Updated 10th November 2022

Cooking oils: What to use and when

We use it to stir fry, roast, and even to make dressings. Cooking oil is a staple in our kitchens, but the health benefits and risks make this oil one the most controversial ingredients we regularly use.

The health conscious among us could be tempted to switch from traditional oils to trendy alternatives, but with so many options, it can be difficult to figure out which oils are best for you.

In today’s short episode of ZOE Science & Nutrition, Jonathan and Sarah ask: What cooking oils should you use and when? 

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Studies referenced in today's episode:

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Transcript

[00:00:00] Jonathan Wolf: Hello and welcome to ZOE Shorts, the bite-sized podcast where we discuss one topic around science and nutrition. I'm Jonathan Wolf, and as usual, I'm joined by Dr. Sarah Berry. And today's subject is cooking oils. 

[00:00:18] Sarah Berry: From sunflower to soya bean to olive and coconut oil. There are loads of oils out there. But it's tricky to know which ones are best to cook with. Plus, more and more people are searching 'cooking oil bad' on Google.  

[00:00:34] Jonathan Wolf: So, wait Sarah, are you saying cooking oils are bad for us?  

[00:00:37] Sarah Berry: It's a bit more complicated than that, Jonathan. 

[00:00:40] Jonathan Wolf: Okay, I'm intrigued. Let's get into it. 

[00:00:47] Sarah Berry: Let's imagine a typical home kitchen. You might picture some vegetables roasting in the oven, or maybe a stir fry sizzling in a hot pan.  

[00:00:55] Jonathan Wolf: It sounds yummy. So what oils would they typically be used to make this feast?  

[00:01:01] Sarah Berry: So chances are it's gonna be vegetable oil and the most common vegetable oil is rapeseed oil, as it's called in the UK, or canola oil as it's called in the US. Otherwise, it's often a blend of vegetable oil such as sunflowers, soybeans, and other oils.  

[00:01:17] Jonathan Wolf: And we did some research with a friend of Sarah's who is a world expert on this, and there are a lot of other popular oils. So there's sunflower oil, there's olive oil, coconut peanut, and sesame. And in case you are wondering, apparently the french fries at McDonald's are cooked in a blend of rapeseed and sunflower oil at ratios to make the oil as stable as possible. And hopefully Sarah you will explain that a bit more in a minute. 

[00:01:43] Sarah Berry: I will, but that ratio is top secret, so I can't divulge that information, what I can divulge is that all the fats and oils that we cook with and that we consume are made up of a mixture of saturated and unsaturated fats and different oils have different proportions of these types of fats. 

For example, most vegetable oils such as rapeseed which is also like I said called canola oil and sunflower have a lot of these healthy unsaturated fats. Whilst tropical oils such as palm oil and coconut oil tend to have an equal proportion of saturated fats and unsaturated fats, and depending on the type of saturated fat in these tropical oils, these oils tend to be less healthy for us. 

But Jonathan, it's really important to think about what happens to the oil when we cook with it.  

[00:02:30] Jonathan Wolf: And I think one thing that people often ask about is this thing called the oil ‘smoke point’, right Sarah? I understand that's the point when an oil begins to burn and smoke, as I have definitely experienced when cooking, getting distracted and you look back and you know the smoke is pouring towards the fan. 

So if you heat the oil near to or past that point, the taste of the oil can change and I think some of the other nutrients in the oil can also be degraded.  

[00:02:59] Sarah Berry: Yeah, that's correct, Jonathan. And I think that the way I often think about this is according to three important factors that affect an oil when you cook with it, which change its taste, but also change potentially some of the health effects. 

And these three factors are moisture, air, and temperature, These can change the structure of the oil as well as oxidize the oil. And it's these changes in structure and these changes in oxidation that can have potentially unfavorable health effects. But how much fat changes during cooking is dependent on your cooking method. 

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For example, the temperature at which you're cooking, how long you're cooking it for, and also really, really importantly, whether you are repeat frying. So reusing the oil as well. As a general rule of thumb, it's good to pick oils that have a higher smoke point. It's good to avoid heating above 170 degrees centigrade or also 340 degrees Fahrenheit and avoid this repeated use of the same oil for frying as you might use, for example, in deep frying. 

