Can You Get Sick From Eating Rancid Oil?

Consuming rancid edible oil may leave an unpleasant taste, but it may not make you sick right away.
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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 at all costs. For starters, they simply don't taste good. Since these spoiled foods can also have negative health effects, stay far away from them.



Consuming rancid edible oil may leave an unpleasant taste, but it may not make you sick right away. However, the compromised oil can develop harmful free radicals that cause long-term cell damage and potentially lead to the development of chronic diseases.

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Learn About Heart-Healthy Oils

With an impressive variety of oils available for cooking, baking and other culinary uses, it's a challenge to choose heart-healthy oils that suit your needs. You should also steer clear of several oils and fats that can negatively affect your health. Fortunately, the Cleveland Clinic provides guidance on both fronts.

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Two general types of oils provide some impressive health benefits. Plant-based monounsaturated fats have been recognized for their ability to decrease your heart disease risks. Polyunsaturated fats are also sourced from plants and contain valuable omega-3 fatty acids that help knock down your odds of developing coronary disease.

On the flip side, it's difficult to present saturated fats in a positive light. Mostly animal-based, these fats may elevate your heart disease risk in the long run. Examples include full-fat dairy products, lard and butter. Palm, coconut and palm kernel oils also receive this dubious distinction.

Man-made trans fats are the worst as they ratchet up your heart disease risk more than other oil varieties. Margarine, shortening and the ubiquitous "partially hydrogenated oil" fall into this category.


Effects of Consuming Rancid Oil

Several interrelated factors can gradually cause oils and fats to spoil, or become rancid food. By definition, rancidity refers to natural spoilage caused by changes in the substances' chemical structure, notes North Dakota State University.

Exposure to warm temperatures, oxygen and light are major factors in rancidity progression. Generally speaking, oils become rancid faster than solid fats.


Vegetable-based oils can lose their optimum food quality after a relatively short period of time, states the University of Nebraska-Lincoln. For example, after one to three months of room-temperature storage, vegetable oils' quality has noticeably degraded.

So, what happens if you consume a rancid oil, such as flaxseed oil? This versatile oil, long used as a fiber and food source, contains beneficial omega-3, linoleic and oleic fatty acids. Its extremely high polyunsaturated fatty acid makeup makes it highly prone to quality degradation and oxidative damage, according to the Oklahoma Cooperative Extension Service.



By comparison, fresh flaxseed oil has a nutty flavor, derived from the oil's cyclic peptides. The same oil, stored at room temperature, gradually develops a bitter-tasting flavor. Ironically, while the cyclic peptides negatively change its taste, they may help the oil develop useful immunosuppressive properties.

Health Hazards of Rancid Oil

For a different perspective on oils' rancidity, the ‌Journal of Food and Nutrition Sciences' ‌May, 2018 edition included a study that evaluated the rancidity and other properties of mustard and corn oils. Each product was stored at room temperature during the study.


Researchers determined that incorrect storage can cause the oils to become rancid and acquire an undesirable flavor and smell. Air, heat, light and some varieties of metal also contribute to the development of this rancid food. Contamination by environmental microorganisms present in raw materials and processing and storage equipment are factors as well.

So, are rancid oils a health hazard? The study's researchers say "yes," noting that rancid oil forms dangerous free radicals that can contribute to cell damage. The compromised cells have been linked to the development of Alzheimer's disease, diabetes and other diseases which manifest over time. Free radicals have also been shown to damage arteries, and to function as carcinogens.


In addition to free radicals' 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.

Maybe you've thought about using a deep fryer, but you wonder if heating the cooking oil could change its composition, potentially causing a health hazard. Hygiene Food Safety confirms that this possibility does exist, as oils experience chemical changes from exposure to heat, light and improper storage conditions.



Essentially, the oils degrade into toxic chemical compounds. During that process, you'll likely notice that they have a rancid smell and taste, along with a darker color. They may also appear to become thicker over time. Their chemical breakdown rate varies with the type of oil used.

To extend the oil's useful life, run it through a filter daily, which removes solids that help it degrade. Recording oil changes will also be useful. Taken together, these preventive actions help you to minimize the health risks and also what you spend replacing your fryer oil.

Storage in Extremely Hot Conditions

Storing oil in extreme heat, as might be encountered during vehicle storage, can also have detrimental effects. A July 2016 study published in the ‌Journal of Analytical Methods in Chemistry‌ profiled the effects of high-heat storage on three extra-virgin olive oil (EVOO) varieties.

Conducted via a lab simulation, the study utilized stove-based heating treatments performed at different temperatures over a two-week and three-week period. Researchers aimed to gauge the deterioration of the EVOO properties that influence the oils' nutritional and therapeutic attributes.

Specifically, they wanted to simulate the outcomes likely to occur during storage, transport and usage conditions in hot climates. Olive trees are typically grown in climates with very warm summers.

The three EVOO varieties showed different changes in quality over the test period. However, a sensory evaluation showed that the oils collectively changed from an "extra-virgin" to "virgin" classification after extended heat exposure. Their fatty acid content didn't demonstrate much change.

Heart-Healthy Benefits of Nuts

Regular nut consumption, as part of a well-balanced diet, can promote good heart health, the Mayo Clinic emphasizes. Crunchy, protein-rich nuts contain beneficial omega-3 fatty acids that can help to regulate heart rhythms.


Nuts' unsaturated fats tend to decrease your blood's "bad" LDL cholesterol levels and can also help lower heart disease-related inflammation. These delicious snacks may also help your arteries' linings become healthier and can also contribute to a lower risk of dangerous blood clots.

Most nuts are also packed with beneficial vitamin E, which contributes to lower artery plaque levels. Plus, they contain the compound l-arginine, which improves artery wall flexibility, making your arteries less susceptible to blood clots. Some nut varieties also contain plant sterols, known for their ability to help decrease cholesterol.

Let's not forget their fiber content, which gives you that "fuller" feeling so you consume less food. Fiber also helps knock down your cholesterol levels and may help prevent type II diabetes.

To reap the health benefits of nuts, eat them in place of foods rich in saturated fats, such as meat, dairy products and eggs. Because nuts are high in fat and calories, limit consumption to a handful at a time. Or, enjoy one or two tablespoons of a tasty nut butter or spread.

Effects of Eating Rancid Nuts

As is the case with edible oils, roasted or raw nuts can become rancid if processed or stored in improper conditions, notes Colorado State University Extension. This tendency toward rancidity results from their unsaturated fat content.

If you open a container of nuts and see that they have a paint-like odor and an unpleasant taste, you now have rancid nuts and should discard them. As a guideline, note that their shelf life varies, depending on the nut variety and storage environment.

Pecans and walnuts have the shortest shelf life, while hazelnuts and cashews can be safely kept for the longest periods. You can extend nuts' shelf life by storing the package in the freezer.

Because of faulty storage procedures, nuts may also become contaminated with molds producing harmful toxins that often survive processing and make their way into the finished food product. If you consume mold-contaminated nuts, you may experience serious health problems.

To prolong your favorite nuts' shelf life, the American Heart Association recommends that you keep 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.