Research shows that eating very high amounts of carbohydrates (more than 6.5 grams per kilogram of body weight daily) in the 1 to 3 days before endurance competition significantly increases muscle energy stores by approximately 192 units compared to lower intake. According to Gram Research analysis of 63 studies involving 641 athletes, the best carb-loading strategy depends on your available time: 36 to 48 hours with standard carbs, or 24 to 36 hours if you combine high carbs with prior intense exercise and high glycemic index foods like sports drinks.
A major analysis of 63 studies involving 641 athletes shows that eating the right amount of carbohydrates before competition can significantly boost muscle energy stores. Researchers found that athletes who consumed high amounts of carbs (more than 6.5 grams per kilogram of body weight daily) increased their muscle glycogen, the stored energy muscles use during exercise, by nearly 192 units compared to lower carb intake. The study reveals that the best carb-loading strategy depends on how much time you have before competition, what type of carbs you eat, and whether you do depleting exercise first. However, because athletes respond differently to the same carb intake, more research is needed to pinpoint the perfect formula for each person.
Key Statistics
A 2026 meta-analysis of 63 trials involving 641 athletes found that consuming very high carbohydrate intake (more than 6.5 grams per kilogram of body weight daily) increased muscle glycogen stores by approximately 192 units compared to moderate intake.
According to the systematic review published in the Scandinavian Journal of Medicine and Science in Sports, athletes who combined prior intense exercise with high carbohydrate intake could rebuild muscle glycogen stores in 24 to 36 hours, compared to 36 to 48 hours without prior exercise.
The meta-analysis of 18 high-quality studies showed that trained endurance athletes demonstrated significantly stronger glycogen storage responses to high carbohydrate intake than recreationally active individuals, indicating that training status affects carb-loading efficiency.
The Quick Take
- What they studied: How much carbohydrate athletes should eat in the days before competition to fill up their muscles with stored energy (glycogen), and what factors affect how well this works.
- Who participated: 641 athletes from 63 different studies, ranging from recreational exercisers to trained competitors. The studies looked at various carbohydrate amounts, timing, and exercise routines done before competition.
- Key finding: Athletes who ate very high amounts of carbs (more than 6.5 grams per kilogram of body weight per day) increased their muscle glycogen stores by about 192 units compared to those eating lower amounts. This boost was consistent across different types of athletes.
- What it means for you: If you’re an endurance athlete preparing for competition, eating high-carb foods for 1 to 3 days before your event can meaningfully increase your energy reserves. However, the exact amount that works best varies from person to person, so you may need to experiment during training to find your optimal strategy.
The Research Details
Researchers conducted a systematic review and meta-analysis, which means they searched five major online databases for all published studies about carbohydrate intake and muscle energy storage through June 2026. They found 63 trials that measured muscle glycogen directly using tissue samples (biopsies) taken at least 24 hours after athletes consumed specific amounts of carbohydrates and did specific exercises.
The team analyzed the data in two ways. First, they looked at all 63 studies descriptively to understand the patterns and differences. Then, they performed statistical analysis on 18 of the highest-quality studies to find clear relationships between carbohydrate intake and muscle glycogen levels. They also examined whether factors like exercise type, carbohydrate timing, and athlete fitness level changed the results.
This approach is powerful because it combines evidence from many smaller studies to find reliable patterns that individual studies might miss. By measuring muscle glycogen directly through biopsies rather than relying on indirect measures, the researchers could see exactly how much energy athletes stored. The meta-analysis also allowed them to identify which factors matter most, helping athletes and coaches make better decisions about pre-competition nutrition.
The study included both randomized controlled trials (the gold standard) and non-randomized studies, which means some results are more reliable than others. The researchers found significant variation between studies, suggesting that factors beyond just carbohydrate intake influence results. The fact that 18 studies were strong enough for detailed statistical analysis, while 45 were only reviewed descriptively, indicates that high-quality research in this area is still limited. The authors themselves noted that more well-controlled studies are needed to confirm their recommendations.
What the Results Show
The analysis revealed a clear relationship between how much carbohydrate athletes ate and how much glycogen their muscles stored. For recreationally active people, eating more carbs correlated with higher muscle glycogen levels. For trained athletes, this relationship was even stronger, meaning their bodies were more efficient at storing carbs as muscle energy.
The biggest finding was that consuming very high carbohydrate amounts (more than 6.5 grams per kilogram of body weight daily) significantly increased muscle glycogen by approximately 192 units compared to moderate intake. To put this in perspective, a 70-kilogram (154-pound) athlete would need to eat more than 455 grams of carbohydrates daily to reach this very high intake level.
The timing and type of carbs also mattered. Athletes who did a depleting exercise session (intense exercise that empties glycogen stores) followed by high-carb eating, especially with high glycemic index carbs (foods that quickly raise blood sugar like white bread or sports drinks), could rebuild their glycogen stores faster, in 24 to 36 hours rather than 36 to 48 hours.
