What if the reason you fall apart when the gels run out isn't a fuelling mistake on the day, but the fact that your body has never learned to do anything except burn sugar? That's the question Barry Murray kept circling on the podcast, and it cuts against the grain of almost everything the modern, carb-maximising corner of cycling nutrition preaches.
Murray is a consultant nutritionist and lecturer, and his interest sits in a part of the field that's become unfashionable as the sport has swung hard toward 120-grams-an-hour fuelling. He's not anti-carb. But he's spent years on the physiology of how the body uses fat, and his core argument is that most cyclists have a metabolism running on a single setting — and they don't even know there's another one.
The expertise comes after the certificate
It's worth knowing where Murray's thinking comes from, because it explains the contrarian streak. "I have learned more since I finished in academia than I did when I was in academia," he said. "What I did was I just dug deeper and deeper into all the physiology and the mechanisms behind your metabolism."
That's a useful frame for any nutrition claim you encounter: does the person understand the mechanism, or are they repeating a protocol? Murray's case for fat adaptation isn't a fad diet wearing a lab coat. It's built on how the energy systems actually work, which is also why he's careful about who it suits and how it's done.
Why everyone burns carbs
Here's the heart of it. Most riders rely on carbohydrate, Murray argues, not because fat-burning is impossible for them but because they've never given their body the chance to develop it. "One of the main reasons why people still rely on carbs," he said, "is they haven't given their bodies enough time or progression from eating a 70 or 60% carbohydrate diet. They haven't given their body what I think is about six months of a gradual reduction."
Think of metabolic flexibility as a skill the body has to be coached into, slowly. If you live on a high-carbohydrate diet and always ride fuelled, your body has no reason to get good at burning fat — the sugar is always there, so it uses the sugar. Take that away gradually, over months, and the machinery for burning fat efficiently upregulates. Take it away suddenly, and you just bonk your way through ruined sessions and conclude that low-carb "doesn't work for you."
The slow progression
The part that separates Murray's approach from the crash-diet version is the patience. He describes building it the way you'd build any adaptation: gradually, with progressive overload applied to the fast rather than to power. Start with a one-hour fasted ride, then move up to ninety minutes, then to two hours, while slowly reducing the carbohydrate share of the diet over roughly six months.
That progression is the whole thing. It's the same principle as building your aerobic base or stepping up your in-ride carbohydrate — a stress applied at a dose the body can adapt to, increased over time. The riders who try fasted training and hate it almost always skipped the progression: they went from a 60% carb diet to a four-hour fasted ride and learned nothing except how it feels to run out of fuel.
To make the progression concrete: you might spend the first month doing one short fasted ride a week — an easy hour before breakfast — while nudging the carbohydrate share of your diet down a little, weighted toward your rest and easy days. Over the following months that fasted ride stretches toward ninety minutes and then two hours, always kept easy, while your hard sessions stay fully carb-fuelled throughout. By the far end of roughly six months, the body that once needed feeding from the first hour can roll through a long endurance ride on its own stores. Rush any of those steps and the adaptation doesn't come faster — it just doesn't come.
Where carbs still win
This is where the balance matters, because fat adaptation has been oversold in some corners as a replacement for carbohydrate, and it isn't. The physiology is clear: fat is a wonderful fuel for long, low-intensity work, but it cannot be burned fast enough to power high-intensity efforts. When the road tilts up and the effort goes hard, your body needs carbohydrate, and no amount of fat adaptation changes that.
So the balanced position — and the one consistent with how the World Tour nutritionists actually fuel their riders — is that this is a both/and, not an either/or. Metabolic flexibility can give you a deeper, more durable engine for long endurance days and spare your glycogen for when it counts. But on race day, and in your hard sessions, you still fuel with carbohydrate, because that's what the intensity demands. The modern fuelling research and the fat-adaptation research aren't enemies; they answer different questions about different intensities. Knowing which question you're asking — long and steady, or short and hard — tells you which fuel to lean on, and your daily carbohydrate intake should flex around that.
Who it's for — and who should leave it alone
Metabolic flexibility isn't for everyone, and being honest about that is part of taking it seriously. The rider it suits is the one doing a lot of long, steady endurance work — the ultra-distance rider, the big-base masters cyclist, the person whose events are measured in hours of controlled effort rather than repeated hard surges. For them, a deeper fat-burning capacity is a real asset: it spares glycogen, steadies energy over long days, and reduces the dependence on constant feeding that can wreck a stomach over a twelve-hour ride.
The rider who should be careful is the one whose riding is short and sharp, or who's already struggling to fuel hard sessions, or who has any history of disordered eating or under-fuelling. Pushing carbohydrate down in those situations doesn't build a better engine; it digs a hole. The masters context matters here too — older riders are more prone to under-recovering and to losing muscle when energy intake drops, so the gradual, well-fuelled-around-hard-days approach is non-negotiable.
How to know it's working
If you do experiment with it, judge it by the right signals rather than the scale or a single bad ride. The sign that fat adaptation is taking hold is that your long, easy rides stop feeling fragile — you can go further before the familiar hollow sets in, your energy is steadier without constant topping-up, and a missed feed on an endurance day isn't the catastrophe it once was. That's the adaptation Murray is describing: a body that can lean on its enormous fat stores at low intensity instead of panicking the moment the sugar runs low.
What it should not do is blunt your hard sessions. If your intervals are falling apart, your power on the climbs is down, and you're dreading the quality work, that's the signal you've cut carbohydrate too far or too fast — the progression has tipped into restriction. The fix is to put the carbs back around the hard work, keep the fat-adaptation stimulus to the easy rides, and let the two systems do their separate jobs. Done that way, it's not a low-carb diet at all. It's a more complete metabolism, fuelled correctly for whatever the day demands.
The takeaway
Murray's contribution isn't a diet to adopt wholesale. It's a reminder that your metabolism is more trainable than you've been told, and that carb-dependence is often a habit rather than a fixed trait. If your long endurance rides would benefit from a steadier, more fat-fuelled engine, the road there is slow and gradual, built over months, not weekends. And if you take it, do it with eyes open: fat adaptation makes your easy riding more robust. It doesn't fuel the finish. For that, the carbs go back in.
Hear the full conversation with Barry Murray on the Roadman podcast. For the other side of the fuelling question, read what the World Tour nutritionists actually do, and take your own fuelling puzzle to the Roadman community on Skool.