How Much Carbohydrate Do You Really Need to Carb Load? New Research on Muscle Glycogen

Carb loading is one of those sports nutrition strategies that sounds simple until you start looking at the actual recommendations. Eat more carbohydrates before a race, fill up your glycogen stores, and you'll have more fuel available when you need it. That's the basic idea, and decades of research support it.

But how many carbohydrates do you actually need? Is 500 grams per day enough, or should you be pushing closer to 800 grams? Do you need three days of carb loading, or can you accomplish the same thing in 24 to 48 hours?

And perhaps the most important question: Are athletes consuming far more carbohydrates than necessary to maximize muscle glycogen?

A 2026 systematic review and meta-analysis published in the Scandinavian Journal of Medicine & Science in Sports examined these questions by evaluating the relationship between carbohydrate intake and muscle glycogen storage.

The researchers reviewed 63 experiments involving 641 participants, with 18 trials included in the quantitative meta-analysis. Their findings help clarify how much carbohydrate is needed, how long athletes should carb load, and why two people following similar strategies can end up with very different glycogen concentrations.

What makes this research particularly useful is that it examined actual muscle glycogen measurements obtained through muscle biopsies rather than relying on performance outcomes or estimates of carbohydrate intake.

The results reinforce the importance of carbohydrate loading for endurance athletes, but they also suggest that the amount of carbohydrate consumed, the duration of loading, training status, and recent exercise all influence how effectively glycogen stores increase.

TLDR

A 2026 systematic review and meta-analysis examined how carbohydrate intake influences muscle glycogen storage before endurance exercise.

• Higher carbohydrate intake significantly increased muscle glycogen. Consuming more than 6.5 grams per kilogram of body weight daily produced substantially greater glycogen concentrations than lower intakes.
• The researchers recommend more than 8 g/kg/day for 36–48 hours before endurance competition when the goal is to significantly increase glycogen stores.
• Traditional recommendations of 10–12 g/kg/day may not be necessary for everyone, although the study did not establish a universal maximum or prove that 8 g/kg is optimal.
• Training status matters. Trained athletes generally demonstrate a greater capacity to store glycogen than untrained individuals.
• Exercise before carb loading can influence the response. Prior glycogen-depleting exercise combined with high-glycemic carbohydrates may allow more rapid glycogen storage, sometimes within 24–36 hours.
• Individual responses vary considerably, so there isn't one carbohydrate-loading protocol guaranteed to work equally well for every athlete.
• Practical takeaway: For a long endurance event, aim for roughly 8–10 g/kg/day during the final 36–48 hours, adjust for your individual needs, and use familiar, easily digested carbohydrate sources.

What Is Muscle Glycogen, and Why Does It Matter?

When you eat carbohydrates, they're broken down into sugars that can be used for energy. Some glucose is used immediately, while some is stored as glycogen, primarily in your skeletal muscles and liver.

Muscle glycogen is especially important during moderate- to high-intensity exercise because it provides a readily available source of carbohydrate energy.

Your body can also use fat during endurance exercise, but fat oxidation cannot always supply energy quickly enough to support higher intensities. As exercise intensity increases, carbohydrate metabolism becomes increasingly important.

Under typical resting conditions, the body stores approximately 400 grams of glycogen in skeletal muscle and another 100–120 grams in the liver, although these amounts vary with body size, diet, and training status.

During prolonged exercise, muscle glycogen concentrations progressively decrease. As those stores become limited, maintaining a given exercise intensity becomes more difficult.

That's one reason athletes often experience a substantial decline in performance during long races when carbohydrate availability becomes inadequate.

Carb loading attempts to increase muscle glycogen above normal resting concentrations before an event begins, giving athletes a larger supply of stored carbohydrate to draw from during competition.

It's important to distinguish this from carbohydrate intake during exercise. Carb loading increases the fuel available at the start, while consuming carbohydrates during a race helps maintain carbohydrate availability as exercise continues.

For longer events, both strategies can matter.

How Was the New Study Conducted?

The researchers conducted a systematic review of studies published through June 2026 that investigated carbohydrate intake and skeletal muscle glycogen concentrations.

To qualify, studies needed to report carbohydrate intake and exercise status for at least 24 hours before muscle glycogen was measured through a muscle biopsy.

The researchers identified 63 experiments involving 641 participants for the descriptive analysis. Eighteen trials met the additional criteria for inclusion in the meta-analysis.

The studies included recreationally active individuals, endurance-trained athletes, well-trained athletes, and a smaller number of untrained participants.

