Updated 28th April 2022

Fats and oils: What's the real story?

Today we’re talking about fat, a delicious component of our food with a terrible reputation.  

Fats have been broadly associated with weight gain and heart disease until recently.

A mountain of new scientific evidence suggests this is wrong and that it's not as simple as "all fat is bad." Indeed, eating more healthy fat might actually reduce heart disease for many people.  

In this podcast, Jonathan speaks to Dr. Sarah Berry to learn about what science tells us today, whether it is possible to lose weight on a high-fat diet, what oils we should be cooking with, and the different types of fats.

Dr. Sarah Berry is one of the world's leading experts on human nutrition, and she has personally run over 20 randomized clinical trials looking at how humans respond to different fats.

If you want to uncover the right foods for your body, head to joinzoe.com/podcast and get 10% off your personalized nutrition program.

Transcript

[00:00:00] Jonathan Wolf: Welcome to ZOE science and nutrition, where world-leading scientists explain how their research can improve your health.

Today, we're talking about fat, a delicious component of our food with a terrible reputation. Fat can be found in many different forms from olive oil and avocados to bacon and butter. But until recently all fats have been linked to weight gain and heart disease. We now know this to be wrong, but the fallout from the smear campaign against fats remains.

So how on earth did we get here? Let's look back

America, 1940. 

In a host of laboratories across the country. Scientists are working feverishly to identify the cause of heart disease, which is killing over a million Americans each year. A number of these scientists uncover similar findings, a correlation between high cholesterol. and diets high in saturated fats with cholesterol linked to heart complications, the hypothesis is that a low-fat diet could benefit those at risk. Fast forward to the 1980s and things have got rather confused. Low-fat diets were being recommended to everyone, not just those at risk of heart disease, governments, doctors, and food manufacturers, the world over were touting the low-fat diet as the route to better health and weight loss.

Unfortunately, there was little evidence that a low-fat diet was helping anyone. During the same decades that the low-fat approach took hold in the developed world that populations were putting on weight, fast. Food manufacturers' new low-fat offerings tasted unappealing. So they loaded them with sugar. With sugar so cheap that profitability increased. 

Seeing an opportunity. They did everything they could to influence the debate funding, biased research that downplayed the risks of sugar and highlighted the dangers of fat. Only now, so many decades later has the impact of this lobbying begun to fade a mountain of new scientific evidence suggests that it's not as simple, as fat as bad.

Indeed. Eating more healthy fat might actually reduce heart disease for many people. In this episode, we'll be finding out what science tells us today. We'll learn. If it's possible to lose weight on a high-fat diet, what oils we should be cooking with and what are the different types of fats. I'm joined by my good friend, Dr. Sarah Berry, one of the world's leading experts on human nutrition, who has personally run over 20 randomized clinical trials, looking at how humans respond to different fats. Sarah, it's always such a pleasure to discuss food with you. We had an enormous number of questions about fats and about cooking with oils today.

And I hope we're going to manage to address a lot of those. Why don't we start with a quickfire round of questions from our listeners? And so the first question that we have is what's healthier for most people: a poached egg or an egg fried in olive oil? 

[00:03:12] Dr. Sarah Berry: Egg fried in olive oil. 

[00:03:14] Jonathan Wolf: Okay. I think that's gonna be a surprise for many people.

Okay. Can you eat a high-fat diet and still lose weight? 

[00:03:21] Dr. Sarah Berry: Yes, but it's hugely variable between people. 

[00:03:25] Jonathan Wolf: So I guess the following question is, can you eat a low-fat diet and lose weight? 

[00:03:31] Dr. Sarah Berry: Yes. But it's hugely variable between people, but it's harder for most people actually to lose weight on a low, fat than a high-fat diet.

[00:03:41] Jonathan Wolf: I think it will surprise a lot of people. And we can talk a bit more about it. Another question we had to come up with a lot is whether olive oil is safe if you fry or roast with it so that the oil gets hot. 

[00:03:52] Dr. Sarah Berry: Absolutely. It's safe. Just a note that the levels of all these wonderful antioxidants, these polyphenols that are in olive oil will actually reduce though if you do heat it excessively.

So it might not be as healthy, but it's still absolutely safe. 

[00:04:07] Jonathan Wolf: And what about coconut oil? Is that something we should all be eating more of? 

[00:04:11] Dr. Sarah Berry: I think the jury is still out. So based on current evidence, no. 

[00:04:15] Jonathan Wolf: Can eating fats reduce blood sugar spikes? 

[00:04:18] Dr. Sarah Berry: Yep. Yes.

[00:04:20] Jonathan Wolf: Can too much fat lead to inflammation? 

[00:04:23] Dr. Sarah Berry: Yes. But depends on the type of fat, the food it's in and the amount you'll have.

[00:04:29] Jonathan Wolf: Final short question, as we age, does our ability to metabolize high-fat foods change? 

[00:04:35] Dr. Sarah Berry: Absolutely. Yes. 

