommend focusing on whole, minimally processed foods and choosing more stable fats for cooking. Oils such as avocado, extra virgin olive, butter, ghee, and coconut oil are better choices due to their higher resistance to oxidation. Delicate oils like flaxseed and walnut are best used cold to preserve their beneficial properties.

Ultimately, the conversation surrounding seed oils is not just about whether they are good or bad—it is about the larger role they play in the processed food industry. The real issue is not necessarily the presence of seed oils in diets but the sheer volume in which they are consumed. By prioritizing whole, natural foods and minimizing reliance on processed products, consumers can make more informed choices that support long-term health.