Carbohydrate intake varied considerably between studies, as did the duration of loading, the amount of exercise performed beforehand, and the participants' training status.

The researchers categorized carbohydrate intake as follows:

The meta-analysis compared lower-to-moderate carbohydrate intakes with higher-to-very-high intakes to determine how those differences affected muscle glycogen concentrations.

Researchers also examined whether loading duration, training status, carbohydrate type, and prior exercise helped explain differences between studies.

Higher Carbohydrate Intake Significantly Increased Muscle Glycogen

The most important finding was that higher carbohydrate intake produced significantly greater muscle glycogen concentrations than lower intake.

When researchers compared diets providing no more than 6.5 g/kg/day with diets providing more than 6.5 g/kg/day, the higher-carbohydrate conditions produced an average increase of approximately 192 mmol/kg of dry muscle mass.

The result was statistically significant, with a p-value below 0.0001.

That is a substantial difference in measured muscle glycogen concentration, and it reinforces why carbohydrate loading has remained a standard practice in endurance sports nutrition.

However, the studies also showed considerable variability. The statistical heterogeneity was very high, with an I² value of 94%.

That means the size of the glycogen response differed substantially between studies, beyond what would be expected from sampling error alone.

The direction of the evidence is clear: eating more carbohydrates generally increases muscle glycogen. The exact amount needed to maximize those stores is considerably less certain.

This distinction matters when turning the research into practical recommendations. We can be confident that carbohydrate availability influences glycogen storage without assuming that every athlete needs the same intake.

How Many Carbohydrates Do You Actually Need?

The researchers concluded that consuming more than 8 grams of carbohydrate per kilogram of body weight per day for 36–48 hours is a practical strategy for significantly increasing muscle glycogen before competition.

That's a little different from traditional guidelines that frequently recommend 10–12 g/kg/day for the final 36–48 hours before an endurance event.

However, the study did not demonstrate that 8 g/kg/day is the optimal amount or that consuming more provides no additional benefit. In fact, the researchers found that glycogen concentrations generally continued to increase with carbohydrate intake, and the exact point at which storage reaches its maximum remains unclear.

For athletes, the useful takeaway is that 8 g/kg/day is a reasonable evidence-informed starting point, not a proven upper limit. Higher intakes may be appropriate depending on the event, training status, previous glycogen depletion, and how well an athlete tolerates large quantities of carbohydrate.

Here's what those targets look like at different body weights.

These are daily carbohydrate totals, not amounts that need to be consumed in one meal. They also include carbohydrates from regular foods, beverages, and sports nutrition products.

For many athletes, even 8 g/kg/day represents a significant increase from their normal diet. Someone weighing 175 pounds would need approximately 630 grams of carbohydrate daily, which can be difficult to consume without planning.

This is where carbohydrate-rich drinks and familiar sports nutrition products can be useful. The goal is to reach an appropriate daily carbohydrate intake without making the digestive system work unnecessarily hard.

Is There a Point Where More Carbohydrates Stop Helping?

You might assume that muscle glycogen storage reaches a clear ceiling and that eating additional carbohydrates beyond that point accomplishes nothing.

Physiologically, there must be limits to glycogen storage. However, identifying the intake that maximizes storage across different athletes is more complicated.

The researchers found a positive relationship between carbohydrate intake and muscle glycogen concentrations. Among endurance-trained participants, carbohydrate intake explained approximately 49% of the variation in measured muscle glycogen in their exploratory analysis.

Some subgroup findings suggested that the benefits might begin to level off as carbohydrate intake increased. Other analyses showed continued increases at higher intakes, with no clear plateau.

The researchers noted that relatively few study conditions examined intakes near 12 g/kg/day, making it difficult to identify an upper threshold confidently.

This study does not prove that 8 g/kg/day is enough to maximize glycogen in every athlete. It supports that intake as a practical recommendation for substantially increasing stores while acknowledging that higher intakes may produce additional benefits.

There's also a difference between maximizing muscle glycogen in a laboratory and finding the best strategy for race-day performance. An athlete who consumes an enormous amount of carbohydrate but experiences bloating, nausea, or diarrhea may be worse off than someone who uses a slightly lower, well-tolerated intake.

That's why I would rather see athletes practice a realistic loading strategy during training than chase the highest possible carbohydrate number immediately before an important race.

How Long Should You Carb Load?

Traditional carbohydrate-loading strategies sometimes involved several days of hard training, carbohydrate restriction, and then a large increase in carbohydrate intake.

Modern approaches are much simpler.

