What is unhealthy about peanut oil?

November 18, 2025 •

4 min read

Modern Western diets contain significantly more omega-6 fatty acids than omega-3s, and the widespread use of oils like peanut oil for frying contributes to this imbalance. While peanut oil is a popular choice for high-heat cooking, there are several noteworthy health concerns to consider.

Quick Summary

Peanut oil contains pro-inflammatory omega-6 fatty acids and is susceptible to oxidation at high temperatures, which can produce harmful free radicals. Unrefined versions pose a risk to those with peanut allergies due to residual proteins, necessitating mindful consumption.

Key Points

High Omega-6 Content: Peanut oil is very high in omega-6 fatty acids, which can disrupt the body's omega-6 to omega-3 ratio, contributing to chronic inflammation.
Oxidation During High-Heat Cooking: Despite a high smoke point, peanut oil's polyunsaturated fats are susceptible to oxidation when heated, creating free radicals that damage cells and increase disease risk.
Significant Allergen Risk: Unrefined or cold-pressed peanut oil contains allergenic proteins and is dangerous for those with peanut allergies. Even refined oil poses a cross-contamination risk.
Aflatoxin Contamination: Peanuts can be contaminated by aflatoxins, carcinogenic compounds produced by fungus. While controlled in commercial products, the risk remains, particularly with less-regulated sources.
Refining Strips Nutrients: The refining process, while removing allergens, also strips away beneficial antioxidants like vitamin E and phytosterols found in unrefined versions.
Better Alternatives Exist: Healthier cooking oils like avocado or olive oil offer a better fatty acid profile and superior stability, making them safer choices for high-heat cooking.

The Imbalance of Omega-6 Fatty Acids

One of the most significant health concerns regarding peanut oil is its high content of omega-6 fatty acids, specifically linoleic acid. While omega-6s are essential, the key to good health lies in a balanced ratio of omega-6 to omega-3 fatty acids. Historically, human diets featured a much more balanced ratio, perhaps closer to 1:1 or 4:1. The typical modern Western diet, however, is heavily skewed, with ratios often exceeding 15:1 due to the overconsumption of processed foods and vegetable oils high in omega-6s.

When the body has a disproportionately high level of omega-6s compared to omega-3s, it can trigger a pro-inflammatory state. Chronic, low-grade inflammation is a known risk factor for a variety of serious conditions, including heart disease, obesity, inflammatory bowel disease, and certain cancers. Therefore, regularly cooking with an oil so rich in omega-6s, especially when combined with other dietary sources, can exacerbate this inflammatory imbalance.

Common Sources of Omega-6s to be Aware Of:

Vegetable oils like corn, soybean, and safflower oil
Processed snack foods
Fast food, which is often fried in high omega-6 oils
Many packaged baked goods
Certain salad dressings

Oxidative Stress from High-Heat Cooking

Despite its high smoke point, which makes it a popular choice for deep frying, peanut oil's chemical structure makes it susceptible to oxidation. Oxidation occurs when unsaturated fats are exposed to heat, air, or light, causing them to break down and form harmful compounds known as free radicals.

Polyunsaturated fats are particularly vulnerable to this process due to their multiple unstable double bonds. Peanut oil contains a considerable amount of polyunsaturated fat (around 30%) and is often used for high-temperature applications like frying. The free radicals created during this oxidative process can damage cells throughout the body, a condition known as oxidative stress. This cellular damage is associated with premature aging, various chronic diseases, and increased risk of cancer. While some studies show peanut oil's oxidation rate can be slower than other oils, its common use in high-heat frying is still a significant concern.

The Allergy Factor: Refined vs. Unrefined Oil

Peanut allergies are among the most common and severe food allergies, sometimes causing anaphylaxis. For those with peanut allergies, consuming unrefined (cold-pressed or gourmet) peanut oil is extremely dangerous. This is because the unrefined process does not remove the allergenic proteins, leaving them present in the final product.

