How to eat sugar without gaining weight with Prof. Tim Spector and Prof. Sarah Berry

How can you enjoy sugar without gaining weight, fuelling cravings or crashing later in the day? The answer, surprisingly, is not to cut it out.

In today’s episode, Prof. Tim Spector and Prof. Sarah Berry discuss which forms of sugar affect your blood sugar levels most, and what small changes you can make today to reduce the impact.

They also explore how sharp blood sugar spikes and dips may affect hunger, energy, inflammation, and long-term health.

Sugar is not the enemy. But could a few small changes help you enjoy sweet foods without the cycle of cravings, hunger and energy crashes?

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Jonathan: Tim, can my sugar intake negatively impact my mental health?

Tim: It can.

Jonathan: Sarah, honey is a natural product. Is it much healthier than sugar?

Sarah: No.

Jonathan: Tim, should I try and keep my blood sugar level as low as possible?

Tim: No.

Jonathan: Sarah, does our brain need blood sugar to work?

Sarah: Yes.

Jonathan: And finally, Tim, can too much sugar increase my risk of diabetes?

Tim: Yes, it can.

Jonathan: One thing I have to admit is I have a little bit of a guilty secret about sugar that I don't think I've talked about on this podcast before. But when I first met Tim and Sarah right at the beginning of starting ZOE, I put two sugars into my tea, and I drank seven or eight cups of tea a day.

I had a sweet tooth. I think in general, I was just eating a typical American or British diet where everything was sugary, and I was just used to it. No one thinks that sugar is good for them. They all know that, you know, if you have loads of sugar, it'll probably make you overweight. We're all told, like, if we give lots of it to our children, it makes them hyperactive.

On the other hand, we're all constantly told that fruit is good for us, and that's stuffed full of sugar. And then there's all these other alternatives to regular table sugar, all of them claiming to be healthier. So it's all a bit confusing and complicated, and I hope you're gonna make sense of this sort of sickly sweet puzzle and give us all a guide about what we should be doing.

Sarah, what is sugar?

Sarah: So sugar is a type of carbohydrate. It is made up of sugar molecules, which we call saccharides, and that stems from the Greek term for sugar. And there's two main kind of forms of saccharides that we talk about in nutrition. There's what we call monosaccharides, which are the very simple sugars that are made up of one sugar molecule.

And the key ones that are relevant to us are glucose, fructose, and galactose. So they're just single sugar molecules. Then you have something called disaccharides, which are basically two simple sugar molecules joined together. So you have sucrose, which is what's really common table sugar, the sugar that you are adding to your tea, for example, and that's made up of a glucose molecule joined to a fructose molecule.

And then you have, for example, lactose, which is a sugar that's commonly found in milk, and that's made up of a glucose molecule with a galactose molecule.

Jonathan: It's already got a little bit complicated, and I think already points to some of the complexity whenever I turn the food label over, right, and understand this, the glucose and the sucrose and the fructose.

But I'm interested in the thing you said at the beginning, Sarah, about like we need sugar to survive. Can you explain what's going on there?

Sarah: So we need sugar in our blood to survive, but we actually don't need to consume sugar to survive, and that's really, really important to remember. So our cells need sugar.

Our cells need glucose, for example. We need sugar in order to fuel our cells. We need it for our brain. Our brain preferentially uses glucose as its energy source. But actually, we can make sugar in our bodies. So we can use a certain process in our body where we convert protein into sugars, into glucose, for example, where we can also, to a lesser extent, also convert fat into sugars, into glucose.

We also need to remember that other carbohydrates like starch, so the kind of carbohydrate that's in rice, that's in pasta, that's in potatoes, and that's in many vegetables, are actually really, really long chains of these simple monosaccharides, these simple sugars, these glucose molecules. So when we're having potato, for example, although we might not think of that as a sugar, we break that down also to these glucose molecules.

So yes, we need sugar in terms of circulating in our blood, but we don't need to consume it.

Jonathan: To just make sure I've understood that, I've got sugar in my blood right now. That's the glucose you're talking about. But it doesn't necessarily come from eating something that has sugar in it. It could be that my body is making it from something completely separate, or it could be that, you know, I had some bread for breakfast, and that bread actually is getting broken down when I digest it into sugars that go into my body.

Sarah: Correct. Yes.

Tim: So if you do a lot of exercise, you run a marathon or something, you're not ingesting, or you have a long fast overnight, your body will maintain those sugar levels, even if you've used up... The sugar might be coming from your muscles or from other sources.

Sarah: So when you consume sugar, some of that sugar is broken down to its various components.

Same with carbohydrates, so that you've got glucose circulating in your bloodstream. That can be used for immediate fuel, immediate fuel for your brain, for your muscles, or for all of your cells that need energy for, to work, to breathe, to live. Any excess is stored as a compound called glycogen, and that's like your storage form of sugar.

So when you're going on a long run, when you've used up the glucose that's circulating, you start to release the glycogen stores from your liver, muscles and to be used for immediate sources of glucose. When you've then used up all of your glycogen stores, then you start to use glucose that's being made by your liver.

Jonathan: I've never run a marathon. Do I need to worry about running out of sugars in my body and having to switch to some alternative fuel source or else, like, desperately have something with sugar in it?

Sarah: No, absolutely not. Obviously, if you are an elite athlete, then you want to keep your glycogen stores up. For, but for the majority of the population, if you're consuming calories, whether it's in the form of protein, fat, carbohydrate, you will be able to produce the sugar that your body needs.

