Which are the Best Oils for Cooking?

Oils and fats are used for cooking and flavouring food in many ways. Here are some:

• Frying – pan frying, deep frying
• Oven – baking, roasting
• Searing – grilling, sautéing, stir-frying, braising
• Cold serving – salad dressings, drizzling, garnishing, marinades, sauces, dips, mayonnaise

So, which are the best oils for cooking and use in the kitchen?  To begin with let´s remember the types of fats that are present in oils and fats.

TYPES OF FATS

Fats are either saturated or unsaturated, and most foods with fat have both types. But usually there is more of one kind of fat than the other. The types of fats are:

Saturated fat

Saturated fat is solid at room temperature, which is why it is also known as “solid fat.” It is mostly in animal foods, such as milk, cheese, and meat. Poultry and fish have less saturated fat than red meat. Saturated fat is also in tropical oils, such as coconut oil, palm oil, and cocoa butter. You’ll find tropical oils in many snacks and in non-dairy foods, such as coffee creamers and whipped toppings. Foods made with butter, margarine, or shortening (cakes, cookies, and other desserts) have a lot of saturated fat. Saturated fat can raise your cholesterol. USDA Dietary Guidelines, the American Heart Association as well as general medical and nutritional advice recommend limiting your intake of saturated fats and opting for monounsaturated and polyunsaturated fats instead.

Trans fat

This is a fat that has been changed by a process called hydrogenation. This process increases the shelf life of fat and makes the fat harder at room temperature. Harder fat makes crispier crackers and flakier pie crusts. Trans fat can raise your cholesterol, so eat as little trans fat as possible. You’ll find it in: processed foods, snack foods, such as chips and crackers, cookies, some margarine and salad dressings and foods made with shortening and partially hydrogenated oils. Most trans fats raise your LDL cholesterol (the “bad” cholesterol) while lowering your HDL cholesterol (the “good” kind that helps keep blood vessels clear). According to the American Heart Association, trans fats increase your risk of developing heart disease and stroke and are associated with a higher risk of type 2 diabetes.

Unsaturated fat

Unsaturated fat is liquid at room temperature. It is mostly in oils from plants. If you eat unsaturated fat instead of saturated fat, it may help improve your cholesterol levels. Try to eat mostly unsaturated fats. Monounsaturated fat and polyunsaturated fat are types of unsaturated fat.

Monounsaturated fat: This fat is found in avocado, nuts, olive oil and vegetable oils, such as canola and peanut oils. Eating foods that are high in monounsaturated fats may help lower your “bad” LDL cholesterol. Monounsaturated fats may also keep “good” HDL cholesterol levels high.

Polyunsaturated fat: This type of fat is mainly in vegetable oils such as safflower, sunflower, sesame, soybean, and corn oils. Polyunsaturated fat is also the main fat found in seafood. Eating polyunsaturated fat in place of saturated fat may lower LDL cholesterol. The two types of polyunsaturated fats are omega-3 and omega-6 fatty acids.

• Omega-3 fatty acids are found in foods from plants like soybean oil, canola oil, walnuts, and flaxseed. They are also found in fatty fish and shellfish as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Salmon, anchovies, herring, sardines, trout, mackerel, nuts, seeds and algae are high in EPA and DHA.
• Omega-6 fatty acids are found mostly in liquid vegetable oils like soybean oil, corn oil, and safflower oil.

The total fat content includes saturated, trans fat, monounsaturated and polyunsaturated fat.

All  cooking oils are composed of three different types of fatty acids: monounsaturated fats, polyunsaturated fats and saturated fats. Each oil is categorized based on which type of fatty acid is the most prominent in it. For example, olive and canola oils are considered mostly monounsaturated fat, while corn and soybean oils contain mainly polyunsaturated fat. Coconut oil is predominantly saturated fat.

COMPARING SOME COMMON COOKING OILS

Here is a look at 10 popular cooking oils.

Fats and oils exposed to high heat can form various harmful compounds. This is particularly true of oils that are high in polyunsaturated fats, including most vegetable oils like soybean and canola. If we want to minimize our exposure to potentially harmful and carcinogenic compounds, we should only cook with fats and oils that are stable at high heat.

Smoke Point & Oxidative Stability

There are two properties of cooking oils that matter most when determining their stability under high heat:

• Smoke point: The temperature at which the fats begin to break down and turn into smoke.
• Oxidation stability: Oxidation is a chemical reaction that occurs with a combination of the oil and oxygen. The rate of oxidation is accelerated by high temperatures, water, acids and catalysts. When heated, oils breakdown and create by-products such as polar compounds. These have been consistently associated with negative health outcomes.

