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Does Intermittent Fasting Cause Muscle Loss?

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What is Intermittent Fasting | How Short-Term Fasting Works | Does Intermittent Fasting Causes Muscle Loss | Prolonged Fasting Effects on Muscle Mass | How To Maintain Muscle Mass during Intermittent Fasting

Intermittent fasting has recently gained immense popularity as a weight loss and health-promoting strategy. However, as with any dietary approach, there are concerns about potential negative side effects, including muscle loss. This article will discuss the factors that may influence muscle loss and examine the available scientific evidence. 

If you are considering intermittent fasting as a dietary approach or are simply curious about the potential risks and benefits, this article will provide valuable insights into the impact of intermittent fasting on muscle mass

Does Fasting Cause Muscle Loss?

Short answer is NO, if the fast is a short-term fast, there is evidence that it helps to preserve and even build muscle mass if the right diet is followed along with regular exercises.

We will dive into the details of this in this article below….

What is Intermittent Fasting?

Intermittent fasting is a dietary approach where you deliberately do not consume any calories for a certain number of hours in a day and eat all your calories in the non-fasting hours. Some popular intermittent fasting schedules are 16/8 fasting, 5:2 fasting, and one day a week fasting. Intermittent fasting is also known as time-restricted eating, as you restrict your eating to the eating windows in a 24-hour period. 

Does Intermittent Fasting Cause Muscle Loss?
Does Intermittent Fasting Cause Muscle Loss?

Why is There a Controversy on “Does Intermittent Fasting cause Muscle Loss?

Intermittent fasting is a debated weight loss tool, with some believing it works by simply cutting calories while others think it shifts the body from sugar-burning to fat-burning mode. If it is just a calorie-cutting method, it could also result in a loss of lean tissue. 

However, if intermittent fasting encourages the body to mobilize fat stores while preserving lean tissue, it would be an ideal weight management strategy. Both the above explanations are correct. When breaking a fast, there is built-in calorie restriction while the liver’s glycogen stores are depleted, leading to the mobilization of fatty acids. To determine if intermittent fasting causes a loss of lean body mass, more research is needed to understand how the body obtains energy during fasting periods. 

Understanding how Short-Term Fasting Works

Short-term fasting is primarily a period of 16-24 hours of fasting, not more. So let us look at what happens to the body during this kind of fasting.

It is imperative to discuss how the body will use energy over 16-24 hours of fasting. During this period, the liver will break down a large amount of glycogen to glucose, which the body will utilize to maintain its functioning. When the glycogen stores deplete, the body will look for alternative energy sources.

Now, the options for the body for energy sources are:

  • Gluconeogenesis: Here, the liver could use lactate, amino acids, or glycerol to produce glucose, which can be used directly as an energy source. 
  • Fat Tissue: Fatty acids can be released from the fat tissues in the body and metabolized to ketones, which can be directly employed as an energy source. 
  • Muscle: If inadequate amino acids are available for gluconeogenesis, the body’s muscles can be broken into amino acids, sent to the liver, and used as an energy source.

During the initial 16-24 hours of fasting, gluconeogenesis does not increase even as glucose production decreases due to falling glycogen stores. While gluconeogenesis occurs at its usual baseline rate, it does not accelerate during the early stages of fasting. This means that breaking down muscle to obtain amino acids for energy is not the initial step when glycogen stores are low. Instead, the body metabolizes fat into ketones, which are used as energy sources.

Does Intermittent Fasting Cause Muscle Loss?

Is it a Myth That Intermittent Fasting Causes Muscle Loss?

It is not necessarily a myth that intermittent fasting can cause muscle loss, but it is also not true for everyone. The impact of intermittent fasting on muscle mass and strength may depend on several factors, including the type of fasting, the duration of fasting, and the individual’s age, sex, and physical activity level. 

A study examined the effects of intermittent fasting combined with resistance training on lean body mass. The study concluded that if intermittent fasting was employed along with resistance training, it generally maintains lean body mass and can also promote fat loss.

Here are some interesting observations that point to the fact that intermittent fasting, on the contrary, can help to preserve and even increase muscle mass. 

Human Growth Hormone (HGH), And Intermittent Fasting

Does fasting cause muscle loss

 There was a study that looked into growth hormone levels after a period of intermittent fasting. The study found that in humans who fasted for 37.5 hours, the basal growth hormone concentrations were increased 10-fold. This means that there is more availability of HGH after fasting, which can help you with the maintenance of muscle mass and even muscle growth.

