Carbohydrate Loading for Runners: Does It Work? Complete Guide 2026
Carbohydrate loading before a marathon is one of the most misunderstood race preparation strategies. We explain the physiology, the optimal protocol for Australian athletes and why most recreational runners do it wrong.
Carbohydrate loading before a marathon is one of the most misunderstood race preparation strategies in running. Ask ten runners how they carb load and you will hear ten different answers β from "a big bowl of pasta the night before" to week-long depletion diets that leave people miserable and flat on race morning. Most recreational runners either do too little to make a difference, or eat so much fat and fibre alongside their carbohydrates that they start the race bloated and uncomfortable.
This complete guide explains the physiology behind carb loading, who actually benefits, the modern evidence-based protocol used by elite and Australian Institute of Sport athletes, and practical meal plans you can follow in the 36β48 hours before your race.
Why Carbohydrate Loading Works
Your muscles and liver store carbohydrate as glycogen. A typical trained runner stores roughly 400β500 g of glycogen in muscle and around 80β100 g in the liver β enough to fuel approximately 90β120 minutes of running at marathon effort, depending on body size and pace.
When muscle glycogen runs low, your body relies increasingly on fat, which is a slower fuel source. Pace drops, effort skyrockets and you experience the dreaded "wall" β usually somewhere between 28km and 35km of a marathon. Carbohydrate loading increases glycogen stores above their normal level (sometimes called "supercompensation"), pushing that wall further away and giving your in-race fuelling a bigger buffer to work with.
Research consistently shows that properly carb-loaded athletes can maintain race pace for longer, with improvements in performance of around 2β3% in events lasting more than 90 minutes. For a 4-hour marathoner, that could be 5β7 minutes.
Who Should Carb Load?
Carbohydrate loading is only worthwhile for events where glycogen depletion is a limiting factor:
- Marathons β the classic use case and where the benefit is clearest
- Ultramarathons and long trail races β beneficial, although in-race fuelling becomes even more important
- Half marathons for slower runners β if you will be running for more than about 90β100 minutes, a shorter, moderate load can help
- Long triathlons and endurance cycling events
For 5km and 10km races, and fast half marathons, a full carb load is unnecessary. Normal glycogen stores are enough, and the extra body weight from stored glycogen and water may even be a small disadvantage. A normal, carbohydrate-rich dinner the night before is all you need.
The Old Method vs the Modern Protocol
The Classic Depletion Model
Carbohydrate loading was first studied by Scandinavian researchers in the late 1960s. The original protocol involved a hard, glycogen-depleting run about a week out, followed by three days of very low carbohydrate eating while still training, then three days of high carbohydrate eating. It did increase glycogen β but it also left athletes fatigued, irritable, prone to illness and anxious in the final week before a race.
The Modern Approach
Later research showed that the depletion phase is unnecessary for trained athletes. Well-trained muscles can reach near-maximal glycogen storage with just 36β48 hours of high carbohydrate intake combined with a training taper. This is now the standard recommendation from sports dietitians in Australia and internationally.
How Much Carbohydrate Do You Need?
The evidence-based target is 10β12 g of carbohydrate per kilogram of body weight per day for the 36β48 hours before your race. This is much more than most people realise.
| Body weight | Daily carb target (10β12 g/kg) | Approximate equivalent |
|---|---|---|
| 50 kg | 500β600 g | About 8β10 cups of cooked pasta worth of carbs |
| 60 kg | 600β720 g | |
| 70 kg | 700β840 g | Roughly 3β4 times typical daily intake |
| 80 kg | 800β960 g | |
| 90 kg | 900β1,080 g |
Hitting these numbers with pasta alone is almost impossible without feeling sick. The trick is to spread carbohydrate across 6β8 meals and snacks, and to use denser, lower-fibre sources such as white rice, white bread, juice, sports drinks and lollies.
Step-by-Step Carb Loading Protocol
7β3 Days Before the Race
Eat normally with a moderate to high carbohydrate intake (around 5β7 g/kg per day). Your training should already be tapering. There is no need to restrict carbohydrate or do depletion runs. This is a good time to plan your loading menu and buy your foods.
48β36 Hours Before the Race
Begin the load. For a Sunday morning marathon, this typically means starting on Friday morning. Increase carbohydrate to 10β12 g/kg per day and reduce training to a short, easy run or rest.
At the same time, reduce fat and fibre. You are not eating more total food so much as swapping foods. Swap wholegrain bread for white bread, brown rice for white rice, and cut back on butter, cheese, oily sauces and large salads. Fat and fibre fill you up without contributing to glycogen, and fibre in particular can lead to gut issues on race day.
The Day Before the Race
Continue the high-carbohydrate intake, but make the evening meal moderate rather than enormous, and eat it early (around 5β6pm for a morning race). The big pasta-party dinner the night before is the least important part of the load β most of the work is done by consistent intake across the previous day and a half.
Race Morning
Eat a pre-race meal of 1β4 g/kg of carbohydrate, 2β4 hours before the start. Overnight, your liver glycogen is partially depleted, so this meal tops it back up. Familiar, low-fibre options work best β white toast with honey or jam, a bagel, rice cakes, a banana, sports drink, or creamed rice.