When cooking oils are exposed to heat, oil degradation occurs, and by-products are produced (free fatty acids, secondary products of oxidation, polar compounds). Some by-products of oil degradation have adverse effects on health. The smoke point of an oil is believed to be correlated with the safety and stability under heat, although technical evidence to support this is limited. The aim of a recent study⁵ was to assess the correlation between an oil’s smoke point and other chemical characteristics associated with stability / safety when heating. A number of common cooking oils were heated up to 240^oC and exposed to 180^oC  for 6 hours (the standard deep-frying temperature), with samples assessed at various times, testing smoke point, oxidative stability, free fatty acids, polar compounds, fatty acid profiles and UV coefficients.

The results are summarized in the table below.

Correlation between final polar compounds after heating and initial oil parameters

Extra Virgin Olive Oil (EVOO) yielded low levels of polar compounds and oxidative by-products, in contrast to the high levels of by-products generated for oils such as canola oil. EVOO’s fatty acid profile and natural antioxidant content allowed the oil to remain stable when heated (unlike oils with high levels of poly-unsaturated fats (PUFAs) which degraded more readily). This study reveals that, smoke point does not predict oil performance when heated. Oxidative stability and UV coefficients are better predictors when combined with total level of PUFAs. Of all the oils tested, EVOO was shown to be the oil that produced the lowest level of polar compounds after being heated closely followed by coconut oil.

KEY FINDINGS OF THE STUDY

The key findings of the study:

• Extra Virgin Olive Oil was found to be the safest and most stable oil to cook with, followed by Coconut Oil.
• The top performing oils produced the least number of polar compounds after heating.
• Production of polar compounds was more pronounced for refined oils which are higher in polyunsaturated fat such as Canola oil, Grape Seed oil and Rice Bran Oil.
• An oil’s smoke point correlated poorly with the likelihood of the oil to break down and form harmful compounds when heated.

BOTTOM LINE

• The key factors that correlated strongly with how likely an oil is to break down and form harmful compounds when heated are:
  • The more refined an oil is, the more likely it is to break down. (Due to the refining process, refined oils already contain secondary products of oxidation prior to cooking.)
    • RECOMMENDATION: use cooking oils that have undergone minimal processing / refining, to minimize exposure to harmful compounds.
  • The less natural antioxidants an oil contains, the more likely it is to break down and form harmful compounds.
    • RECOMMENDATION: use cooking oils that have high levels of antioxidants, as this increases the oils resistance to break down.
  • The more polyunsaturated fat in the oil, the more likely it is to break down and form harmful compounds (oxidation occurs more readily with multiple double bonds present in the fatty acids).
    • RECOMMENDATION: use cooking oils that have lower levels of polyunsaturated fat, to reduce the level of oil breakdown when heated.
• OVERALL, look for oils that:
  • are produced naturally and have not undergone refining
  • contain high levels of stable monounsaturated fat and low levels of polyunsaturated fat and
  • contain high levels of natural antioxidants.

Personal taste and flavour preferences as well as traditions influence the types of oils we use for cooking. However it is important to bear in mind the suitability of each oil we choose for each use and to consider the health implications.

There are many scientific studies and industry articles on the subject available on the Web. A number of these are listed below as well as on our Resources page. For more detailed information on EVOO, go to: Extra virgin olive oil´s (EVOO) health and medical benefits.

There is more to our long term health than the oil we use obviously – although it is a very important component. A sound life style and diet also make a huge impact on our overall health. The Japanese and Mediterranean diets are renowned for their effects on health and medical condition as well as longevity. People living in Japan and the Mediterranean basin have statistically longer life spans and also suffer less from a number of well-known medical conditions.  See, for example, Spain´s Mediterranean diet.

REFERENCES

1. Healthwise, “Types of fats”, 7Nov18, HealthLink British Columbia
2. Bruno A, “10 of the Healthiest Cooking Oils, Explained”, 19Aug19, Condé Nast Self.
3. Nierenberg C, “The Science of Cooking Oils: Which Are Really the Healthiest?”, 21Jul17, Future US, Inc.,LiveScience.
4. Gunnars K, “Is Olive Oil a Good Cooking Oil? A Critical Look”, 23Nov18, Red Ventures Co., Healthline Media.
5. De Alzaa F, Guillaume C & Ravetti L, “Evaluation of Chemical and Physical Changes in Different Commercial Oils during Heating”, 5May18, Acta Scientific Nutritional Health 2.6 (2018): 02-11.
6. Dietitian Connection, “Cracking the myth behind cooking with Extra Virgin Olive Oil”, 27Sep18, Dietitian Connection.
7. DGF, “Physical properties of fats and oils”, FachGruppen, Deutsche Gesellschaft für Fettwissenschaft e.V. (DGF).
8. Molina-Garcia, L., Santos, C.S.P., Cunha, S.C. et al. “Comparative Fingerprint Changes of Toxic Volatiles in Low PUFA Vegetable Oils Under Deep-Frying”, Journal of the American Oil Chemists´ Society, 94, 271–284 (2017).