Ask ten runners about carbohydrate loading and you'll get ten different versions of the same story: a giant bowl of pasta the night before a marathon, a slightly queasy start line, and a nagging suspicion that none of it actually helped. The plate of spaghetti has become such a cliché that plenty of experienced runners have quietly written the whole idea off. But the science behind carbohydrate loading for running is sound — it's the execution that most people get wrong.
Done properly, carb loading isn't about one enormous meal. It's a two-to-three day strategy to top up the glycogen stored in your muscles and liver so you don't run out of fuel before the finish. For any event lasting longer than about 90 minutes, that stored glycogen is the difference between holding your goal pace and grinding to a halt. This article walks through what the research actually shows, who benefits, and how to load without waking up on race morning feeling like a bloated sofa.
What Carbohydrate Loading Actually Does
Your body stores carbohydrate as glycogen in two places: roughly 400-500g in the muscles and another 80-100g in the liver. That's around 2,000 calories of readily available fuel. It sounds like a lot, but a 70kg runner burns through roughly 60g of carbohydrate per hour at marathon effort, and glycogen is the tank that empties first. When it runs dry — the infamous "wall" or "bonk" — pace collapses and everything hurts. This usually strikes somewhere between mile 18 and 22 for runners who haven't fuelled well.
The original loading protocols from the 1960s were brutal: a depletion phase of hard training on a low-carb diet, followed by a few days of heavy carbohydrate intake to trigger a rebound "supercompensation". It worked, but it left runners exhausted and irritable during the depletion phase. The good news is that modern research has shown the depletion step is unnecessary. A study by Bussau and colleagues demonstrated that trained athletes could maximise muscle glycogen in just 24-36 hours by eating around 10-12g of carbohydrate per kilogram of body weight per day while tapering training. For a 70kg runner, that's 700-840g of carbs daily — a genuinely large amount that takes planning to hit.
Does Carbohydrate Loading for Running Still Work?
Yes — but only for the right events and the right runners. The evidence is strongest for continuous efforts lasting 90 minutes or more: marathons, ultras, and long trail races. Research consistently shows that elevated pre-race glycogen can improve endurance performance by around 2-3%, which over a marathon can translate to several minutes. For a 5K or even most half marathons run at a hard pace, the benefit is marginal because you simply won't deplete your stores in that time.
Where carbohydrate loading for running falls down is in the details. Three mistakes crop up again and again. First, runners try to load in a single evening meal, which the digestive system can't process — glycogen storage happens over days, not hours. Second, they eat more fat and protein rather than more carbohydrate, feeling full without actually topping up the right tank. Third, they load on high-fibre foods like wholemeal pasta, brown rice, and vegetables, then spend race morning glued to a portaloo. During the loading window, this is the one time to choose white bread, white rice, ripe bananas, and low-fibre options. Also worth noting: each gram of glycogen is stored with around 3g of water, so a proper load adds 1-2kg of body weight. That's normal and it's not fat — it's fuel and hydration you'll draw on during the race.
How to Load Without the Bloat
Start two to three days out and keep it simple. Cut back on fibre, fat, and protein slightly to make room for carbohydrate without overeating overall. Spread your intake across five or six smaller meals and snacks rather than two enormous plates — this is far easier on the gut and more effective for storage. Favour easily digestible sources: white rice, pasta, potatoes, bananas, honey, oats, and sports-specific carbohydrate.
A practical way to hit the numbers: build each meal around a fist-sized portion of white rice, pasta, or potato, then bridge the gaps with liquid and semi-solid carbs your gut barely notices — a glass of fruit juice here, a banana with honey there, a few energy pastilles on the drive to the expo. Liquid and chewable carbohydrate sits lighter than another plate of solid food and is far easier to keep down when you're already full. Many runners find they simply can't reach 8-10g/kg on whole foods alone without feeling wretched, and that's exactly why blending real food with concentrated carbohydrate works so well.
Hydration matters too. Because glycogen binds water, drink to thirst throughout the loading period and don't panic about the scale creeping up. On race morning, a light carbohydrate breakfast of 1-2g per kilogram, eaten three hours before the gun, tops up the liver glycogen that depletes overnight. Then during the race itself, keep feeding — aim for 60g of carbohydrate per hour to spare your stored glycogen and delay fatigue (our guide to what to eat during a marathon covers the race-day plan in detail, and if you're counting sachets, here's how many gels a marathon actually takes). Loading and in-race fuelling work together; one without the other leaves performance on the table.
What We Use at FTP Endurance Fuel
Hitting 10g of carbohydrate per kilogram from pasta alone is genuinely hard — you'd be eating almost constantly. This is where a concentrated, easy-to-digest carbohydrate source earns its place, both during the final loading push and out on the road. We built our Mixed Fruit Energy Pastilles around a 1:1 glucose-to-fructose ratio, which uses two separate absorption pathways in the gut to move more carbohydrate into the bloodstream per hour with less GI distress — exactly what you want when you're trying to pack in fuel without feeling stuffed.
Each pastille is a known, measured dose of carbohydrate, so you can count them rather than guessing. In the final 24 hours before a long race, a handful alongside your meals helps close the gap to your daily target painlessly. During the race, they're compact enough to carry a whole event's worth in a single pocket. If you're not sure how your gut handles them mid-run, the taster pack is a low-commitment way to trial them on a long training run first — because race day is never the day to try something new.
So does carbohydrate loading still work? Absolutely — for endurance events over 90 minutes, a well-executed two-to-three day load remains one of the few nutrition strategies with real evidence behind it. Skip the depletion phase, spread your carbs across the days rather than cramming one meal, keep the fibre low, and pair your loading with steady in-race fuelling. Practise it in training, dial in the amounts that sit well in your stomach, and you'll toe the start line with a full tank. Fancy putting it to the test on your next long run? Grab a taster pack and find out what proper fuelling feels like.
