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Do You Lose Muscle When Fasting? The Truth Revealed

Hold on to your dumbbells and your protein shakes, dear readers. We are about to discover the mystery of muscle loss while fasting!

Sometimes when people follow a fasting plan, they worry about losing muscle. Although the goal is to lose overall weight, there is the fear it could deflate their muscles. In fact, one of the most common questions asked of trainers is – will I lose muscle while fasting? If such thoughts also cross your mind, this article could burst those bubbles.

Before going further, let’s explore the intricacies and facts behind muscle loss as well as whether you could lose muscle during fasting.

Do You Lose Muscle When Fasting?

To understand muscle gain and loss you should know how muscle growth occurs. You may gain muscle mass while lifting weights with sufficient protein intake. Your body constantly regenerates old proteins and synthesizes new proteins, which helps increase muscle mass. The more you train and consume protein, the higher your muscle mass can increase. 

However, muscle loss typically occurs when you are physically inactive and/or do not consume enough protein (4). Below, we have explained the fasting muscle loss question in detail:

Consuming protein helps protect and build muscle mass.

Simply put, as long as you consume enough protein in the eating window of intermittent fasting, you should not lose muscle mass. Doing resistance training also helps maintain muscle mass during weight loss. However, extreme fasting with minimal to no protein intake can result in rapid weight loss, including muscle mass. If you want to fast while preserving muscle mass, then it’s important to both resistance train and eat enough protein during your eating window. 

Muscle loss can occur when the protein in your body gets broken down into amino acids which are then used to make other proteins or may be converted into glucose to maintain glucose levels (3). When you haven’t consumed enough protein, your body turns to muscle tissue to get protein, which is largely made up of protein. You can help prevent muscle loss during intermittent fasting by consuming adequate protein during the eating window. A central issue with the discussion around intermittent fasting and muscle loss is that much of the research on fasting and muscle loss involves long-term fasting, like where people don’t eat for weeks.

But if you are fasting for a day or less it is less likely that your body will need to break down a significant amount of its protein stores. During the first 16 to 24 hours of fasting, the body maintains blood glucose levels primarily through breaking down glycogen, which is stored carbohydrate  (9). Once glycogen is depleted, the body will turn to its fat and protein stores for energy. 

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Does Fasting Affect Muscle Growth?

To understand whether or not fasting affects muscle growth, it is crucial to understand how fasting works and affects muscle growth. First, you must know that muscle growth requires sufficient calorie intake and sufficient amounts of protein. If you are not getting enough calories, you may not have the energy to perform the exercises necessary for muscle building.

Typically, people do intermittent fasting with the goal of losing weight. The fasting periods help with weight loss by reducing overall food and calorie intake. This isn’t the most conducive situation for muscle building, which most bodybuilders will tell you requires a calorie surplus, not a calorie deficit. 

It’s probably more realistic to focus on maintaining muscle mass during intermittent fasting and weight loss. 

How Do I Prevent Muscle Loss When Fasting?

Some people fast for religious reasons, while others do so to lose weight. When pursuing weight loss, most aim to preserve muscle mass and only lose fat. By now you must have understood that adequate protein is the key to maintaining or increasing muscle mass. To do this, you may look to protein-rich foods like chicken, beef, fish, eggs, legumes, and dairy products.

Apart from this, protein-rich foods also reduce hunger and are more filling than carbs or fats. 6 Moreover, protein has a high thermic effect of food, helping you burn a few more calories during digestion than carbs and fats (5)

Another vital thing to note is that several factors can contribute to muscle loss, including lack of physical activity, certain medical conditions, inflammation, and age-related sarcopenia (10).

The two factors which are within our control are protein intake and physical activity.  Knowing this, consuming enough protein and working out regularly will preserve your muscle mass and prevent loss.

Now that you have learned that the key to maintaining muscle mass fast is being physically active and eating protein-rich meals, here are some tips you need to follow to maximize muscle mass.

Be Active

Our bodies are designed to be efficient, so if you are not physically active, your muscles are not in heavy use, which can lead to decreased muscle mass. You can counter this by working out, doing micro workouts, and simply moving more. Try to incorporate exercises targeting all major muscle groups.

When you reach your 30s or 40s, your muscle mass starts to decline gradually. This tells us that it is important to exercise and focus on building or maintaining muscles. 


Avoid Extreme Dieting

Maintaining muscle mass can be difficult when dieting, so you may need to consume more nutrition if you are low on energy levels. Low energy levels can affect muscle maintenance and growth, regardless of whether you are fasting or just continuously eating less. It is best to avoid stressful eating habits and extreme dieting plans, as they lead to severe energy deficits and more extreme weight loss, including loss of lean mass (13).

Another common dieting fad, yo-yo dieting, is harmful as the endless cycles of constantly losing or gaining weight often reduce muscle mass. It also makes weight loss harder as resting metabolic rate is partly linked to muscle mass, and yo-yo dieting can produce a high body fat percentage. With this in mind, focus on mindful eating instead of crash diets, which will help you prevent overconsumption or underconsumption.