The review found evidence that substantial glycogen increases can occur within 24–48 hours, particularly when carbohydrate intake is high and training volume is reduced.

However, the researchers cautioned that differences in exercise, carbohydrate quantity, and participant training status made it impossible to isolate the ideal loading duration.

Some studies demonstrated rapid glycogen increases within approximately 24 hours, while others found that 48–72 hours produced greater storage than shorter protocols.

The authors ultimately recommended 36–48 hours of more than 8 g/kg/day as a practical approach for significantly increasing glycogen before competition.

For a Saturday morning marathon, that generally means emphasizing carbohydrate intake on Thursday and Friday while reducing training volume.

For an ultramarathon or long-distance cycling event, the same general approach can be useful, although the ideal strategy will depend on expected event duration, training demands, and how much carbohydrate the athlete can comfortably consume.

You generally don't need to spend an entire week aggressively carb loading, and you certainly don't need to deliberately exhaust yourself immediately before a race just to deplete glycogen.

Do You Need to Deplete Glycogen Before Carb Loading?

The original carbohydrate-loading protocols developed decades ago involved deliberately depleting muscle glycogen before consuming large amounts of carbohydrate.

The reasoning was that depleted muscles would become particularly responsive to carbohydrate intake and subsequently store more glycogen than normal.

There's a physiological basis for this. Glycogen-depleting exercise stimulates processes involved in glycogen resynthesis, including increased glycogen synthase activity in the exercised muscle.

The review found that prior exercise can influence how quickly and how much glycogen accumulates during loading.

However, deliberate exhaustive exercise is not a prerequisite for effective carbohydrate loading in endurance-trained athletes.

Several studies demonstrated substantial glycogen increases with high carbohydrate intake without a demanding depletion session immediately beforehand.

This is important because adding an exhausting workout close to competition creates additional fatigue and potentially interferes with recovery.

For most endurance athletes, normal training followed by a taper and increased carbohydrate intake is a more sensible approach than attempting to recreate older depletion protocols.

The practical goal is to arrive at the starting line with full glycogen stores and minimal residual fatigue, not to maximize glycogen storage at the expense of recovery.

Does the Type of Carbohydrate Matter?

Carbohydrate quantity was the strongest overall factor identified in the review, but carbohydrate type may also influence how quickly glycogen is replenished.

The researchers discussed evidence that high-glycemic-index carbohydrates can support faster glycogen restoration, particularly during shorter recovery periods following exercise.

High-glycemic carbohydrates generally produce a faster rise in blood glucose, which can support glucose availability and muscle glycogen synthesis.

However, the review also noted that relatively few studies directly compared carbohydrate types. Many studies used mixed diets, and some didn't describe carbohydrate sources well enough to classify their glycemic index.

That limits how confidently we can recommend one carbohydrate source over another for a full 36–48-hour loading period.

For practical purposes, foods such as rice, potatoes, pasta, bread, cereal, fruit, and sports drinks can all contribute to carbohydrate loading.

You don't need to eliminate complex carbohydrates or consume nothing but sugar. What matters most is achieving the necessary carbohydrate intake while keeping digestion comfortable.

That said, high-fiber foods can become problematic when carbohydrate targets are very high. Eating enormous portions of beans, vegetables, and whole grains may make it difficult to reach your target without feeling excessively full or experiencing gastrointestinal discomfort.

During the final day or two before a race, choosing more easily digested, lower-fiber carbohydrate sources can make the process much more manageable.

Where GlycoFuel Fits Into Carb Loading

One of the challenges with carbohydrate loading is simply getting enough carbohydrates into your diet.

If you're aiming for 600–800 grams daily, relying entirely on solid food can become uncomfortable. Large meals may leave you feeling bloated, and trying to force down more food when you're already full isn't particularly enjoyable.

This is where a carbohydrate supplement can be useful.

GlycoFuel from Simply Good Supplements is an option for athletes who want a convenient carbohydrate source to help meet their fueling needs.

Rather than treating carbohydrate supplements as something that only belongs in a bottle during training, you can use them as part of your overall carbohydrate strategy when your daily intake requirements are unusually high.

For example, an athlete targeting 650 grams of carbohydrate daily might obtain most of that from regular meals and use a carbohydrate drink to help close the remaining gap.

The important point is that GlycoFuel doesn't replace the need to calculate your total carbohydrate intake. It simply offers another way to reach that intake, particularly when consuming additional solid food becomes difficult.

I also wouldn't suggest that any particular carbohydrate supplement automatically produces greater glycogen storage than an equivalent amount of carbohydrate from food. The review doesn't establish that.

