How long do bodybuilders fast? Understanding protocols for muscle and fat loss

October 15, 2025 •

5 min read

For decades, bodybuilders were advised to eat small meals every few hours to fuel muscle growth. However, the landscape has shifted, and many now explore intermittent fasting, prompting the question: how long do bodybuilders fast for optimal results? The answer depends heavily on the individual's specific phase—cutting fat or building mass—and their training schedule.

Quick Summary

Bodybuilders often utilize intermittent fasting protocols like the 16:8 method to manage fat loss during cutting phases. The duration of fasting varies based on the training plan, with careful consideration given to nutrient timing, especially protein intake, to preserve lean muscle mass. Longer or more intense fasting protocols carry a higher risk of muscle loss if not managed correctly with high protein consumption during eating periods.

Key Points

Moderate Fasting is Preferred: Most bodybuilders opt for shorter, more manageable protocols like the 16:8 method, especially for cutting, to balance fat loss with muscle preservation.
Long Fasts Risk Muscle Loss: Fasting durations of 24 hours or longer, while effective for weight loss, carry a greater risk of muscle catabolism if not carefully managed.
Protein is Non-Negotiable: Regardless of the fasting window, bodybuilders must ensure a high protein intake during their eating periods (1.2-1.6g/kg) to protect and repair muscle tissue.
Timing Workouts is Key: Aligning resistance training sessions with the eating window allows for proper fueling before and recovery nutrition immediately after, optimizing performance and muscle growth.
Listen to Your Body's Cues: Performance drops or excessive fatigue are signs that your fasting protocol or nutrient timing needs adjustment. There is no one-size-fits-all approach.
Focus on Cutting, not Bulking: Intermittent fasting is primarily used by bodybuilders during a fat loss (cutting) phase and is generally not recommended for optimal muscle gain (bulking) due to high caloric needs.

The Science Behind Intermittent Fasting and Bodybuilding

Intermittent fasting (IF) is an eating pattern that cycles between periods of eating and fasting, rather than a diet that dictates what foods to eat. This approach has gained traction in the bodybuilding community for its potential to improve metabolic health and aid fat loss. The key mechanisms at play involve changes in hormone levels and how the body uses energy. During a fasted state, insulin levels drop, and human growth hormone (HGH) levels can increase, creating an environment that favors fat burning while helping to preserve muscle mass.

Common Intermittent Fasting Protocols for Bodybuilders

Different IF methods offer varying levels of restriction and flexibility, allowing bodybuilders to choose a protocol that aligns with their goals and lifestyle.

16/8 Method (Leangains): This is one of the most popular protocols among bodybuilders. It involves fasting for 16 hours and restricting all daily food intake to an 8-hour window. This method is manageable for most people and often used during a cutting phase to create a moderate caloric deficit. Workouts are often timed towards the end of the fasting window, with the first meal consumed post-training to maximize recovery.
The Warrior Diet (20/4): This more intense protocol involves a 20-hour fast and a single, large meal within a 4-hour eating window. While effective for fat loss, it can be challenging for bodybuilders to consume enough calories and protein in such a short period to support muscle growth, especially during a bulking phase.
Alternate-Day Fasting (ADF): This involves a 24-hour fast every other day. While potentially effective for rapid fat loss, it carries a higher risk of muscle loss for bodybuilders, as the extended caloric restriction can be catabolic if not managed meticulously.
Spontaneous Meal Skipping: For those who don't want a rigid schedule, simply skipping a meal like breakfast on occasion can provide some metabolic benefits without the commitment of a structured IF plan.

Maximizing Muscle Retention While Fasting

One of the biggest concerns for bodybuilders using IF is the potential for muscle loss. However, strategies exist to mitigate this risk, making IF a viable tool for physique athletes, particularly during a cut.

Prioritize Protein: Maintaining a high protein intake is non-negotiable. Aim for 1.2 to 1.6 grams of protein per kilogram of body weight during your feeding window to provide the necessary amino acids for muscle repair and synthesis.
Time Your Workouts: Schedule resistance training sessions close to your eating window. This allows you to fuel your workout and consume a high-protein, carbohydrate-rich meal shortly after to kickstart recovery.
Resistance Training: Consistent, heavy resistance training is crucial. This stimulus tells your body that the muscles are needed, prioritizing their retention over breaking them down for energy, even in a calorie deficit.
Stay Hydrated: Drink plenty of water and zero-calorie fluids like black coffee or tea during your fasting period. This helps manage hunger and supports overall bodily function.
Listen to Your Body: Pay close attention to your energy levels, strength, and recovery. If performance suffers, it might be necessary to adjust your fasting window or caloric intake.

