Seed oils have become one of the most controversial topics in the world of nutrition. Some claim they are inflammatory and harmful, while others argue they are neutral, or beneficial, to a balanced diet. With so much conflicting information, what’s the real story behind seed oils? 

To help sort fact from fiction, Flavor & Fettle’s in-house nutritionist and dietician, Karen Zinka, is here to help. With her expertise and practical perspective, she’ll explore the claims, explain the science, and offer tips on how (or if) to incorporate this topic into your lifestyle. Read her thoughts on the topic below.

What Are Seed Oils?

Seed oils are vegetable oils extracted from seeds and commonly used in cooking, processed foods, and restaurant meals. The most common include:

• Canola oil
• Soybean oil
• Corn oil
• Sunflower oil
• Safflower oil
• Grapeseed oil
• Cottonseed oil

These oils are widely used because they are cheap, versatile, and have a neutral flavor. They also have a high smoke point, making them suitable for frying and baking.

The Controversy: Are Seed Oils Bad for You?

The debate over seed oils largely centers on their omega-6 fatty acid content and their role in inflammation, heart health, and metabolism.

Omega-6 Fats & Inflammation

What’s the concern?
Seed oils are rich in omega-6 fatty acids, which are a type of polyunsaturated fat. While omega-6s are essential for health, they should be balanced with omega-3 fatty acids (found in fish, flaxseeds, and walnuts). An excess of omega-6s relative to omega-3s is believed to promote chronic inflammation, which may contribute to conditions like heart disease and obesity (Johnson & Fritsche, 2012).

What does the research say?
Current studies show mixed results. Some research suggests that high omega-6 intake can contribute to inflammation if the diet is lacking in omega-3s. However, other studies indicate that omega-6s from whole foods and even seed oils do not inherently cause inflammation unless consumed in excessive amounts or alongside a highly processed diet (Johnson & Fritsche, 2012).

Processing & Oxidation Risks

What’s the concern?
Most seed oils are produced through high-heat industrial processing (including chemical solvents like hexane), which may create oxidized fats and harmful compounds that could negatively impact health (Ramsden et al., 2016).

What does the research say?
Some studies suggest that repeatedly heating seed oils (such as in deep-frying) can produce toxic byproducts like aldehydes, which may contribute to oxidative stress and inflammation (Ramsden et al., 2016). However, when used cold or in moderate amounts, seed oils are unlikely to pose a significant risk.

Heart Health & Cholesterol

What’s the concern?
Some critics claim that seed oils contribute to heart disease, despite being high in unsaturated fats (which are typically considered heart-healthy).

What does the research say?
Multiple studies suggest that replacing saturated fats (like butter) with unsaturated fats (including seed oils) can lower LDL ("bad") cholesterol and reduce the risk of cardiovascular disease (Mozaffarian et al., 2010). However, some argue that focusing on whole food sources of healthy fats (like olive oil, avocado, and nuts) may be a better choice than relying on industrially processed oils.

Are There Better Alternatives to Seed Oils?

If you’re looking to limit seed oil consumption, here are some alternatives:

• Avocado oil – High smoke point, neutral taste, rich in monounsaturated fats. 
• Olive oil – Well-researched for heart health, best for low-to-medium heat cooking.
• Coconut oil – High in saturated fat, stable at high temperatures, but best used in moderation.
• Grass-fed butter/ghee – Good for high-heat cooking, contains beneficial compounds, but high in saturated fat.

Should You Avoid Seed Oils Completely?

You may consider cutting back if you consume a large amount of ultra-processed foods, have chronic inflammation or metabolic issues, or prefer to focus on whole-food sources of fats like olive oil, avocado, and nuts. 

However, you probably don’t need to worry about the harms of seed oils if you already eat a balanced diet with plenty of omega-3s, whole foods, and fiber or if you use seed oils in moderation. 

Seed oils are not inherently toxic or dangerous, but excessive consumption, particularly in highly processed diets, may contribute to an imbalance in omega-6 to omega-3 ratios.

If you want to be more mindful of your intake, consider focusing on whole-food fats, cold-pressed oils, and limiting fried and processed foods.

1. Ramsden, C. E., Zamora, D., Majchrzak-Hong, S., et al. (2016). Re-evaluation of the traditional diet-heart hypothesis: Analysis of recovered data from the Minnesota Coronary Experiment (1968–73). BMJ, 353, i1246. https://doi.org/10.1136/bmj.i1246

2. Johnson, G. H., & Fritsche, K. (2012). Effect of dietary linoleic acid on markers of inflammation in healthy persons: a systematic review of randomized controlled trials. Journal of the Academy of Nutrition and Dietetics, 112(7), 1029-1041. https://doi.org/10.1016/j.jand.2012.03.029

3. Mozaffarian, D., Micha, R., & Wallace, S. (2010). Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS Medicine, 7(3), e1000252. https://doi.org/10.1371/journal.pmed.1000252