Most people enjoy fried foods. However, the frying process causes chemical changes in the food and oil. That’s why using just any oil is not best. For frying, you need to choose oils that are resistant to high-temperature cooking and have a favorable fatty acid profile.

Oils contain different types of fatty acids, including saturated, monounsaturated (MUFA), polyunsaturated (PUFA), and trans fatty acids. It is advised to consume unsaturated fats (MUFA and PUFA) instead of saturated and trans fats.

However, oils with higher MUFA and lower PUFA content are preferable for frying. This is because frying turns PUFA into trans fats and other harmful compounds (such as lipid oxidation products), which aren’t good for your health. So less PUFA means fewer harmful compounds.

Besides the oil’s fatty acid profile, its antioxidant content and smoke point are also important. The smoke point is the temperature at which oil starts smoking, and in the process, it produces harmful compounds. On the other hand, a high antioxidant profile in oil makes it more resistant to creating those harmful compounds.

Olive oil is the primary cooking oil in the Mediterranean diet and is also used for frying. It contains more MUFA than PUFA, making it less likely to produce harmful compounds. Extra virgin olive oil contains 69.2% MUFA, 9.07% PUFA, and 15.4% saturated fats.

Olive oil also has a good smoking point of 410 degrees Fahrenheit (210 degrees Celsius) for frying. However, virgin olive oil has a lower smoking point at 320-338 degrees Fahrenheit (160-170 degrees Celsius). Additionally, olive oil is rich in antioxidants, which increase the oil’s resistance to creating harmful compounds.

Frying increases the oil’s free fatty acid content (FFA), indicating decreased oil quality because these free fatty acids can turn into harmful compounds through a process called oxidation. A study looked at FFA generation in olive, canola, and peanut oils during frying. Potato chips were deep-fried at 347 degrees Fahrenheit (175 degrees Celsius) for 28 hours in 30-minute frying cycles. FFA in oils increased as frying was prolonged, and the highest FFA content was seen in canola oil, with the lowest in olive oil.

Avocado oil contains 70.6% of MUFA, 13.5% of PUFA, and 11% of saturated fats. It also has a high smoke point above 482 degrees Fahrenheit (250 degrees Celsius). A study also showed that avocado oil has similar stability to olive oil when exposed to heat of 356 degrees Fahrenheit 180 degrees Celsius) for nine hours.

A study compared changes occurring in avocado, soybean, sesame seed, and almond oil while frying potato chips. Total antioxidant capacity was still the highest in avocado oil after five frying cycles compared to other oils.

Rice bran oil could be another alternative for deep-frying foods. It has a high antioxidant capacity and a smoke point of 449 degrees Fahrenheit (232 degrees Celsius). Rice bran oil consists mostly of MUFA (39.3%), followed by PUFA (35%) and saturated fats (19.7%).

Rice bran oil can also be blended with other oils. A study looked at the blends of rice bran oil with olive oil, sunflower oil, and palm oil. Its combination with olive oil and palm oil was found to be the most resistant to deterioration (most stable).

Peanut oil contains 57.1% MUFA, 19.9 % PUFA, and 16.2 % saturated fats. It also has a high smoke point of about 446 degrees Fahrenheit (230 degrees Celsius). 

A study compared the stability of four selected oils to heat: peanut, canola, soybean, and corn oil. The harmful compounds was highest in corn oil and lowest in peanut oil.

Interestingly, highly refined peanut oil is safe for people with peanut allergies. However, cold-pressed, expelled, and extruded peanut oils still have allergens.

Although canola oil has high MUFA (63.3%), low PUFA (28.1%), and saturated fats (7.36%), deep frying with canola oil can produce an undesirable taste. However, canola oil blends with high oleic acid are more heat-resistant. When buying canola oil, you can check for labels that state it contains high oleic acid for deep frying. 

A study compared the changes in canola oil, corn oil, peanut oil, palm oil, and sunflower oil during the frying of French fries. The results showed that peanut oil has the lowest harmful compounds and good antioxidant stability, followed by canola oil. In contrast, sunflower, corn, and soybean oil were the least stable and exhibited the highest deterioration.

When you’re choosing oil for frying, consider:

• Oil fatty acid profile: Oils with high PUFA cause the production of more harmful compounds when heated, compared to oils with high MUFA or saturated fat. Although saturated fats (such as coconut oil) are stable in heat, it’s still not recommended to use high saturated fat for frying due to its negative health effects. This is because fried food also absorbs the oil.
• Smoke point: The smoke or smoking point is the temperature at which oil begins to evaporate. This process causes chemical changes in the oil, resulting in an undesirable appearance and taste and the formation of harmful compounds. Therefore, a high smoke point is more desirable for frying.
• Processing method: Processing methods also affect oil stability by changing antioxidant content. Mechanical processes, as used in producing extra virgin olive oil, preserve the oil’s natural antioxidant content. However, refined oils (that may be bleached or heated) lose some antioxidants, so they’re generally added later as additives.

Oxygen is needed to produce lipid oxidation products; therefore, shallow frying causes more lipid oxidation products. These compounds can cause DNA and cell damage, leading to health conditions.

For shallow frying, using MUFA-rich fats is still more suitable. A study compared lipid oxidation products in avocado oil, extra virgin olive oil, corn oil, and soybean oil in cycles of shallow frying. As expected, PUFA-rich oils (corn and soybean oil) resulted in the highest generation of lipid oxidation products compared to avocado and olive oil.

For shallow frying, you can also use other oils with high MUFA and low PUFA and saturated fats, such as canola, rice bran, almond, peanut, and olive oil.

Oil’s fatty acid composition changes when exposed to heat. Frying reduces PUFA and increases saturated and trans fatty acids. Therefore, oils with high PUFA content are not suitable for frying. High PUFA oils include:

• Corn oil: 52.9% PUFA, 13.4% saturated fats
• Sunflower oil: 62.4% PUFA, 9.4% saturated fats
• Sesame oil: 41.2% PUFA, 16.9% saturated fats
• Soybean oil: 57.6% PUFA, 14.9% saturated fats
• Safflower oil: 79.1% PUFA, 9.3% saturated fats
• Grape seed oil: 74.9% PUFA, 10.4% saturated fats

A study looked at changes in coconut, olive, rapeseed, and sunflower oil composition when heated. The results showed that coconut oil was the most resistant, and sunflower oil was the least resistant to heat. Although saturated fats are stable at high temperatures, their high consumption is associated with an increased risk of heart disease. Therefore, it’s not recommended to use oil with high saturated content regularly. Oils high in saturated fat include:

• Coconut oil: 18.2% PUFA, 92.1% saturated fats
• Butter: 2.52% PUFA, 45.6% saturated fats

If you’d like to use these oils, you can use them with little to no heating, such as adding them to salad dressing.

Deep frying foods generates harmful compounds and often lowers both the oil’s and food’s nutritional quality. You can use high MUFA and low PUFA oils such as olive oil, avocado oil, rice bran oil, and peanut oil for frying. However, regardless of which oil you use, the most important thing is to avoid reusing oils to reduce the generation of harmful compounds.