While highly refined peanut oil undergoes extensive processing that removes almost all protein allergens, making it generally safe for most people with peanut allergies, caution is still warranted. There is always a risk of cross-contamination in restaurants and food preparation environments, even with refined oil. Anaphylaxis UK and other organizations advise individuals with severe allergies to exercise extreme caution or avoid peanut oil entirely to be safe.

Potential Aflatoxin Contamination

Peanuts are susceptible to contamination by a fungus called Aspergillus, which produces a toxic and highly carcinogenic compound called aflatoxin. Aflatoxin exposure, even at low levels over time, has been linked to severe health issues, including liver damage and an increased risk of liver cancer. While modern processing techniques and quality control significantly reduce the risk of aflatoxin contamination in commercially available peanut oil, the potential remains, particularly in products from less regulated sources.

Comparison Table: Peanut Oil vs. Healthier Alternatives


Feature	Peanut Oil	Avocado Oil	Extra Virgin Olive Oil
Omega-6 Content	High	Low	Low
Omega-3 Content	Very Low	Low	Very Low
Oxidation Stability	Susceptible to oxidation at high heat due to PUFAs	High stability due to high MUFA content	High stability due to high MUFA content
Best Use Case	Deep-frying, stir-frying (caution advised)	High-heat cooking, grilling	Low-to-medium heat cooking, dressings
Allergen Risk	Unrefined is high risk; refined is low risk but cautious	Extremely low	Extremely low
Fatty Acid Profile	High in omega-6s, decent MUFAs	Very high in monounsaturated fats (MUFAs)	Very high in monounsaturated fats (MUFAs)

Conclusion

While peanut oil may have some potential benefits, such as its high vitamin E content and decent monounsaturated fat profile, the drawbacks present significant health concerns. The high concentration of pro-inflammatory omega-6 fatty acids, the risk of harmful free radical formation during cooking, and the unavoidable allergy risk of unrefined versions all weigh against its frequent use. For those seeking healthier cooking alternatives, oils like avocado oil or extra virgin olive oil offer better fatty acid profiles and superior oxidative stability. Ultimately, moderation is key when using any cooking oil, and understanding what is unhealthy about peanut oil is crucial for making informed dietary choices. For further reading on the inflammatory effects of high omega-6 intake, consider reviewing scientific studies such as those referenced in the National Institutes of Health research library.

Frequently Asked Questions

Peanut oil contains a high ratio of omega-6 to omega-3 fatty acids, and consuming too much omega-6 has been linked to increased inflammation, which is a risk factor for heart disease. However, some studies also highlight its monounsaturated fat content, which can be heart-healthy when consumed in moderation and as part of a balanced diet.

The pro-inflammatory reputation of peanut oil comes from its high omega-6 fatty acid content. While omega-6s are essential, a modern diet often has a heavy imbalance, and excessive intake can contribute to inflammation in the body.

Highly refined peanut oil is generally considered safe for most people with peanut allergies because the intense processing removes the allergenic proteins. However, unrefined or cold-pressed peanut oil is not safe. It is always wise for individuals with severe allergies to consult a doctor before consuming any peanut oil.

When heated, especially for high-heat cooking like deep frying, the polyunsaturated fats in peanut oil can undergo oxidation. This process creates free radicals, which are unstable molecules that can cause cellular damage and oxidative stress in the body.

Aflatoxins are toxic compounds produced by a fungus that can contaminate peanuts. Modern, high-quality peanut oil is processed to remove aflatoxins, but the risk of contamination exists, particularly in less-regulated markets.

Compared to extra virgin olive oil, which is very high in stable, monounsaturated fats, peanut oil has a less favorable fat profile due to its high omega-6 content. Olive oil is less prone to oxidation and is generally considered a healthier option, especially for low-to-medium heat cooking.

You don't need to completely avoid peanut oil, but you should use it in moderation and be mindful of your overall omega-6 intake. For high-heat cooking, consider more stable alternatives like avocado oil. Individuals with peanut allergies should consult their allergist regarding refined peanut oil and avoid unrefined types.