What matters is the total amount consumed, how well it's tolerated, and whether it fits into the athlete's overall fueling plan.

Why Recharge Can Be Useful After Hard Training

Carbohydrate loading before competition is only one part of the glycogen equation. Replenishing glycogen after training is also important, especially for athletes completing long sessions or training multiple times per day.

This is where Recharge from Simply Good Supplements fits into the conversation.

Recharge is one of my favorite products in our lineup, partly because I think post-exercise carbohydrate intake is often overlooked by athletes who focus almost exclusively on protein.

Protein is important for muscle repair and adaptation, but protein alone doesn't replace the carbohydrate used during training.

Following a demanding endurance session, consuming carbohydrates helps replenish the glycogen that was depleted during exercise. This becomes particularly important when the next training session is approaching and there isn't much time available for recovery.

Recharge contains carbohydrates, including sugars, which I suspect some people view as a negative.

In this particular context, however, rapidly available carbohydrates are a feature rather than a drawback.

When glycogen restoration is a priority, especially during short recovery windows, sugars can provide readily available carbohydrate for glycogen synthesis. The review supports the broader importance of carbohydrate availability and discusses the benefits of high-glycemic carbohydrates for rapid glycogen restoration.

That doesn't mean sugar is necessary after every workout. If you finish training and have an entire day before your next session, regular carbohydrate-rich meals can generally accomplish the same goal.

But after a long run, demanding ride, or two-a-day training session, a convenient recovery product can make it easier to begin replenishing glycogen without waiting for a full meal.

Recharge is intended to make post-workout fueling more convenient, not to replace good nutrition or guarantee faster recovery than an equivalent, well-planned meal.

How to Put the Research Into Practice

Let's use a 175-pound endurance athlete preparing for a Saturday morning marathon as an example.

At approximately 79 kilograms, an intake of 8 g/kg/day works out to about 630 grams of carbohydrate daily.

For the final 36–48 hours, the athlete could distribute that carbohydrate across breakfast, lunch, dinner, snacks, and beverages rather than attempting to consume unusually large meals.

A practical approach might include carbohydrate-rich breakfasts, rice or pasta with lunch and dinner, easily digested snacks between meals, and carbohydrate-containing drinks when needed.

The athlete would also reduce training volume during this period, allowing glycogen stores to increase without immediately using large amounts of the carbohydrate being consumed.

Here's an example of how the daily carbohydrate intake might be distributed.

This is an illustration of carbohydrate distribution, not a prescribed meal plan. Actual food choices and serving sizes should be adjusted to the athlete's needs and gastrointestinal tolerance.

The biggest mistake would be waiting until the evening before the race and attempting to consume the entire carbohydrate target in one enormous pasta dinner.

Carb loading works best as a planned increase in carbohydrate intake over the final day or two, not as one oversized meal.

Athletes should also maintain appropriate fluid intake. Glycogen is stored alongside water, so increases in body weight during carbohydrate loading are normal and don't necessarily indicate increased body fat.

What About Carb Loading for Ultramarathons?

Ultramarathons present an interesting challenge because carbohydrate availability becomes increasingly important as event duration increases.

For a 50K, 50-mile, 100K, or 100-mile event, starting with well-stocked glycogen stores is useful, but it won't eliminate the need for carbohydrate intake during the race.

Even substantial glycogen stores are finite. During prolonged exercise, carbohydrate oxidation continues, and stored glycogen alone cannot support many hours of racing.

That's why I think ultrarunners should treat carbohydrate loading and race-day fueling as two separate but complementary strategies.

Carb loading helps maximize available stored carbohydrate before the start. Fueling during the race helps maintain carbohydrate availability as those stores are used.

A good carb-loading strategy cannot compensate for inadequate fueling during a 100-mile race.

For longer events, gastrointestinal tolerance becomes particularly important. Athletes need to practice consuming carbohydrates during training, including the types and quantities they intend to use on race day.

The same principle applies to carbohydrate loading. If an athlete has never consumed 700 grams of carbohydrate in a day, the final 48 hours before an important ultramarathon isn't the ideal time to find out how their digestive system responds.

Does Carb Loading Help With Shorter Workouts?

Not every workout requires aggressive carbohydrate loading.

The primary purpose of carb loading is to increase muscle glycogen availability for prolonged or demanding exercise where carbohydrate stores may become a limiting factor.

For a typical 30–60-minute workout, normal dietary carbohydrate intake is often sufficient, particularly if the athlete is eating enough overall.

