The great calorie deception: Are food labels misleading?

Millions of us are counting calories every day. But do we know if those numbers truly reflect the energy we get from eating?

It’s about time that we debunked the “one-size-fits-all” approach to calorie counting and unmasked the outdated methodologies that contribute to inaccuracies in food labeling.

In today’s episode, Jonathan and Dr. Sarah Berry ask: How exactly do we measure calories, and is calorie counting actually effective?

Follow ZOE on Instagram.

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

Mentioned in today’s episode:

The Wilbur Olin Atwater Papers from the United States Department of Agriculture

Is there a nutrition topic you’d like us to explore? Email us at, and we’ll do our best to cover it. 

Episode transcripts are available here.


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

[00:00:17] Sarah: Jonathan, we hear about calories, or in fact the lack of calories, all the time. They're the target of numerous diet plans, and shop shelves are packed with low-calorie alternatives of popular foods, but before we can think about cutting calories, we have to count them first. And this is exactly what 86 million people are already doing in the U.S. through the use of calorie-counting apps. 

[00:00:41] Jonathan: 86 million people. That's a lot of people.  

[00:00:44] Sarah: That's a lot, lot of people. I'd love to know what that is in terms of percent of the US, but I don't, I can't I don't off the top of my head know what what the population is  

[00:00:54] Jonathan: A large part of those who are over, uh, 20, I guess.   

[00:00:58] Sarah: And I imagine it's the same in the UK, that people are using the information on food labels to attempt to accurately monitor their calorie intake. 

[00:01:09] Jonathan: But Sarah, how accurate is this method and can we trust the calorie numbers that are on these labels? 

[00:01:16] Sarah: So our understanding of calories and the limitations of calorie labelling is really changing now, and this area of study could help have big implications on what foods we decide to eat.  

[00:01:29] Jonathan: Well, it sounds like we better get started then. 

Hi, I have a small favour to ask. We want this podcast to reach as many people as possible as we continue our mission to improve the health of millions. And seeing this show grow motivates the whole team at ZOE to keep up the hard work of creating new episodes each week. It also makes my mom proud. So if you've ever enjoyed this podcast, please hit that subscribe button. 

Ok Sarah. So imagine I've walked into a convenience store. I've picked up a jar of peanut butter, and straight away I can see on the label the sugar, the fat, the salt, and the calories. Now I can picture the first three of those like really easily, but when it comes to the calories, it's actually a lot harder to imagine really what that is. 

So if we just start with the basics, what actually are calories?  

[00:02:18] Sarah: So a calorie is a measure of energy, and we use it as a way to quantify how much energy there is in a specific food or a meal.  

[00:02:26] Jonathan: Okay, so how much energy is there in just one calorie?  

[00:02:30] Sarah: So a calorie is the unit we use to measure the energy in our food that's equal to the amount of energy needed to raise the temperature of one litre of water by one degree Celsius.  

[00:02:41] Jonathan: You've completely lost me there. I thought calories were about putting on weight. Why are we suddenly heating up water?  

[00:02:48] Sarah: Because this is what we do in science. We make things tricky. Um, but it's, it is the way that we as scientists, um, measure the amount of calories in a certain food. So let's take the peanut butter that you've just grabbed off the shelf now to work out its calorie content. 

We'd put it into something called a bomb calorimeter. Okay,  

[00:03:08] Jonathan: so that sounds kind of scary. How does this bomb work?  

[00:03:13] Sarah: Um, so we take your peanut butter and we place it into a sealed container, which is called a bomb. And this is surrounded by some water, a known amount of water. The peanut butter is then burned to a total crisp, and the change in the water temperature around it is measured. 

If it changes by 50 degrees, then we can say that there's 50 calories in that quantity. Of peanut butter. And Jonathan, every nutritionist out here who's done a nutrition degree will know that this is one of the standard lab practicals that you do in your first year. And that as an academic, I've taught students how to do this for countless years. 

