Why Rancid Cooking Oil is Bad For You?

When it comes to the health of our families, we make sure we purchase a heart friendly healthy cooking oil, even if it is a little pricier. Then how is it that our oil still becomes distasteful? Just as foods become rancid due to excessive exposure to air, water, or light, cooking oil, too, becomes rancid and unfit to use.

What is rancid oil?

For most, rancid oil is not a common cooking terminology, yet we’ve all come across it or used rancid oil in our cooking. Rancidity usually signifies unsavoury flavours and displeasing odours that are the outcomes of degrading fats. When fats in cooking oil are exposed or come in contact with extreme heat, light, or oxygen, they start to decay and our oil begins to smell or taste different. In other words – it turns rancid and becomes unsuitable for further consumption.

How often do we take cooking oil used for frying, let it cool down, and then store it back in a container? And then how often have we complained about the foul taste after reusing? Sounds all too familiar, correct?

Oil becomes rancid when overheated. This usually happens when we use it for frying and by reusing this oil we are unknowingly helping it go more rancid! Each time we heat an oil, its smoke point lowers and it becomes more susceptible to heat, in turn lowering its smoke point. When this fried ‘put aside’ oil is sticky, darker, smells foul, or leaves a residue in the container, it certainly is rancid.

We inadvertently consume more rancid oil than we know. Have you ever thought why the taste of the street food we eat is not consistent every time? Sometimes it is yummy and at other times just off and stinky. Well, it is because that favourite vada pav was fried in overused oil that has become rancid.

 SmokePoint: cooking oilSmoke points of oils

Have you ever left your oil on the stove to heat and returned to find it fuming? That is your cooking oil’s threshold limit of burning or simply, its smoke point.

  • A smoke point is a temperature at which oil stops simmering, starts burning, and lets off smoke. At this point, the nutrients and fats in an oil rapidly break down and decay. The smoke that is released from this process is often more toxic than the deteriorated oil itself.
  • So why is smoke point important? Every cooking oil has a different smoke point. Certain oils have a higher smoke point than the others do. Some oils like our common vegetable oil (canola, sunflower, corn oil and peanut oil) are made out of a process involving high heat. In addition, refining vegetable oil makes it very unstable and easily prone to rancidity.
  • Choosing the right oil that best suits your needs and is “healthy” can be daunting. For a high temperature cooking, use a cooking oil that has a high smoke point, for low temperature cooking, use oils that have low smoke points or high in Omega3 fatty acids (and to cook without any oil switch to Royal Prestige.)

The Indian style of cooking usually requires oil for almost everything. We sauté all our vegetables and curries in cooking oil, add tadka to our dals, and definitely fry a lot of snacks and breads to accompany the vegetables. All of these activities require cooking for longer periods or on a high temperature. Thus, it is suggested that we use oils with a high smoke point.

Our very own canola oil is surely not a healthy fat. This is because in its manufacturing process, it is heated to a point that destroys most of its beneficial properties. It is then just deodorised to make it taste and smell fresh. Hence, it is toxic much before it reaches its smoke point. You must have experienced a dark residue or a metallic stench after frying your puris in common vegetable or canola oil. Those are stark signs of rancidity.

Both olive oil and coconut oil are known for health benefits and nutritional value. Lately, in India, many of us have completely shifted to olive oil as it is marketed as a ‘healthy’ oil. We agree it is the best when it comes to salad dressings. However, olive oil is a big ‘NO’ for frying or searing or any sort of Indian cooking that mostly requires high heat because it has a low smoke point.

Health effects of rancid oil

Not all fats are extremely harmful that does not mean they are healthy either. According to the American Health Association, polyunsaturated fats reduce bad cholesterol levels thereby lowering the risk of a heart disease. But this holds true only when we consume a moderate amount and not in excess. A big example of such a fat is olive oil that quickly becomes rancid.

Rancid oils work on the cells of our body and weaken them. They deplete the body’s vitamin B and E resources, have harmful health effects and are known to be linked to the following:

  • Diabetes
  • Botulism and other digestive disorders
  • Cancer
  • Infertility
  • Alzheimer’s disease
  • Atherosclerosis/ coronary diseases
  • Accelerated aging
  • Degeneration of tissues
  • Weight gain
  • Damaging DNA

Choose a cooking oil that suits your cooking needs. Things used in control and in the right manner have never done much harm!


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