Jonathan: So can you explain to us what happens, like, in my body when I eat, like, a sugary drink? You know, like an energy drink or an energy bar, something that has got sugar inside it?

Sarah: What happens will differ slightly depending on whether it's in a liquid form, like a drink, whether it's in a solid form, like an energy bar, or whether it's actually intrinsic, actually in its natural form within a food, and we can follow up a little bit on that later.

But ultimately, what happens is you consume this food that's containing this sugar. Depends also on the type of sugar it is, whether it's the lactose or whether it's the sucrose. But most of the sugar that we get in the UK comes from table sugar, comes from sucrose. Most of the sugar that people get in the US comes from a source called high-fructose corn syrup But how you process them is very similar.

So high-fructose corn syrup and table sugar, or sucrose in the UK, both consist of these glucose and these fructose molecules. You consume your drink, your food, whatever that contains these. What happens is it passes into the gastrointestinal tract. It goes to your stomach, enters your small intestine.

You have enzymes there, in the case of sucrose, that break apart the glucose from the fructose molecule. If in the US you're having your food that's sweetened with the high-fructose corn syrup, the glucose and the fructose are already separated, so you don't have that initial breakdown. These simple sugars, the glucose and fructose, then pass through the lining of our small intestine, the cells that we call the enterocytes.

They enter the bloodstream. The fructose goes to the liver where it's reprocessed to either create more glucose or processed to create fat, triglycerides, and then the glucose circulates in the blood for a little bit to go to various places. So you have quite a short, sharp increase in circulating blood glucose.

It peaks around 15 to 30 minutes, depending on the source of food that it's come from. Returns to baseline around two hours, again, depending on the food source that it's come from. When it circulates in the blood, some goes to the liver where it's used for storage, some goes immediately to cells, to muscles, some to your brain, et cetera, where the cells use it for immediate energy.

Tim: And the other thing is we have a natural defense system in our bodies because if the sugar builds up to high levels in our blood vessels, it's actually quite toxic. Glucose, in a way, is a bit of a poison in our system, and that's why we have this very careful sensing mechanism that produces insulin to drive down those levels so it never stays at high levels for very long, 'cause you then get damage to all the blood vessels in your body and your brain, et cetera.

And that's what happens in certain forms of diabetes. So we've got a really sensitive system for controlling how quickly the glucose is absorbed and then comes down, and there's also a role of our gut microbes inside the intestine that, it is looking like increasingly important, but very difficult to study.

Sarah: And I think this is really important to pick up on insulin. So within minutes of glucose hitting your bloodstream, you release the hormone insulin. The hormone insulin is really important to control that level of blood glucose, 'cause at high levels it is toxic. And then it kind of, in simple terms, moves the glucose out of the bloodstream to the different places.

And insulin plays a really important role in what we call glucose dynamics, so in the shape of the glucose curve after you've had a meal, and it's quite relevant to how also different foods impact our glucose response, which we can pick up on a bit later.

Jonathan: And so this rise and fall of my blood sugar, my blood glucose after like a sugary drink, is that normal as a human being or is that only because we're now having sugary drinks that we, you know, our ancestors obviously didn't eat in the savanna?

Sarah: So, increase in circulating blood glucose after consuming sugar or any carbohydrate is a normal physiological response. It's a normal physiological response that our bodies are well able to handle because of the production of hormones like insulin and some other gut hormones as well that control those levels very carefully.

The problem is that we're now consuming foods that release glucose often very quickly into our bloodstream. We're consuming foods that also might have excessive amounts of sugar. And so the kind of foods that many of us are eating now tend to elicit, so bring about a bigger increase in circulating blood glucose than many of the more natural whole foods that we would've been eating years ago.

And so we are exposed to greater excursions, so greater peaks, and also interestingly, greater dips in circulating blood glucose.

Tim: We've evolved naturally to deal with episodic high amounts of sugar. And an example is when I spent time with the Hadza tribe, these hunter gatherers in East Africa. Every now and again they'd all, the tribe would go crazy over a find of a lot of honey up a tree.

And for two days they'd just gorge themselves on that. They weren't really interested in hunting or anything else. It was amazing.

Jonathan: So for two days they just ate honey?

Tim: Exactly, yes. So they must be really stressing their sugar sensors at that point. But then they would go, you know, several weeks without any honey, and they'd go back to their other regular diets.

And I think that's probably what we evolved to be able to deal with, these different food sources. But not having the equivalent of five tablespoons of honey every day mixed in with their other food. And I think this is the difference between the modern world that we see now, that little bits of either the sugar itself or, you know, fake sugars are put into all our foods.

Jonathan: So what happens if, like me, you're having two teaspoons of sugar or like, you know, six cans of regular Coke or whatever every day?

Tim: Then this is a stress that we weren't evolved to deal with. Your organs like the pancreas, what's inside your system here, feeds into the intestines, is producing this insulin, eventually gets tired, and eventually it stops working as well.

And so you have to produce more of it, and that then leads to a whole breakdown in the system. So that's really what we think is driving a lot of this problem of this epidemic of type 2 diabetes. And that's why we're seeing much more type 2 diabetes in children, which was totally unknown 40 years ago, because they're being, instead of you know, breast milk, they're given formula feed with lots of sugar in it, and then they're onto, straight onto pouches and ultra-processed foods, high amounts of sugar, then sugary drinks all the time.

And it's just an excess that combined with these other things in unhealthy habits we have at the moment and ultra-processed foods combination is causing these big problems, and our then inability to deal really efficiently with sugar.

Sarah: I think as well, Jonathan, what some of the new evidence is showing where sugar is particularly problematic is where it's consumed in an environment of excess calories.