Sample Carb Loading Day (70 kg Runner, ~750 g Carbohydrate)
Breakfast: 2 cups of rice bubbles or cornflakes with milk, 2 slices of white toast with jam, 250 ml orange juice (~150 g)
Morning snack: 2 crumpets with honey, banana (~80 g)
Lunch: large white bread roll with chicken and minimal salad, 1 cup of fruit juice, a cereal bar (~130 g)
Afternoon snack: 600 ml sports drink, a handful of jelly lollies, 2 rice cakes with jam (~110 g)
Dinner: 2.5 cups of cooked white rice or pasta with a low-fat tomato-based sauce and lean protein, a bread roll (~170 g)
Evening snack: creamed rice or low-fat custard, tinned peaches, 300 ml cordial or juice (~110 g)
Total: approximately 750 g of carbohydrate, with moderate protein and relatively low fat and fibre. Notice how much of this comes from liquids and simple sugars β that is deliberate.
Expect to Gain Weight β That's a Good Sign
Each gram of stored glycogen is stored with approximately 3 g of water. A successful carb load usually increases body weight by 1β2 kg. Many runners panic when they see this on the scales and assume they have overeaten. In fact, it is evidence that the load has worked. You may also feel slightly heavy or stiff on your shakeout run β this sensation typically disappears once the race begins.
Carb Loading for Female Runners
Early studies suggested women did not respond to carbohydrate loading as well as men. Later research found the main issue was that female participants were eating too little total energy β increasing carbohydrate as a percentage of a lower calorie intake did not significantly increase the absolute amount. When women eat the same carbohydrate per kilogram of body weight with sufficient overall energy, they can increase glycogen stores effectively.
Female runners who habitually under-eat, or who are concerned about weight gain before a race, often benefit from working with an Accredited Sports Dietitian to plan a load they are comfortable with. Menstrual cycle phase may have small effects on carbohydrate metabolism, but meeting the 10β12 g/kg target matters far more.
The Most Common Carb Loading Mistakes
- Only loading at one meal β a single huge pasta dinner the night before does not deliver anywhere near enough carbohydrate
- Eating too much fat β creamy pasta sauces, pizza, garlic bread with butter and desserts add calories but not much glycogen, and slow digestion
- Too much fibre β wholegrains, legumes, large salads and lots of vegetables in the final 48 hours can mean urgent toilet stops mid-race
- Trying new foods β race-week travel and expo food stalls are not the place to experiment
- Underestimating how much is needed β most recreational runners hit 5β6 g/kg and think they have carb loaded
- Too much alcohol β it impairs sleep, hydration and glycogen storage
- Not practising β try your loading protocol before a long training run, such as your last 30β32km run, so you know how your gut responds
Carb Loading and In-Race Fuelling Work Together
Even a perfect carb load will not carry most runners through a marathon on its own. You still need to take in carbohydrate during the race β typically 30β60 g per hour for most recreational runners, and up to 90 g per hour for well-trained athletes who have practised gut training with glucoseβfructose products.
Think of carb loading as filling your fuel tank before you leave, and gels or sports drink as topping it up on the way. Both are essential. Our guide to nutrition during long runs covers in-race fuelling, and our roundup of the best energy gels in Australia compares the main products. High-carb options such as Maurten Gel 160 and SiS Beta Fuel make higher hourly targets easier to reach.
Does Carb Loading Work for Ultramarathons?
Yes, but its relative importance decreases with distance. In a 100km race, pre-race glycogen stores fuel only a small fraction of total energy needs. Ultra runners still benefit from starting full, but in-race fuelling with a combination of carbohydrate drinks, gels and real food becomes the main determinant of success. Ultra runners also tend to run at lower intensity, which uses a higher proportion of fat as fuel.
Carb Loading on a Low-Carb or Keto Diet
Some runners follow low-carbohydrate diets in training. Research suggests long-term low-carb adaptation reduces the body's ability to use carbohydrate efficiently at higher intensities, which can impair marathon performance even after a carb load. If you train low-carb but want to race at a high intensity, discuss a strategy with a sports dietitian well before race week. A sudden high-carbohydrate load can also cause gut discomfort if your body is not used to it.
Carb Loading When Travelling to a Race
Many Australians travel interstate for big races β Gold Coast, Sydney, Melbourne or overseas majors β which makes carb loading harder. Unfamiliar restaurants, plane food and long days on your feet at expos all work against you. Pack portable carbohydrate staples such as rice cakes, muesli bars, dried fruit, sports drink powder and long-life juice. Book accommodation with a kitchenette if possible, or locate a supermarket near your hotel on arrival. Choose plain restaurant meals β steamed rice dishes, simple pasta with tomato sauce, pancakes or bread β rather than rich, creamy or spicy menus.
Frequently Asked Questions
Should I carb load for a half marathon?
If you will run faster than about 1:40, a normal high-carbohydrate day before is enough. If you will take two hours or more, a moderate 24-hour load of 7β10 g/kg is worthwhile.
Can I carb load with lollies and soft drink?
Simple sugars are useful for reaching your targets without feeling stuffed, and are perfectly acceptable for a short loading window. Combine them with starchy staples such as rice, bread and pasta.
Will carb loading make me feel sluggish?
Some heaviness is normal due to water stored with glycogen. Excessive sluggishness usually comes from too much fat and fibre, or too much food late on the night before.
Do I need to stop eating protein?
No. Keep moderate protein at each meal, but let carbohydrate take the largest share of your plate.
The Bottom Line
Carbohydrate loading works β when it is done properly. Skip the old-fashioned depletion phase, aim for 10β12 g of carbohydrate per kilogram of body weight for the 36β48 hours before your marathon, reduce fat and fibre, eat a carbohydrate-rich breakfast 2β4 hours before the start, and back it all up with a practised in-race fuelling plan. Accept the extra kilogram or two on the scales as proof of a full tank. Practise the whole process before a long training run and you will arrive at the start line with fuel to burn.
This article is general information only. For a personalised plan, particularly if you have diabetes, gut conditions or a history of disordered eating, please speak with an Accredited Sports Dietitian.
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