Let’s talk about cooking oil

Health Advice

Article by: Consultant Dietitian Su Hua Cheng


Are you picking the right oil for your cooking?

Extra virgin olive oil, canola oil, coconut oil, soybean oil, palm oil…There are so many cooking oils on the market, which one should I buy?  Before choosing the right oil, let’s get to know oil first. 

What are cooking oils?

Cooking oils are usually extracted from seeds, kernels, and mesocarp. The extraction process determines whether the oil is unrefined or refined. 

Unrefined oil is made by pressing seeds in the presence of minimal heat (cold or expeller pressed) and without undergoing any chemical treatment. Hence, unrefined oils retain the original flavour and colour, and most of the nutrients. Unrefined oils are usually labelled as raw/pure, virgin or extra virgin. Unrefined oil tends to have a low smoke point; therefore, it is best used for salad dressing.  [1]

Whereas, refined oil is made by pressing oil at a high temperature then followed by chemical treatment such as bleaching and deodorizing.  These processes reduce the original flavour, colour and odour as well as some of the nutrients and antioxidants. Unlike unrefined oils, refined oils are more heat resistant and have a higher smoke point. Therefore, refined oils are suitable for normal cooking practices.[1] Many of the cooking oils in the market are refined oils such as soya bean, canola, rice bran and grapeseed oil. [2]

Since most of the cooking oils are refined,
do they have any differences? 

All types of cooking oils contain about the same 15g of total fat and 135 calories per tablespoon.  [3] What makes them different is their proportion of saturated, monounsaturated, and polyunsaturated fats. This proportion can be varied from oil to oil, which determines their nutritional value and stability. [2] By knowing the health impact of each type of fat, your choice in cooking oils will be easier to make. 

Saturated fats are considered as unhealthy fat because they tend to raise ‘bad’ cholesterol and increase the risk of heart disease. [4] Animal fats are typically known to be rich in saturated fats. 

Unsaturated fats mainly come from vegetables, seeds or nuts. They are healthy fat that helps lower bad cholesterol and reduce the risk of heart disease and stroke. [5]There are two types of unsaturated fat:

i. Monosaturated fats
ii. Polyunsaturated fats. It can be further classified as
– Omega-3 fatty acids
– Omega-6 fatty acids

Although refined cooking oils have a higher smoking point, their heat stability is also determined by their proportion of types of fat. In general, refined oils that are rich in saturated fats have a higher smoking point followed by monosaturated fats and polyunsaturated fats. [6]

How to choose the right cooking oil?

Choose cooking oil according to your cooking method as different oil has different smoking point. 

  1. Choose oils that are rich in omega-3 for raw application such as salad dressing and drizzling and omega-6 for low heat cooking. This is because polyunsaturated fats are particularly unstable when heated at high temperatures due to their chemical structure. [1,2] 
  2. Choose oils that are rich in monosaturated fats for shallow frying, baking or stir-frying. [1,2] Monosaturated fat such as olive oil and canola oil are great for medium-heat cooking because they are generally more stable than polyunsaturated fat and healthier than saturated fat.
  3. Choose oils that are rich in saturated fats, especially plant-based oil for deep-frying. [1,2] Plant-based oil such as coconut oil have a high smoke point, hence they don’t break down easily at high temperatures to produce harmful compounds like poly- and mono-unsaturated fat. Besides, coconut oil contains medium-chain triglycerides (MCTs) which are rapidly absorbed and used by the body. After digestion, MCTs travel to the liver, where they are immediately used for energy, thus preventing fat storage.[8] However, that doesn’t mean that you can have fried foods all the time, as too much intake of saturated fat put you at risk for heart disease. 

Common Q&A

What happens if I overheat oil?

When oil starts to smoke, it means the oil has reached its smoke point and started to produce harmful compounds. [2] Moreover, overheated oil will deteriorate the nutrients in foods. If you notice the oil starts to smoke lightly, immediately remove the pan from heat and let it cool a bit before starting to cook. However, if you notice that the oil starts to emit a lot of smoke, discard the oil. 

Can I reuse cooking oil?

Reusing cooking oil in food preparation is a common practice, especially for deep-fried foods. Every time when oil is being reused, there will be a significant drop in its stability and smoke point, making it smoke easily. This results in a large production of carcinogenic compounds.  Studies have shown that large consumption of reused cooking oils and inhalation of cooking fumes can lead to cancer including lung, colorectal, breast and prostate cancers. [9] Try to avoid using reused oil in your food preparation. 

How should I store cooking oil?

When oils are exposed to oxygen and heat, they go rancid and start to form toxic compounds. [6] Proper storage can prolong the shelf life of your oils. Keep oils in a cool, dry place out of direct sunlight. You may also choose a dark colour glass bottle for better protection from the deteriorating effects of sunlight.[2] In addition to that, always make sure the lid is tightly closed to reduce exposure to oxygen. 

How many fats should I incorporate into my diet? 

According to WHO, it is recommended not to exceed 30% of total energy intake. [10] Remember that your fat intake isn’t just come from cooking oil, it also from other sources such as meat, baked goods, dairy products and etc. Therefore, try to limit your intake of oil to 6 teaspoons per day. It is important to keep an eye on your overall fat intake to prevent unwanted weight gain. 


References:

  1. Wai Ng T, Appukutty M, Shyam S, Voon P, Selvaduray K. Cooking Oils in Health and Sports. Perform. Enhanc. Health. 2019;:751-756.
  2. How coconut oil, olive oil and rice bran oil stack up [Internet]. Heart Foundation New Zealand. 2022 [cited 28 March 2022]. Available from: https://www.heartfoundation.org.nz/about-us/news/blogs/choosing-cooking-oils 
  3. Energy & Nutrient Composition [Internet]. Health Promotion Board. 2011 [cited 28 March 2022]. Available from: https://focos.hpb.gov.sg/eservices/ENCF/FoodAnalysis.aspx?p=1 
  4. Dietary Fats [Internet]. American Heart Association. 2021 [cited 28 March 2022]. Available from: https://www.heart.org/en/healthy-living/healthy-eating/eat-smart/fats/dietary-fats 
  5. Types of Fat [Internet]. HARVARD T.H. CHAN. 2022 [cited 16 April 2022]. Available from: https://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/fats-and-cholesterol/types-of-fat/#:~:text=Unsaturated%20fats%2C%20which%20are%20liquid,number%20of%20other%20beneficial%20roles
  6. Functions, Classification And Characteristics Of Fats [Internet]. Eufic.org. 2014 [cited 3 April 2022]. Available from: https://www.eufic.org/en/whats-in-food/article/facts-on-fats-the-basics 
  7. No need to avoid healthy omega-6 fats – Harvard Health [Internet]. Harvard Health. 2019 [cited 16 April 2022]. Available from: https://www.health.harvard.edu/newsletter_article/no-need-to-avoid-healthy-omega-6-fats 
  8. Shah ND, Limketkai BN. The use of medium-chain triglycerides in gastrointestinal disorders. Pract. Gastroenterol. 2017 Feb 1;160:20-5. 
  9. Ganesan K, Sukalingam K, Xu B. Impact of consumption of repeatedly heated cooking oils on the incidence of various cancers-A critical review. Crit Rev Food Sci Nutr. 2019 Feb 4;59(3):488-505.
  10. Healthy diet [Internet]. Who.int. 2020 [cited 3 April 2022]. Available from: https://www.who.int/news-room/fact-sheets/detail/healthy-diet 

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