Muscles and Fasting: Is Intermittent Fasting a Good Combination for Building Muscle?

Intermittent fasting and muscle building: can they work together? More and more athletes and fitness enthusiasts are experimenting with fasting to lose fat while building muscle mass. But is that realistic, or do you risk losing muscle mass instead? Opinions differ, and the science paints a nuanced picture. In this article, you’ll learn what research says about intermittent fasting and muscle growth: protein intake, autophagy, hormones, and workout planning. Whether you’re an experienced athlete or just starting strength training, after reading this article you’ll know how to use fasting without hindering your muscle building. We’ll cover different fasting schedules and protein intake, and give you a practical weekly plan.

What exactly is intermittent fasting?

Intermittent fasting (IF) is not a diet in the traditional sense, but an eating pattern. You alternate periods of eating with periods of fasting. Unlike regular diets, IF does not prescribe what you should eat, but when you eat.

The most popular fasting schedules

There are several forms of intermittent fasting, each with its own advantages and disadvantages for muscle building:

• 16:8 method: fasting for 16 hours and eating for 8 hours. This is the most popular schedule and also the most practical for athletes. For example, you can skip breakfast and eat between 12:00 and 20:00.
• 14:10 method: fasting for 14 hours and eating for 10 hours. A gentler option that works well as a starting point, with more room for meals.
• 20:4 method (Warrior Diet): fasting for 20 hours with an eating window of just 4 hours. This schedule is much harder to follow and less suitable if you need to consume a lot of calories and protein for muscle growth.
• 5:2 method: eating normally for five days and severely restricting your calorie intake (approx. 500-600 kcal) for two days. This schedule is used more for weight loss than muscle building.
• Alternate Day Fasting (ADF): fasting or severely restricting your food intake every other day. Recent research shows that this schedule does not necessarily inhibit muscle protein synthesis, provided you get enough protein on eating days.

For muscle building, the 16:8 schedule is the most studied and the easiest to follow. It gives you enough time to meet your daily protein and calorie needs while maintaining a consistent fasting routine.

What does the science say about fasting and muscle mass?

The relationship between fasting and muscle building is more complex than many people think. Here are the key findings.

Protein synthesis during fasting

A frequently asked question is whether fasting reduces muscle protein synthesis. A study in Clinical Nutrition (2024) examined the effects of alternate-day fasting and continuous energy restriction on protein synthesis in muscle tissue. The researchers found no significant differences in the rate of muscle protein synthesis between the groups, provided total protein intake was similar. So meal timing appears to matter less than total daily protein intake.

Maintaining muscle mass with strength training and fasting

A 2022 study compared intermittent fasting with continuous energy restriction, both combined with a 12-week strength training program. Both groups received at least 1.4 grams of protein per kilogram of body weight per day. The result: similar changes in body composition and muscle strength in both groups. Intermittent fasting therefore doesn't have to hinder your muscle development, as long as you get enough protein.

Systematic reviews

A systematic review in Nutrients (2020) analyzed several studies in humans on intermittent fasting combined with strength training and lean mass. The conclusion: lean mass is generally maintained when intermittent fasting is combined with strength training. Whether it limits the development of new muscle mass depends on adequate protein intake and energy balance.

Autophagy and muscle building

Autophagy is often cited as a reason to fast, but how relevant is it to muscle growth?

What is autophagy?

Autophagy (literally, "self-eating") is a cleanup process in your cells in which old proteins and cell components are broken down and reused. Research has linked this process to fasting, exercise, and calorie restriction.

Autophagy in muscle tissue: what does the research say?

This is where things get interesting. A study in Nutrition (2022) found that intermittent fasting activated autophagy markers in the liver of mice, but not in muscle tissue in mice or humans. The effect on human skeletal muscle therefore appears to be more limited than is often claimed.

Animal research in mice also showed that muscle mass was maintained while body fat decreased during intermittent fasting. Whether this also applies to humans is still unclear.

What does this mean for athletes?

In humans, it is still unclear exactly what autophagy in muscle tissue means for recovery or muscle growth. So don't view autophagy as a reason to fast for more muscle. Protein, energy, training, and sleep remain the foundation.