So the bomb calorimeter actually gives me nightmares sometimes.  

[00:03:56] Jonathan: So what you're saying is that this process gives us the calorie number that we then see on that jar of peanut butter that I've bought in the store?  

[00:04:05] Sarah: Not quite, as you know, I always say it's a little bit more complex than that, so, the bomb allows us to work out the net calorie content, so the net calorie content of the peanut butter, but we don't actually absorb all of those calories when we eat it. 

[00:04:19] Jonathan: Wow. I didn't realize. So what you're saying is that we know that this peanut butter contains 50 calories, you know, if you burnt it all and turned it into heat, but when I eat it and uh, my body extracts some of that energy for me to use, I might only absorb like 40 of these calories?  

[00:04:35] Sarah: Exactly. A man called Wilbur Atwater recognized the significance of this, and at the end of the 19th century, he ran thousands of tests with hundreds of foods. 

And this involved measuring the energy content of the food, using this bomb calorimeter, and then also feeding these foods to people, collecting their poo, and then putting their poo through the bomb calorimeter to see how much of the energy wasn't actually. Used. He spent 20 years doing this, Jonathan, so please don't ever moan about, you know, any of your work again, because imagine 20 years of dealing with people's poo. 

[00:05:11] Jonathan: I have to say that that is dedication. 20 years of feeding people different food and burning their poo. And I, I am impressed the, um, the Victorians were made of, um, stern stuff, weren't they?  

[00:05:24] Sarah: Well, I think it's just us scientists, Jonathan, we are a dedicated lot.  

[00:05:28] Jonathan: I think that's right. Thankfully for the rest of us, you do it so we don't have to. 

So, so what did he find?  

[00:05:34] Sarah: Um, so this allowed him to calculate the available calories, and we can do this, estimating them from the amount of protein, fat, and carbohydrate that there are in any food. So what he deduced is that there's nine calories for every gram of fat. Okay. There's four calories for every gram of carbohydrate and four calories for every gram of protein. 

Okay. And so if we put that into context, that means that for every gram of fat, there's about double the amount of calories than there are for, for example, carbohydrate and protein. Which is why I think people often think, oh my gosh, fat is, uh, you know, fattening. Now these are known as the Atwater factors. 

This nine is four and this four, and this is what the food industry uses to work out what calorie number to put on the food label.   

[00:06:25] Jonathan: Ok, so actually it all sounds quite straightforward. We just look at the number of grams of fat, of carbohydrates and protein in any food. We multiply it by your factors, the nine and the four, and the four, and boom. 

We have the calories for every food. It's straightforward and we know what to eat.  

[00:06:43] Sarah: Yeah, but Jonathan, you know, there's always a but with me and always a but in science, so I can't keep it that simple. Um, now this way, counting calories was created over 120 years ago and recently our understanding of the actual caloric availability, so how much we really do absorb of certain foods has changed, but our labelling method has not changed. 

We also now know, for example, that protein takes energy for us to digest it. So the protein Atwater factor of four is about 30% out. So it's about a 30% overestimation.  

[00:07:21] Jonathan: Wow. So actually what you're saying is our food labels are basically lying to us?  

[00:07:27] Sarah: Well, let's look at fats and let's look at my favourite food, Jonathan, that I always use as an example to illustrate the complexity of nutrition. 

And that, of course, is the humble nut.  

[00:07:40] Jonathan: Well, we looked at the research and Sarah, don't you actually have a recent paper on exactly this?  

[00:07:44] Sarah: Yeah, so I've got a number of papers looking at, um, energy, um, availability from nuts and how they affect our health. And there was actually an earlier paper in 2012 that found that the Atwater factors overestimated the calorie content of nuts by 30%. 

So about 30% of the calories from nuts were actually coming out in the poo. And we've seen similar results, um, since, uh, in, in my own studies, uh, looking at why this is happening. And what's clear is that these Atwater factors don't really account for the complexity of different foods. And I think what's really interesting is that the caloric availability can be different even when we are comparing exactly the same food. 

