How many times can cooking oil be reused?

Today, I read an interesting article in New Straits Times entitled "How many times can cooking oil be reused?" According to the article, one should avoid reusing oil more than twice or the oil has turned black, smell rancid or has turned thick and sticky [Ref. 1, see excerpt below for full article ].

Should we follow the article guidance? Personally, I will not follow.

I will share why this is a nutrition misconception and why cooking oil should not be reused at all. Reusing cooking oil poses a great danger to people's health.

Here are the reasons [Ref. 2]
1.  Most cooking oils contain small amounts of malondialdehyde - a possibly carcinogenic substance that affects enzymatic activity, speeds up the process of aging, and is cytotoxic. The malondialdehyde level in oil will increase 10 times or more when the oil is used repeatedly.

2. The oil used for deep-frying is kept at higher-than-boiling temperatures for extended periods of time. This causes unsaturated fatty acids (unstable in nature) in plant oils to oxidize continuously, resulting in the formation of harmful, or even carcinogenic, substances.

3. Oil that is used repeatedly will have a lowered smoke point, and toxic substances are produces more easily in such oil.

I learned this knowledge through Dr Chen Jau Fei, renowned Nutritional Immunologist. She is giving a health talk on 26th November. Please details here. Please contact me if you would like to get the ticket.

See other posts related to cooking oil
1. How do you choose cooking oil?

Regards,
Pei Lin LEE
Health Speaker/Consultant

References
1. The Straits Times,. "How many times can cooking oil be reused?"  12 Nov. 2016
2. J.F. Chen, "Nutrition. Immunity. Longevity"