Seed oils, also sometimes called vegetable oils, have earned a controversial reputation. Some critics believe that consuming seed oils increases inflammation, weakening the immune system and making you more susceptible to chronic diseases.
Seed oils are not inherently unhealthy, and may actually have health benefits, especially when you consume them in moderation.
A major criticism of seed oils focuses on their unsaturated fat content and the possibility that it contributes to inflammation and heart health issues.
Many critics of seed oils also point to the processed nature of these foods. In production, oil needs to be extracted from the seeds and then refined, a process that removes unwanted compounds.
Solvent chemicals, often hexane (derived from crude oil), help extract the oil from the seeds. Some people are concerned about the levels of this product in commercial seed oils.
Concerns also revolve around deodorization, one of the final steps to lighten the color and remove odor from the oil. This process may increase the trans fat content, which is one of the more harmful types of dietary fat.
However, there’s currently little research supporting these criticisms. In most studies, the health benefits of seed oils outweighed the risks.
Health concerns with seed oil consumption have to do with both the composition of the oils, how they’re manufactured, and their use in processed foods.
1. Inflammation
Seed oils may have high levels of omega-6, a polyunsaturated fat. They are rich sources of linoleic acid, a type of omega-6 that you can only get through diet.
Linoleic acid is a precursor to arachidonic acid, which may play a role in inflammation (the immune response). Increased inflammation throughout the body raises infection risk and contributes to chronic diseases like asthma, heart disease, stroke, and cancer.
However, a wide-ranging meta-analysis found no significant effects of omega-6 levels on inflammation. Only small amounts of linoleic acid convert to arachidonic acid in the body.
2. Cardiovascular Diseases
Researchers have linked high levels of the linoleic acid in fats to increased risk of heart disease and atherosclerosis (hardened arteries).
However, other studies have found that seed oils may actually protect the heart. In a 2019 analysis of 30 studies, researchers found that higher levels of linoleic acid in a person’s diet lowered their chances of cardiovascular diseases, stroke, and death. Seed oils also contain omega-3, another fatty acid, and oleic acid, which support the health of your heart and blood vessels.
Potentially more important for heart health than the amount of omega-6 on its own is how much there is in comparison to omega-3s. Though there’s still debate, higher ratios of omega-6 to omega-3 content in your diet may increase the risk of cardiovascular diseases. Canola and corn oils have a low omega-6 to omega-3 ratio, about 2:1.
3. Health Effects of Processing
Some deodorized oils contain small amounts of trans fats, and frying or cooking with seed oils can raise levels. However, seed oils generally aren’t a significant source of trans fat.
Another concern relates to the use of hexane in extracting seed oils. But in commercially available seed oils, there’s little to no hexane. The levels are too low to be dangerous.
4. Seed Oils and Ultra-Processed Foods
Seed oils like canola and sunflower are common in processed and ultra-processed foods like chips, fast food, or frozen meals. Regular over-consumption of these foods can lead to a range of conditions, including obesity, diabetes, cardiovascular diseases, and others.
That said, the negative impacts on health associated with these foods are more likely caused by other ingredients—such as excess salt, added sugar, and high-fructose corn syrup—and the replacement of some fruits and vegetables with these foods.
There’s a great deal of evidence that seed oils—when used moderation—offer many health benefits. These include:
1. Better Control of Cholesterol
Seed oils are rich in unsaturated fats. These help with essential body functions and break down low-density lipoprotein (LDL, or “bad”) cholesterol.
2. Lowered Risk of Cardiovascular Disease
Studies have linked the unsaturated fats in seed oils to reduced risk of heart disease, stroke, and other cardiovascular disease.
3. Antioxidant Properties
Seed oils are rich sources of the antioxidant vitamin E. These help prevent oxidation, chemical reactions that produce free radicals (substances that damage cells and contribute to chronic disease).
4. Improved Blood Sugar Control
Seed oils may also boost sugar metabolism by reducing insulin resistance. Some research found that replacing carbohydrates and saturated fat with unsaturated fat in canola oil can help control blood sugar in people with diabetes or prediabetes.
Unsaturated fats like those found in seed oils are an essential part of a healthy, balanced diet. If you’d like to incorporate them, here’s what to keep in mind:
- Moderation: Using a few tablespoons of seed oil to cook with or on salad isn’t risky. Seed oils are high in calories, so the key is to use them in moderation.
- Smoke point: The smoke point is the temperature at which an oil burns. It’s high for canola, avocado, and peanut oil, making them good options for high-heat cooking. Other seed oils are better for low-heat cooking or salad dressings.
- Single use: If you re-use seed oils, is can increase the trans fat and saturated fat content. Discard leftover oil after cooking or deep frying.
- Storage: Store seed oil bottles at room temperature, sealed tightly, and in a pantry or dark place. Use them within 6-12 months of purchase, and three months after opening.
- Safety: Seed oils are safe for most people. Those who are allergic to seeds like peanuts or sesame should avoid those oils, which can trigger attacks.
