Discover our full range of health benefit guides, including how much fat should I eat each day and our helpful guide on saturated fat.
The science bit
Oils and fats are made up of chains of smaller fatty acids, when these chains are held together by single bonds, they are known as “saturated” fats; when double bonds are in place, they are referred to as “unsaturated”.
There are three types of fatty acid chains – short, medium and long. It’s the length of these chains that determine how our bodies metabolise them and how efficient they are at providing us with energy.
What’s the issue with heating oils?
Some oils are better suited to high temperature cooking than others, and that’s because oils change structurally when they’re heated. When a recipe requires us to fry food, we expose the oil to an increase in temperature, additional moisture from the food as well as oxygen in the air – all three of these factors trigger chemical reactions, which cause changes that are likely to impact the oil, including how it tastes.
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How much an oil changes will depend on the temperature used, how long you cook with it, the oil you’ve chosen and the presence or not of any protective antioxidants, these might be nutrients like vitamin E or natural compounds called polyphenols, which are found in unrefined oils, like virgin olive oil.
What is the ‘smoke point’?
An oil’s ‘smoke point’ is the temperature at which it starts to burn, and as its name suggests you’ll see smoke rising from the pan and filling your kitchen. When this happens, the oil has started to break down, and it’s likely to form harmful compounds such as aldehydes. If you consume oil that’s been handled like this on a regular basis, it may contribute towards the risk of diseases, like cancer and heart disease.
Knowing the smoke point of an oil may help you select the oil most suited to the task you have in mind. However, it’s worth bearing in mind that factors affect the smoke point – fresher oil has a higher smoke point, and as soon as you combine oil with the food you’re cooking, you will reduce its smoke point because it will have started to react with moisture from the food.
As a general rule, the more tightly packed the fatty acids in an oil, the more stable the oil is for cooking. This means saturated fats and MUFAs are more likely to be able to cope with high temperatures and as a result less likely to change.
*Please note the smoke points given are guidelines only. Values vary depending on how fresh the oil is, how refined it is and its fatty acid composition. Other factors which influence smoke point include the volume of oil used, the surface area of your pan, whether the oil is in contact with a food (because this adds moisture), the degree of exposure to air and light and the speed at which the temperature increases.
Selecting an oil
One of the first things to consider is how the oil has been processed because this will influence how it performs during cooking and ultimately how healthy it is. Labels stating ‘virgin’ or ‘extra virgin’ suggest the oil has been minimally processed, without the use of chemicals. ‘Cold-pressed’ tells us the oil has been extracted using no heat and as a result nutrients and enzymes will remain in the finished product. Oils carrying these descriptions are often referred to as unrefined oils.
Refined oils, on the other hand, are processed using chemicals. They may have a higher tolerance for heat because the refining process removes nutrients, enzymes and other sensitive compounds, which are more likely to burn. However, they may contain chemical residues and won’t retain their natural nutrients or enzymes, although they will benefit from a longer shelf life.
What are the healthiest cooking oils?
1. Olive oil
A key component of the Mediterranean diet, olive oil is made from the juice of the olive fruit and is known for its many health benefits, from protecting against heart disease to reducing the risk of type 2 diabetes.
Olive oil is a MUFA, which means it only has one double bond and this makes it more resistant to the changes incurred when cooking. In fact, oleic acid the predominant MUFA found in olive oil is thought to be 50 times less likely to oxidise (combine with oxygen) than linoleic acid, which is the predominant PUFA found in vegetable oils like sunflower and corn oil. If you opt for the virgin olive oil, you’ll also benefit from the protective antioxidant properties of numerous polyphenols and nutrients like vitamin E.
Smoke point:
- Refined – 200-240C (465F)
- Unrefined – 160-190 C (375F)
Verdict: For temperatures up to 180-190C virgin olive oil is a great choice. Better still, extra virgin olive oil (EVOO), which is made from pure, cold-pressed olives, is reported to have the lowest oxidation rate of any cooking oil. This makes EVOO an ideal choice when cooking at home as long as you don’t overheat it. If you do a lot of frying and are on a tight budget, you might opt for a refined olive oil, and replenish regularly when using prolonged cooking methods.
