Can You Get Sick From Eating Rancid Oil?
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Can You Get Sick From Eating Rancid Oil?

Can You Get Sick From Eating Rancid Oil?
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Updated on August 6, 2025
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While heart-healthy oils are an important part of your balanced diet, you should avoid consuming rancid oil and rancid nuts. They become rancid through a process called oxidation. For starters, oxidized oils simply don’t taste good and lose nutritional value.

However, more than just leaving an unpleasant taste, regularly consuming rancid oil may have harmful, long-term health effects. The compromised oil can develop harmful free radicals that cause long-term cell damage and potentially lead to the development of chronic diseases.

Can Rancid Oil Make You Sick?

While it can have a pretty offensive odor, will you get sick if you just ate rancid oil? Researchers suggest that though the effects may not be immediate, studies have linked rancid oil to harmful effects over time. Oxidation causes the oil to produce free radicals that can damage cells and drive disease-forming processes. Then, the free radicals react with oxygen, producing even more harmful substances.

Studies have linked these compromised cells to the development of diseases that manifest over time. Free radicals might have links to atherosclerosis, or stiff arteries that increase heart disease risk, as well as promote cancer development and trigger allergic reactions.

Research on mice also found that oxidized olive oil may contribute to liver and gut inflammation. This led to issues with fat metabolism, tissue and cell damage in the gut and liver, liver enlargement and scarring, and the start of liver injury. While the results of a study on mice might not directly translate to the same outcomes in humans, they still provide a strong caution against consuming oxidized oil.

In addition to the chronic disease risks, rancid oils can trigger digestive system distress. These harmful substances can also drain vitamins B and E from your body, another effect of consuming rancid food, according to a study on mustard and corn oils.

If you’ve considered using a deep fryer, the Food Safety and Inspection Service advises storing the oil you plan to reuse in a lightproof, sealed container for up to three months. It’s safest to discard reused deep-frying oil that’s become foamy, cloudy, or foul-smelling.

The chemical breakdown rate varies with the type of oil used. To extend the fryer oil’s useful life during reuse, run it through a cheesecloth or sieve daily, which removes solids that help it degrade. You should also refrigerate the oil when it’s not in use. Recording oil changes will also be useful.

How Does Oil Become Rancid?

Several linked factors can gradually cause oils and fats to become rancid. The fats combine with oxygen in the air and fundamentally change their chemical composition.

Exposure to warm temperatures, oxygen, and light are significant factors in speeding up rancidity. Generally speaking, oils tend to become rancid more quickly than solid fats. Researchers have determined that storing at high temperatures can cause the oils to become rancid, resulting in an undesirable flavor and odor. Every additional 50 degrees Fahrenheit increase may double the oxidation speed.

Contamination by environmental microorganisms and metals present in raw materials, as well as processing and storage equipment, is also a factor. Plant-based oils such as canola, olive, corn, and peanut oils tend to oxidize faster than solid, saturated fats, as they generally contain more unsaturated fats.

Effects of Eating Rancid Nuts

As is the case with edible oils, roasted or raw nuts can become rancid if they undergo improper processing or storage. This tendency toward rancidity results from their unsaturated fat content.

If you open a container of nuts and notice a paint-like odor and an unpleasant taste, they’re rancid. You’ll need to discard them. As a guideline, note that their shelf life varies, depending on the nut variety and storage environment.

Due to faulty storage procedures, nuts may also develop contamination with molds that produce harmful toxins called mycotoxins, which often survive processing and enter the finished food product. If you eat mold-contaminated nuts, you may experience serious health issues, including potentially fatal liver problems for people who consume enough mold.

To prolong the shelf life of your favorite nuts, store the package in your refrigerator. You should also follow this practice when storing nut butters and nut oils in already-opened jars. If you plan to use nuts in a recipe, taste one before stirring in the entire package and potentially ruining the dish.

The Takeaway

  • Rancid oils won’t give you a foodborne illness, but they have links to long-term health problems like atherosclerosis, heart disease, cancers, allergies, and others. They can also affect nutrient levels by causing digestive distress.
  • The oxidation process that makes oil rancid may also severely deplete the nutritional value of heart-healthy, polyunsaturated fats. These oils generally spoil faster than solid, saturated fats.
  • Air and light exposure, excessive heat during storage, and contamination with microbes and heavy metals can speed up the oxidation process.
  • Store oils and nuts away from light and heat to help them keep for longer.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
  1. Gharby S et al. Vegetable oil oxidation: Mechanisms, impacts on quality, and approaches to enhance shelf life. Food Chemistry: X. May 10, 2025.
  2. Bao Y et al. Dietary oxidized lipids in redox biology: Oxidized olive oil disrupts lipid metabolism and induces intestinal and hepatic inflammation in C57BL/6J mice. Redox Biology. March 1, 2025.
  3. Okparanta S et al. Assessment of Rancidity and Other Physicochemical Properties of Edible Oils (Mustard and Corn Oils) Stored at Room Temperature. Journal of Food and Nutrition Sciences. May 2018.
  4. Deep Fat Frying and Food Safety. U.S. Food Safety and Inspection Service.
  5. Garden-Robinson J. Prairie Fare: Is It Time for an Oil Change in Your Kitchen? North Dakota State University. April 20, 2017.
  6. Zhou J et al. Nuts: An overview on oxidation, affecting factors, inhibiting measures, and prospects. Journal of Food Composition and Analysis. March 2025.
  7. Mycotoxins. World Health Organization. October 2, 2023.
  8. Go Nuts (But Just a Little!). American Heart Association. August 23, 2024.
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Natalia Johnsen, MD

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Member of American College of Lifestyle Medicine

Natalia Johnsen, MD, practices internal medicine and lifestyle medicine. She works as an internist for the Vancouver Clinic in Vancouver, Washington.

Johnsen trained and worked as ob-gyn in Russia before coming to the United States in 2000. Subsequently, she interned in internal medicine at the University of Nevada and completed her residency at a Stanford-affiliated program in Santa Clara, California. After that she worked as a general internist for two years before to switching to full-time hospital work.

Johnsen has always been fascinated by the effects that lifestyle can have on physical and mental health, and she fell in love with the concept of lifestyle medicine as a specialty after seeing patients struggle with issues that could have been prevented had they known more about a healthy lifestyle. To make an impact on her patients through lifestyle interventions, she launched her own lifestyle medicine clinic, Vivalso Health and Longevity.

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Barbara Hazelden's interest in healthy living began decades ago, during her high school and college years. Always a non-smoker, she also adopted a vegetarian lifestyle for health and ethical reasons. Today, her dietary regimen essentially remains the same, although she recently banished gluten from her menu as well. Barbara does, however, continue to enjoy her dark chocolate every day. During the past few years, Barbara has also been working to simplify her personal life. She has gradually been gravitating toward a minimalist lifestyle, clearing out excess furniture and dust magnets from her house, and removing mental cobwebs that could keep her from moving forward. As a previous everydayhealth.com writer, she welcomes the chance to again contribute to the company's healthy living-focused mission.

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