A recreational lifter completing a moderate gym session generally doesn't need to consume 8–12 g/kg/day simply to maximize muscle glycogen.

Likewise, someone going for a short, easy run is unlikely to benefit meaningfully from an aggressive two-day carb-loading protocol.

Carb loading becomes more relevant as exercise duration, intensity, and total carbohydrate demand increase.

For endurance competitions lasting roughly 90 minutes or longer, starting with adequate glycogen stores can become increasingly important. The exact benefit depends on the event, the athlete's usual diet, and their ability to consume carbohydrate during exercise.

The goal should be matching carbohydrate availability to the demands of the activity rather than assuming more is always better.

Important Limitations of This Research

Although this review provides valuable information, there are several limitations worth understanding.

First, the studies showed very high heterogeneity, meaning glycogen responses varied substantially even when researchers grouped studies by carbohydrate intake. Differences in training status, exercise protocols, loading duration, and dietary conditions made it difficult to isolate the effect of any single variable.

Second, the participants were predominantly young men. Only about 12% of participants were women, which limits how confidently the results can be generalized across sexes and age groups. The authors noted that available evidence suggests men and women can achieve similar glycogen increases when carbohydrate intake is appropriately matched, but more research is needed.

Third, the primary outcome was muscle glycogen concentration, not race performance. Although glycogen availability is important for endurance exercise, this meta-analysis did not directly establish which carbohydrate-loading strategy produces the best race results.

Finally, the review could not determine the exact carbohydrate intake at which muscle glycogen storage reaches its maximum. The researchers specifically highlighted the need for more studies examining very high intakes, including 12 g/kg/day or greater.

These limitations don't undermine the general value of carbohydrate loading. They simply mean that recommendations should be treated as practical starting points rather than precise physiological rules that apply equally to everyone.

What I Think This Study Actually Tells Us

I think the most useful finding is that athletes don't need an overly complicated carbohydrate-loading strategy to substantially increase muscle glycogen.

The biggest factor appears to be consuming enough carbohydrate, with loading duration, training status, and recent exercise influencing the response.

For most endurance athletes, more than 8 g/kg/day for approximately 36–48 hours is a reasonable evidence-based approach when preparing for an event where glycogen availability matters.

However, I wouldn't interpret that recommendation as proof that consuming 10–12 g/kg/day is unnecessary. The researchers couldn't identify a definitive saturation point, and some athletes may benefit from higher intakes.

The other important takeaway is that carbohydrate source matters less than many people assume, particularly when there is enough time to replenish glycogen.

Sports nutrition products can certainly make it easier to consume large quantities of carbohydrate. That's one reason we developed products such as GlycoFuel for fueling and Recharge for post-exercise recovery.

But neither product changes the underlying physiology. Your muscles respond to carbohydrate availability, not the marketing on the package.

That's something I think gets overlooked when athletes start searching for increasingly complicated fueling strategies.

The Bottom Line

A 2026 systematic review and meta-analysis examined 63 experiments involving 641 participants to determine how carbohydrate intake influences muscle glycogen storage.

The researchers found that higher carbohydrate intake significantly increased muscle glycogen concentrations, although responses varied considerably between individuals and studies.

Based on the available evidence, they recommended consuming more than 8 grams of carbohydrate per kilogram of body weight daily for 36–48 hours before endurance competition to significantly increase glycogen stores.

The exact intake required to maximize glycogen remains uncertain, and the review did not demonstrate that higher intakes are unnecessary.

For athletes, the practical takeaway is relatively straightforward. Calculate your carbohydrate needs, increase intake during the final day or two before a demanding endurance event, reduce training volume, and choose foods and drinks you know you can tolerate.

Products such as GlycoFuel and Recharge can help make carbohydrate intake more convenient around training and competition, but regular carbohydrate-rich foods work too.

The best carb-loading strategy is one that provides enough carbohydrate, fits your training schedule, and leaves you feeling ready to perform rather than uncomfortably full.

About the Author

Matt Mosman, MS, CISSN, CSCS, is the founder and Chief Science Officer of Simply Good Supplements. With a background in exercise science, sports nutrition, and strength and conditioning, Matt focuses on turning research into practical advice that athletes, parents, and everyday active people can actually use.

References

Jones RO, Areta JL, Fortis HO, Pugh J, Louis JB. Dietary Carbohydrate Intake and Skeletal Muscle Glycogen: A Systematic Review and Meta-Analysis to Determine Optimal Carbohydrate Loading Strategies. Scandinavian Journal of Medicine & Science in Sports. 2026;36:e70379. https://doi.org/10.1111/sms.70379.