[00:04:37] Jonathan Wolf: Brilliant. Thank you, Sarah. Well, I think we're going to dive into more detail on one of those questions. I think a lot of us were brought up to feel that fat was fundamentally unhealthy. If we put aside those sort of special magic fats that we need to live and think about them, you know, the majority of things are reading like can fat ever be healthy?

I think we've had this view, I think, you know, saturated fats are bad unsaturated, good. So can this healthy, and is it as simple as sort of saturated versus unsaturated, help us to understand how we can figure the. 

[00:05:04] Dr. Sarah Berry: Yeah. So firstly can fat be healthy? Absolutely. It's a really important component of our diet.

And I think, you know, a lot of us are living with the remnants of this resurgence of low-fat diets, and low-fat products in the eighties and nineties. You know, I was a teenager growing up in the nineties, everything on the shelves was, you know, proclaiming to be healthy because it's low fat and. You know, we really need to move beyond this, the evidence in terms of not just obesity, but in terms of many different health outcomes ranging from cardiovascular disease to type two diabetes does not support any favorable effect of having a low-fat diet over having a moderate-fat diet.

And so I think that's really important to remember, and we can pick up on this later as well, maybe around how, you know, it's actually damaging, I think people trying to lose weight by having these very high refined carbohydrate diets in this effort to stick to this low-fat diet that supposedly will be wonderful for weight loss.

We've taken in nutritional research, generally quite a reductionist view in how we've considered the health effects of foods. And that we have traditionally looked at nutrients and this same quite reductionist view has also been taken when it comes to fat. So typically in the past, we just bagged all saturated fats into one bag of saturated fats, MUFA, which monosaturated fats into one group and polyunsaturated into another group.

But it's a lot more nuanced than this. And it depends on the type of fatty acid within these groups, but it's also very dependent in terms of the health effect that the fatty acid has on what other fatty acids there are in the diet, but also the food that it's delivered in. And I often think a really simple way to try and think about how healthy or unhealthy fat is, is to think about whether it's intrinsic or an extrinsic fat. And this is a term that isn't really used much. It's a term that I like to use when I'm explaining this to people because I think it's a way that most people can understand a bit more easily. So when I say extrinsic fat, I'm talking about the fat that's added to food.

So I'm talking about the fat that might be added, joined, cooking at home, or fat that might be added to a highly processed or any kind of processed food. And so, therefore, when we think about the health effect of that fat, that's an extrinsic fat added to the food. We can think about it a little bit more simply about it based on what kind of fatty acid it is.

Now, if we think about the health effects of fat that's intrinsic, it's all your inner food. So this could be, for example, a fat that's in an avocado or the fat that is already in a piece of meat, then it's really important we consider the other components of the food that it's actually found within.

And so it is new. And so it is difficult. And therefore, I think actually the simplest way to consider the health effects of fat is to consider it in the context of the meal that you're eating and your overall dietary patterns. 

[00:08:10] Jonathan Wolf: Got it. And we can talk a bit, I think about specific examples. I think lots of people will be saying, yeah, that's great but I actually want this practical advice. I think we'll come back and really talk about specific fats towards the end. You already touched a little bit on this question about weights, and I think I'd love to understand that a bit more because, you know, if I put on weight, it's because I'm storing fat in my cells, right. That's how my body is doing that. And we know that. Because when we evolved, you're like, wow, I really need that. Right. I might not be able to find any food tomorrow on the Savannah. And thankfully I've got all those fat stores and this is why I'm fat. We can live for a long time without any food. Right.

And why people can fast, you know, as long as we've got water, we can do that. So obviously that's an essential thing, but I'm storing fat. So can you explain how is it possible for people to put on weight if they're reaching low-fat diets? Because they're not actually putting any fat into their body. 

[00:08:59] Dr. Sarah Berry: So any excess energy is converted into fat.

So if we consume excess carbohydrates, if we have a diet devoid of fat, any excess energy from carbohydrates is converted into fat and stored in our body in fat. So regardless of the source of the excess calories, whether it's from carbohydrates or fats, the excess calories are deposited as fat. 

[00:09:23] Jonathan Wolf: Got it. And this is why this idea, well, I must need fat because you know, I'm going to put on weight.

It doesn't really make any sense because basically, well, if I just swap my fat for Coca-Cola actually you're saying it's just the same thing, right? My body has the ability to swap this backward and forth. 

[00:09:39] Dr. Sarah Berry: Yeah, our bodies are really clever adapting to what nutrients are available to us. And it's an area of huge contention in the nutrition world.

That is the area of whether you should be consuming a high fat or a high carb diet. So you have these low-fat zealots promoting low-fat diets and many low carbs alerts who are loggerheads with the low-fat zealots about which is the best approach to lose weight. And I think that we're going to see more evidence emerging around this, in the future, but there are lots of studies already out there.