So we shouldn't fear sugar itself because we have evolved to handle small amounts of sugar, episodic sugar, et cetera. But where we're getting the problems and is where we're in this environment where people are generally consuming excessive amount of calories, and where that excessive amount of calories is coming from sugar.

That's where we're seeing that it's becoming a problem. And the other thing that I don't think people talk about enough as well is where sugar causes a dip in circulating blood glucose. So we're very focused, if you look in any social media about, you know, this peak in circulating glucose, God forbid, you know, you should flat line your glucose.

No. Where I think that there's a real problem is that if you have sugar, particularly added sugar, this is free sugar that's not in a kind of food structure, so the kind of sugar you would have from, you know, a can of Coke, for example, or from a chocolate bar. What happens is that when the sugar enters your bloodstream, you release insulin, and quite often, because it's entering your bloodstream so quickly, you have this overshoot of insulin.

You have too much insulin. That overshoot of insulin tries to very quickly get the sugar, the glucose out of your bloodstream. And so because of that overshoot of insulin, you have this dip in circulating glucose about two to four hours. That dip in circulating glucose, we know from our own ZOE research, causes people to consume their next meal sooner, causes people, if they have that dip, to consume about 320 calories more over a day, which is huge.

Causes people to feel less energetic, less alert, lower mood. You know,

Tim: I had that. I mean, that was my breakfast in the old days, was a muesli and an orange juice before going to work. And, you know, at 10:30, I had this real dip, and I was tired and hungry and had to have some more sugar. But we just didn't think at that point, "Oh, what was I doing three hours before?" And this is why it's important that we understand the science.

Jonathan: You're saying that I might have something that causes a big spike in my blood sugar, but actually the thing that you should be really worried is after the spike, your blood might come down and actually go below its starting point.

And then I think, Sarah, you said, not only do I feel tired and hungry, I end up eating more than 300 more calories across the day?

Sarah: So our ZOE research shows that those who have a dip after having their breakfast, so the kind of breakfast that causes them to have this dip in circulating glucose, consume on average 320 calories more that day.

When we've also looked within an individual, so let's say take Tim one day where he has his muesli versus another day where he has his wonderfully healthy, full-fat yogurt, nuts, et cetera. On the day that he would've had his muesli, what we find is that that would cause him to eat about 100 calories more that day compared to if he's had his healthier breakfast that doesn't cause that dip, so he's not on that roller coaster throughout the day.

Now, I think it's important to say it doesn't mean that the peak doesn't matter. It's just that I think there's so much focus at the moment on your peak in circulating glucose, and you see all these sugar hacks, how to dampen your peak, how to flat line. We do know, again, from our own research and other research, that if you have a really large increase in circulating blood glucose, you do have an increase in inflammation.

You do have an increase in oxidation. Now, at short, small levels, absolutely, that's not a problem. Our bodies are clever. You know, inflammation isn't necessarily, if it's short term, bad for us. But where we're having the kind of foods that are causing these massive peaks and then these dips, if you're repeatedly, you know, stimulating your immune system, then it can become a problem over time.

Tim: So a little bit of stress is good for you-

Sarah: Yep ...

Tim: too much overloads the system.

Jonathan: Did I hear you say that if I am eating sugar every day, then that can actually increase my level of inflammation?

Sarah: So eating sugar to excess, depending on the source of sugar, yes, can increase inflammation.

Jonathan: And Tim, you talked about mental health at the beginning being linked to sugar, which I think is probably a big surprise.

It's a big surprise to me. I suspect it's a big surprise for a lot of listeners. How does that fit into this story?

Tim: Well, I don't think we should view mental health as being very different to just another organ in the body. The brain is there. The brain sucks up, you know, twenty, twenty-five percent of our energy, and, you know, it's only five percent of our weight.

So it's the most energy hungry organ in the body. So it's super sensitive to what it's getting as its energy source. And if you deprive it, you know, you give it too much or too little, that will stress the system. But we do know that when you're having repeated really high sugar spikes in the blood, that stimulates the immune system to create inflammation, which is just a sort of dialing up the thermostat on your immune system.

And that then travels from your gut to your brain via the vagus nerve. And you've got immune cells in your brain, and they will pick that up, this inflammation. And that has been shown to be associated with a whole range of mental and brain disorders, everything from slight cognitive loss, Alzheimer's to depression and even schizophrenia.

So we know that- The way glucose is controlled is very much linked to our immune system, and that's linked to all these kinds of diseases. And they all come back to, you know, controlling those key systems in our body and making sugars and glucose a really key factor.

Jonathan: Tim, are you saying that if I had just kept drinking my, you know, eight to maybe 10 cups of tea with the two spoons of sugar, that could actually have increased my risk of something like Alzheimer's?

Tim: That's correct, yes. Lots of data now linking not only type 2 diabetes with Alzheimer's, giving you a three or four times risk over your lifetime, but also poor diet related to sugar intake, sodas, free sugars, increasing risk of these as well.

In observational studies, but still there's a lot of them. So it does start to make sense once you start understanding the mechanisms, that your brain is very sensitive, and that by changing the environment of the immune system, you will change your brain's response, and everything from depression to dementia can be a result.

Jonathan: Now, I wasn't overweight, so I was thinking, "This is totally fine. It's having no effect on my body whatsoever." So was I fine and I didn't need to worry about any of these risks?

Tim: Weight has an interesting effect. So it's definitely bad for all things to be overweight, 'cause that increases your risk of all these outcomes like Alzheimer's, et cetera.