[00:03:58] Jonathan Wolf: So oils that have a high smoke point and therefore meet those criteria. Include rapeseed, canola, and sunflower blends. What about virgin olive oil? So that doesn't have such a high smoke point, and so I think various people have said that you shouldn't cook with it, but I think it's more complex than that. 

[00:04:20] Sarah Berry: Yeah, it's a real balancing act because oils like extra virgin olive oil have more of these bioactive nutrients such as polyphenols. Which are special because they have antioxidant properties. It means that they reduce the impact of free radicals caused by oxidation. But the flip side of this is that they're more sensitive to heat because of their lower smoke point. 

And what happens is when you heat an oil, like extra virgin oil, it can lose some of its benefits. And so what can happen is if it's exposed to light and air for a long time and heated, you lose some of these healthy polyphenols. Now, refined oils usually have higher smoke points, as you pointed out, but they often have less of the beneficial plant chemicals that we find in olive oils. 

[00:05:09] Jonathan Wolf: And I think one of the things you've already mentioned is generally if you're just cooking at home for yourself, you don't cook these things for very long, right? And so there's sort of focus around smoke point. Very different from being at home versus thinking about some sort of restaurant, which is cooking things over and over. Is that right?  

[00:05:28] Sarah Berry: That's correct. I think when we need to think about the health effects of cooking with oils, we need to separate what happens in a more commercial or in the food industry versus what we actually do at home. So I think it'd be good to dig into the potential health risks, Jonathan, of cooking oils a bit more because there are a lot of myths out there. 

[00:05:51] Jonathan Wolf: I think that sounds like a great idea. And so people talk about what about the compounds sort of reduced during, you use this word oxidation, right? This is basically where oil is going past this smoke point and it's, it's changing. So there's this talk about this can potentially increase blood pressure and cholesterol and cause vascular inflammation and this all sounds terrible.  

[00:06:12] Sarah Berry: Yeah, and I think it's really important to pick up on this, Jonathan, because this is where I think there's a lot of myths out there. So a couple of points I want to mention is, firstly, most of the evidence around what you've just pointed out about all of these dangerous effects of cooked oils is actually from animal studies. 

Secondly, and even more importantly, the harmful effects of cooking oil generally only happen when oil is used over and over again at really high temperatures. For example, in the old-fashioned home deep fat fryer where the oil might be used repeatedly over a month. So bear in mind, very few people use deep fryers now at home and the general way in which we cook our food now at home using oils doesn't generate most of these unfavorable and harmful compounds.  

[00:06:59] Jonathan Wolf: Got it. So we are talking about restaurants and fast food chains and places like this where oil is going to be used repeatedly for long periods of time at these high temperatures. 

Now, I think there are laws right in the US or in Western Europe about having to change their oil regularly and sort of legal limits on the level of these unfavorable compounds. Is that right?  

[00:07:26] Sarah Berry: Yeah. So there are very clear rules in place in the EU, the UK, and in America regarding, the levels of particular compounds that are allowed to be in commercial oils. I do think certainly many of the big food companies adhere to this very well.  

[00:07:44] Jonathan Wolf: And we had a lot of questions on this, so I'm gonna ask you about a few other oils that some people were incredibly excited or confused about. What about avocado oil?  

[00:07:54] Sarah Berry: Yeah, Jonathan avocado oil is an interesting one. It came, only about a couple of years ago to be, sold commercially. If I'm honest with you, I think it's a load of nonsense. I think it's a ripoff. Basically. It's sold as having, these wonderful properties cuz it's high in unsaturated fats. Actually, in my opinion, it's almost no different to rapeseed oil. The only difference is you'll pay about 50 times more per liter for it. 

[00:08:22] Jonathan Wolf: What about coconut oil? Isn't that supposed to have some sort of super healthy properties, it's all-natural, et cetera? 