Hormones, fasting, and muscle growth

Intermittent fasting affects several hormones involved in muscle building.

Growth hormone (HGH)

Studies show that growth hormone (Human Growth Hormone) levels can rise during fasting. What this means in practice for your body composition, including losing fat and maintaining or building muscle, is still unclear.

Testosterone

Testosterone plays a role in muscle building. Short-term fasting does not seem to negatively affect testosterone levels, but a prolonged and substantial calorie deficit can lower testosterone. So make sure you get enough calories and fat during your eating window.

Insulin sensitivity

Research into intermittent fasting and insulin sensitivity has produced mixed results. For your muscles, the most important thing is to get enough protein and energy during your eating window, especially around your workout.

Cortisol

One caveat: fasting can temporarily increase cortisol levels. Cortisol is a stress hormone associated with muscle breakdown when levels remain high for a long time. So it’s best not to combine fasting with other stressors, such as lack of sleep or overtraining.

How much protein do you need for fasting and muscle building?

Protein is an important part of your diet if you do strength training. With intermittent fasting, you have less time to meet your daily protein needs, so planning is important.

How much protein do you need?

For building muscle while intermittent fasting, most studies recommend:

• 1.6 to 2.2 grams of protein per kilogram of body weight per day
• For an 80 kg person, this means 128 to 176 grams of protein per day
• Spread this across at least 3 meals within your eating window (with a 16:8 schedule)

Protein distribution across meals

Research shows that spreading protein evenly across multiple meals is more beneficial for muscle protein synthesis than eating all your protein in one or two large meals. Aim for 30-50 grams of protein per meal.

Practical protein schedule (16:8, eating window 12:00-20:00)

How do you combine intermittent fasting with strength training?

The timing of your workout in relation to your eating window is an important consideration.

Option 1: Training at the start of your eating window

Train just before or shortly after your eating window opens. Advantage: you can eat a protein-rich meal right after your workout.

Option 2: Training during your eating window

Plan your training for the middle of your eating window so you can eat both before and after your workout. This is useful if you like to eat before training.

Option 3: Training while fasted

Some athletes deliberately train while fasted. This may lower your training intensity. If you choose to do so, eat a meal containing protein and carbohydrates immediately after training.

Training adjustments when fasting

• Volume: maintain your training volume, but watch for signs of overtraining.
• Intensity: you can keep using the same weights, but listen closely to your body.
• Frequency: 3-5 strength training sessions per week are manageable on a 16:8 schedule.
• Progressive overload: keep applying the principle of progressive overload. This is the most important driver of muscle growth, regardless of your eating pattern.

Fasting and recovery after training

Online, you often read that fasting is supposed to help with recovery after exercise.

What do we really know?

Intense strength training causes small amounts of damage to muscle tissue. This is normal and part of muscle growth. There is research on fasting and certain blood markers, but it has not been shown that fasting leads to faster recovery or less muscle soreness in athletes.

What recovery really depends on

Recovery mainly comes down to the basics:

• Enough sleep
• Enough protein and energy during your eating window
• A well-structured training plan with rest days
• Don’t try to do too much too soon

Supplements and fasting

With fasting and strength training, the basics remain the same: enough protein, enough calories, a good training plan, and enough sleep. Dietary supplements are no substitute for a varied and balanced diet.

Black Maca

Black Maca is a tuber from the Andes that has traditionally been eaten there and is now also available as a dietary supplement. Black maca is also part of our collection, which includes cordyceps, moringa, and spirulina.

Looking for single ingredients around exercise, such as electrolyte powder or magnesium? You'll find them in our natural sports nutrition. What to use before, during and after exercise is set out in sports nutrition: what to use and when.

