Which cooking oil is the healthiest? | 117三行

Eat a variety of oils at the same time, don't just focus on one.

Written by | Shi Jun

Source: Yiran Suixin

There are so many cooking oils on the market: peanut oil, soybean oil, rapeseed oil, rice oil, coconut oil, olive oil... Most of them claim to be healthier. Which cooking oil is the best? In the "Cholesterol Centennial Study" series, we have analyzed that saturated fat is not as bad as imagined, so there is no need to exclude lard and butter directly.

When choosing cooking oil, in addition to cholesterol content, there are two other points to consider:

1) The stability of cooking oil is very important but often overlooked. It is not only about which oil is the healthiest at room temperature, but more importantly: does the oil still retain its healthy ingredients at the cooking temperature you usually use?

2) The smoke point of cooking oil determines whether the oil is suitable for stir-frying or salad dressing.

Stability of cooking oil Chinese people pursue color, aroma and taste when cooking, and many dishes require stir-frying with hot oil over high heat. When stir-frying at high temperatures, special attention should be paid to using oil that is not easily oxidized or soured.

When oils and fats oxidize, they react with oxygen to form free radicals and compounds that are harmful to your body.

Whether in a low-temperature or high-temperature environment, the most important factor that determines the ability of edible oil to resist oxidation and acidification is the relative saturation of fatty acids in the oil.

Saturated fatty acid molecules have only single bonds, monounsaturated fatty acids have one double bond, and polyunsaturated fatty acids have two or more. It is these double bonds that are chemically reactive and sensitive to heat.

Figure 1: Representative structures of fatty acids

Therefore, cooking oils with high saturated and monounsaturated fat content are very heat-resistant, but oils with high polyunsaturated fat content are very unstable at high temperatures and are not suitable for high-temperature stir-frying [1].

What is the smoke point? During the heating process, the oil temperature will get higher and higher. When it reaches a certain temperature, the oil will start to smoke or even burn. This temperature is called the smoke point. When cooking, if the oil temperature exceeds the smoke point of the oil, it will not only burn the food, produce toxic gases and harmful free radicals, but also destroy the beneficial nutrients and phytochemicals in the cooking oil.

Therefore, it is very important to choose oil with a suitable smoke point according to different uses. Oil with a low smoke point is suitable for cold dishes, while oil with a relatively high smoke point is suitable for stir-frying.

The smoke point depends on the amount of free fatty acids (FFA) in the oil: the lower the FFA content, the higher the smoke point. The more refined the oil, the lower the FFA content and the higher the smoke point.

The table below lists the smoke points and fatty acid compositions of some common oils.

One thing worth noting is that there is no direct correlation between a high smoke point and high stability. Stability and smoke point are two indicators that are determined by different factors and need to be considered separately.

Figure 2: Composition and smoke point of several common cooking oils | Source: Compiled by the author

Let’s take a closer look at the characteristics of several common edible oils.

Canola Oil

Canola oil comes from rapeseed, but is highly processed to remove a toxic, bitter substance called euric acid.

Judging from its ingredients alone, canola oil has a pretty good fatty acid composition:

• Most fatty acids are monounsaturated (about 64%).

• There are also 9-11% polyunsaturated omega-3 fatty acids. The ratio of omega-6 to omega-3 fatty acids is a perfect 2:1. (For details about the ratio of the two, see "Is fish oil really as good as the legend says? Do pregnant women need to supplement fish oil?")

• Contains more plant sterols (about 0.9% by weight), which can reduce the body's absorption of cholesterol.

However, canola oil undergoes very demanding processing before it becomes the final product.

The top four vegetable oils sold in the U.S. are soybean oil, canola oil, palm oil, and corn oil. These oils are often referred to as RBD oils.

RBD stands for three words: refined, bleached, and deodorized. These three words describe the manufacturing process of RBD oil. (Go to "Fanpu" to watch the production of canola oil | Source: https://www.youtube.com/watch?v=omjWmLG0EAs)

The plant material (usually seeds) is first squeezed to force the oil out, and then the squeezed material is chemically extracted with a low-boiling point solvent (most commonly hexane) to extract the maximum amount of oil.

Hexane is a very volatile solvent (boiling point 69°C) with low toxicity (lethal dose in rats 49.0 ml/kg). Refined vegetable oils extracted with hexane are estimated to contain about 0.8 mg of residual hexane per kg of oil.

Although there is currently no evidence that consuming foods containing trace amounts of residual hexane is harmful to health, I personally feel that if it is eaten every day, the cumulative effect of long-term intake cannot be evaluated.

It’s also worth noting that these RBD oils may contain trans fats, which are harmful to your health.

In order to achieve the "light taste" that consumers want, vegetable oil refining has to go through the final step: deodorization. The deodorization process requires heating the oil to over 200°C (sometimes even up to 235°C) under vacuum to remove volatile components such as free fatty acids and phospholipids.