But it doesn't mean that just because you're not overweight, you're not at risk. it still increases the risk, not as much as if you were obese. Also, you might have fat on the inside that you can't see. We've discussed this concept before of you being a potential TOFI, Jonathan, which is, you know, thin on the outside, fat on the inside, and that's because we have this thing called visceral fat around our organs, our liver, that can weigh up to a couple of kilos, and very hard to see it without scans.

And this is why a lot of Asians, particularly South Asians, suffer from lots of diabetes without necessarily being obese. So you might have a risk of- Having metabolic upsets without necessarily everyone saying, "Aha, I, you know, it's because you're overweight."

Jonathan: And is it possible for me to have a raised level of inflammation from eating all of this, like, food with sugar in it without it sort of being obvious in terms of weight gain?

Or will I only have the inflammation that you're talking about? Like, is it only if I put on weight that you get this inflammation?

Tim: No, it seems to be independent of that, and it'd be increased if you had extra body weight, but we don't think those systems are sort of closely correlated. So the fact that you're getting inflammation has all kinds of effects on the body which might vary between people.

So some people might get more effects in the brain, others might get more effects in where their weight is distributed. Some might get more effects in the heart. They're not necessarily all gonna be the same in everybody, but you just got to realise that this is a very major risk factor for all kinds of problems.

But people don't always think about, you know, if I'm having lots of sugar, what's that gonna do to me? Okay, inflammation, what does that do? Well, it might be a reason that you're a bit lethargic, that you're not, you know, doing your podcast very well. you're not sleeping well. You're, you know, hungrier than you should be.

All these things are related to low-level inflammation.

Jonathan: Before we move on to, like, understanding the different types of sugars, there's just two specific things in my mind. I've heard people talk about sugar being directly related, and I've never heard someone tell me that it's related to, like, my mental health or Alzheimer's.

But I've definitely heard people talk about sugar being related to my risk of acne, and I also feel like I've heard people talk about sugar causing cancer. Are either of these true?

Sarah: So there's evidence to show that people that have higher intakes of sugar in some instances have an increased risk of some cancers.

But it's quite complicated because it's difficult to tease apart what's the effect of the sugar versus all of the other components that are coming with a high sugar diet. People typically with a high sugar diet might be less healthy in other areas, might smoke more, might also have lots of other unhealthy components.

You can partially adjust for this, but not fully. Where I think the evidence is quite strong is that there's this indirect effect rather than the direct effect necessarily of sugar. Yes, there might be some small direct effect of sugar in terms of cancer, but most of the evidence is an indirect, where sugar is associated with an increased risk of excess calorie consumption and therefore obesity.

So people with a higher sugar intake tend to have higher levels of BMI, so tend to be living with obesity. and then we know that having more adipose tissue, so fat tissue creates this very pro-inflammatory state, releases other hormones, et cetera, et cetera. And we know that it's that excess adiposity, that excess fat tissue that is particularly harmful for many cancers.

So it's more likely to be that indirect effect

Jonathan: So it may not be just eating sugar, but the weight gain from the sugar. I am actually more at risk of cancer if I put on weight?

Sarah: Yes. So there's many cancers. Colon cancer is a great example. There's other cancers as well, like breast cancer. You have significantly increased risk of colon cancer if you are overweight because you have metabolic disturbances, you have increased inflammation and so forth.

Tim: It's most cancers actually. I think the majority is, there's a link with obesity, and we think it's because those fat cells produce these inflammatory chemicals which just sends the immune system in a state that it can't function normally and can't fight the cancer cells. So it's distracted by all this upregulation of the thermostat.

So that is the current theory about why obesity is related to cancer.

Sarah: there's some interesting data that's been coming out recently showing that if you limit your sugar intake, so go on, like, a ketogenic style diet, so where you have almost no carbohydrates, you're not increasing any circulating glucose, that if you're going through treatment for cancer like chemotherapy, that it can actually improve your response to cancer treatment because there's this theory that you're starving the cancer cells of important fuel because you're starving them of sugar, of glucose, but you're still going to be producing glucose anyway in the body.

So it's something that is a kind of watch this space, but I know lots of people are talking about it, so it's important to mention that while we talk about cancer. But I do think that there is no strong evidence that sugar on its own, independent of excess calorie intake, independent of obesity, is a carcinogenic.

And the WHO, the World Health Organization, does not class it as a carcinogenic.

So a cancer-causing agent

Jonathan: I've also read people saying, like, sugar is the cause of everything that's, like, happened to our health over the last 40 years in terms of, you know, obesity and diabetes. Is it that simple? Is it sugar that's the problem behind all of this?

Sarah: Absolutely not. Look, we all want a simple answer. 20 years ago, fat was demonized. You know, any fat in a food was considered the worst thing. Now it's sugar that's demonized. Absolutely, there's a problem that we're consuming too much free or added sugar in our food that's causing in short-term increases in inflammation.

It's causing excess calorie, but it's not the baddie of everything that we consume. It's often a marker of actually a bad food intake. Yeah.

Tim: The first epidemiology studies that really showed this were studies, which is easy to do, is that how many, you know, sodas, fizzy drinks do you have per day? And the correlation was absolutely with all these conditions and diseases, including obesity, diabetes, cancer, heart disease.

They were the first indications that this was a problem, and that hasn't gone away. But as Sarah says, it's very hard to tease apart all those things. They're definitely not good for you. but how much that whether it's, you know, it's definitely not 100% of the problem. exactly how much is quite difficult to work out.

Jonathan: And what about acne?

