Cooking oils: what to use and when
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Hello, and welcome to Zoe Shorts, the Bite Size 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.

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. So wait, Sarah, are you saying cooking oils are bad for us? It's a bit more complicated than that, Jonathan. OK, I'm intrigued. Let's get into it.

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. Sounds yummy. So what oils would they typically be using to make this feast? So chances are it's going to be a 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 oils such as sunflower, soybean and other oils.

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, sesame. And in case you're 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 will explain that a bit more in a minute.

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 oil have a lot of these really 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 tropical 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.

And I think one thing that people often ask about is this thing called the oil smoke point, right, Sarah? And I understand that's the point when an oil begins to burn and smoke, as I have definitely experienced when cooking, getting distracted, and then you look back and 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.

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. And these really simply put can change the structure of the oil as well as oxidising the oil. And it's these changes in structure and these changes in oxidation that can have potentially unfavourable health effects.

but how much of that changes during cooking is really dependent on your cooking method. For example, the temperature at which you're cooking, how long you're cooking it for, and also really, really importantly, whether you're 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 definitely avoid this repeat use of the same oil for frying as you might use, for example, in deep frying. So oils that have a high smoke point and therefore sort of meet those criteria, Sarah, right, include rapeseed, canola, sunflower blends,

What about virgin olive oil? 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, right? 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 really special because these 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, 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 really healthy polyphenols.

Now, refined oils usually have higher smoke points like you pointed out, but they often have less of the beneficial plant chemicals that we find in olive oils. And I think one of the things you've already mentioned, right, is

generally, if you're just cooking at home for yourself, you actually don't cook these things for very long, right? And so this sort of focus around smoke point is just very different for being at home versus thinking about some sort of restaurant which is cooking things over and over. Is that right? Yeah, that's correct. I think when we think about the health effects of cooking with oils, we need to separate out

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 actually dig into the potential health risks, Jonathan, of cooking oils a bit more because there are a lot of myths out there. I think that sounds like a great idea. And so

People talk about what about the compounds that are reduced during, you use this word, oxidation, right, which is basically where oil is going past this smoke point and it's actually changing. And so there's this talk about this can potentially increase blood pressure and cholesterol and cause vascular inflammation. And this all sounds terrible. 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 happens 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 that very few people actually 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. Got it. So we're really talking about restaurants and fast food chains and places like this where the oil is going to be used repeatedly for long periods of time, you know, 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, Sarah? Yeah. So there's very clear rules in place in the EU, in the UK and in America regarding the levels of particular compounds that allow to be in commercial oils.

And I do think certainly many of the big food companies adhere to this very well. And we had a lot of questions on this. So I'm going to ask you about a few other oils that some people were incredibly excited or confused about. What about avocado oil? Yeah, Jonathan, avocado is an interesting one. It came only about a couple of years ago to be sold commercially and it's

And if I'm honest with you, I think it's a load of nonsense. I think it's a rip off. Basically, it's sold as having these wonderful properties because 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 per litre for it. What about coconut oil? Isn't that supposed to have some sort of super healthy properties? You know, it's all natural, etc. So that's a really good question. And it's actually a really controversial area, coconut oil, even in nutritional research. And

firstly something just to say for cooking I don't think it's a good choice it's got a really low smoke point so it's oxidised really easily in terms of its health effects anyway 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 actually 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.

Definitely no coconut oil then. And final one, which is controversial for a number of reasons. What about palm oil? Yes, 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 pack labelling.

And it's a really 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. And you remember at the beginning I mentioned to you these tropical oils have really high amounts of saturated fat. And the particular type of saturated fat in palm oil isn't really great for our health. So Sarah, what's the overall verdict then? Are cooking oils bad for you? 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 repeatedly over several weeks.

Got it. And then maybe let's just talk for a minute about what people will really use. As a result of many conversations with you, Sarah, I end up basically 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 have 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? Yeah, I think so, Jonathan, because

you're not reusing the fat, you're not reheating it and also you're 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.

And so if you were to fry your egg, generally your pan would heat the oil to about 160, 170. And so I think given the applications that we use at home, a light kind of 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 the rapeseed or canola oil is also a good option. And what about you, Sarah? As one of the world's experts on fats, what do you use at home?

Well, Jonathan, I actually 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 is a lot of people that will be listening to this that 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, causes heart disease.

So I think it's important to say that we're not necessarily saying cooking with rapeseed oil is especially healthy. But what I do believe is that it's not unhealthy to cook with.

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 sort of sprays. It's going to 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?

I'm a real advocate of people consuming a decent amount of fat in their diet, a decent amount of healthy fats. And 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're doing this.

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

I think that sounds like a brilliant idea and a great place to wrap up. If you'd like to understand more about the fats that are right for you, by all means, do come and try Zoe's personalized nutrition program to improve your health and manage your weight. And you can get 10% off by going to joinzoe.com slash podcast. I'm Jonathan Wolfe. And I'm Sarah Berry. Join us next week for another Zoe podcast.