HGH is a protein-like hormone composed of a chain of 191 amino acids. It is produced by somatotropic cells in the pituitary gland. It is crucial for developing chondrocyte cells, which promote collagen synthesis in skeletal muscles and tendons, leading to muscle growth and structure. 

Moreover, HGH plays a crucial role in protein metabolism by reducing protein oxidation. Excess protein intake is not wasted but used to build muscle mass. In fact, if you are to consume enough protein during your feeding window, the excess HGH produced after fasting can help you to build more muscle.

Myostatin Levels And Intermittent Fasting

Myostatin, a protein produced and released by muscle cells, limits muscle growth by inhibiting myogenesis. Higher levels of myostatin in humans can hinder muscle growth. However, research suggests that testosterone can decrease myostatin levels, leading to increased muscle growth. 

A study by the International Journal of Sports and Health found that even a small amount of testosterone can cause a significant decrease in myostatin levels throughout the body, allowing individuals to build more muscle while fasting. 

Further, the European Journal of Endocrinology discovered that fasting could increase luteinizing hormone production, resulting in higher levels of testosterone and a decrease in myostatin, which can help build muscle. 

Insulin Sensitivity And Autophagy During Intermittent Fasting

Practicing intermittent fasting will improve your body’s sensitivity to insulin. This is crucial for muscle growth. Insulin helps transfer nutrients to the cells in the body, including amino acids, which are the building blocks of protein. When insulin sensitivity improves, muscles in the body are better attuned to utilizing micro and macronutrients, supporting muscle growth. 

Prolonged Fasting Effects on Muscle Mass

Prolonged fasting can have a negative effect on muscle mass. When the body enters a fasted state, it breaks down stored glucose and fat for energy. If the fast continues for an extended period, the body may break down muscle tissue to provide energy, leading to muscle loss. 

However, the degree of muscle loss during prolonged fasting can vary based on factors such as the fast’s length, the individual’s starting muscle mass, and nutritional status. 

Does Intermittent Fasting Cause Muscle Loss?

How To Maintain Muscle Mass While Doing Intermittent Fasting?

Some things must be considered if you want to preserve your muscle mass while intermittent fasting. Check out the following suggestions.


Resistance training is recommended to preserve and build muscle mass while practicing intermittent fasting. In this study, a group of men managed to retain all their muscles during 16/8 intermittent fasting and loss of body fat. Another study found that 25-40 minutes of cardio exercise helped maintain lean muscle mass while the subjects practiced alternate-day fasting. 

You Need to eat More Calories Than you Burn

To preserve your muscle mass or grow it while intermittent fasting, you have to ingest more calories than what is being burned in the fasting period. You may have associated intermittent fasting with a calorie deficit, but that is not the case. You can have as many calories as you want in the feeding window, and the key here is choosing the right intermittent fasting schedule

Eat a Sufficient Amount of Carbs and Protein

Does intermittent fasting cause muscle loss

What you eat in your feeding window is crucial to maintaining muscle mass. Concentrate on ingesting enough protein because your muscles are made from protein. It will be optimal to spread your protein intake throughout the feeding window, not just one meal. You should aim at getting 0.6-0.9 g of protein per lb. of body weight. 

Similarly, your carb intake has to be sufficient if you want to survive workout sessions while doing intermittent fasting. Carbs will add glycogen to your body, which can be utilized to go through periods of exercise without impinging on muscle mass for energy. Aim at 1.8-3.2 g of carbs per lb. of body weight. 

Conclusion – Does Intermittent Fasting Cause Muscle Loss?

It is a myth that intermittent fasting can lead to muscle loss. On the contrary, if the fast is a short-term fast, there is evidence that it helps to preserve and even build muscle mass if the right diet is followed along with regular exercises. Prolonged fasting, on the other hand, can lead to muscle loss. As with any dietary approach, it is important to consult a doctor or dietician before you embark on intermittent fasting. 

Also need help fasting? Check out the Best Intermittent Fasting Mobile Apps we recommend to help you on your journey.

Need Help choosing food and meals while intermittent fasting, try one of our Intermittent Fasting Meal Plans, you can choose based on your diet.

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