Understanding the Controversy: Why is canola oil now considered unhealthy?

October 7, 2025 •

4 min read

Despite being promoted for decades as a heart-healthy fat, a growing number of nutritionists and health experts are questioning the safety of canola oil due to its highly refined nature, potential for inflammation, and conflicting research findings. The debate over why is canola oil now considered unhealthy? stems from a re-evaluation of how this and other industrial seed oils impact our bodies.

Quick Summary

Concerns about canola oil's healthiness have emerged due to its intensive processing, genetically modified origins, and unstable polyunsaturated fats, which can lead to inflammation and oxidative stress when heated, despite its initially favorable fat profile.

Key Points

Intensive Processing: The extensive refining, bleaching, and deodorizing process uses high heat and chemical solvents like hexane, damaging nutrients and potentially introducing trans fats.
Omega-6 Imbalance: As a source of omega-6 fats in a diet already rich in them, canola oil can contribute to an unbalanced ratio of omega-6 to omega-3, which promotes inflammation.
Oxidative Damage: Its polyunsaturated fatty acids are unstable and prone to oxidation when exposed to heat, creating harmful free radicals that cause cellular damage.
Conflicting Evidence: Independent animal studies have linked canola oil to increased inflammation, memory impairment, and weight gain, contrasting with industry-funded studies.
GMO Concerns: The majority of canola is genetically modified, raising concerns for those who wish to avoid GMO products and potential exposure to associated herbicides like glyphosate.
Alternatives Exist: Healthier alternatives such as extra-virgin olive oil and avocado oil offer more antioxidants, are less refined, and provide more stable fats for cooking.

From Healthy Darling to Dietary Concern

For years, canola oil was celebrated by mainstream health organizations for its low saturated fat and high monounsaturated and omega-3 content. However, modern nutritional science and a closer look at its production have sparked a major re-evaluation. The shift in perception is driven by new understandings of inflammation, oxidative stress, and the unintended consequences of high-heat, industrial processing.

The Intensive Refining Process

The journey of canola oil from seed to bottle is far from simple and is a primary source of concern for many experts. Unlike cold-pressed oils like extra-virgin olive oil, commercially available canola oil is heavily refined, bleached, and deodorized (RBD) to achieve its neutral color and taste. This multi-step process often involves:

High-Heat Extraction: Seeds are crushed and heated to extract the initial oil, which can cause damage to delicate polyunsaturated fats.
Solvent Extraction: After initial pressing, the remaining oil is extracted using a chemical solvent, most commonly hexane, to maximize yield. Although most hexane is removed, trace amounts may remain.
Bleaching and Deodorizing: The oil is passed through a clay filter to remove chlorophyll and other pigments, and then steam-distilled at high temperatures to eliminate unpleasant odors and tastes. This deodorization step can create small amounts of artificial trans fats and further damage beneficial omega-3s.

Omega-6 to Omega-3 Imbalance

While canola oil contains both omega-3 (ALA) and omega-6 (linoleic acid) fats, the typical Western diet already provides a massive surplus of omega-6 fatty acids from processed foods. A balanced ratio of omega-6 to omega-3 is crucial for managing inflammation, with an ideal ratio being closer to 1:1. However, the modern diet is estimated to have a ratio closer to 20:1, and canola oil, while not the highest source, contributes significantly to this imbalance. This can promote systemic inflammation, which is a risk factor for many chronic diseases.

Instability and Oxidative Stress

The polyunsaturated fats (PUFAs) in canola oil are more fragile and prone to oxidation than the more stable monounsaturated fats found in olive oil or saturated fats found in coconut oil. When canola oil is heated to high temperatures, especially during deep-frying or repeated use, it can become oxidized. Oxidized oils are unstable and release free radicals, which cause cellular damage and oxidative stress within the body. This is linked to chronic health problems, including heart disease and cognitive decline.

The GMO Question

Over 90% of canola crops in the United States and Canada are genetically modified (GMO) for herbicide resistance. While the direct health impact of GMOs on humans is a subject of debate, the practice of engineering crops for herbicide tolerance leads to increased use of herbicides like glyphosate. Concerns exist over residual pesticide levels in refined products, though regulators often state levels are within safe limits. For individuals wishing to avoid GMO products, conventionally produced canola oil is a source of concern.