2. Avocado oil
Pressed from the fruit of the avocado tree, this oil is often likened to olive oil. It’s rich in MUFAs, especially oleic acid, which increases the oil’s stability at high temperatures. There are numerous studies to support its many health benefits, including those for the cardiovascular system. One aspect in which avocado beats olive oil is in its smoke point, which is higher for both the refined and unrefined versions.
Smoke point:
- Refined – 270C (520F)
- Unrefined – 190-205C (400F)
Verdict: Although avocado oil has multiple uses, including frying, sautéing, browning and roasting, it’s a comparatively expensive oil, which may limit its use in day-to-day cooking. Being a subtle-flavoured oil, it allows the other ingredients in your recipe to shine through.
3. Rapeseed oil
This general-purpose oil has half the saturated fat content of olive oil, is high in MUFAs including oleic acid, and contains PUFAs with a favourable omega-6 to omega-3 fatty acid ratio (2:1). Rapeseed oil also has the highest polyphenol content of the seed oils, although it’s worth saying that the quality of the oil is affected by a number of factors, including harvesting, storage and the extraction process.
In some countries, the term rapeseed oil is used to refer to the type of oil employed for industrial use, with canola oil being the edible cooking oil. However, in the UK, ‘rapeseed oil’ is used interchangeably for both and the term ‘canola’ is rarely used.
Smoke point:
- Refined – 204-246C (475F)
- Unrefined – 204 -230C (450F)
Verdict: A useful choice when a neutral flavoured oil with a good smoke point is needed such as sautéing, grilling and baking. When selecting rapeseed oil choose a cold-pressed version because it has a superior fatty acid profile and a higher level of protective polyphenols, carotenoids and vitamin E.
4. Ghee (clarified butter)
Ghee is made by simmering butter – moisture evaporates away, the milk solids are removed and what is left is a clear golden oil. The low level of moisture combined with the higher saturated fat content gives ghee its high smoke point and long shelf life. It is also free of lactose and the milk protein casein making it a suitable option for those with lactose intolerance or milk allergy.
Studies comparing the use of ghee versus vegetable oils at temperatures of 180C suggest ghee creates fewer damaging acrylamides than vegetable oils.
Smoke point:
- Refined – 250C (485F)
- Unrefined – 232C (450F)
Verdict: Its high smoke point makes ghee suitable for high temperature cooking including roasting and frying. However, for baking, butter with its sweeter, milder flavour is a better choice unless you have a lactose intolerance or dairy allergy.
5. Coconut oil
Although coconut is referred to as an oil, it’s actually a fat that melts from solid to liquid at just above room temperature. It has a distinctive flavour and texture which creates a unique mouthfeel and may not suit all dishes. Composed predominantly of saturated fat (92%), coconut oil has received a lot of attention because of its relatively high level of medium chain fatty acids.
Coconut oil, because of its high saturated and low unsaturated fat content, is more resistant to oxidation than the unsaturated oils like sunflower and olive oil. However, despite this, it has a relatively low smoke point, which is why its use in deep fat or prolonged frying may lead to the production of harmful substances, including polycyclic aromatic hydrocarbons.
Smoke point:
- Refined – 232C (450F)
- Unrefined 171C – 175C (350F)
Verdict: Choose virgin coconut oil, because the extraction methods used ensure higher levels of antioxidants, including vitamin E and protective phytonutrients. This oil is best used sparingly in the diet because of its high saturated fat content, lack of essential fatty acids including linoleic and linolenic fatty acids, and its relatively low smoke point. Keep for sautéing and baking.
6. Red palm oil
Red palm oil is derived from the fruit of the oil of the palm tree but is not to be confused with palm kernel oil which comes from the seed of the same plant. The latter is widely used in processed foods, has been stripped of its antioxidant properties and has a yellowish-white colour. Red palm oil, on the other hand is mildly processed and retains its carotenoid and vitamin E content, hence its red colour – these nutrients are thought to account for why red palm oil may reduce the risk of atherosclerosis and high blood pressure. That said red palm oil is high in saturated fat although more of which are the medium chain variety and it has no trans fats.
Smoke point:
- Refined – 232C (450F)
- Unrefined – 232C (450F)
Verdict: Red palm oil is less refined than palm oil and retains more of its protective nutrients making it a healthier option. Being high in saturated fat (although lower than butter) red palm oil is stable at high temperatures making it a useful choice for frying and roasting
7. Sunflower oil
Sunflower oil is low in saturated fat, and depending on the type you choose may be high in the PUFA, linoleic acid or high in the MUFA, oleic acid. A high oleic acid sunflower oil is considered more stable for cooking.