And I think there's no clear consensus around this. You know, it's tough to lose weight regardless of where your energy sources coming from, the odds are stacked against us, unfortunately, and this is because like you said Jonathan, you know, evolutionary. we have been primed to be able to conserve energy, to conserve bodyweight so that we can survive in periods of fasting.

And so that was fine prior to the environment we live in, but we now live in this obesogenic environment. We live in this environment, or most of us do of highly processed foods with highly bioavailable nutrients. 

[00:10:47] Jonathan Wolf: And I can just pick up my phone now, right. And order. It's amazing how much food I can now order to my house without getting up from my seat.

Is that sort of what you're talking about in this environment that we're in? 

[00:10:57] Dr. Sarah Berry: Yeah. So the fact that for most individuals it's highly accessible, but also an interesting concept that's been evolving over the last 10 years is this area around accessibility in terms of bioaccessibility. So yes, you can pick up your phone and in 10 minutes you could probably have something delivered on a bike to your house with goodness knows what kind of food in it, but another area that we're becoming aware of there's the importance of how food is processed. And we know that by processing food, you make food, more bioaccessible. And what that means is the food is in a format that it's really more easily digested. You're absorbing more calories. You're absorbing the energy more quickly.

You're processing it more quickly. And we know that this is detrimental for lots of different reasons. And, given how clever our bodies are maintaining the set point in our weight in maintaining and preserving energy. We're kind of fighting a losing battle to a certain extent because we have this highly accessible food.

We have these highly bioaccessible nutrients and then our body and the feedback loops that we have between our gut and our adipose tissue, so our fat tissue where we're storing the energy and our brain is so powerful and a lovely example that I heard recently that I think really brings home just how challenging this is, is that this feedback loop works in such a way that if you or I were to reduce our energy intake by 200 calories a day. So if we were to go try and go on a lower calorie diet, forget what nutrient this is coming from for the moment. But we, as you do so energy by 200 calories a day. The hunger feedback loop that would occur in response to these stimulating areas and operating related to hunger and fullness would actually drive an increased energy intake of about 750 calories.

So we're only having a deficit, so a loss of 200 pounds. But the drive-in our brain to consume more is actually for about 750 calories. Now, when we're highly motivated in those first few months, or the first few weeks to lose weight, then our motivation can overpower this to a certain extent, but we cannot keep that up lifelong.

And this is why in the long-term many diets do fail regardless of the nutrients. 

[00:13:19] Jonathan Wolf: And so with that context, one would think that fats were still a bad thing and you think they were a bad thing because they have more calories than carbs for the same way. Right, Sarah? And maybe you can tell us exactly what that difference is, but it would sort of seem logical and lots of people have talked about this while you wouldn't want to eat fats because they're very energy-dense. And it sort of seems obvious that actually, you're going to put on more weight, therefore eating them than carbs. And so you said right at the beginning, actually, it's not true, but can you help us to unpick that? Because it seems like totally in conflict with what seems logical. 

[00:13:55] Dr. Sarah Berry: Yeah, and this is why the whole low-fat diets and low-fat products have been such a success because it is in conflict with what seems logical because per gram of fat, there are nine calories per gram of carbohydrate, there are four calories. So if I was to consume 50 grams of fat, yeah, it's more than half a difference in terms of the calories per amount of food. But what that doesn't consider is that when we consume this food, what actually happens during the digestion process and this feedback process, how it affects different hormones, not just the hormones in our brain, feeding back to us about how hungry or full we feel, but also hormones that affect how we deposit fat and how we release fat. And there's something called the carbohydrate-insulin hypothesis that is advocated by the proponents of the high, fat, low carb diets. And this is based on the principle. If you consume lots of carbohydrates, you're increasing your insulin secretion by increasing your insulin secretion in that immediate period after consuming high carbohydrate foods, what that does is it stops the fat being released from your adipose tissue.

So from the fat tissue in your body, it also causes more deposition of fact that's circulating back into the adipose tissue. So if you were to go on a low carb diet and consume a high-fat diet, you produce very little insulin. So what that means is that means that you're not having that blockage of preventing the fat coming out from the adipose tissue.

So you would have more fat being released in the adipose tissue and you wouldn't have the fat being pushed back in the adipose tissue. Now, mechanistically. That's great, but the evidence doesn't necessarily support this when we translate this to clinical trials. And I think a really important note to pick up on this is because it's different for everyone. What works for one person doesn't necessarily work for another person. And there's a great study that illustrates this called the diet fit study, that one of our colleagues, Jonathan, that you know, very well, Christopher Gardner led and he allocated people randomly to either consume for a period of time, either a very high carbohydrate, low-fat diet, or very high fat, low carbohydrate diet.

And he then followed them up over a period of time and assess their change in weight. Now he found that everyone lost a little bit of weight, but he found that there was absolutely no difference in the amount of weight loss between the high carb people and the high-fat people.

[00:16:34] Jonathan Wolf: On average, right? 

[00:16:36] Dr. Sarah Berry: Yeah. So this is on average.

