Healthy vs Unhealthy Oils: Which Cooking Oils Should You Choose?

Cooking oils can be confusing. Olive oil is often promoted as healthy, coconut oil has had its moment in the spotlight, and seed oils are regularly criticised online. So which oils are actually better choices?

Quick answer: For everyday health, the type of fat matters. Oils rich in unsaturated fats — including olive, canola, sunflower, peanut and soybean oils — can be good choices as part of a balanced diet. Saturated fats, including those found in coconut and palm oil, are best limited, while industrial trans fats should be avoided as much as possible.

The way you store and use an oil matters too. Heat, oxygen and light can gradually affect oil quality, so it makes sense to choose an appropriate oil for the cooking method and store it properly.

What makes an oil healthy or unhealthy?

It is more useful to look at an oil’s overall fatty-acid profile than to label every oil simply “good” or “bad”. Dietary fats include monounsaturated, polyunsaturated, saturated and trans fats.

Monounsaturated and polyunsaturated fats are generally the preferred fats for heart health. Olive oil is rich in monounsaturated fat, while oils such as canola and sunflower provide unsaturated fats. Saturated fat is found in larger amounts in foods such as butter, coconut oil and palm oil.

Replacing foods high in saturated fat with foods containing unsaturated fats can help improve blood cholesterol levels and support cardiovascular health.

Are seed oils unhealthy?

There is a lot of discussion online about seed oils such as canola, sunflower and soybean oil. Claims that all seed oils are inherently “toxic” are not supported by mainstream dietary guidance.

These oils contain unsaturated fats, and reputable health organisations include them among suitable choices for replacing fats that are higher in saturated fat. Rather than fearing one ingredient, it is more useful to consider the quality of your whole diet and how the oil is being used.

What happens when cooking oils oxidise?

Oxidation is a chemical process that can occur when fats react with oxygen. Heat, light, air and prolonged storage can speed up changes in an oil. Over time, an oil may develop an unpleasant smell or flavour and become rancid.

High-temperature cooking and repeatedly heating the same oil can also cause chemical changes. This does not mean that every food cooked in oil becomes harmful, but it is sensible to avoid repeatedly overheating or reusing cooking oil.

If an oil smells stale or rancid, discard it rather than trying to use it up.

Is fried food always unhealthy?

An occasional fried food can fit within an otherwise balanced diet. The bigger concern is a dietary pattern that regularly includes deep-fried takeaway foods, pastries and highly processed snack foods.

These foods can contribute substantial kilojoules, saturated fat, salt and, depending on the product and how it was made, trans fat. For everyday cooking, grilling, baking, steaming, roasting and lightly sautéing foods can make it easier to build a balanced diet.

What are trans fats?

Trans fatty acids can occur naturally in small amounts in some animal foods and can also be produced during food manufacturing. Industrial trans fats have traditionally been associated with partially hydrogenated oils.

Trans fats are particularly undesirable because they can raise LDL cholesterol. Food Standards Australia New Zealand reports that average trans-fat intake in Australia is relatively low, but checking ingredient lists is still useful when choosing packaged foods.

Look for terms such as partially hydrogenated oil or hydrogenated vegetable fat on ingredient lists.

What are the best oils for everyday cooking?

There is no single oil that everyone must use. Useful everyday choices include extra virgin olive oil, canola oil, sunflower oil, peanut oil and soybean oil. These provide mainly unsaturated fats and can suit different cooking methods.

What about coconut oil?

Coconut oil is often marketed as a health food, but it is high in saturated fat. That does not mean you can never eat it. However, it is not necessary to replace olive oil or other unsaturated oils with coconut oil for health reasons.

If you enjoy coconut oil for its flavour, consider it an occasional choice rather than your only everyday cooking oil.

How should you store cooking oils?

Good storage can help maintain oil quality. Keep oils tightly sealed and away from excessive heat, air and direct sunlight. A cool, dark cupboard is suitable for many oils. Follow the storage instructions on the bottle and pay attention to the best-before date.

Buying a bottle size that you will realistically use can also help prevent oil sitting open for a long period.

How can you choose healthier fats?

You do not need to eliminate fat from your diet. Fat is an essential nutrient, and the quality of the fat you eat is important.

Practical choices include using unsaturated oils instead of butter or other fats high in saturated fat, eating nuts and seeds, including avocado and olives, and eating fish if it suits your diet. At the same time, limit highly processed and deep-fried foods rather than focusing on one oil as the cause of poor health.

When comparing packaged foods, use the nutrition information panel and ingredient list. Comparing similar products per 100 g can make it easier to identify options lower in saturated fat.

Frequently Asked Questions About Cooking Oils

Is olive oil healthy?

Olive oil is rich in monounsaturated fat and is widely recommended as a healthy source of dietary fat. It can be used for dressings and everyday cooking.

Are seed oils bad for you?

Current mainstream nutrition guidance does not support the claim that seed oils are inherently harmful. Canola, sunflower and soybean oils provide unsaturated fats and can form part of a healthy eating pattern.

Should I throw cooking oil away after one use?

You do not necessarily need to discard every oil after a single use, but repeatedly heating and reusing frying oil can degrade its quality. For home cooking, avoid repeatedly overheating oil and discard oil that has developed an unpleasant smell, flavour or appearance.

Is coconut oil healthier than olive oil?

Coconut oil contains considerably more saturated fat. For everyday heart health, dietary guidance generally favours oils rich in unsaturated fats, such as olive oil.

Does frying create trans fats?

Small amounts of trans fats can form during high-temperature cooking, but industrially produced partially hydrogenated oils have historically been a more important source. Limiting deep-fried and highly processed foods remains sensible.

A practical approach to healthy fats

Nutrition does not need to revolve around fear of individual foods. I prefer to look at the whole dietary pattern: what someone eats most of the time, how foods are prepared and whether those choices suit the individual.

For most people, choosing predominantly unsaturated fats, limiting saturated fat and keeping highly processed and deep-fried foods as occasional choices is a practical place to start.

About Mick Jordan

Mick Jordan is a naturopath and Sports and Remedial Massage Therapist based in Brighton, Melbourne, with more than 30 years’ experience in natural therapies. He has a particular interest in nutrition, digestive health, sports performance and recovery, and takes an individual approach to helping clients improve their health and wellbeing.

This article provides general health information and is not a substitute for personalised medical or dietary advice. If you have high cholesterol, cardiovascular disease, a medical condition or specific dietary needs, speak with an appropriately qualified health professional.