The History and Evolution of Carb Loading
The original protocol from the late 1960s was pretty brutal, honestly. Scandinavian researchers had athletes completely drain their glycogen through exhaustive exercise plus near-zero carbs for several days. Then they'd flip to massive carb intake right before the event. The idea was that starving the body first would make it overcompensate and store even more glycogen during the loading phase.
It worked — but the process was awful. Athletes felt destroyed during the depletion phase, injury risk went up, and the mental toll of going into a major race already exhausted was real. Not exactly ideal race prep.
By the 80s and 90s, researchers figured out the depletion phase wasn't actually necessary. You could get the same glycogen elevation just by tapering training and eating more carbs over 2–3 days. Same result, way less suffering. That was a big deal.
More recently, some studies have shown you can get meaningful glycogen loading in as little as 24–36 hours if carb intake is high enough. The direction sports nutrition has moved is toward practical protocols that actually fit around real training schedules and normal life — less extreme, more sustainable, equally effective.
What Does the Research Actually Say in 2026?
The evidence is solid. But the details matter a lot.
The clearest finding across decades of research is that carb loading helps performance in events lasting 90 minutes or more at moderate to high intensity. This has been shown repeatedly across marathon running, long-distance cycling, triathlon, cross-country skiing, and similar disciplines.
A well-known 1981 study by Karlsson and Saltin showed that carb-loaded athletes ran significantly faster in the second half of a 30km race compared to those who hadn't loaded — because they still had fuel when everyone else was running on empty.
More recent meta-analyses back this up. For events beyond 90 minutes, carb loading can improve performance by roughly 2–3%, sometimes more depending on the study. For elite athletes where seconds define careers, that number is massive. For recreational athletes chasing a goal time, it can genuinely be the margin between hitting it and falling apart in the final stretch.
But here's what most people skip over: the evidence for carb loading helping shorter or anaerobic efforts is basically nonexistent. A 45-minute CrossFit class, a 5km time trial, an hour in the gym — none of these push glycogen depletion anywhere close to a performance-limiting level. For these, carb loading does nothing useful. You just need to eat well and show up hydrated.
There's also a diminishing returns issue. If you already eat a consistently high-carb diet day to day, your glycogen stores are likely already well topped. The additional loading effect compared to someone coming from a moderate carb baseline is going to be pretty small.
Who Should Actually Carb Load?
Coach Ankush Kumar is straightforward about this with his athletes at TQFA: most people who carb load don't actually need to.
You probably benefit if you're competing in something lasting 90 minutes or longer — marathons, half or full ironmans, long cycling events, trail running, open water swimming. You also need to be a reasonably trained endurance athlete, because untrained muscles simply don't store glycogen as efficiently and show less supercompensation response. Your baseline diet should be moderate in carbs, giving room for meaningful upward loading. And ideally you've already tried it in training and know how your gut handles higher carb days.
You probably don't need it if your event is under 60–75 minutes, even if it's intense. Same goes for gym sessions, HYROX races, 10km runs, or recreational sport. If you're in a significant calorie deficit trying to lose fat, loading carbs in that context won't meaningfully supercompensate glycogen anyway. And if you've never tried it before and the race is tomorrow — that's not a strategy, that's a gamble.
Common Mistakes — And Why Most People Do This Wrong
Loading for the wrong event
This is the most widespread mistake by far. A recreational gym-goer eating three plates of pasta before a 45-minute bootcamp class isn't doing anything useful. Glycogen isn't going to become a limiting factor in that session under any circumstances. They're just eating a lot before light exercise and feeling heavy doing it.
Starting too late
Eating a massive pasta dinner the night before a race is not carb loading. It's just a big meal that will probably give you bloating, bad sleep, and an uncomfortable start line experience. Real carb loading starts 2–3 days out and involves a gradual, sustained increase across multiple meals over several days. One dinner doesn't cut it.
Treating it as a reason to eat everything
Carb loading is not a free pass to eat unlimited food. The approach involves increasing the proportion of carbs while reducing fat and protein slightly, keeping total calories reasonably controlled. Eating significantly more total calories than usual adds body weight beyond the expected glycogen-water gain, and that extra weight isn't helping anyone cross a finish line faster.
Choosing the wrong carb sources
Some athletes go heavy on high-fibre carbs during loading — beans, lentils, loads of vegetables, wholegrain everything. Then they wonder why their stomach is a disaster on race morning. During loading, simpler lower-fibre carbs are generally far better tolerated. White rice, white pasta, bread, bananas, sports drinks — these digest easily, absorb efficiently, and are much kinder to your gut in the days before competition.
Never practising it before race day
This one genuinely baffles coaches. Your first ever carb loading experience should absolutely not happen the week of your goal race. People respond differently. Some athletes feel fantastic on high carb intake — energised, light, ready. Others feel sluggish, bloated, and uncomfortable. You need to know which you are before it matters. Practice it during a training block, around a lower-stakes workout or tune-up race, and pay attention to how your body reacts.