Fasting During Bulking vs. Cutting Phases

Intermittent fasting can be a powerful tool, but its application differs significantly depending on whether a bodybuilder is bulking or cutting.

Intermittent Fasting for Cutting

During a cutting phase, the primary goal is to lose fat while preserving as much muscle as possible. A moderate caloric deficit is required, and IF can simplify this process by condensing calorie intake into a shorter window. This can make it easier to avoid overeating and can promote fat oxidation. Protocols like 16:8 are well-suited for this purpose.

Intermittent Fasting for Bulking

For bodybuilders in a bulking phase, the goal is to be in a caloric surplus to promote muscle growth. This is where IF can become challenging. Consuming the high number of calories and protein needed for growth within a restricted eating window can be difficult. For those with high caloric needs, this may lead to feeling overly full or missing macro targets. Therefore, while possible, IF is generally less common or implemented more cautiously during a bulk.

Comparison of Fasting Methods and Bodybuilding Phases


Method	Primary Goal	Muscle Retention	Calorie Management	Ease of Implementation
16:8 (Leangains)	Fat Loss (Cutting)	High (if protein is sufficient)	Easier to manage deficit	Moderate
20:4 (Warrior Diet)	Aggressive Fat Loss	Moderate (higher risk)	Challenging to hit targets	Hard
Bulking (No Fasting)	Muscle Gain (Bulking)	Optimal	Easier to meet surplus	Easy
Cutting (No Fasting)	Fat Loss (Cutting)	High (with frequent feeding)	Requires constant monitoring	Hard

Breaking the Fast Safely

How a bodybuilder breaks their fast is just as important as the fasting period itself. After a period of fasting, the body is primed to absorb nutrients, and starting with the right foods is key for recovery and avoiding digestive issues.

Start with easily digestible foods: Begin with a small, nutrient-dense meal to ease the digestive system back into action. Options include vegetable broth, a simple smoothie, or lean protein sources.
Prioritize protein and carbs: The first full meal should focus on high-quality protein to support muscle protein synthesis and complex carbohydrates to replenish glycogen stores.
Avoid overeating and processed foods: After a fast, it can be tempting to binge. However, this can cause an insulin spike and digestive distress. Stick to whole, nutrient-dense foods and avoid excessive sugars and fats immediately after fasting.

Conclusion

Ultimately, how long do bodybuilders fast depends on their individual goals and how they respond to different protocols. For those focused on fat loss during a cutting phase, intermittent fasting, particularly the 16:8 method, can be an effective and sustainable tool when combined with a high-protein diet and consistent resistance training. However, during a bulking phase, the caloric and protein demands can make IF more challenging. The key to successful fasting for any bodybuilder lies in careful planning, prioritizing nutrition during eating windows, and listening closely to your body's signals to avoid compromising hard-earned muscle mass. As with any significant dietary change, consulting with a sports dietitian or healthcare professional is advisable to ensure it aligns with your health and fitness goals. Intermittent Fasting and Bodybuilding: Can You Do Both for Muscle ...

Frequently Asked Questions

While it's possible to maintain muscle during a 24-hour fast, it's generally not recommended for bodybuilders. Research suggests that muscle loss can occur with fasts longer than 36 hours. For bodybuilders, shorter intermittent protocols like 16:8 are safer for preserving muscle mass while losing fat.

The 16:8 method is often considered the best starting point for bodybuilders, especially during a cutting phase. It provides a manageable 8-hour eating window to consume enough calories and protein while still promoting fat loss.

Bodybuilders should schedule their eating window around their training. It's best to consume a balanced meal with protein and carbs before a workout and another protein-rich meal soon after, within the eating window, to maximize muscle recovery and growth.

For most intermittent fasting protocols (like 16:8), supplementing with BCAAs is not strictly necessary, provided you consume enough total daily protein. However, some bodybuilders take BCAAs before a fasted workout as a precautionary measure.

Intermittent fasting is generally not ideal for bulking. The high caloric and protein demands of a bulking phase can be very difficult to meet within a restricted eating window, which could hinder muscle growth.

To maximize muscle recovery, break your fast with an easily digestible meal containing high-quality protein and complex carbohydrates. For instance, a meal of lean meat or eggs with brown rice can effectively replenish glycogen stores and initiate muscle repair.

The main risks for bodybuilders are the potential for muscle loss, especially with prolonged or aggressive fasting, and insufficient energy for high-intensity training. These risks are higher if adequate protein and overall caloric intake are not met during eating periods.