Why Long Fasts (Over 22 Hours) Aren’t Ideal for Maximizing Muscle and Leanness

Long fasts—like those lasting 36-72 hours—have gained popularity for benefits like autophagy, improved insulin sensitivity, and metabolic reset.

When the goal is to build an incredible physique – long fasts are incredibly detrimental.

Now, I’m the first to recommend fasting as an incredible tool.

But when you fast too long, you starve the fat and the muscle.

And often, I see most people want to use it as an extreme weight loss tool, as opposed to mastering eating on a daily basis.

My preferred method is to fast for the first 5 hours of the day.

This typically means around an 8-hour eating window.

Quote from the study[1] – “Our results suggest that an intermittent fasting program in which all calories are consumed in an 8-h window each day, in conjunction with resistance training, could improve some health-related biomarkers, decrease fat mass, and maintain muscle mass in resistance-trained males.”

I don’t think you have to be exact here.

I’ve found a range of 16-22 hour fasts seem to work best.

I like fasting the first part of the day because it helps me easily hit a deficit and add muscle while staying lean.

It also allows for a big dinner (fits social lifestyle).

It also helps me be more productive, has health benefits, etc.

I know 24, 36, and even up to 72-hour fasts have become popular.

I don’t recommend extending your fasts to 22 hours and beyond.

Here’s why.

1. Muscle Protein Breakdown Increases

Fasting beyond 22 hours can push your body into a state where muscle protein breakdown increases, especially when glycogen stores are fully depleted.

While your body will first rely on fat stores for energy, prolonged fasting eventually leads to amino acids being pulled from muscle tissue for gluconeogenesis (the creation of glucose to fuel essential processes).

This can result in muscle loss over time.

2. Suppressed Protein Synthesis

Muscle building relies on a balance between protein synthesis and protein breakdown.

Long fasts suppress mTOR (the pathway responsible for muscle growth) and protein synthesis, meaning your body isn’t repairing or building muscle efficiently during extended fasts.

Shorter fasts (16-22 hours) avoid this issue by balancing fat-burning benefits with sufficient time for anabolic (muscle-building) processes.

3. Lower Testosterone Levels

Long fasts can lower testosterone, particularly when combined with high stress (elevated cortisol) and reduced caloric intake.

Testosterone is critical for maintaining lean muscle and promoting fat loss.

If your testosterone drops, it hinders your ability to stay lean and build strength.

4. Metabolism Slows

While fasting for 16-22 hours can boost your metabolism and fat-burning efficiency, extended fasts (36+ hours) may cause your metabolism to slow down to conserve energy.

This shift can make it harder to maintain a lean physique in the long term, especially if you frequently alternate between extreme fasting and normal eating.

5. Reduced Training Performance

Prolonged fasting can leave you feeling weak, lethargic, and unable to train effectively. Training during a long fast often leads to suboptimal strength and poor recovery, which can negatively impact muscle growth.

Your body requires sufficient glycogen and amino acids to perform at your best in the gym, which isn’t possible during extended fasts.

6. Hormonal Disruptions

Cortisol levels rise significantly during long fasts. While this is a natural response to fasting, chronically elevated cortisol can lead to muscle breakdown, fat retention (especially around the midsection), and decreased recovery.

Leptin and thyroid hormones, both of which regulate energy balance, can also drop, reducing your ability to stay lean and perform at your peak.

The Sweet Spot: 16-22 Hour Fasts

Fasting 16-22 hours strikes the perfect balance for maximizing fat loss, muscle retention, and hormonal health.

During this window, your body burns fat efficiently, maintains muscle tissue, and supports testosterone and growth hormone levels.

Breaking the fast with high-protein meals ensures you replenish amino acids to kickstart recovery and muscle growth.

*I’ve been using 16-22 hour fasts successfully for over a decade.

How to Stay Lean and Muscular While Fasting

• Keep Your Fast Short: Stick to 16-22 hours to reap the fat-burning benefits without sacrificing muscle.
• Prioritize Protein: Break your fast with a protein-rich meal to support recovery and muscle repair.
• Train Smart: Avoid intense strength training during extended fasts—your body needs fuel to perform.
• Support Hormonal Health: Optimize testosterone and recovery with the right nutrients, like those found in Kino Mojo (zinc, magnesium, Tongkat Ali).

Bottom Line:

While long fasts can have health benefits in certain contexts, they aren’t ideal if your primary goal is to maximize muscle and leanness.

When you are relatively lean your body can mobilize about 400-600 calories per day from body fat.

Larger deficits than this eat into muscle.

Focus on shorter, more strategic fasting windows to stay anabolic, strong, and lean.

Talk Soon,

Greg O’Gallagher

P.S.

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