Carbohydrate loading began with a biopsy needle.
In the 1960s, Swedish researchers Jonas Bergström and Eric Hultman used small muscle samples to measure something runners could previously only guess at: how much glycogen the muscles stored after different diets. Their work showed that exercise lowered muscle glycogen, carbohydrate restored it, and a high-carbohydrate diet could push the tank above its usual level.
The original protocol was memorable for all the wrong reasons. Athletes depleted glycogen with hard exercise, ate very little carbohydrate for several days, then reversed course and ate a mountain of it. Modern runners can skip the nutritional whiplash. Taper the training, raise carbohydrate for the final 36–48 hours, and arrive with fuller stores.
Who actually benefits from carb loading?
Carbohydrate loading is most relevant before events lasting longer than about 90 minutes. That includes the marathon and, for many Citizen Runners, the half marathon. It is not necessary before a 5K or an easy Saturday run.
Muscle glycogen is stored carbohydrate. It supplies a large share of the energy needed at marathon pace, but the body can only store so much. Loading aims to begin the race with more glycogen available. It does not eliminate the need to fuel during the marathon, and it does not rescue pacing that gets ambitious at mile six.
How much carbohydrate does the research support?
A 2026 systematic review and meta-analysis found that carbohydrate intake above 8 grams per kilogram of body weight per day for 36–48 hours significantly increased muscle glycogen. Traditional marathon guidance has often used 10–12 g/kg/day over the same period. That higher range is effective in laboratory protocols, but it is also a remarkable amount of food.
| Body weight | 8 g/kg per day | 10 g/kg per day |
|---|---|---|
| 140 lb / 63.5 kg | About 510 g carbohydrate | About 635 g |
| 160 lb / 72.6 kg | About 580 g | About 725 g |
| 180 lb / 81.6 kg | About 650 g | About 815 g |
Those numbers explain why “I ate pasta Friday night” is not really a loading plan. They also explain why blindly chasing 12 g/kg can make a recreational runner feel miserable. In a recent controlled study of endurance-trained adults, 10 g/kg/day for 48 hours produced higher muscle glycogen than 6 or 8 g/kg/day. Gastrointestinal symptoms did not differ significantly, but fullness increased. The biomarker improved, while fullness became the practical constraint.
Glycogen is not the same as a guaranteed faster marathon
This distinction matters. The evidence that high carbohydrate intake raises muscle glycogen is strong. The evidence that carb loading independently improves race performance is less tidy, especially when runners also fuel appropriately during the event.
A 2026 review noted that few carbohydrate-loading studies used double-blind, placebo-controlled designs. In the two that did and also provided carbohydrate during exercise, loading did not produce a clear additional performance benefit. That does not make loading useless. It means: the strategy increases the fuel stored before the race, while the exact performance benefit varies with the runner, race duration, starting glycogen, pacing, and in-race fueling.
How to eat more carbohydrate without feeling stuffed
Spread it across the day
Five or six moderate feedings are usually easier than three enormous meals. Begin at breakfast instead of trying to repair the whole plan with a restaurant-sized dinner. Add a bagel, banana, juice, rice, bread, cereal, pretzels, potatoes, or a familiar sports drink to meals and snacks you already tolerate.
Choose lower-volume foods
Race week is not a contest to eat the most virtuous bowl of beans. Whole grains, legumes, large salads, and piles of vegetables are excellent everyday foods, but their fiber and volume can make high carbohydrate targets uncomfortable. For the final day or two, many runners do better shifting some intake toward white rice, regular pasta, bread, pancakes, cereal, peeled potatoes, bananas, applesauce, juice, and sports drinks.
This is a temporary race strategy, not a new food philosophy. Research on low-fiber or low-FODMAP approaches for endurance athletes is promising but still limited, so reduce only the foods that have caused trouble in your own training. Do not discover an intolerance on Saturday because the internet assigned you a new diet on Friday.
Turn down fat and protein slightly, not completely
Fat and protein are filling. Keeping their portions moderate makes room for more carbohydrate without forcing total calories through the roof. You still need protein and normal meals. The goal is to change the proportions for 36–48 hours, not to live on syrup.
Use liquids as support
Juice, a smoothie, chocolate milk, or a tested sports drink can add carbohydrate without another plate of food. Liquid carbohydrate is not magical, but it can be practical when appetite and stomach space are the limiting factors. Keep hydration sensible; carb loading is not an invitation to overdrink plain water.
Expect the scale to move
Glycogen is stored with water. In one human recovery study, each gram of glycogen was stored with at least about 3 grams of water. A small increase in body weight during loading is therefore expected and is not the same as suddenly gaining body fat.
Do not respond by cutting food or fluid the night before the race. You are stocking fuel and the water associated with it. That is the assignment.
Do not forget race morning and the race itself
Carb loading does not make race-morning breakfast optional. Sports-nutrition guidance commonly recommends 1–4 g/kg of carbohydrate during the 1–4 hours before exercise, scaled to timing and tolerance. More time before the start generally allows a larger meal.
During a marathon, practiced runners may target roughly 60–90 g of carbohydrate per hour, depending on pace, gut training, and the mix of carbohydrate sources. Use the breakfast and fuel you tested in long runs. The final 48 hours should be pleasantly boring.
Where our formula fits
Carbohydrate loading has a specific job: stocking muscle glycogen for a long race. Our Runner Multivitamin has a different job. We include a broad foundation of vitamins, minerals, and probiotics in our two-tablet daily serving to help provide daily nutritional security when training, work, travel, and family life make perfect eating difficult.
We still want your race-week carbohydrate coming from food and familiar sports nutrition. Our formula does not replace calories, carbohydrate, sodium, or fluid. Take it with a normal meal as part of the routine you already know, and let the carb-loading plan handle the fuel.
Carb-loading FAQ
Do I need a giant pasta dinner?
No. Pasta can help, but total carbohydrate across 36–48 hours matters more than one meal or one specific food.
Should I do a depletion run first?
No. Modern marathon guidance does not require the old low-carbohydrate depletion phase. A normal taper plus high carbohydrate intake is the simpler approach.
Should women use a different strategy?
The same body-weight-based framework can apply, but total energy intake must be high enough to make the target achievable. Individual response, menstrual status, body size, and gastrointestinal tolerance can influence the plan, so practice it before an important race.
What if 8–10 g/kg feels impossible?
Do not force food until you feel sick. Start by measuring your normal intake during a practice race week, then increase it with lower-volume carbohydrate foods and drinks. A sports dietitian can personalize the target if you have repeated GI trouble, diabetes, or another medical condition.
The bottom line
For a marathon, taper your running and raise carbohydrate for the final 36–48 hours. Research supports more than 8 g/kg/day for meaningfully increasing muscle glycogen, while 10 g/kg/day may push stores higher at the cost of more fullness. Spread the intake across the day, use familiar lower-volume foods, expect some water-weight gain, and keep race-morning and in-race fueling in the plan. Carb loading should feel organized, not heroic.
Sources
- Hultman and Bergström: muscle glycogen synthesis in relation to diet
- 2026 systematic review and meta-analysis of carbohydrate intake and muscle glycogen
- Dose-response study of 6, 8, and 10 g/kg/day carbohydrate
- 2026 review of blinding and ecological validity in carbohydrate-loading research
- Contemporary nutrition strategies for distance runners and race walkers
- Muscle glycogen and water storage after prolonged exercise
Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Runners with diabetes, gastrointestinal disease, kidney disease, or another medical condition should discuss major nutrition changes with a qualified healthcare professional.