Consume Protein

Even if you are working out and eating mindfully, you still won’t be able to build muscle if you skip the most important thing, i.e., protein. Proteins are the building blocks of muscle. Not consuming them enough can certainly affect your muscle mass. Also, a review found that high protein diets combined with resistance training may help retain more muscle mass during weight loss, although it may not completely prevent all muscle loss (1).

This means, to build muscle or to maintain as much muscle as possible while losing weight, you must consume enough protein. Around 1g of protein per pound of body weight is often suggested.

Read more: Green Tea Intermittent Fasting: Benefits and Side Effects

Will I Lose Muscle If I Water Fast for 7 Days?

Water fasting is a new dieting routine that has been trending recently. It includes fluids, mostly water, for 24-72 hours to lose weight. Even though some people claim that it offers health benefits, it also poses risks to specific individuals and is unsuitable for everyone. Severe water fasting can lead to rapid weight loss. This weight likely includes muscle mass, too (8).

The reason is that water fasting focuses on consuming fluids. Without necessary protein intake, your muscle mass may decline as the body resorts to muscle tissue to procure amino acids for protein synthesis and for energy.. You are likely to lose muscle if you fast for 7 days. Therefore, you should not be on fluids only. Instead, you should consume healthy balanced meals and sufficient nutrients to maintain muscle mass.

Do You Lose Fat or Muscle First When Fasting?

Our bodies undergo a lot of transitions when we are fasting. It is essential to understand the different stages it goes through while fasting. During fasting, our body goes through a fed-fast cycle, which affects our hormone levels and metabolism.

Below, we walk through these stages in detail (14).

Fed State

Fed state refers to the initial hours of fasting when our body digests and absorbs nutrients from our most recent meal. During the fed state, our blood glucose levels rise, leading to insulin secretion, which is responsible for transporting glucose into our cells. Any extra glucose is stored in the muscles as glycogen, which can be converted into sugar when needed for energy. During the fed state, the leptin hormone, responsible for suppressing appetite, increases, and ghrelin, responsible for hunger stimulation, decreases.

Early Fasting State

About 3-4 hours after eating, your body enters the early fasting state, which lasts until about 18 hours after eating. During early fasting, your blood glucose and insulin levels decline, causing your body to convert glycogen into glucose for energy. By the end of this state, your body starts searching for another energy source as glycogen stores are depleted.

This speeds up the process of lipolysis, which breaks down fat cells’ triglycerides into smaller molecules that can be used as an alternate fuel source. Amino acids, the building blocks of proteins, are also converted by your body into energy.


Fasting State

The period of fasting might range from roughly 18 hours to two days after your last meal. Your body starts breaking down protein and fat stores for energy at this stage because your liver’s glycogen stores have been exhausted. Ketone bodies, a particular kind of chemical created when your body turns fat into fuel, are produced as a result.

Additionally, this puts your body into a metabolic condition known as ketosis, when it burns fat as its primary energy source. But once you go into the fasting state, the shift into ketosis might not occur immediately; it may happen later.

Decreased appetite, weight loss, exhaustion, and elevated levels of ketones in the blood, breath, or urine are some of the most typical symptoms of ketosis. Other approaches can also be used to reach ketosis, such as the ketogenic diet, which involves drastically reducing your intake of carbohydrates.

In addition, keep in mind that variations of intermittent fasting with shorter fasting windows, such as 12 to 18 hours a day, might not reach this state because, unless you also follow a very low-carb diet, ketosis might not be achieved with fasts shorter than 24 hours.

Long-term Fasting State

Your body goes into the long-term fasting state when you fast for longer periods of time. This usually starts around 48 hours after you eat. This condition is also referred to as the “starvation state.”

Insulin levels will continue to drop while beta-hydroxybutyrate (BHB), a kind of ketone body, will gradually increase after a prolonged fast. Also, your liver keeps producing sugar through a process known as gluconeogenesis, which is the brain’s primary energy source. At this time the brain receives energy from ketone bodies as well.

Be advised that muscle breakdown occurs during the starvation mode. Long-term malnutrition causes the organs to deteriorate and eventually quit functioning. Remember that most individuals shouldn’t fast for an extended period and it should only be done under medical supervision.

In short, your body utilizes energy from glycogen stores in the liver and muscles during the initial hours of fasting. Once those stores run out within 24-48 hours of fasting, your body then shifts to breaking down fat and extracting energy from it through a process known as lipolysis. When your body is in a prolonged state of fasting, your muscles break down through a process known as catabolism.

To avoid losing muscle while fasting, eat healthy balanced meals with plenty of protein and exercise regularly, especially strength training. It is also better to fast for shorter periods, as longer fasts can lead to more muscle loss.

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Which Is the Best Intermittent Fasting Exercise?