[00:08:30] Jonathan: Okay. So how can that happen, Sarah?  

[00:08:32] Sarah: So Jonathan, imagine if you go into the store and grab a pack of whole almonds, which I know that you love to munch on as a snack. And also grab a bag of ground almonds. Now the back of a pack of labeling are gonna be identical, aren't they? For these two bags. 

[00:08:48] Jonathan: Because you just explained this, right? When you burn it all up, they just work out, um, the number of calories that's gonna be the same and they apply this, um, magic formula that you were describing. Is, is that right?  

[00:09:00] Sarah: Yeah, absolutely. So the carbohydrate, the protein, and the fat contents are exactly the same for these ground and for these whole almonds. 

But critically, the calories that we absorb are not the same despite what it's saying on the back of pack labelling. And this is because the process of. Grinding the nuts breaks the cell walls, which leads to the release of lipids and other macronutrients and micronutrients like vitamin E, meaning that you can absorb a lot more of the energy, which therefore changes the amount of calories that you are actually absorbing from the ground versus the whole nuts. 

[00:09:37] Jonathan: So I guess if we step back for a moment, it's not really that surprising, is it? I think, you know, if we compare to 120 years ago, people thought of our bodies as being very simple, right? Like a steam engine. That was the most complicated thing that they'd really built. And today we know that our bodies are unimaginably complicated, so it's probably not that surprising, right? 

That our body can't just treat it as if it was being burnt up. And I guess this is a brilliant example, is it where the label should be really different between that ground nut and that whole nut? Because actually what we care about is not what happens if you burn it in a furnace. We actually care about what happens when we try and break it down and, and turn it into energy that we can use.  

[00:10:16] Sarah: Yeah and I think this is a great example of just how rapidly our understanding of food and nutrition is evolving. When I think back to when I first started my academic career 25 years ago, we were still very focused on nutrients, on fat protein, you know, fibre carbohydrate rather than necessarily thinking about foods. 

And I started my research on nuts and food structure and energy, um, content based on food structure. You know, probably about 20 years ago, and this was all very novel at the time, thinking about actually food isn't just a case of four nutrients. It's got thousands of chemicals and the structure of the food modulates, how we process those chemicals, how we absorb the energy and the health impacts it has on our body. 

[00:11:00] Jonathan: It's amazing. One of the consequences of this though, is it feels like our current food labels are looking less and less trustworthy. 'cause you're just telling me we can't really trust the calories. And you're also telling me, you know what, thinking about things in terms of like protein and fat is this massive simplification that is, you know, represents how the science was 25 years ago. 

Um, It sounds like what is needed is like more in-depth tests on individual foods to get more accurate results for each of us?  

[00:11:31] Sarah: Yeah, that would be ideal. But the reality is that's really challenging to do considering we have millions of different, um, foods out there. But if we think about these ground nuts and these whole nuts, you know, it would be great if we could communicate to people that there is this huge difference in the energy, um, that you absorb based on whether they're ground and their whole. And we've done lots of work, um, on this ourselves, where we actually look at how chewing, for example, impacts the energy content. And so I do these studies which are called mastication studies, which are basically studies where we get people to chew foods like nuts and then spit them out at the point at which there are about to swallow and we can see how much energy is available at the point of swallowing from these foods. Now these are even less glamorous, I think, than the poo studies that, um, Wilber Atwater had to do. So I've done poo studies in my career.  

[00:12:25] Jonathan: I'm just imagining how embarrassed your son is when you explain that you've been doing all these mastication studies at work. 

[00:12:29] Sarah: He doesn't listen to me, Jonathan, anyway, when talking about my work. 

[00:12:34] Jonathan: So probably lucky in this case.  

[00:12:38] Sarah: Um, and what's really interesting is the point at which you are about to swallow, let's say a whole nut. You are only breaking enough of the cell wall structure to release about 10% of the energy.  

[00:12:50] Jonathan: Oh, that's amazing. 