Tim: Yeah, acne used to be thought of as something that if you ate the wrong things, you ate too much chocolate, you're gonna get acne. And so you, everyone was blamed for having spots because you've been secretly munching all these snacks. we did a twin study over about 15 years ago, because my wife's a dermatologist, and it showed quite convincingly that genetics were probably the major factor in acne.

You know, the oiliness of your skin, how those, all the follicles, are working overtime with excess oils or not. And so currently, diet has a fairly negligible effect in our analysis, and not saying it has no effect, but it's a pretty small one. Most of it is now due to genetics, people with the wrong skin, and using TikTok routines on their face, putting far too much other oils on top.

Jonathan: So it sounds like sugar isn't quite as evil maybe as I had thought as I'm coming in. But I'm also conscious that a number of times you talked about different types of sugars and, like, free sugars and added sugars. I don't understand what any of that means.

Sarah: So I think that is actually the most important factor to think about when we think about the impact of sugar on health, whether it's free or whether it's intrinsic.

What we mean by free sugars are basically sugars that are outside the structure of a food. I think that's the most simple way to think about it. So that includes added sugar. So in the UK, that would typically be sucrose, so table sugar added by yourself or by manufacturers. In the US, that would typically be high-fructose corn syrup added, as food is processed.

But free sugars also includes honeys, syrups, and fruit juices. So when we think of free sugars, it's the sugar that's either added by us at the table or manufacturers into the food, but it also includes the fruit juices, the fruit syrups, honey, and so forth.

Tim: So I think most of the problem is not people adding a spoon of sugar to their food these days.

It's the hidden sugars in many of these ultra-processed foods that you're not actually aware that you're having because they've been masked by other ingredients and chemicals. I think in general, if you look overall in the last 20 years compared to, you know, the 1950s, we're eating much more sugar that's disguised in foods than we were in the past.

And of course, it's massively subsidized in most countries in the world, so it's incredibly cheap ingredient. And so it's often easier for manufacturers to put sugar in than anything else because it's so cost effective, because taxpayers are paying for it.

Jonathan: Could we talk about drinks for a minute? Because I think you mentioned that was a big part of where we get these added sugars or free sugars in our diet. Are drinks really different? So you know, if I drink a Coca-Cola, I think we all sort of know that that's bad for us.

After all, that's why we've had these diet colas for ages. But if I have an energy drink, you know, and there are lots of those that talk about, you know, using that with sport, is that much better for me?

Sarah: Energy drinks are highly variable, so it depends on the type of energy drink. But most energy drinks are packed full of sugar.

Most types of Coca-Cola are packed full of sugar. They're absorbed really quickly because firstly, you're consuming it liquid, and then it's really rapidly absorbed into your bloodstream. So you have this very big peak in circulating blood glucose. You're likely, therefore, to have your insulin overshoot, and likely to have a dip in circulating glucose.

That's very different to if you're consuming that sugar in the form of a fruit or a whole food. Very different.

Tim: We always say that the Cokes and the Pepsis, you know, a can of that will have on average around eight spoons of sugar in it, and we go for other alternatives, and you might look at things that look healthier, like iced teas and things like this, and they've often got even more.

And some ginger beers have like... can have 50% more sugar, or some of these traditional lemonades. So just look on the back and see how many grams of sugar there is in that drink, knowing that, you know, the rough rule of thumb is around four grams is a teaspoon.

Jonathan: What about these energy drinks?

Because I feel the marketing suggests that it's mid-afternoon, I'm having a slump, and like I need some energy, and so I should have an energy drink sort of to fit with it. I feel that's marketed in a very different way from, you know, the Coca-Cola or the traditional lemonades. Is that a different sort of sugar in there?

Sarah: It depends. So some of these energy drinks have the sugar already broken down to the individual components. So they might be particularly high in glucose, for example. So unlike table sugar, that's glucose and fructose, it might just be the glucose or it might have the sucrose, so the glucose and the fructose.

It depends on the energy drink. Either way, you're going to absorb that glucose really quickly. And yes, maybe when you're on the bike, you've used up your glycogen stores and you need a bit of circulating glucose, having an energy drink is fine and you're going to quickly use that glucose. But because you're having an afternoon slump or a mid-morning slump, absolutely, I think it's the worst thing that you can do because then you just continue that rollercoaster of energy dips because of this big surge in glucose and this big dip.

Tim: I think it's a bit of a con as well, because if you speak to sports scientists, they'll tell you that generally we're built to go two to three hours exercising before we need things like electrolytes or glucose. Obviously, you think about our evolution running around on the plains of East Africa, we weren't stopping every 20 minutes for a glucose drink.

Yes, you might need it after a three-hour cycle or in marathons and things, but for the stuff most people are doing, it's absolutely just marketing.

Jonathan: What about orange juice? I know lots of people in my family who will have orange juice at breakfast because they feel they're doing something really great for their health.

Tim: Well, I think they're making a big mistake.

I was brought up on orange juice. I gave it to my kids. It was part of our family. But orange juice is essentially full of sugar. It's got some things that are better than a Coca-Cola. It's got some vitamins and natural things. It's got potassium. But essentially, a lot of it is the sugar that is coming from the fruit.

And because they're not eating it as the whole orange, it's being released as Sarah has said, much quicker than you would get eating an orange, and you're not getting that fiber to also dampen down that absorption. So it's a really unnatural sugar rush you're getting from orange juice.

Delicious though it might be, it should be a rare treat, not a daily option.

Jonathan: So help me to understand then right at the beginning why I shouldn't be giving up fruit. And I've definitely heard people say, "Well, fruit is really high in sugar, so clearly that's bad for you. And just as we should be cutting out the orange juice, you know, we should be cutting out the orange as well."

