Is Eating Rancid Oil Bad for Your Health?


We all know that oil that has gone bad smells rancid and tastes stale, but what are the health effects of using rancid vegetable oil in cooking? Does spoiled oil contain some toxic substances that makes eating food containing rancid oil dangerous, or is it just unpleasant to the palate? HealWithFood.org embarked on a mission to find out whether rancid oil is really bad for you. Here are the results – three interesting facts you should know about rancid oils in relation to human health:


Eating rancid oil is bad

Rancid Oils May Cause Cancer

Plant-based oils, such as safflower oil and sunflower oil, contain plenty of polyunsaturated fatty acids (PUFAs) which oxidize easily in the presence of light, heat, or oxygen in the air. Many of the oxidation products of PUFAs have been reported to have cytotoxic (toxic to cells) and mutagenic (capable of changing the DNA) effects. Cytotoxic and mutagenic substances are commonly known to increase the risk of cancer, and indeed, a 2002 study published in the journal Anticancer Research reported that rancid oils not only appear to be involved in tumor promotion but also in tumor initiation. This study was carried out on mice, and rancid corn oil was used as the source of spoiled fatty acids.


Rancid Oils Deplete Vitamin E Levels

Edible oils – such as extra-virgin olive oil, almond oil and sunflower oil – are excellent dietary sources of vitamin E. For example, just one tablespoon of extra-virgin olive oil contains nearly 2 milligrams of vitamin E, which corresponds to a whopping 10% of the reference daily value for vitamin E. Vitamin E is a powerful antioxidant that can protect the human body from dangerous free radicals that have been linked to an increased risk of numerous diseases and health problems. However, rancid oil appears to be capable of depleting vitamin E levels. A 1996 study published in the journal Aquaculture Research reported that blood levels of α-tocopherol acetate (a type of vitamin E) increased significantly in African catfish when the fish were given extra doses of α-tocopherol, but that those levels saw a significant drop when the fish were given rancid oil to eat.


Some Oils Are More Prone to Oxidation

Polyunsaturated fatty acids (PUFAs) include the essential fatty acids, including the super-healthy omega-3s that are being touted by nutritionists and health gurus around the world. However, compared to fats that are rich in saturated fatty acids (such as coconut oil or butter), edible oils that are rich in PUFAs are highly unstable and prone to oxidation. This means that many healthy, plant-based sources of dietary fat – such as hemp seed oil, walnut oil, grape seed oil, and unrefined safflower and sunflower oils – can go rancid within a very short period time. Oils like olive oil, avocado oil, and macadamia nut oil, on the other hand, have a longer shelf life due to their lower concentration of PUFAs and higher concentration of monounsaturated fatty acids (MUFAs).


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Sources:
1. P. Perjesi et al (2002). Effect of rancid corn oil on some onco/suppressor gene expressions in vivo. A short-term study. Anticancer Research, Jan-Feb;22(1A):225-30.
2. R. Baker and S. Davies (1996). Oxidative nutritional stress associated with feeding rancid oils to African catfish, Clarias gariepinus (Burchell) and the protective role of α-tocopherol. Aquaculture Research, Volume 27, Issue 10, pages 795-803.