Common mistakes when fasting and building muscle

Watch out for these pitfalls:

1. Eating too little protein: the biggest mistake. Make sure you get at least 1.6 g of protein per kg of body weight, despite the shorter eating window.
2. Fasting for too long: a 16:8 schedule is fine for building muscle. Longer fasts (20:4 or 24 hours) make it almost impossible to get enough protein and calories.
3. Training without the chance to recover: if you train while fasted, eat as soon as possible after your workout.
4. Too few calories: fasting must not be an excuse to create too large a calorie deficit. To build muscle, you need at least your maintenance calories, preferably a slight surplus.
5. Neglecting sleep: sleep is important for recovery. Fasting shouldn’t come at the expense of your sleep.

Weekly plan: combining fasting and muscle building

Here’s an example weekly plan for a 16:8 schedule with strength training:

Who is fasting and muscle building suitable for?

Intermittent fasting combined with muscle building isn’t equally suitable for everyone:

Well suited for:

• Experienced athletes who want to change their body composition (recomposition)
• People who prefer a structured eating pattern
• Athletes who want to lose fat and maintain muscle mass at the same time

Less suitable for:

• Beginners who are still getting used to strength training
• Hardgainers who struggle to get enough calories
• People with an eating disorder or a problematic relationship with food
• Pregnant women or women who are breastfeeding

Frequently asked questions

Do you lose muscle mass from intermittent fasting?

Not necessarily. Research shows that muscle mass is generally maintained when intermittent fasting is combined with strength training and sufficient protein intake (at least 1.6 g/kg body weight). However, the risk of muscle loss increases with prolonged fasting (more than 24 hours) or too few calories.

Can I build muscle with a 16:8 schedule?

Yes, the 16:8 schedule is the most suitable fasting schedule for building muscle. You have an 8-hour eating window, which is ample time for 3-4 protein-rich meals. Studies show that the results are comparable to a regular eating pattern, provided your total protein and calorie intake are on track.

Should I take BCAAs while fasting?

BCAAs (branched-chain amino acids) were often recommended in the past to preserve muscle mass while fasting. Recent research suggests BCAAs aren’t necessary if your total daily protein intake is sufficient. What’s more, BCAAs technically break your fast because they trigger an insulin response.

When is the best time to train with intermittent fasting?

It depends on your personal preference and schedule. Most literature recommends training just before or at the start of your eating window so you can eat a protein-rich meal right after your workout.

How do you get through the fasting period successfully?

Drink enough (water, tea, black coffee). Your body generally gets used to the fasting rhythm within 1-2 weeks. Also make sure your last meal of the day contains enough fats and complex carbohydrates.

Conclusion

Muscle building and fasting can work well together if you approach it wisely. Research shows that intermittent fasting does not significantly inhibit muscle protein synthesis and that muscle mass is maintained with sufficient protein and consistent strength training. A 16:8 schedule with 1.6-2.2 grams of protein per kilogram of body weight per day, spread across 3-4 meals within your eating window, is a good starting point.

The effects of fasting on insulin sensitivity, autophagy, or recovery are often mentioned, but have not yet been clearly demonstrated in athletes. Think of fasting primarily as a way to structure your meal times.

Start slowly, listen to your body, and be consistent. Building muscle is a marathon, not a sprint, and intermittent fasting can be a useful tool.

Scientific sources

1. Templeman, I. et al. (2024). Short-term intermittent fasting and energy restriction do not impair rates of muscle protein synthesis. Clinical Nutrition. PubMed
2. Stratton, M.T. et al. (2022). Intermittent fasting and continuous energy restriction result in similar changes in body composition and muscle strength when combined with a 12 week resistance training program. European Journal of Sport Science. PubMed
3. Keenan, S. et al. (2020). The Effects of Intermittent Fasting Combined with Resistance Training on Lean Body Mass: A Systematic Review of Human Studies. Nutrients. PMC
4. Dirks, M.L. et al. (2022). Intermittent fasting activates markers of autophagy in mouse liver, but not muscle from mouse or humans. Nutrition. PubMed
5. Duan, Y. et al. (2023). Intermittent fasting reduces mouse body fat while maintaining muscle mass by regulating protein synthesis and autophagy. Food & Function. PubMed

This article is for informational purposes and is not medical advice. Dietary supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, or if you are pregnant or taking medication, consult your doctor or pharmacist.