UNTAPPED with Spencer Matthews
Carb Loading & Gels: What Runners Need To Know | Extra Mile
18 Jun 2026
Transcript generated automatically by AI and may contain errors.
Chapter 1: What is the main topic discussed in this episode?
Hello, everyone, and welcome to Untap the Extra Mile with me, Spencer Matthews. And me, Oli Patrick. Today, we're talking carbs. Carbs. I love carbs. So do I. Thank God. So, listen, we've all heard the term carb loading. What are carbs actually doing when we run, and how does your body use them?
Carbs got demonized, didn't they? Carbs fell foul of diet culture. And people were like, no carbs before Marbs, which I believe was no carbohydrate before my holiday in Marbella.
Chapter 2: What does carb loading actually do for runners?
Marbella? Marbella. Marbella, that's my Versace moment. So principally, carbohydrate is one of our foundational macronutrients. So it is little molecules of glucose bound together into more complicated structures, forming carbohydrates. And carbohydrate, protein and fats, these form macros. Why carbs are interesting? Is there the only real macro that you and I can live without?
So we do need protein. Protein, the building block of the human machine. We make proteins, but we need protein for growth and repair, obviously. Protein sources, of course, your animal meats, your dairies, your things that could be made from soy, so tofu and various other vegan options. And then we've got fats, which are also an essential nutrient. Most of our cells' membranes are made from fats.
Our brains, as we sit here, are made pretty much from fat. So fat is a critical nutrient for cells, for immunity, for general health. But carbs, this sort of molecule of sugar bound together, we can live without because we can make carbohydrate from fats and proteins.
Isn't it strange that diet culture has changed so much over the years, but also the advice has just varied enormously, drastically. People eating no fat and less fat in certain products and, as you say, completely cutting out carbs and all these different diets. We needn't single out individual diets and go into that. Perhaps that's a conversation for another day.
But today, just focusing on carbs. Interesting to hear that you can live without carbs. I didn't know that. Could you be a great... and fast runner without carbs?
That is a great question. And the general theory would be across the population, probably not. Because when we've spoken previously on this podcast about energy systems, you know, when we're burning fuel at low intensities, if you and I sit here now... you know, in a relatively fasted state. Neither of us have had a big brekkie as far as I'm aware. And, you know, we're deeper into the day.
We're probably creating the energy to sit and talk using fat smashed together with oxygen. That's our energy. If we went out for a run and we increasingly demanded more energy in our legs to power us and more energy into my heart and my lungs. The whole system is going up. As that intensity rises, I can't just do that using fat and oxygen alone.
I'll bring in the magical glucose molecule in its stored form, glycogen. So I store carbohydrate in my body as glycogen. When exercise intensity goes above a certain threshold, which the fitter I am, the deeper that threshold will be. But as I increase intensity, I'll need carbohydrate stored in my body, releasing glucose, and that will fuel our athletic performance.
So historically, the answer to that was no. But there was a big trend towards keto.
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Chapter 3: How does glycogen fuel athletic performance?
And I've also, again, got to just look at what the impact that training is on whether I am more sedentary that day, whether I get my active steps in. All these things matter. And what we get with high-intensity work is we get a bigger... post-exercise oxygen consumption. Have you heard EPOC? Yes. So EPOC is really what is the sort of biological cost of the training session in its repair stage.
So after we finish a really heavy hit session, I've got to rebuild the tissues that have been broken down. I've got to clear out all the metabolic byproducts of that session. That has an oxygen cost to it as well. So when you do high-intensity work, you get a bigger EPOC, and that might mean more calories burnt as a totality over the next 24 hours
compared to the Zone 2 workout, which felt easier, but didn't burn me as many calories. So from a weight management point of view, we're interested in whatever you can do on a regular basis and match that against your dietary impact more than a carbohydrate discussion per se.
Let's talk about carb loading specifically. So at a very basic level, I think most people listening to this have heard of hitting the wall. You hear about people hitting the wall at various stages of a marathon. It's very common around the 30-kilometer mark, 30 to 35K.
The theory behind that is that if you went into the race with adequate glycogen levels, that that probably wouldn't happen if you are loading up well throughout the race. That hitting the wall is essentially, as I understand it, and please feel free to correct me, that your body has ran out of glycogen.
If your glycogen levels are adequate, you should feel the energy to persist at kind of tempo pace, threshold pace even, although hopefully not too much threshold on marathon day. But when that runs out, say you're not carb loading, you're not gelling, your body would then try to burn other energy sources. And that kind of
tacking over from burning this source to that source would result in you being essentially out of action during that period you know you would have to slow down stop you know for your body to to manage that different combustion love it you're rubbing off on me i think that's that's a very fair take you know i think the wall itself is a more complicated as you said it's a bit of
psychological self-talk, it's central governor theory, it's dehydration, it's wear and tears, all those things. If we're looking at glycogen depletion, that's very real around that period of time. So we will eat carbohydrates and we will then be able to store at Grasso.
We'll wolf down mama's meatballs at Grasso and lovely protein in the meatballs, but lots of, again, quality carbohydrate in the pasta. And then we will store that we'll turn that into muscle glycogen and liver glycogen. So we've got two main places where we can store carbohydrate, like a little hamster tucking away its food in its cheeks. And we've probably- Delicious.
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Chapter 4: Why do runners hit the wall during races?
But this is where you go, I want to enter my event with stores of glycogen that are appropriate for the demands of my event. If I'm running a 5k, I'm not going to go through those glycogen stores. If I'm doing an event, probably.
And we used to think... So you're really not burning any fat when you run a marathon then because, you know, it's not like you're... I mean, you may warm up briefly before it and jog a K or two or something. So, you know, whatever. Sure, you'll burn some fat then.
I mean, like from crossing the start line, you're broadly speaking going to push yourself to... Well, you'll be at your race pace immediately, right? So kind of... For most people who are racing, you will be in zone three and that will creep up probably to zone four.
You shouldn't be in zone five really at all. And some people do manage to go in there. And again, I would defer to Stephen on things like this in terms of... of where you should be for your optimized marathon performance.
Anything less, by the way. Sorry to interject. 5K, your max heart rate. Send it. Max heart rate, zone 5, whatever. 10K, probably about zone 4. You're probably not max heart rating in that. Shouldn't be, yeah. Well, I mean, obviously some people will, but essentially the longer the distance, the... the less borrowed time you want to be on.
Spot on. But that's the point. So the longer the time, the more I need to depend on fat because my carbs won't get me there. And therefore, I've got to find an ability to use fat oxidation.
And that again, will be all the training you're doing now is increasing how much you can use fat at higher intensities of workload to allow you to run a two hour 45 with yes, carbohydrate, but some contribution of fat. So it's never pure. If I'm raw zone five sprinting, it's just anaerobic glycogen. If I'm walking, it's probably predominantly fat. But in between, it's a blend.
What about... So we're looking at carbs just as a food source. What about different kinds of carbs? Or roughly speaking, are they kind of all the same? So if I'm looking at... you know, the ideal way of carb loading for, you know, a marathon. Say you've got the marathon on the Sunday, you may start carb loading properly on, say, Thursday, Wednesday, Thursday, Friday.
You know, you start to build into it. Maybe with like a really heavy carb day on the Friday, maybe less so on the Saturday, just so that you don't feel, you know, big and bloated morning of your race.
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