High temperatures can cause small amounts of unsaturated fatty acids — especially omega-3 and omega-6 fatty acids — to be converted into trans fats.

This also reduces the levels of beneficial omega-3 fatty acids. Heating bleached canola oil at 220°C for 10 hours reduced the level of linolenic acid, a healthy omega-3 fatty acid, by nearly 20%.

Figure 3: Trans fat content of several common vegetable oils. Average results of various oil samples [2, 3]. Hydrogenated soybean oil was used as a control. Source: The author compiled the graph based on the data from the reference literature.

High temperatures can also affect the stability of oils and fats, causing them to deteriorate.

"Cold-pressed" canola oil exists, but it is very expensive and rare on the market.

Therefore, although there are many advertisements saying that canola oil is the healthiest oil, I personally do not recommend long-term consumption of this highly processed product, but it is fine to use it occasionally.

There are two points that must be pointed out about trans fats: 1) You will often see some vegetable oil bottles in supermarkets with "0 grams of trans fat" written in large letters in a conspicuous place. But if you read the small print on the back carefully, the complete sentence is "0 grams of trans fat per serving". This "per serving" refers to one tablespoon, or about 14 grams of oil. Almost all vegetable oils sold in supermarkets contain a small amount (≤ 5%) of trans fat, but the FDA allows any ingredient less than 0.5 grams to be written as 0 grams, so these manufacturers use large letters to promote this rounded conclusion. For example, one serving of canola oil actually contains 0.2g of trans fat.

2) As with the deodorization process, deep frying also produces a lot of trans fats. Many fast food restaurants reuse deep frying oil. At 185°C, frying French fries for 7 hours a day, the trans fat content of canola oil will increase from 2.4% to 3.3% after one week. Long-term deep frying will also produce a lot of unsaturated fatty acid oxidation products that are harmful to the human body.

Try to eat less fried food, especially those in restaurants.
Other vegetable oils are highly processed and refined products like canola oil. Therefore, the intake of the following oils should also be controlled and not used every day for a long time: Soybean oil

Corn oil

Cottonseed oil

Sunflower oil

Sesame oil

Grapeseed oil

Safflower oil

Rice bran oil

Olive Oil You may have heard that olive oil is good for your heart. It is considered a key ingredient in the Mediterranean diet for its health benefits.

It can increase the level of good high-density cholesterol (HDL) in the blood and reduce the amount of oxidized low-density cholesterol (LDL) [4, 5].

Although most of the fat in olive oil is monounsaturated, studies have found that olive oil can still retain most of its nutrients when heated at 180°C for 36 hours and is still very heat-resistant[6], so it can still be used for cooking.

Regular olive oil is processed the same way as other RBD oils. If you want no residual hexane and virtually no trans fat, choose Virgin and Extra Virgin Olive Oil.

Virgin and extra virgin olive oils are not extracted with solvents and are not deodorized. They taste better and have more nutrients and antioxidants.

Many people dislike olive oil because they don't like its strong flavor, which is not as bland as deodorized oils. But America's Test Kitchen found that the taste of extra virgin olive oil heated at 177°C for 10 minutes was almost indistinguishable from heated soybean oil. Most of the flavor substances evaporated after heating.

Because of its high content of unsaturated fatty acids, olive oil should be stored in a cool, dry place to prevent it from going rancid.

Avocado Oil: Avocado oil is similar to olive oil in composition, mainly monounsaturated fat, with a small amount of saturated fat and polyunsaturated fat, and is used similarly to olive oil. It has the highest smoke point among all oils (~270ºC), making it suitable for high-temperature cooking.

Coconut Oil: In the past few years, coconut oil has been very popular and has been labeled as a "superfood". It is said to be rich in nutrients and has therapeutic effects, especially good for the brain, and can relieve Alzheimer's disease. Many websites once listed it as the number one healthy food, and celebrities including goddess Gwyneth Paltrow and Internet celebrity Kourtney Kardashian endorsed it. From 2013 to 2017, the sales of coconut oil in the UK increased from about 1 million pounds to 16.4 million pounds, a 16-fold increase.

Coconut oil is extracted from the flesh of the coconut. It is not a new food, having been used extensively in Africa, Asia, and South America for centuries. Coconut oil became a staple in processed foods in the United States in the mid-20th century. By the 1940s, it became the primary source of non-dairy fat in the American diet until it was replaced by vegetable oils.

More than 90% of the fat in coconut oil is saturated fat, more than lard or butter. Two tablespoons contain 20 grams of saturated fat.

Because of this, the oil is very stable, being semi-solid at room temperature and lasting for months, even years, without going bad.

Labeling coconut oil as a "superfood" is ultimately a marketing ploy that can lead people to believe they are eating a healthy diet when the opposite is true -- for example, eating a "superfood" after a deep-fried meal is fine.