[00:08:33] Sarah Berry: It's actually a really controversial area, Coconut oil, even in nutritional research. And firstly, something just to say about cooking, I don't think it's a good choice. It's got a really low smoke point, so it's oxidized easily, in terms of its health effects, I think that there is some suggestion that coconut oil when consumed as part of the coconut can be healthy, but when it's extracted from the coconut and the other properties in the coconut, I don't think that there's much evidence to say that it's a healthy option. 

There are some studies published that have shown that there are some health benefits, but I would question those studies and I certainly wouldn't consume it myself in large amounts. 

[00:09:15] Jonathan Wolf: Definitely no coconut oil then and the final one, which is controversial for several reasons. What about Palm oil?  

[00:09:22] Sarah Berry: so palm oil is used a lot commercially in cooking by the food industry because it has fantastic functional properties. You'll find that not many people cook with it at home, but you will find that in nearly all processed foods. Palm oil is on the back of the pack labeling. It’s a tricky one because you've got the environmental concerns regarding palm oil. And also we know that palm oil isn't the best oil for us in terms of our health. You remember at the beginning I mentioned to you these tropical oils have high amounts of saturated fat, and the particular type of saturated fat in palm oil isn't great for our health. 

[00:10:05] Jonathan Wolf: So Sarah, What's the overall verdict then? Are cooking oils bad for you?  

[00:10:10] Sarah Berry: So my opinion is using cooking oils in the way that we typically use them in the home. There is no evidence to show that they're bad for our health unless we repeat deep frying them over several weeks. 

[00:10:30] Jonathan Wolf: Got it. And then maybe let's just talk for a minute about what people will use and I would say from my own side as a result of many conversations with you, Sarah, I end up using extra virgin olive oil for almost everything that I cook with. 

So I fry with it. I also use it a lot where I would've used butter because, of all of these properties should I feel comfortable about that If I'm stir-frying something or I'm frying an egg does that feel good from a health perspective?  

[00:10:57] Sarah Berry: Yeah, I think so, Jonathan, because you are not reusing the fat. You're not reheating it. Also, you are not heating it to an excessive temperature. So remember I said at the beginning, an ideal temperature is around 170 degrees centigrade or 340 degrees Fahrenheit. So if you were to fry your egg, generally your pan would heat the oil to about 160 or 170. And so I think given the applications that we use at home, a light olive oil would be a really good option, but I do also think a very standard vegetable oil that you can get from the supermarket that has rapeseed or canola oil is also a good option. 

[00:11:37] Jonathan Wolf: And what about you, Sarah, as one of the world's experts on fats? What do you use at home?  

[00:11:44] Sarah Berry: Well, Jonathan, I don't do the cooking at home. My husband does all the cooking, so it depends on what he likes. I think Jonathan, a really important point though to mention is there are a lot of people that will be listening to this. I might have also listened to many other podcasts that talk about seed oils being the evil of our diet and cooking with seed oils causes cancer or causes heart disease. 

And so I think it's important to say that we are not necessarily saying cooking with rapeseed oil is especially healthy, but what I do believe is that it's not unhealthy to cook with. 

[00:12:24] Jonathan Wolf: And I think there are probably a lot of people listening to this who are still saying, Well, hang on, I use one of these sprays that's gonna put like one calorie of some sort of chemical to cook with because I don't want to fry my food because it's unhealthy. What would you be saying to them? 

[00:12:44] Sarah Berry: So I'm a real advocate of people consuming a decent amount of fat in their diet. A decent amount of healthy fats so I think that trying to reduce the amount of fat that you put on the pan is not a good way to either improve your health or improve your weight if they're the two reasons that you are doing this. 

And I'm sure that we can do maybe another podcast on this, Jonathan, all around the effects of fat and it’s association with weight but also it's the association with health and dispelling hopefully many of the myths there are around low-fat diets.  

[00:13:22] Jonathan Wolf: I think that sounds like a, a brilliant idea and a great place to wrap up. 

If you'd like to understand more about the foods that are right for you, then by all means do come and try ZOE's personalized nutrition program to improve your health and manage your weight. You can get 10% off by going to joinzoe.com/podcast.

I'm Jonathan Wolf.  

[00:13:44] Sarah Berry: And I'm Sarah Berry.  

[00:13:45] Jonathan Wolf: Join us next week for another ZOE Podcast.

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