We are tempted to work out during intermittent fasting to maximize weight loss and fat burn. This may work initially, but prolonged fasting and working out will lower your energy levels and cause you to feel exhausted. Take it slow and structure your workouts around your daily routine and requirements. Many people find that it works best to exercise during their eating window, to ensure that they have enough energy to power their workout.

The best exercises during intermittent fasting are walking, gentle yoga, and Pilates (6). As fasting depletes our energy levels, doing strenuous exercises during fasting may contribute to a decline in muscle mass. That said, begin by exercising moderately, and only go for intense workouts if you’re in an eating window and can fuel up.

Here are some tips to make the most out of your fasting workouts:

  • 16:8 is a common fasting trend involving consuming meals for 8 hours and fasting for 16 hours. Most people may benefit from working out during the eating window and others during the fasting window. It all depends on personal preferences. If you prefer working out on an empty stomach, work out during the fasting state, and if you prefer working out on a full stomach or need the energy for a more intense workout, do it during the feeding window.
  • Another important thing to consider is the type of food you consume, depending on your regular exercise. All exercise requires energy, and carbohydrates are the body’s primary energy source. Make sure you have something rich in carbs before your workout, especially if it is going to be a long or intense session.
  • You should consume the right sort of nutrients after your workout. If you are doing strength training, you should consume more protein. Ideally, you should consume some carbohydrates and at least 20g of protein around 30 minutes after your workout.

Read more: Intermittent Fasting and Running: A Winning Combination or a Terrible Mistake?



  • How do you keep muscle while fasting?

To maintain muscle mass while fasting, you should do strength training and consume protein-rich meals in your eating window to fuel your body and help your muscles repair and grow. You should also balance your meals with healthy fat, carbohydrates, and fiber..

  • Can muscles recover while fasting?

Yes, your muscles can recover during fasting as long as you consume protein-rich foods during your eating window to fuel your muscles and prevent them from breaking down.

  • Does fasting for 72 hours cause muscle loss?

Fasting for 72 hours is extreme and may affect your muscle mass. If you are fasting excessively and not getting enough nutrition, your muscle mass will be compromised as your body will use it as a fuel source and turn to alternative energy sources once it depletes. This tells us that consuming healthy balanced meals and drinking water prevents dehydration and malnutrition.

  • How can I bulk while fasting?

If you want to bulk up while fasting, remember to do strength training and work out regularly. Also, consume healthy protein-rich meals to aid muscle recovery and growth. Try to maintain your healthy lifestyle without going to the extreme.

The Bottom Line

If you often think – do you lose muscle when fasting? Then, the simple answer is not necessarily.

So, what is the verdict on fasting and muscles? It is not a breakup but more like a temporary break. Short-term fasting won’t ditch your muscles, but long-term fasting without enough protein? That is a recipe for muscle loss disaster. Thinking of a 3-day fasting fling? Don’t be extreme – keep it short and sweet.

Remember, moderate workouts and proper nutrition during intermittent fasting are crucial to keeping your muscles happy. Remember, balance, balance, balance!


This article is intended for general informational purposes only and does not address individual circumstances. It is not a substitute for professional advice or help and should not be relied on to make decisions of any kind. Any action you take upon the information presented in this article is strictly at your own risk and responsibility!


  1. Body Composition Changes in Weight Loss: Strategies and Supplementation for Maintaining Lean Body Mass (2018, ncbi.nlm.nih.gov)
  2. Can you build muscle while intermittently fasting? (n.d., centr.com)
  3. De novo lipogenesis in humans: metabolic and regulatory aspects (1999, pubmed.ncbi.nlm.nih.gov)
  4. Does Intermittent Fasting Pose Any Risk of Muscle Loss? (n.d., bulknutrients.com)
  5. How Protein Can Help You Lose Weight Naturally (2023, healthline.com)
  6. How to Exercise Safely During Intermittent Fasting (2023, healthline.com)
  7. Improvements in coronary heart disease risk indicators by alternate-day fasting involve adipose tissue modulations (2010, pubmed.ncbi.nlm.nih.gov)
  8. Is muscle and protein loss relevant in long-term fasting in healthy men? (2021, pubmed.ncbi.nlm.nih.gov)
  9. Physiology, Fasting (2023, ncbi.nlm.nih.gov)
  10. Sarcopenia: Causes, Consequences, and Preventions (2023, academic.oup.com)
  11. The protein-retaining effects of growth hormone during fasting involve inhibition of muscle-protein breakdown (2001, pubmed.ncbi.nlm.nih.gov)
  12. The role of protein in weight management (2008, pubmed.ncbi.nlm.nih.gov)
  13. Weight-Loss Outcomes: A Systematic Review and Meta-Analysis of Weight-Loss Clinical Trials with a Minimum 1-Year Follow-Up (2007, sciencedirect.com)
  14. What Are the Different Stages of Fasting? (2023, healthline.com)
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