So traditionally in nutritional research, what we do is take the average response. When we put someone on a diet, let's say we have 50 people going into a dietary trial at the end of it. We look on average, what's the change. So when he looked at the two different diets on average, there was no difference, but then he went and looked at the individuals. So he looked at all of the different individuals consuming the high fat, and all of the individuals consuming the high carbs. And he found that there was a hugely variable response. He found that for some individuals, the high-fat diet worked really well in promoting weight loss, whilst in others, it was terrible.

It caused a weight increase. And then the same for the high carb. You found that for some people, this is a really effective means, but for other people, it was really ineffective and it really highlights, something that I'm very passionate about is this whole area of personalized nutrition, which is at the heart of all of the research I'm doing together with ZOE and yourself on the predicted program of research.

And I think it really highlights that yes, we can talk about these lovely fancy mechanisms to do with how we metabolize fat or carbohydrate and the carbohydrate-insulin theory, but actually it boils down to what works for you and the diet fit study, I think has great. It's an illustration of that as well as our own predicted research and that we need to move beyond this one size fits all approach.

We need to be thinking on a personalized level. 

[00:18:01] Jonathan Wolf: Maybe just before we switch to another topic, I think to be interested about sort of like the behavioral impact on this and how it makes us feel. So one of the things that people often ask me is, well, how has your diet changed since you started ZOE? And the answer is it's changed a lot.

And one of the biggest ways it's changed is that I now eat a lot more fat than I did. I was absolutely sure that fat was bad for me. Five years ago, my dad was basically put on a very low-fat diet because he was told he had very high cholesterol in his thirties. So this is now, you know, sort of 40, 45 years ago.

And so that means that at home, you know, we ate these very low-fat diets as a result. We of course. Lots of carbohydrates because that's what you do to fill it in. And of course, lots of refined carbohydrates, pasta, bread and things like this. So I then did these ZOE tests and it turns out that actually my blood sugar control was really quite bad and actually my blood fat control was much better.

And so that's what the advice is pushing. But I still feel really guilty when I eat cheese, like it's, even though I've seen this and I also have noticed the way that actually my hunger is lower when I'm eating these high-fat foods like I still have this basic feeling that it's a bit naughty, isn't it? Like, it's not the right thing to do.

And what are your thoughts on that Sarah? 

[00:19:17] Dr. Sarah Berry: I've got loads of thoughts. I'll just touch on a few that I think might resonate with people. So you mentioned your father, for example, being put on a low-fat diet because he had high cholesterol and this is still a common perspective that lots of people have around.

How do I reduce my cholesterol levels? Well, let's consume low-fat diets because it contains cholesterol because will increase my cholesterol levels. The first thing, just to mention that I hope most people now are aware of, but in case they're not is that, if you consume dietary cholesterol, which is contained in some foods, dietary cholesterol, doesn't increase your circulating cholesterol.

So it doesn't actually increase your blood cholesterol levels, or it does only to a minimum. It's the type of fats that you're consuming that increase your cholesterol levels. So yes, we know that some saturated, fatty acids might increase your cholesterol levels.

[00:20:09] Jonathan Wolf: And can you say what sort of foods those are? Sarah, just for those of us who don't think about things in this chemical way. 

[00:20:16] Dr. Sarah Berry: Yeah. So we know the kind of saturated fatty acids that are in butter palm oil in animal fats, for example, can increase our cholesterol. Now, cholesterol is made up of good and bad cholesterol. And what we particularly don't want is increasing good cholesterol alongside an increase in bad cholesterol and saturated fatty acids increase our bad cholesterol. Some of them do also increase our good cholesterol. So again, it's a little bit more complicated. I'm sorry to say, depending on the type of saturated fatty acid, what we do now know, which I don't think we were so aware of 30, 40 years ago is. The carbohydrates can have a really big impact also on our cholesterol levels and also on our circulating triglyceride levels, which we also know is an independent risk factor for cardiovascular disease.

So if you consume a diet high in refined carbohydrates and by refined carbohydrates, I mean bread, I mean, pasta, I mean rice, I mean also a lot of the processed carbohydrates, like snack bars, crisps that you might consume. What this does is at the level of our liver, it promotes the production of lipids.

So this is another word for the kind of fats that are produced in our body. And that increases our cholesterol levels and increases our levels of circulating triglycerides. To loop back to what you mentioned about cheese. I think that's a really good example of how we need to move beyond the simplistic approach of thinking about the types of fat.

So I just said that actually, the type of saturated fat you have in butter is bad for us. Now dairy cheese. So fermented dairy such as cheese and yogurt has really similar fatty acid composition to butter, but actually, it doesn't have the same favorable effects on our health as butter does. And the reason is, is because of this matrix, the kind of special structure in which the fatty acids sit within the dairy products that are fermented within the cheese and the yogurt.

