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Can Low-Carb Diets Hurt Your Muscle Gains?

Can Low-Carb Diets Hurt Your Muscle Gains?

Low-carbohydrate (low-carb) diets are often praised for their fat-loss benefits, blood sugar control, and appetite regulation. But if your goal is building muscle, going too low on carbs might be working against you.

Recent studies are showing that low-carb diets can reduce muscle protein synthesis, limit training intensity, and impair long-term muscle hypertrophy. Let’s break down why that happens — and what the science says.

Why Carbs Matter for Muscle Growth

Muscle growth is driven by the balance between muscle protein synthesis (MPS) and muscle protein breakdown (MPB). Resistance training and protein intake stimulate MPS — but carbs play a key supporting role by:

  • Restoring glycogen to fuel high-volume training

  • Reducing cortisol, a catabolic hormone that can increase muscle breakdown

  • Spiking insulin, which helps shuttle amino acids into muscle and suppress MPB

What Happens on a Low-Carb Diet?

Recent research shows that restricting carbs can blunt key anabolic signals and performance metrics critical for building muscle:

1. Reduced Muscle Protein Synthesis

A 2024 study (PMID: 38322313) found that resistance-trained individuals following a ketogenic diet had lower rates of muscle protein synthesis post-exercise, compared to those consuming moderate-to-high carbs. The authors linked this to reduced insulin and mTOR signaling.

2. Lower Training Volume and Power Output

Another study from 2023 (PMID: 37669420) showed that athletes on a low-carb diet experienced significantly reduced training volume and power output during strength sessions. This matters because training volume is a key driver of hypertrophy.

3. Impaired mTOR Activation

The mTOR pathway is critical for muscle growth. A 2022 review (PMID: 35466234) noted that very-low-carb diets may blunt mTORC1 activity by reducing energy availability and insulin signaling — both of which are stimulated by carb intake.

Summary of Key Findings

Impact Area Low-Carb Effect Citation
Muscle protein synthesis Decreased PMID: 38322313
Training volume & power Reduced PMID: 37669420
mTOR signaling Blunted PMID: 35466234
Cortisol levels Increased PMID: 30830365

What’s the Takeaway?

While low-carb diets can be effective for fat loss, they may not be ideal for muscle growth. Especially if you're lifting heavy and trying to pack on size, carbs are more than just energy — they’re anabolic allies.

If you're set on staying low-carb, you might consider targeted carbs around workouts, or cyclical approaches that reintroduce carbs during training phases to support performance and recovery.

Final Thought

Muscle isn't just about lifting and protein — it's also about having the fuel to perform and recover. Going too low on carbs may leave your gains on the table.

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