So even after all that chewing, you've hardly broken out any of the energy from the nut.   

[00:12:54] Sarah: Yep. and so if we put this into kind of physical context, we know that the cell of an almond is tiny. Okay. It's about 50 micrometres, which is smaller than a grain of sand it's absolutely minuscule. Now, from our chew and spit studies, we know that you actually swallow, um, uh, particles at the size of about 0.5 to one millimetre. 

Ok, so they're quite large little particles that you are, you are swallowing. And so because of that, you've actually got within that clump of one millimetre almond particle. You've got loads and loads of intact cells which are encasing all of the energy, all of the fat, for example, from the cells. 

Now, some of this is broken down in your gut, but not all of it is. So you've got about 10% released from chewing. You've got about another 60% released 'cause of the enzymes and everything else that's going on in your gut, and that's where you then get about 30% coming out the other end.  

[00:13:54] Jonathan: Got it. So even with all those microbes helping you out, something like a nut, you can't, you can't get all of it out if it was a whole nut.  

[00:14:01] Sarah: Yeah, exactly.  

[00:14:03] Jonathan: So how is that different from if I eat the ground nuts? So you told me that on the back of the pack, the, the, the labelling is exactly the same?  

[00:14:10] Sarah: Yeah. So if you were to take a ground nut that's been commercially ground, so not the kind of grinding that we might do in our kitchen where, you know, we, we blend something, but that's commercially ground to a really small particle size, then you get nearly all about 95 to a hundred percent of the energy released. So that's why you'll absorb all of the energy from the ground nut.  

[00:14:36] Jonathan: So there's this huge difference then between eating a real nut and eating some sort of processed food where the, the nut has been like ground in a, in a factory.   

[00:14:46] Sarah: Yeah, exactly. Because you are fracturing all of these cells. You are, you know, all of the energy and fat is bursting out and therefore it's available in your gut for your body to absorb all of that.  

[00:14:57] Jonathan: So let's say we solve for that, Sarah. Yeah. Could we then, like if we were able, I understand it'd be expensive, but if we did have a label for each of these different foods where that was measured carefully, would that then give everybody an accurate view of the calories that they will take out of a food?

[00:15:11] Sarah:  So, no, because it doesn't reflect how unique we are as individuals, yes, it will give us a good average. But as you know, Jonathan, from all of our, our ZOE PREDICT research, There is no such thing as Mr. Or Mrs. Average.  

[00:15:27] Jonathan: How big is this personalization? How real is that?  

[00:15:29] Sarah: So, again, I can use nuts as an example, um, of, of showing you, you this, and again, this is from studies, uh, that we've done. 

So if you take a handful of nuts, studies have shown that one person might absorb 62 calories from the handful of nuts. Another person might absorb 168 calories from exactly the same handful of nuts,  

[00:15:50] Jonathan: 62 against 168. That's crazy. That's like more than double. 

[00:15:53] Sarah: Yep. And this is from just taking a bag of whole almond nuts, this research has come from. 

Now if you eat nuts every day for a week, this actually equates to a difference in absorbed energy between people of 434 versus 1,176 calories. So this is a difference, Jonathan, over a week between individuals who are having whole almonds of 730 calories.  

[00:16:21] Jonathan: Wow. So that's an enormous difference. 

And it still said exactly the same thing of the label for the two people.  

[00:16:26] Sarah: Yeah. So imagine them both standing in the store. Um, you know, what calories they think they are getting from the nuts that they're about to buy can be vastly different, but the label won't tell them that. So this is two things that are happening. 

One thing is the, is the inaccuracy of the label itself 'cause of the complexity of the food. The other is the inaccuracy 'cause the complexity of us as individuals.  

[00:16:49] Jonathan: That's really interesting. And Sarah, I know we've seen in our own, um, ZOE PREDICT study that there are really big differences between how different people respond to the foods they eat. 