So you could feed people, a moderate cheese diet and moderate butter diet. The cheese wouldn't have any unfavorable effects yet. Actually, the butter would have an unfavorable effect despite having a similar fat composition. 

[00:22:32] Jonathan Wolf: And despite the fact that actually basically the cheese comes from the butter, right, Sarah?

So that's like even more surprising to help us to unpack that a little bit. It sounds a bit magical.

[00:22:44] Dr. Sarah Berry: It is because food is really complicated and it's magical because how we process food has a huge impact on its health outcomes. So how we process dairy, whether it's butter or whether it's cheese or whether it's our yogurt can hugely impact how our body responds to it and the same applies to how we process other foods, whether it's consuming whole foods or consuming pureed food or consuming whole almonds or consuming ground almonds, where you're changing the matrix. It has a huge impact on this the accessibility that I mentioned earlier. So the release of nutrients and how our body processes them. And I think dairy is a really nice example of how we need to look beyond the nutrients.

And we need to think about the food that it's actually contained within.

[00:23:37] Jonathan Wolf: So basically the food labels, which vast effort I'll put onto all of these foods, and which, you know, in many countries, right? There's the states or the UK included talk about sort of saturated or unsaturated. I'm not necessarily really giving you any information that is helpful.

Is that what you're saying, Sarah? 

[00:23:59] Dr. Sarah Berry: Yes, in my opinion, I think it's worth mentioning that broadly speaking, epidemiological studies. So these big studies that we'll be following people over a number of years or looking at one point in time and thousands of people, and then looking at certain health outcomes and looking at dietary intakes.

They do consistently show that a high saturated fatty acids diet is less favorable than a high mono or polyunsaturated fatty acid diet at the population level. But when we do clinical trials, what we know is once we start to tease this apart, it becomes really apparent that that's too simplistic and at an individual level and at a food level, it's again, far too simplistic that we need to consider the type of fatty acids.

But more importantly, we need to consider the food it's in. 

[00:24:46] Jonathan Wolf: And this is because you're lumping all of these different things together. So you're saying like, well, somebody who's eating lots of animal fats and I think yours, you still think animal fats are not particularly healthy. Is that right, Sarah? 

[00:24:56] Dr. Sarah Berry: Yeah.

So I would say that you could have foods that contain the same fatty acid composition. So animal fat and some particular other tropical oils, for example, contain the same fatty acid composition, but could have different impacts on health outcomes because of the source, because of the matrix that they're in, it has a huge impact.

And so I do think that whilst labeling can be useful, broadly speaking. I think we need to be very, very careful to not be too caught up in labeling. And there's an example I often use to do with almonds. Now, this isn't related to the fatty acid composition, but it's related to how I think being preoccupied with labeling can actually potentially even make us select more unfavorable health choices.

So if we were to consume whole almonds. Almonds have a very special matrix. I have a very rigid cell structure. So what happens is, is that remains intact largely as we chew them and they pass through our digestive tract and we only absorb about 60% of the energy. So about 40, 30% of the energy and fat is excreted.

So it reaches our large intestine where it's great food for our microbiome, which is fabulous but also it's a lot lower energy. Now, if we were to grind those almonds up, so we break this magic matrix, we break the cell walls, we release all the fat, we're going to absorb everything. And so that you suddenly have a food that has about a 30 to 40% higher energy content in terms of what we're absorbing than the whole almonds. However, if I was to go into a supermarket and look at a bag that had whole almonds intact, as we typically would consume for snack versus the whole almonds ground up like we might use this an ingredient, the backup pack labeling would show that they had identical energy values.

They wouldn't show that per a hundred grams. You had this huge difference of, you know, several hundred calorie difference. And so I think that's a really nice example of how we need to think about food. Is it in its original matrix? Is it unprocessed? Does it contain healthy, other nutrients like fiber and mono and polyunsaturated fatty acids, rather than looking at that backup pack labeling?

[00:27:15] Jonathan Wolf: That's really powerful advice, right. In general, thinking more about this as food, rather than as the set of numbers on the back. And of course, all of this labeling, you know, I think it was still being done with good intent, right? But actually isn't very helpful. And of course, if it had been really helpful, then we would have seen all these wonderful health outcomes over the last 30 or 40 years, which we haven't seen either.

We've been teasing our listeners for ages. Let's get down to the bit that they probably have been like, oh, this is the bit, I care about, so. The number one question that we had is what are the best oils to cook with? So let's start with that.

[00:27:48] Dr. Sarah Berry: So I'm going to say it's complicated seeing us though, we've already started on that, that the, I feel I'm allowed to say that it depends on what you're cooking, how you're cooking it and what temperatures and for how long as a rule of thumb an oil that has a lot of monounsaturated fatty acids.

So this is, for example, oleic acid that is particularly high in some types of sunflower oil and olive oil. Tends to be a very good oil to cook with. And the reason for that is because it's a very stable oil. Once you start adding polyunsaturated fatty acids and remember, these are the ones that have more double bonds, and these double bonds are very easily oxidized.