Animal fats (lard, tallow, etc.) The composition of animal fats will vary depending on what the animal eats. If the animal eats a lot of grains, the fat will contain quite a bit of polyunsaturated fat. Animals that eat grass will have more saturated/monounsaturated fatty acids.

Therefore, naturally raised animal fats are a better choice for cooking. Lard has a low smoke point (~182ºC) and is suitable for medium temperatures.

Butter In the past, people generally believed that butter was high in saturated fat and unhealthy.

However, only processed margarine is bad[7]. Real butter is not bad and is actually nutritious. It not only contains vitamins A, E and K2, but also rich in conjugated linoleic acid (CLA) and butyrate.

But regular butter contains small amounts of sugar and protein, and there is a risk of burning it if used for stir-frying.

If you want to avoid this and are not afraid of the trouble, you can make clarified butter or ghee to remove lactose and protein. It is very simple to make, and those who are interested can refer to the video below (please go to the "Fanpu" state-owned enterprise).

Compared to butter from cows fed grains, butter made from milk from grass-fed cows contains more vitamin K2, CLA, and other nutrients, so you may want to consider it if you have the means.

Nut Oil and Peanut Oil There are many types of nut oils on the market, and some of them taste great. However, they are rich in polyunsaturated fats, so they are unstable and can be used for salad dressing, but not for stir-frying or other high-temperature cooking.

However, there is one exception - macadamia nut oil, which, like olive oil, is rich in monounsaturated fatty acids and can be used for low or medium temperature cooking. The disadvantage is that it is more expensive.

Peanut oil is similar. Peanuts are not nuts, but their ingredients are similar. Because peanut oil has a high smoke point (~230ºC), it is the first choice for restaurants to fry food. However, this practice ignores the stability of peanut oil: peanut oil contains more unsaturated fat, has poor stability at high temperatures, and is easily degraded.

On top of that, peanut oil is high in omega-6 fatty acids. These are bad fats that tend to cause inflammation and various other health issues. I would not recommend long-term use.

How to cook relatively healthily Heat the oil until it is shiny but not smoking, then put the food in the pan. Do not let the food cool in the pan after cooking, because the food will absorb all the excess oil. The correct way is to take it out immediately and pour out the excess oil.

Precautions for storing cooking oil Don't buy a large amount at once. Buy small quantities so that you can use it up before it goes bad.

The main catalysts that cause edible oils to oxidize and deteriorate are heat, oxygen and light.

Therefore, olive oil and other oils rich in unsaturated fatty acids should be stored in a cool, dry, dark place, and make sure to screw the cap on immediately after use.

Conclusion 1. The best strategy in nutrition is to have a diverse diet and choose a variety of cooking oils according to your needs. For example, you can use avocado oil or high-grade extra virgin olive oil for high-temperature cooking; you can use lard, butter or macadamia oil for medium-temperature cooking; and you can use nut oil or olive oil for salads. However, try to avoid highly industrially processed oils.

2. It is best to use a moderate amount of each. I personally change the type of oil from time to time. Don't stick to the same oil for years. The current research results are new every day. Plans are not as fast as changes. As long as the amount is moderate, there will be no problem.

3. Avoid overheating. Overheating the oil not only affects the taste, but also destroys the fatty acids and nutrients it contains. Some people may say that oil is so troublesome, so I just boil it in water without any oil, isn't it healthy? Let's not talk about whether foodies will be scared by this idea. In the next article, we will talk about whether this method is reliable from a scientific perspective.

References

[1] G. MARTIN et al., HEALTH EFFECTS OF OXIDIZED HEATED OILS1. Foodservice Research International 13, 41-55 (2001).

[2] H. Azizian, JK Kramer, A rapid method for the quantification of fatty acids in fats and oils with emphasis on trans fatty acids using Fourier Transform near infrared spectroscopy (FT-NIR). Lipids 40, 855-867 (2005).

[3] OK SEAN., GW SARA., W. VIRGINIA., C. I‐CHEN., LEVELS OF TRANS GEOMETRICAL ISOMERS OF ESSENTIAL FATTY ACIDS IN SOME UNHYDROGENATED US VEGETABLE OILS1. Journal of Food Lipids 1, 165-176 (1994).

[4] O. Castaner et al., The effect of olive oil polyphenols on antibodies against oxidized LDL. A randomized clinical trial. Clin Nutr 30, 490-493 (2011).

[5] J. Marrugat et al., Effects of differing phenolic content in dietary olive oils on lipids and LDL oxidation--a randomized controlled trial. Eur J Nutr 43, 140-147 (2004).

[6] Y. Allouche, A. Jimenez, JJ Gaforio, M. Uceda, G. Beltran, How heating affects extra virgin olive oil quality indexes and chemical composition. J Agric Food Chem 55, 9646-9654 (2007).

[7] MW Gillman et al., Margarine intake and subsequent coronary heart disease in men. Epidemiology 8, 144-149 (1997).

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