The analysis found that the duration of carb-loading (how many days before competition you eat extra carbs) significantly affected results. Shorter loading periods of 24 to 36 hours worked well when combined with prior glycogen depletion and high glycemic index carbs. Longer periods of 36 to 48 hours were needed when using lower glycemic index carbs (whole grains, legumes) or without prior depletion exercise. The type of athlete also influenced outcomes: trained endurance athletes showed stronger responses to high carbohydrate intake than recreational exercisers, suggesting that training status affects how efficiently the body stores carbohydrate energy.
This meta-analysis builds on decades of sports nutrition research showing that carb-loading works. Previous studies suggested eating high carbs before endurance events, but they showed confusing results about the exact amounts and timing. According to Gram Research analysis, this systematic review provides the most comprehensive evidence to date by combining 63 studies and identifying which specific factors drive the variability in results. The finding that individual responses vary significantly aligns with earlier observations that some athletes respond better to carb-loading than others, though this analysis helps explain why.
The researchers identified several important limitations. First, significant variation existed between studies in how they measured glycogen, the types of athletes studied, and the carbohydrate protocols used, making it harder to draw universal conclusions. Second, only 18 of 63 studies had high enough quality for detailed statistical analysis, meaning some recommendations are based on limited evidence. Third, most studies involved relatively small numbers of participants and focused on specific types of endurance exercise, so results may not apply equally to all athletes or sports. Finally, the studies couldn’t account for all individual factors that influence glycogen storage, such as genetics, training history, and diet quality, which explains why athletes respond differently to identical carbohydrate intakes.
The Bottom Line
For endurance athletes competing within 1 to 3 days, consume 6 to 8 grams of carbohydrate per kilogram of body weight daily during the loading period (moderate confidence). For faster results with limited time (24 to 36 hours before competition), combine this high carbohydrate intake with prior intense exercise and choose high glycemic index carbs like white bread, sports drinks, or white rice (moderate confidence). Athletes should experiment with these strategies during training, not for the first time before competition, since individual responses vary significantly (high confidence).
Endurance athletes competing in events lasting more than 90 minutes (distance running, cycling, triathlon, cross-country skiing) should apply these findings. Recreational athletes doing moderate exercise may see smaller benefits. Team sport athletes and strength athletes should focus on overall daily carbohydrate intake rather than specific loading protocols. People with diabetes or other metabolic conditions should consult their healthcare provider before significantly increasing carbohydrate intake.
Muscle glycogen increases begin within 24 hours of high carbohydrate intake, with maximum storage typically achieved within 36 to 48 hours. The benefits last through your competition if you maintain adequate carbohydrate intake. After competition, glycogen stores return to normal levels within 24 hours if you don’t eat carbs, or faster if you do.
Frequently Asked Questions
How many grams of carbs should I eat before a marathon or long endurance event?
Consume 6 to 8 grams of carbohydrate per kilogram of your body weight daily for 1 to 3 days before competition. A 70-kilogram athlete should aim for 420 to 560 grams daily. Research shows this amount significantly increases muscle energy stores for endurance performance.
What’s the difference between high and low glycemic index carbs for carb-loading?
High glycemic index carbs (white bread, sports drinks, white rice) raise blood sugar quickly and refill muscle energy faster, useful when you have only 24 to 36 hours before competition. Low glycemic index carbs (whole grains, oats, legumes) raise blood sugar slowly and work better with longer loading periods of 36 to 48 hours.
Does carb-loading work the same for everyone?
No. The meta-analysis found significant individual variation in how much muscle energy athletes store from identical carbohydrate intake. Trained athletes respond more efficiently than recreational exercisers. You should test your personal response during training to find your optimal strategy.
Should I do intense exercise before carb-loading?
If you have 24 to 36 hours before competition, doing intense exercise 24 hours prior followed by high carbohydrate intake speeds up muscle energy storage. Without prior exercise, plan for 36 to 48 hours of carb-loading to achieve maximum stores.
How long does carb-loading keep my muscles energized during competition?
Muscle energy stores built through carb-loading last through your competition if you maintain adequate carbohydrate intake during the event. After competition, stores return to normal within 24 hours unless you continue eating carbs to replenish them.
Want to Apply This Research?
- Log daily carbohydrate intake in grams for 3 days before competition, targeting 6 to 8 grams per kilogram of body weight. Track the type of carbs (high vs. low glycemic index) and any prior exercise. Record your competition performance and energy levels to identify your personal optimal strategy.
- Set a reminder 3 days before your next competition to begin carb-loading. Use the app to plan meals with specific carbohydrate targets. If you have 24 to 36 hours before competition, schedule an intense workout 24 hours prior, then immediately consume high glycemic index carbs like sports drinks or white bread with your meals.
- Track carbohydrate intake and competition performance over multiple events to identify your personal response pattern. Note factors like training status, exercise type, and carb quality. Compare your energy levels and performance when you follow the protocol versus when you don’t, adjusting your strategy based on real results.
This research summary is for informational purposes and should not replace professional medical or sports nutrition advice. Individual responses to carbohydrate loading vary significantly based on genetics, training status, and other factors. Athletes with diabetes, metabolic disorders, or other health conditions should consult their healthcare provider or registered dietitian before significantly changing their carbohydrate intake. The findings apply primarily to endurance athletes and may not apply equally to all sports or fitness levels. Always test new nutrition strategies during training, not before competition.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.