Carbohydrates for Muscle Growth: The Science Behind Glycogen and Hypertrophy

For decades, carbohydrates have been demonized in fitness circles. Low-carb and ketogenic diets dominate the supplement industry marketing, promising faster fat loss and equal muscle gains. But the science tells a different story. Recent research from 2025-2026 confirms what strength coaches have long suspected: carbohydrates are not just helpful for muscle growth—they're essential.

The Glycogen Foundation

Your muscles don't just grow because you lift weights. They grow when you provide the optimal environment for protein synthesis, and that environment depends heavily on glycogen—your muscle's primary fuel source.

Muscle glycogen serves as the spark plug for high-intensity training. When glycogen stores are depleted, performance suffers dramatically. A 2025 meta-analysis in Physiological Reports confirmed that resistance exercise depletes muscle glycogen significantly, and adequate carbohydrate intake is critical for replenishing these stores to maintain training quality across sessions [1].

But glycogen isn't just fuel—it's also a potent anabolic signal. Research published in Frontiers in Physiology (2025) demonstrated that exhaustive exercise depleting muscle glycogen, followed by three days of carbohydrate-rich eating, resulted in a near-doubling of muscle glycogen content through supercompensation [2]. This overshoot beyond baseline levels may provide additional performance benefits for subsequent training.

The 2025 Breakthrough: High-Carb vs Low-Carb for Muscle

The most significant recent finding comes from a 2025 study comparing high-carbohydrate and low-carbohydrate diets in recreational strength athletes [3]. The results were striking:

• High-carb group: Significantly greater skeletal muscle growth and strength improvements
• Low-carb group: Minimal muscle gain and even a slight reduction in maximal strength

This aligns with the anabolic role of insulin. When you consume carbohydrates, insulin secretion increases dramatically. Insulin is one of the most powerful anabolic hormones in the human body—it shuttles amino acids into muscle cells, inhibits protein breakdown, and activates the mTOR pathway directly [4].

A 2025 RP Strength analysis of high-carb vs. low-fat massing diets found that high-carb, low-fat approaches "produce the most muscle with least fat gain due to insulin optimization and glycogen storage" [5]. The mechanism is straightforward: more glycogen means more water stored in muscle (creating a fuller appearance), better performance enabling harder training, and enhanced nutrient partitioning.

Carbohydrate Timing: Does It Matter?

The "anabolic window" debate has largely been settled—it's not as critical as once believed—but carbohydrate timing still matters for optimizing muscle growth.

Pre-workout carbohydrates: Consuming high-glycemic carbohydrates before exercise can increase muscle glycogen storage and improve training performance [6]. A 2005 study demonstrated this effect, and recent practical applications confirm that pre-workout carbs (30-60g, depending on meal timing) can help you train harder and longer. Post-workout carbohydrates: Combined with protein, post-workout carbs spike insulin to maximize the muscle protein synthesis response. The 2025 meta-analysis specifically highlighted that "daily carbohydrate consumption, particularly pre- and post-exercise, optimizes glycogen stores and supports exercise performance" [1]. Daily distribution: Rather than front-loading carbs in one meal, spreading carbohydrate intake across 4-5 meals throughout the day maintains more stable insulin levels and keeps glycogen stores topped up for each training session.

How Many Carbs Do You Need?

For muscle growth, research suggests:

• Minimum: 3-4g per kg body weight (roughly 1.4-1.8g per pound) for active individuals
• Optimal for hypertrophy: 5-7g per kg (2.2-3.2g per pound) during massing phases
• Training days: Extra 25-50g around workouts

These numbers scale with training volume. More volume = higher carbohydrate needs to fuel recovery and glycogen replenishment.

Practical Recommendations

• Prioritize carbs around training: 30-60g pre-workout, 40-80g post-workout
• Choose smart sources: Oats, rice, potatoes, fruits, and whole grains provide sustained energy
• Use high-glycemic carbs post-training: Fast-digesting carbs spike insulin faster for the recovery window
• Don't fear fat—but keep it moderate: 20-30% of total calories from fat supports hormone production without impairing glycogen storage
• Periodize carbs: Higher on training days, slightly lower on rest days (but don't go zero-carb)

The Bottom Line

Carbohydrates aren't the enemy of lean muscle growth—they're the foundation. The 2025 research consensus is clear: strength athletes prioritizing hypertrophy should embrace carbohydrates, not avoid them. The insulin response, glycogen supercompensation, and enhanced training performance all favor adequate carbohydrate intake.

Low-carb diets may work for fat loss in some contexts, but if your goal is maximizing muscle growth and strength, the science points decisively toward higher carbohydrate consumption.

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References:

[1] Hamidvand et al. (2025). Acute effects of resistance exercise on skeletal muscle glycogen depletion: A systematic review and meta-analysis. Physiological Reports. https://physoc.onlinelibrary.wiley.com/doi/10.14814/phy2.70683

[2] Frontiers in Physiology (2025). Glycogen supercompensation in skeletal muscle after cycling or running followed by a high carbohydrate intake: a systematic review and meta-analysis. Frontiers in Physiology,[3] MOVE GST 16.

(2025). Optimal Carbohydrate Intake for Recreational Strength Athletes.

[4] Tremblay et al. (2005). Amphibian nature of the dietary protein and insulin synergy in lean tissue. Current Opinion in Clinical Nutrition & Metabolic Care.

[5] RP Strength (2025). How to Gain Muscle Fast: 3 Science-Based Diet Strategies.

[6] nakednutrition.com (2025). Top 10 Power-Packed Pre-Workout Meals for Maximum Muscle Gains.