Conflicting Research and Industry Influence

Making sense of the health implications of canola oil is challenging due to conflicting studies. Some industry-funded reviews have linked canola oil to favorable effects on cholesterol. However, other independent studies, particularly animal studies, have found negative associations, including increased inflammation, memory impairment, and oxidative stress. A notable human study found participants who switched from a diet with refined oils (including canola) to a diet with extra-virgin olive oil showed improved brain function. This highlights the need for more independent, long-term human studies to clarify the effects of refined canola oil.

Comparison of Canola Oil vs. Healthier Alternatives


Feature	Conventional Canola Oil	Extra-Virgin Olive Oil (EVOO)	Refined Avocado Oil
Processing	Highly refined, bleached, deodorized (RBD) using heat and chemical solvents like hexane.	Cold-pressed without chemicals or high heat, retaining nutrients and antioxidants.	Expeller-pressed and refined, but generally retains more nutrients and stability than canola.
Fatty Acid Profile	Balanced ratio of monounsaturated (63%) and polyunsaturated (28%) fats, including both omega-6 and omega-3 (ALA).	Primarily monounsaturated fat (~73%), with lower polyunsaturated content.	Mostly monounsaturated fat (~70%), similar to EVOO.
Antioxidants	Antioxidants and other beneficial plant compounds are largely destroyed during the refining process.	Rich in polyphenols, oleocanthal, and other antioxidants with powerful anti-inflammatory effects.	Contains antioxidants like carotenoids and polyphenols.
Stability / Oxidation	Polyunsaturated fats are prone to oxidation, especially under high heat or repeated use.	Monounsaturated fats are relatively stable during cooking; antioxidants protect against oxidation.	High smoke point and stable fat profile make it resistant to oxidation at high heat.
GMO Status	Over 90% of crops are genetically modified.	Non-GMO.	Generally non-GMO.
Best Uses	High-heat cooking, deep-frying (due to high smoke point, but with risk of oxidation).	Salad dressings, low-to-medium heat sautéing, finishing dishes.	High-heat cooking, grilling, roasting, and sautéing.

Conclusion: Reconsidering Your Cooking Oil Choices

The shift in perspective on canola oil reflects a broader move toward whole, minimally processed foods. While canola oil is not an immediate health risk in small, moderate quantities, the widespread availability of healthier, less-processed alternatives has made its drawbacks more apparent. For those concerned about inflammation, oxidative stress, and the impact of industrial processing, there are clearly superior choices. Substituting refined canola oil with alternatives like extra-virgin olive oil for lower-heat cooking and avocado oil for higher-heat applications provides better nutrition, antioxidants, and peace of mind. The debate over canola oil is a powerful reminder that not all fats are created equal, and the way food is processed can significantly impact its health effects. When choosing a cooking oil, looking beyond simple fat content to consider processing methods and antioxidant value is crucial for optimal health.

Visit Harvard Health's guide to healthy cooking oils for more information.

Frequently Asked Questions

The health concerns associated with canola oil—namely heavy processing, omega-6 content, and oxidation risk—are similar to many other industrial seed oils, including soybean and sunflower oil.

Yes, small amounts of artificial trans fats can be created during the high-heat deodorization stage of canola oil's processing. Although these amounts may be low per serving, they contribute to overall intake.

While omega-6 fats are essential, modern diets are heavily skewed toward high omega-6 intake. Canola oil contributes to this imbalance, which can promote inflammation.

Yes, cold-pressed canola oil is minimally processed without high heat or chemical solvents, making it a healthier option. However, it is more expensive and has a lower smoke point, making it less suitable for high-heat cooking.

Oxidized oils produce free radicals that can cause oxidative stress and cellular damage in the body. This is linked to chronic illnesses such as heart disease, diabetes, and Alzheimer's.

While canola oil has a high smoke point, its polyunsaturated fats are prone to oxidation when heated, especially with repeated use like deep frying. This can create harmful compounds, making it less ideal for high-heat cooking.

For high-heat cooking, avocado oil is a stable and healthy alternative. For baking, you can use refined coconut oil or even substitute with mashed fruit like applesauce for a lighter, fat-free option.