Then what can happen is when you cook with an oil that has a lot of polyunsaturated fatty acids, and an example of this is rapeseed oil or some other variety of sunflower oil, what happens is, those double bonds can become oxidized. And so you get that rancid taste and it's quite obvious. And I don't know whether you've ever tasted that Jonathan if you've used something that's highly polyunsaturated or, or even fish oil if it's left out in the air or heated, you can taste it quite easily that it's got some kind of rancid off-taste.

So from a taste perspective, it's best to use mono and saturated oil. 

[00:29:07] Jonathan Wolf: So olive oil, sunflower oil, which I think is not used as much in the States, right. As it tends to be in Europe. Is there anything else that fits into those categories? So you put it at the top. 

[00:29:16] Dr. Sarah Berry: So olive oil, you would need to use an oleic type of sunflower oil and rapeseed oil is still a pretty good oil to use now in the US one of the main oils that they use for cooking and one of their main oleic acid, so mano is saturated rich oils is soybean oil. That's one of the most commonly consumed oils in the US, it's homegrown. So it's also good in terms of environmental impact because of it being a homegrown oil. So I would say olive oil would be the best one.

And then in the US soybean oil and in the UK, high ALEKS sunflower. Now, something to bear in mind though is us with all fats. It's all about the taste, the functionality. and I personally, don't like to cook with olive all because I find it too fragrant. I find the taste too strong and what's giving it this taste is all of these great polyphenols.

So I would choose to have an oil that works for me in terms of taste. Now, if you like the taste then, and I know you fry with olive oil yourself, Jonathan a lot, then that's great. It is a healthier option. 

[00:30:19] Jonathan Wolf: Yeah. And I, I would say when I first started, I really noticed it and seemed a bit strange. And actually, now I cook with it all the time and actually love it. So I would also say that it's like a lot of things, right. When you're making a change in nutrition, the hardest bit is making a shift because you're in the patterns that you're used to. And, you know, it's a bit like when, you know, you're giving up drinking sugary drinks, right.

And to start with, it's really hard. You're just so used to that. And so I at least speaking for one. I now think of course that's what I would fry my eggs with because not only has Sarah explained to me how good it is, but actually I really like it. But I think that it is an important point, right. That you talked a lot about, about, we eat food for pleasure, and it's really important that you don't think, oh, I can never have anything else.

This is all about finding the right balance. 

[00:31:06] Dr. Sarah Berry: Yeah, and something else to mention is that domestically, so how we would cook at home frying an egg baking olive oil will retain most of its favorable compounds. So these polyphenols, the antioxidant compounds industrially. It would be very difficult to use olive oil because particularly when there's very high-temperature cooking, it would destroy these compounds.

And also because there is a reasonable amount of polyunsaturated fatty acids in olive oil, which again, and if it's used as an added ingredient, industrially would mean that the food would, or the oil would go rancid and the food would have a shorter shelf life. So whilst I think it's great for home cooking home use and particularly adding to salad, so you know, uncooked foods, it's not a good ingredient functionally for the food industry, but also for us, because most of the favorable benefits will have gone. And actually, that brings me on quite nicely to thinking about olive oil in terms of the type of olive oil there is so on the market, there's extra-virgin olive oil, Virgin olive oil, and then just standard olive oil.

And the difference is in how many processing steps it goes through. So extra Virgin olive oil is the least processed and has the most amount of these great polyphenols that are so good for heart health. They've got a microbiome and many more favorable health effects. Once you get to the next level of processing the Virgin olive oil and the following one, the just straight olive oil, nearly all of these favorable compounds have gone, and actually, it's no different to sunflower oil and no different to rapeseed oil. So if you are going to buy olive oil because of its health benefits, you need to get the extra Virgin olive oil. Otherwise, you might as well buy the far cheaper sunflower rapeseed or in the States, soybeans oil.

[00:32:53] Jonathan Wolf: And that's really helpful, Sarah. And I think you talked already about sort of olive oils, sort of magical properties as seen in this big study. We did get a lot of questions about the dangers of cooking with it. Where does that come from? And you said right at the beginning, you know, very confidently.

It's fine. And can you just elaborate briefly on why we can all just be relaxed and put it in the frying pan? 

[00:33:15] Dr. Sarah Berry: Okay because I think there was a lot of scaremongering sometime ago about compounds such as peroxides, polar compounds, and 3MCPDs. If I've got that correct, I'm not even going to try and give you the full name for that.

And these are compounds that are produced when you heat fats when you repeatedly heat fats and you heat them to very high temperatures, especially in the presence of small amounts of water. We know that these compounds firstly are horrible because they make the fat taste horrible. But we also know that some of these have been shown to be carcinogenic at high levels in animal models, not in humans, but in animal models.

The reality is the way that we cook at home, will not produce these compounds. You will not produce these polar and peroxide compounds in the way that typically we consume fats at home. You know, some people might still have the deep fat fryers for frying chips. I don't think many people do this now at home.