Cutting fluids to avoid the scale going up
Glycogen stores water when it's packed into your muscles — roughly 3 grams of water per gram of glycogen. This means effective carb loading will cause some water retention and a small weight increase, typically 1–2 kg. This is completely normal, expected, and actually a sign things are working. Restricting fluids to keep the scale lower undermines everything you're trying to do. That water is part of the fuel system.
What a Practical Protocol Actually Looks Like
Here's a realistic, evidence-based framework for a marathon or long-distance triathlon finishing on a Sunday morning.
Thursday — three days out
Your training taper is underway. Carbohydrate intake goes up to around 7–8 grams per kilogram of body weight. Reduce fat and protein slightly to make room for the extra carbs without massively overshooting total calories. Focus on easily digestible sources — white rice, pasta, bread, fruit, oats. Nothing exotic. Nothing new.
Friday — two days out
Push carbohydrate intake toward 8–10 grams per kilogram body weight. Training is minimal — a short easy run or full rest. Keep fat intake low. Hydrate consistently through the day. This is not the time to introduce any foods your gut hasn't seen before.
Saturday — the night before
Have a moderate, carbohydrate-rich meal in the early evening. Not a feast — a normal-sized, familiar meal. Pasta with a simple tomato sauce works. Rice with lean protein. Bread with banana and honey. Finish eating 3–4 hours before you plan to sleep. Sip water through the evening but don't force excessive fluids right before bed.
Race morning
Eat your pre-race meal 2–3 hours before the start. Keep it familiar and practised. Oats, toast with banana and honey, or a rice-based meal are reliable for most athletes. Keep portions moderate. This is not the moment for experimentation.
Carb Loading and Body Composition: The Honest Conversation
A lot of recreational athletes who've worked hard to get lean before a race feel genuinely uncomfortable watching the scale tick up during a loading phase. It's worth talking about this directly.
The 1–2 kg of weight you gain when carb loading correctly is glycogen and the water attached to it. It is not fat. It will be gone within 24–48 hours after the race once those stores are used up. More importantly — that weight is performance fuel sitting in your muscles. For a marathon runner, going to the start line with fully loaded glycogen stores versus half-depleted ones can be the difference between a strong final 10km and completely falling apart around kilometre 32.
The number on the scale the morning before a race is irrelevant. What's in your muscles is everything.
Know Your Numbers Before You Start
You can't carb load effectively without some baseline awareness of your nutrition. What's your normal daily carbohydrate intake? What are your maintenance calories? How much protein do you actually need to support recovery and hold onto muscle during a taper week when training volume drops?
These things shouldn't be guessed at, especially in the week before something you've spent months preparing for.
Use a calculator to nail your BMR, total daily energy expenditure, and daily protein target before you start adjusting anything. Know where you're starting from. Then you can plan the loading phase intelligently — increasing carbs from a known baseline rather than just eating more and hoping for the best.
Track your training, energy levels, and how your body responds to dietary changes in the weeks leading up to the event. The patterns in that data will tell you far more than your memory will. How did you feel the last time you trained on high carbs? How was your energy late in long runs? What pre-race meals have worked well? These details matter.
Carb Loading in 2026: Still Relevant?
With fat-adapted training, ketogenic diets, low-carb performance nutrition, and metabolic flexibility all getting serious attention in endurance circles — is carb loading even still worth discussing?
Yes. For the right athletes doing the right events.
Fat adaptation has genuine value for ultra-endurance efforts where intensity stays low and fat oxidation can sustain output over many hours. But for moderate to high intensity sustained efforts — your marathon goal pace, your half-ironman bike leg, your competitive HYROX finish time — glycogen is still the dominant fuel. The research consistently shows that carbohydrate availability at those intensities outperforms fat, and glycogen depletion is a real, documented performance limiter.
Low-carb protocols have their place. Dismissing carb loading in favour of current metabolic trends isn't being progressive though — it's just being contrarian without reading the literature.
What has changed is the approach. The brutal depletion phase from the 1960s protocol is gone. Our understanding of timing, individual variation, and optimal quantities is sharper. The strategy is more practical and less disruptive than it used to be. But the core principle — that going into a long endurance event with maximally loaded glycogen stores improves performance — remains as solid as it's ever been.
Final Verdict
Event under 60–75 minutes: Skip it. Eat well, stay hydrated, have a solid pre-event meal. Carb loading won't change anything for you.
Event between 75–90 minutes at high intensity: Maybe. A modest carb increase 1–2 days out is low risk and could help a little, especially if your baseline intake has been moderate.
Event 90 minutes or longer at sustained effort: Yes. A structured 2–3 day loading protocol is appropriate, evidence-backed, and worth doing properly — as long as you've practised it in training first.
And wherever you fall on that spectrum, the fundamentals don't change. Know your numbers. Fuel consistently in the weeks before, not just the days before. Stay hydrated. Never experiment with nutrition for the first time on race day.
Carb loading isn't magic. It's also not outdated. It's a tool. And the value of any tool comes down entirely to using it correctly, at the right time, for the right job.
Want a personalised race nutrition plan built around your specific event, body, and goals? Connect with coach Ankush Kumar (ISSA Certified) at The Quad Fitness Academy (TQFA) — evidence-based coaching that works around you, not a generic template.