One of the main downsides with this seed oil is that it generates more damaging aldehydes than olive, rapeseed or coconut oils, regardless of the cooking method employed. For this reason, it’s recommended for low-heat cooking methods only.
Smoke point:
- Refined – 225-230C (440F)
- Unrefined – 107-160C (320F)
Verdict: Choose a high oleic acid sunflower oil and use for low-heat cooking methods, such as baking.
8. Sesame oil
Commonly used in Asian cooking, sesame oil is made from raw, pressed sesame seeds. It has a neutral flavour and a relatively high smoke point. Sesame oil is rich in active compounds that have anti-inflammatory and antioxidant properties.
Smoke point:
- Refined – 210C (410F)
- Unrefined – 177C (350F)
Verdict: Sesame oil works well for sautéing, roasting and general-purpose cooking. However, because of its intense nutty flavour keep toasted sesame oil for drizzling or dressing.
9. Groundnut (peanut) oil
Also known as peanut or arachis oil, groundnut oil tends to have a mild flavour. It’s high in MUFAs (50%), including oleic acid, and in its unrefined form is a good source of vitamin E. Being made up of 30% PUFAs means groundnut oil is prone to oxidation, although it does boast a relatively high smoke point.
Smoke point:
- Refined – 225-230C (450F)
- Unrefined – 160C (320F)
Verdict: Groundnut’s mild, nutty flavour and high smoke point makes it well suited for stir frying, however, its high PUFA content suggests cooking times should be kept short.
10. Grapeseed oil
Produced from the seeds of grapes, this oil is high in poly-unsaturated fats including linoleic acid and vitamin E. Few studies have been conducted to assess the health implications of grapeseed oil, although it may have benefits for cardiovascular health and insulin management.
Unless the product specifically states how it was processed you should assume it was extracted using chemical solvents.
Smoke point:
- Refined – 215C (420F)
- Unrefined – 176C (350F)
Verdict: With a moderately high smoke point and a neutral flavour grapeseed oil may be used for sautéing and baking.
11. ‘Vegetable’ oil
One of the most common oils used for cooking this is typically a blend of refined oils with a neutral flavour – common oils used include rapeseed, corn and soya. This oil is widely used in food manufacturing, take-away outlets as well as in the domestic kitchen.
The health effects of these oils vary depending on which plants they were extracted from, how they were processed and which fatty acids they contain. Many of these oils are extracted using chemical solvents and may contain other additives such as E900, an anti-foaming agent that prevents hot oil from bubbling when frozen foods are added.
Being vegetable in origin, this oil is high in poly-unsaturated fats and most notably the omega-6 variety. This type of fat is susceptible to oxidation so it doesn’t store well, is easily damaged at high temperatures and by repeated use.
Smoke point:
- Refined – 204-260C (400-500F)
- Unrefined – 176C (350F)
Verdict: Refined vegetable oils may be suitable for single use frying, sautéing as well as baking.
So, what is the healthiest oil?
The oil you choose will depend on the frying time, temperature and whether you want a neutral or flavourful oil. Oils rich in PUFAs, like sunflower and other vegetable oils, generate higher levels of oxidative products called aldehydes than those oils rich in saturated fat, like coconut oil, or MUFAs, like olive oil.
Of all the options listed above, olive oil performs well and is considered superior to most vegetable oils, although you should still aim to keep heating time to a minimum. Using olive oil also improves the quality of fat in the diet, because it has a healthier profile, being rich in MUFAs and low in saturated fats.
For those following a vegan or plant-focused diet, cold-pressed rapeseed oil makes a good choice because of its high levels of the essential fat called alpha-linolenic acid (ALA), which is an important omega-3 fatty acid.
As well as using the right oil for the job, be sure to store your oil in a cool, dry place, out of direct sunlight and preferably in a dark glass rather than plastic bottle. Buy in small quantities so you are regularly replenishing and never re-use.
This article was reviewed on 13 February 2023 by Kerry Torrens, registered nutritionist.
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Kerry Torrens BSc. (Hons) PgCert MBANT is a Registered Nutritionist with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food. Find her on Instagram at @kerry_torrens_nutrition_
https://www.instagram.com/kerry_torrens_nutrition_/?hl=en
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