Sarah: I absolutely disagree with that narrative that I think is becoming a real problem at the moment on social media, that fruit just because it's high in sugar is bad for us. The sugar in fruit is what we call intrinsic sugar. So it's sugar that's encapsulated within the structure of the fruit. So an orange behaves differently to orange juice.

An apple behaves differently to apple juice in terms of how the sugar is processed, but also the response that it elicits. So let's take apples as an example. So if you consume a whole apple versus apple juice, what happens is you have a more gradual increase in circulating blood glucose. You're unlikely to get a dip in circulating blood glucose.

But if you have the apple juice, then you've got this big rush of sugar and then this big dip. So then you're going to have all of these problems like higher inflammation, overconsumption of calories, et cetera.

What's also really important to note is that you've got loads of other great things in that fruit.

You often have lots of components like polyphenols, other vitamins, other minerals that can act on anti-inflammatory antioxidant pathways. So that means, for example, if you were to have, let's say, a big portion of berries or a large portion of an apple, for example, even if you do have an increase in circulating glucose, which you will have because it's a normal response to having the sugar from a food. Yes, firstly, the fibre's blunting it a bit, but also the polyphenols will also counterbalance, so almost like block in simple terms, that increase that the glucose is causing in inflammatory measures.

And so that's why firstly juice behaves differently to the whole fruit because of the change in the fibre and the glucose dynamics, but also why we cannot think of sugar and fruit in the same way as we think of the sugar that you added to your tea because of all the other wonderful components in that fruit.

Tim: I think there are some caveats there. Some of these tropical fruits that we're getting are very high in sugar, you know, watermelon, papaya, and mangoes. Modern grapes are bred to be really high in sugar. When I was a kid, they were sour, you know, slightly sweet at most. Now they're super sweet. I think we...

There is a range within the fruits. And interestingly, after doing the ZOE studies early on, I changed from having a banana as my regular fruit, to an apple or a pear because I could notice a difference in the sugar to fiber ratio, anyway, of some of these fruits. So, absolutely, all fruits are good.

They've all got something good about them, but, you know, not all fruits are created equal.

Sarah: Where there's really interesting evidence is randomized controlled trials that compare people consuming the whole fruit, the pureed fruit, and the fruit juice, and then equivalent amount of sugar. And you see in terms of the health effects, it kind of graded that way, where the whole fruit is best for you.

Then the fruit puree, the second best, that has still all the constituents of that whole fruit, but it's just kind of mashed up. So it's a little bit less good because you've taken away some of the structural elements. Then you've got the fruit juice. That's a little bit worse because you've taken away the fiber, but you might still have some of the beneficial bioactives like polyphenols or antioxidant vitamins.

And then obviously the worst is the sugar. So you kind of, I think, think about it in that graded way. So smoothies are still a really good source of many different bioactives, fiber, et cetera. Just don't drain out the pulp. Keep the pulp in there that's got all the fiber.

Jonathan: And what about most of the smoothies that you would buy at the supermarket?

Sarah: Highly variable. You've got some smoothies that I think are very unhealthy for you, that tend to have all the fibre removed, that have lots of added sugar. You do have some smoothies that can be quite healthy for you, but I think it's quite difficult to know. I would have a look at the back labeling and look at what's free sugar versus what's intrinsic sugar.

The problem is in the UK that's very challenging because the labels in the UK actually just do total sugar. The labels in the US, do differentiate between the free sugar, and the intrinsic sugar.

Jonathan: What about dried fruit?

Sarah: So again, dried fruit is another area that I think we demonize because it's a very concentrated source of sugar because you're taking all the water out of the fruit, so you've got a concentrated source of sugar.

But you've also got a concentrated source of fiber. You've also got a concentrated source of bioactives, so these polyphenols. So I think dried fruit is actually unfairly demonized. Yes, because it's very concentrated, it's very easy to overconsume and before you know it, you've had a huge portion of sugar.

But I think in small amounts, absolutely, it's a really healthy snack.

Jonathan: You know, should I go cold turkey on sugar and just try and cut it out as the best way to make a change from my, you know, traditional diet if I have been eating a lot of sugar?

Sarah: My personal view on that is absolutely not, because I think that food is there to be enjoyed.

I would also say it would be really difficult to go cold turkey, because considering the majority of our food is processed with added sugars that we probably don't even know are in there, that are called all different things on the food label, unless you're going back to basics, cooking everything from scratch, and we don't need to eliminate all sugar from our diet.

We really don't need to. We just need to make sure we're not consuming excess calories from sugar.

Tim: I think a gradual approach is what's needed. I think most of us went through that phase when we were perhaps teenagers, having lots of sugar in our tea and coffee, and we slowly weaned ourselves off it, and that changed your taste buds.

If you like flavored yogurt, then try and, you know, gradually wean yourself off it and get onto plain yogurt, and start reducing the amount of sugar or honey you put into it. You can do this quite easily with a gradual approach. Look at the things you have as a daily habit and just look at them a bit more cynically.

Sarah: Our sweet taste receptors in our mouth do adapt, so our perception of sweetness adapts, and this is a big problem that we have with so many foods having added sweeteners that are really powerful in terms of our perception of how sweet a food is, that a lot of times sugar is swapped out for sweeteners.

They activate our sweet taste receptors even more.

Jonathan: So is swapping from sugary drinks to drinks with sweeteners therefore not, like, the way to sort of make the change out of this high sugar environment?