And if you were to use the same oil for many months and many repeated fires and hundreds of repeat fries, then eventually yes, you would produce these compounds, but it's just not relevant to us. And this is the problem where there's so much scaremongering about dietary links with cancer or other diseases, that are based on situations and scenarios that just aren't relevant to how we as humans actually consume food. So if you are not deep-fat frying, your olive oil for over six months using the same oil with chips, repeat frying every day. I think you're pretty safe to fry and use this at home. 

[00:34:59] Jonathan Wolf: That's really helpful, I think.

And I think also that point, that comes up a lot, right. About the difference between some sort of animal study in a very controlled sort of laboratory. And then the reality of what happens when you do a human study over time. And that I think all the time, right. You see either negative impact or really promising impacts and this animal study, and then it gets rolled out to, you know, humans and you've done, I think more than 30 of these randomized control trials.

Right. That doesn't actually really happen in real life with real people is something that I think for our listeners always to be aware of. Cause it's part of why there are so many confusing, different stories or even contradictory stories. Right? It's not that anybody, each of the pieces of science is correct, but it doesn't necessarily flow through in the way that maybe the media has put on its front page.

[00:35:44] Dr. Sarah Berry: Yeah. And Jonathan, can I pick up on something because well, that people often ask me. And so I think anyone listening might be interested in this people often say, okay, it's fine saying it's safe at home, but what about take-aways? What about your McDonald's fries? What about your corners street kebab shop that might or chip shop that might be using the same oil day in, day out.

Well, firstly, there are very strict regulations across all of Europe and in the US about the level of these compounds allowed, and all food outlets are randomly checked, but as long as you're changing your fat about every week, still, even in that scenario, you're not going to produce enough of these, that you'd be highly detectable and certainly wouldn't have any unfavorable health outcomes.

So even getting your repeat deep-fried chips from your local corner shop in most instances is still going to be okay, and still going to be safe for consumption. 

[00:36:36] Jonathan Wolf: Got it. Now that'd be safe. I imagine that you're going to tell me the quality of those oils is not as good as the oils that I'm going to be using at home?

[00:36:46] Dr. Sarah Berry: So the quality of those kinds of oils will be determined by the functionality. And this is something that we haven't picked up on and might not have time to. And I'd love to come back and spend a whole lot of time talking about the importance of functionality, but those kinds of oils will have a slightly higher saturated fat content.

So the kind of oils that are often used commercially in food outlets will have a higher proportion of fat, such as Palm oil. Actually together with a rapeseed oil blender together, this makes the fat a lot more stable. It means it last longer. And it means it doesn't again, produce these compounds that are produced mainly because of the polyunsaturated fatty acids.

So this is an example where. The food industry has to think of two things. They have to think of the health effects, but they also must think of the functionality as well of the fat. Does it function for the purpose? 

[00:37:40] Jonathan Wolf: That's fantastic. Sarah. So switching to completely different food. Let's talk about eggs for a minute.

Are eggs safe or are they deadly? 

[00:37:49] Dr. Sarah Berry: Well, I'd never heard anyone say that at least. So I'm surprised you're using that word. Are they safe? Like with anything it's up to a certain cutoff of intakes. I think a healthy part of our diet. They contain some really valuable micronutrients, vitamins minerals, and it's something I make sure that my children are getting a regular intake of eggs in their diet, because I know there's such a dense source of nutrients, a good source of proteins, you know, like with any kind of food, it's all about moderation, you know, as boring a message, I know that is everyone wants a cure or food to have, or one food to demonize. Well, I think in moderation, eggs are a really important and, good component of our diet. I wouldn't encourage someone to be having three eggs a day, but I think, you know, the evidence would point to, you know, three to five eggs a week is a good component and healthy diet. 

[00:38:48] Jonathan Wolf: Brilliant. And maybe the last food. Cause I know we could talk for ages, but we're definitely over time.

Can we talk about fish for a minute? So Tim, who's not on right now. It's a bit negative on fish, despite, you know, many of the things that have been said about, you know, omega-3 and omega-6. Love to get your perspective, Sarah. 

[00:39:05] Dr. Sarah Berry: Okay, so to give it some context, I think we should separate fish into two categories. So you've got your oily fish or non-oily fish.

So your non-oily fish is your typical kind of white fish like Cod for example, which is a great source of protein, none of the unfavorable refined carbohydrates, et cetera in it. So it's a really good component of the diet or oily fish or fish such as tuna, not tinned tuna, though. Fresh tuna. , salmon mackerel, and oily fish contain high amounts of very long-chain omega-3 fatty acids.

And these are the fatty acids. I mentioned at the beginning that is essential fatty acids. So they're essential points on such great fatty acids that we cannot make. They're also the fatty acids that produce these pharmacological light compounds that I mentioned earlier that have so many therapeutic effects. Now, there are two factors to consider in this one is can we get these very long chains of omega-3 fatty acids from plant-based sources? Yes, we can. But can we convert them in adequate amounts to very-long-chain fatty acids? It depends. So. You can get omega-3 fatty assets from plant-based sources, such as flax seeds walnuts, but these aren't the very, very long-chain ones.