And I think there's lots of factors, right, that you and Tim and others have explained may sit behind that from who we are in our age and our sex, what lifestyle we lead, sleep, and exercise, you know, the foods that we've eaten.  

[00:17:11] Sarah: Yeah, exactly. And I think it's important we don't forget the microbiome in this as well, Jonathan, because we know that they're unique makeup of our microbes impacts, firstly, how our gut digests our food, but we also know that the microbes eat some of this food that's reaching the large intestine, so it can actually also affect the amount of calories that we're absorbing. 

So we touched a bit, Jonathan, on the fact that calories on the back of pack labelling are deceptive 'cause they don't show us how much energy we're getting out of the food and how our responses are so different between different people. But there's a third factor as well that these calories also don't really tell us anything about how healthy this food is for us. 

And when I'm talking about how healthy the food is, I don't mean the difference just between something that's a junk food and something that clearly isn't a junk food.  

[00:18:05] Jonathan: Okay, Sarah, so what do you mean?  

[00:18:08] Sarah: Okay, so let's take almonds again as an example. So my own studies show that if we feed people whole nuts, um, versus feeding them ground nuts, in the eight hours after you eat these nuts, you have about a 75% lower increase in circulating blood fat, following the whole nuts versus following the ground nuts.   

[00:18:34] Jonathan: And presumably that's very important for someone if they have to watch the levels of their blood fats. 

[00:18:38] Sarah: Yeah, exactly. And another great example that I often use is oats. 

And again, from our own research we see that there's about a 50% lower increase in blood sugar after eating very large oats versus very finely ground oats, and this is really interesting 'cause as opposed to with nuts where we know that whole nuts are not digested to the same level as ground nuts. We know that oats are fully digested, but whether they're large or whether they're fine, but the rate of digestion is different and we know that that also impacts our health. 

So what you are seeing, I think very simply put is by changing the structure, like with the whole almonds or with the oats. Although back of pack labelling is the same, you are essentially changing it from a very slow food to what I call a fast food, which we know is rapidly metabolized and isn't quite so healthy for us. 

[00:19:33] Jonathan: Got it. So it's not just about calories, you're saying it's like actually the impact on our health is different, even though today those labels are saying it's exactly the same thing.

[00:19:40] Sarah: Yeah, so taking those oats, you're still absorbing all of the calories. So yes, the back of pack label on the calorie content would, is correct in terms of whether they're whole or they're finely ground, but actually how your body metabolizes and digests them actually has quite divergent effects on our health.  

[00:19:57] Jonathan: Amazing. So Sarah, uh, we managed to learn a lot more about calories than before, and you got to talk about nuts, which I know will have made you very happy. Thank you. You are very welcome. I always like to create the opportunity for you to talk about nuts. 

Um, so what's the verdict on calories, on food labels? Should we be counting them or is it a waste of time?   

[00:20:19] Sarah: So I think that it's very clear that. We don't absorb all the calories, um, that are available in food and that, um, calorie uh, calculations that are used for back of pack labelling are not accurate for all foods, and it depends on the type of foods. 

It's clear that the structure of food affects the amount of calories, um, that are available, but also that it's gonna be hugely different between different people, and I think something else that's really important to bear in mind is people are using calorie counting as a way of losing weight. We know now that it's actually a really ineffective way of maintaining weight loss once people have lost weight. 

And I would urge people to listen to a future podcast that's coming up or might have been released, um, about weight loss, um, and calories and also to think about the healthiness of a food rather than focusing on the energy content of a food.  

[00:21:19] Jonathan: Amazing. Well, I think food labels are on the way out after this conversation. 

Thank you so much, Sarah. Pleasure. So if after Sarah's amazing explanation, you're ready to abandon calories and would like to try ZOE's personalized nutrition program to understand how the foods you eat can actually improve your health, then you can learn more and get 10% off by going to 

I'm Jonathan Wolf. 

[00:21:41] Sarah: And I'm Sarah Berry. 

[00:21:42] Jonathan: Join us next week for another ZOE podcast.