Tim: You'll get a short-term benefit because you're not getting the harmful metabolic effects of the sugar, but you're still left with a very sweet tooth.

That means that you will be craving sugars. So ideally, you want to be cutting down on both.

Sarah: And the evidence shows as well, even though you'll be cutting out loads of calories from those drinks, the evidence actually shows that you tend to adjust with the rest of your food intake to compensate for that, and so going on diet drinks doesn't mean that you're actually going on a calorie deficit for most people in that free living setting.

Jonathan: That's really interesting. So although you are losing the calories by going from, like, a regular Coke to a Diet Coke- You still are getting, like, all this sweet taste all the time in your mouth, so that's not changing overall what you want to eat, and then you just sort of eat some more other food to make up for it.

Sarah: Yep.

Tim: And that's possibly because of your, you know, your sensors are tickled by these artificial sweeteners into seeking out some of these other less healthy foods.

Jonathan: And if someone's listening to this, and thinking, like, you know, I am eating quite a lot of sweet things, or they're just listening to you say, wow, there's all this sugar hidden in my food that I didn't realise, what should they be looking for on labels?

Because you've also said it isn't always just written, you know, added sugar.

Sarah: So I think in the US it's a lot easier because they separate out free sugars from intrinsic sugars, and I believe that based on the totality of the evidence, the intrinsic sugars as such isn't a problem unless it's excessive.

So they should be looking at labels where the free sugar value is quite low. In the UK, it's more difficult because you just get the total sugar amount. You can look at the ingredient list, and it's useful for people to be aware that the order of the ingredient list is the order of the amount of the ingredients.

So the ingredient that's listed first is what's found in the most amount in that food. The ingredient that's listed last is the least amount. Often, though, there's lots of different types of sugars that are added to sweetened foods, many of which don't say sugar, many of which names people wouldn't even recognise as being a source of sugar.

Tim: They're done deliberately to fool us because they don't want to say, you know, sugar is 80% of this product, and they divide it into five different groups.

Jonathan: So if you're not in the US and you can't see the free sugar number, if you're anywhere else listening to this, how much sugar should I expect in my snack bar to feel this is fine versus actually I'm basically just eating a lot of sugar with this thing?

Sarah: There's a couple of points to mention here. One is where's that sugar coming from? And okay, I said in the UK it's very difficult, but if it is a bar with only five ingredients, and those ingredients are fruit ingredients, dried fruit is, you know, in the top three of those ingredients, and then you've got nuts and seeds, well, it's coming from an intrinsic source.

Personally, and I have to caveat that this isn't like a magic cutoff, if I'm looking at a snack bar for my children or for myself, I probably wouldn't want a snack bar that's got maybe more than 10 grams of sugar in it. But I wouldn't want that 10 grams to be coming from free sugars.

Tim: And just put that in context, that's two and a half teaspoons of sugar.

That's quite generous, I think. I would be looking personally at, you know, one to one and a half teaspoons, which, you know, I can visualize that. Like I said, would I have a bit of food and tip a heaped teaspoon of sugar on it? Might do if I was feeling it, but I wouldn't want to be wanting more than that.

For breakfast cereal, I look at the percentage sugar, so that's, I think, the easiest thing to do. So most of the bad ones are 30% to 40% sugar. And you say, "Really? Do I wanna give my kids something that has... If you just, you know, got rid of everything else, you'd see that huge pile of sugar?" No. So that, get that right down to less than 5%, and then you'd be getting something that's reasonable.

Sarah: And we know how much sugar we should have in terms of our percent energy, so the percentage of the calories that come from sugar. So it's recommended you should try and have less than 10% of your calories from free sugar. You should try and have less than 5% in an ideal world, so WHO have brought out this recommendation that really we should be aiming to have less than 5% as free sugar.

We're not meeting that. In the UK, we're doing pretty okay in terms of the general recommendation. We're around kind of 10, 11%. But in the US, they're really not doing well. They're up 15, 16, 17% of having these free sugars in their diet. So the US is a particular problem, and a particular problem I think because of the use of the high fructose corn syrup that's in so many foods.

Jonathan: And if someone's listening to this, and they'd love some examples of products that maybe look healthy but tend to contain a lot of sugar, what would be the things that we should most watch out for?

Sarah: Breakfast cereals, highly variable. Sweetened yoghurts. So you'll get a lot of yoghurts that might look healthy because they say low fat, or fruit yoghurts, and they might have what looks like a little bit of a raspberry in it, but actually then you've got a load of syrup, and they tend to have quite a lot of added sugar.

Tim?

Tim: Added sauces, so ketchup-

Sarah: Yep ...

Tim: a lot of pickles have really high amounts of sugar in them, and they're disguised because they've also got some sourness and some bitterness.

Jonathan: Final question. Imagine that I'm like, "Oh, in general, I'm doing quite well, but then I just really want a piece of cake," or in my case, like maybe like a pain au chocolat, you know, chocolate croissant.

I'm a big victim, and I have that big slice of cake, and I'm aware that I'm likely to have, like, this big blood sugar spike and then dip. Is there anything that I can do that means I can still eat that, but maybe reduce some of those bad effects that we were talking about earlier?

Sarah: Yeah, so firstly, have that cake, Jonathan.

Life is short. Enjoy it. But there's a couple of things you can do. So one is that we know that moving, so exercise immediately after consuming a high carbohydrate, high sugar load can reduce your blood sugar peak. So that's one thing you can do. The other is pairing foods. If you can pair your sugar source with something that has healthy fats, healthy proteins, it will diminish, so it will reduce your blood sugar peak, and most importantly for me is that it will prevent that dip in circulating glucose.