The ones that we need to produce these pharmacological light chemicals. Now our body can convert some of these plant-based ones to these very long favorable ones, but the conversion rate is quite low. Generally. We only convert about 10%. So. That is why generally as nutritionists and dieticians, we have recommended that people consume the very long-chain omega-3 from fish oil sources because we know that our body's quite inferior or inadequate in terms of how it converts the plant-based sources.

Now, more recently, there's been much questioning as to do we actually need this very long-chain omega-3. Some fish oils. You know, in the first place, why can't we just use the plant-based ones? And this is because the evidence has been quite inconsistent. So there's been a lot of randomized control trials looking at the effects of these fish oil sourced omega-threes on different health outcomes.

The best way to describe why it's been inconsistent is because most of these studies have recruited people that have different baseline levels of intake of oily fish. If you're having an intake that's adequate, then there's no further benefit to increasing your intake of the omega-3 from oily fish. If however, your intake is low, so if you have a low omega-3 status then the evidence I think is quite clear for benefits. So again, this takes us back to it, it depends on who you are. So it's very individualized. So we can't say yes, everyone will get a benefit. It depends if you're already getting a decent amount. There's no point in having a further increase.

So my recommendation is that people do try and have one portion of oily fish in their diet. If you are vegan or vegetarian, you can use ALA sources and you can buy now quite affordable ALA sources from these very long chains. Omega-3. 

[00:42:21] Jonathan Wolf: Brilliant, Sarah. I think that's a wonderful summary of that. We started by can we ever be healthy?

And the starting point is fats are really complicated, but the key message I think is that you can't just think about it as saturated fats are bad unsaturated fats are good. Actually, you need to think about the food we then talked a bit about, is it possible to put on weight if you eat low-fat diets the answer is, absolutely. Yes. And this is because our bodies just have this amazing ability to basically swap between sugars and fats. And so, you know, you can eat no fat, but your body doesn't care if you're eating all of these refined carbohydrates or whatever you can swap back or for. We talked a little bit about cholesterol.

I told you about that. I'm one of many people who still find this idea. Well, you know, is it really all right to eat? Fats are difficult and there are some foods. I think you said that there are some animal fats and foods like butter that can increase our cholesterol, but actually, so can carbohydrates, we discussed a little bit about labels and that they may not, sort of giving you the answers that you're looking for, because you can have a big difference between what the label says versus what you're actually going to feel. And then we talked about, what should we cook with? What should we eat? I wrote down, you know, olive oil is pretty magical. So, you know, that's where you start.

[00:43:35] Dr. Sarah Berry: And only extra virgin as well.

[00:43:38] Jonathan Wolf: And only extra-virgin absolutely that it's really important to get that distinction and that sunflower, oil, and soybean oil were also two oils that had strong, healthy properties. So definitely alternatives to look at. And finally, we touched on a few other foods. You said I am allowed to eat my eggs, but I'm not allowed to eat three a day.

So, you know, Moderation in all things, including moderation, and that we talked a bit about oily fish. I think on balance, your view is that you know, there's a benefit to many people. If you are a vegetarian or vegan, there are alternatives for getting these fats that you can't get otherwise. 

[00:44:13] Dr. Sarah Berry: A fantastic summary, Jonathan.

I think everyone can just skip right to this. 

[00:44:18] Jonathan Wolf: But it just shows what a lot of ground we've covered. I think lots of things that we didn't have time for Sarah, thank you so much for taking the time. And I know that you feel, I constantly try and simplify something, which is very complicated to the light.

Okay. But, so what should people do? So. Thank you for bearing with me, not just in this podcast, but over the last five years. I think that's amazing because this is stuff that I think everybody can just go and go and implement at home. And I hope you will come back again soon. 

[00:44:46] Dr. Sarah Berry: I, well, thank you. It's been fun talking about my favorite topic.

[00:44:50] Jonathan Wolf: Brilliant. Thank you, Sarah, bye-bye. 

[00:44:52] Dr. Sarah Berry: Thanks, Jonathan. 

[00:44:53] Jonathan Wolf: Thank you to my good friend, Sarah Berry for joining me on ZOE science and nutrition today, we hope you enjoyed today's episode. If you did, please be sure to leave us a review and subscribe. If you're interested in learning more about ZOE and the best foods for your body, you can head to join ZOE.com/podcast and get 10% off your personalized program.

Finally, if this episode left you with any questions, please send them in on Instagram or Facebook. And we will try to answer them in a future episode. As always. I'm your host, Jonathan Wolf, ZOE science and nutrition is produced by Fascinate Productions. With support from Sharon Feder and Megan McPherson here at ZOE.

See you next time.