And we've done experiments at ZOE showing this.

Tim: So that's like a yogurt, so-

Sarah: Yeah, have a full-fat yogurt-

Tim: Full-fat yogurt- ...

Sarah: with

Tim: your cake ... on the side with your cake.

Jonathan: And if I've just eaten sort of a meal that has got, let's say it was a healthy meal, and it's got, like, healthy fats and things like that, and not a massive amount of other easily digested carbohydrates, and then have my dessert, am I gonna...

Is that gonna have less of a spike than if I just have it, you know, in the middle of the afternoon or somehow separate from the rest of my meal?

Sarah: Yeah, depends what time distance there is between having your main meal and having your dessert. If it's within the same 30 minutes roughly, then yes, it will absolutely reduce that circulating blood glucose.

We know this from studies where they give like preloads, so they'll give people a preload of fat or particularly protein, and then 30 minutes later or 15 minutes later give a high carb load, and it significantly reduces that peak and also prevents the dip. But Jonathan, what's important to remember, it's not just about that change in circulating blood glucose when you're thinking of pairing.

It's also about what else is in that carbohydrate source that can diminish some of the downstream effects. So pairing it with, for example, nuts, seeds, raspberries that have polyphenols that are gonna dampen down some of the downstream effects that that carbohydrate's having on changes in inflammation.

Jonathan: And just one clarification, 'cause you said the other thing was to do exercise in order to have any impact on my blood sugar?

Sarah: A 10-minute walk, as long as it's within about 20 to 30 minutes of eating your meal, would count as exercise. And the reason that exercise is important is because then your muscles are used, like literally taking, in simple terms, from your blood, the glucose, and using it.

So it's bringing down your glucose response. But you're not even moving at your desk. So many of us might eat and be straight back at our desk if they're really hard workers like I am, obviously. But there's evidence that even just moving our legs, and I know we had an expert on one of our previous ZOE podcasts that talked about a study he had done that showed just twitching, clenching your leg muscles, after you've eaten, that can significantly lower your glucose.

Jonathan: I had better wrap up. I'm just gonna try and do a quick summary. So the thing I'm most shocked by is the link between sugar and sort of dementia and mental health, because I had no idea that these were linked. I think everybody knows that it can increase your weight, but the idea that because the sugar can lead to this increase in inflammation, it can have this impact On your brain is extraordinary.

I'm also really struck that it can increase risks of cancer again, not because the sugar is worse than anything else, but because it's causing this inflammation, that it can have the impact on all these things that we don't tend to think of as being so related to our food. The other thing I'm really struck by is that it's not just that sugar is a particularly deadly component in our food, it's what impact is it having on our body, and in particular, what's sort of happening to our blood sugar as we eat it?

And that therefore, depending upon whether we're eating the sugar all wrapped up inside a piece of fruit, or whether it's just become this sort of free sugar that I can absorb, and Sarah used this brilliant example, has this huge impact, and has an impact in two ways. My blood sugar can really spike.

You said that's a big problem if my blood sugar stays really high. So I have my insulin, I pull it down, but I do this over and over again, I could end up getting diabetes. But interestingly, if I have a dip and it goes below the starting point, it makes me feel tired and hungry. And so weirdly, I then just go and eat another 300 calories on top.

And so you have this thing where you feel really tired at 3:00, you have an energy drink or you have a chocolate bar, and then a couple of hours later you're more hungry than you would've been otherwise, and you eat more calories. So you can see how the sugar is a bit deadly because of course it tastes so great.

And so we have to be really careful about it being hidden in things, and we need to be really careful about food manufacturers making claims. So I'm really struck that you just said, well, energy drinks are obviously just tricking us. Unless you are literally cycling up a hill for two hours, you don't need this energy drink.

It's basically sort of like a Coca-Cola with better branding. And on the other hand, fruit, even though it's got all this sugar, you're saying not only don't worry about it, but actually it's good for us because there's all this other stuff, the polyphenols and the fiber and everything in it, and when you eat it, you have a much slower impact on your blood sugar.

So unlike that energy drink, it doesn't go straight, shoot up and come back down But in all these cases, we probably all have a much sweeter tooth than our ancestors would have done because there's so much sugar in everything. And so you do want to change, but you don't want to go cold turkey. You want to do a gradual reduction.

You want to watch out for particular areas where the sugar is really high and you might not realise. And I heard cereals. Look really carefully at breakfast cereals. Yoghurts, particularly fruit yoghurts, that actually sounds really healthy but is stuffed full of sugar. Sauces like ketchup. And don't switch from sugar to sweeteners because although you are reducing the calories, it's maintaining this really sweet taste, so you're not adjusting your sweetness.

And this is probably part of the why when you move to a diet drink, weirdly you take out all those calories, but you don't lose any weight, and you've still got this sweetness that you're chasing afterwards. But finally, Sarah says, "I can definitely eat my cake 'cause life is for living," which I love. Think a bit about what I can do.

So even just go for a little walk afterwards could really make a difference on its impact, but also pairing it with other... So if I'm eating something with, like, healthy fats and proteins, and then I'm having this, I'm in a much better place than if I ate it on my own. So it's not like I can never have it.

I should be able to enjoy myself, but be thoughtful about maybe how often, how much, and when.

Sarah: Absolutely.

Jonathan: If you enjoyed today's conversation with Sarah and Tim, watch this episode next. It features Professor Walter Willett from the Harvard Chan School of Public Health, and he's the world's most cited nutritional scientist.

In it, he explains the truth about carbs and why they're making us sick.