How Does Muscle Tissue React to Fasting?

02 August, 2020
One of the biggest fears linked to intermittent fasting is that it can destroy muscle mass. Learn more about this in the following article.
 

Most athletes fear that their muscles will be destroyed and used as an energy source for the body if they fast. However, studies show that muscle mass isn’t lost during most fasting regimes.

Consult a nutritionist before making any drastic changes to your diet. Remember that everyone is unique and each individual has specific needs and objectives.

Fasting for less than 24 hours

Muscle destruction doesn’t occur during this kind of fasting. Glycogen deposits and circulating glucose are the first sources of energy used by the body. When this form of fuel diminishes, the fatty acids and amino acids present in the bloodstream are used as a source of energy.

During the last few hours of a 24-hour fast, there may be an increase in lipolysis.  Fatty tissue is the main energy source when circulating glucose and fatty acids diminish.

Even when long exercise sessions are carried out within this period, fasting muscle catabolism doesn’t occur. According to most literature, the body starts to use lean mass and essential amino acids only after 24-48 hours of fasting depending on the specific individual.

Keep in mind that high-intensity exercise shouldn’t be carried out during a fast. Ideally, during this time, exercise should be below 60 percent of your maximum capacity. This will help increase the loss of fatty tissue.

Fasting and muscle mass
 

It isn’t advisable to carry out intense anaerobic exercises since it could increase the risk of injury or dizziness due to the rapid reduction of glycogen deposits. Aerobic exercises, however, can help to improve the efficiency of beta lipid oxidation, and this results in increased performance.

Long-term fasting

Long-term fasting implies a fast for more than three days. During this time, a loss of lean tissue occurs. Long term fasts are usually performed by overweight people and they’re supervised by a medical team.

In addition, leucine supplements are used in order to minimize muscle catabolism. Electrolytes are also implemented in order to prevent cramping and dehydration.

Long term fasting is the least common category, 16:8 fasting is more popular and it doesn’t involve the loss of lean mass. Fasting by 16:8 implies reducing fat mass by avoiding the calories of at least one daily meal.

Did you know that beneficial hormonal changes can also occur while fasting?  GH production is increased and this leads to increased lipolysis. In other words, fasting helps to mobilize fats and increase weight loss.

Foods to break your fast

In order to preserve lean mass, it’s important to pay special attention to the food that you use to break your fast. They should be rich in mono and polyunsaturated proteins and fatty acids. If you’d like to include carbohydrates, its best to opt for those with low glycemic content, for example, potatoes or sweet potatoes.

 

It’s also good to keep in mind that when carrying out an intermittent fast, it’s important to guarantee your daily protein intake. Whey protein supplements could be used if it’s not possible to reach the recommended amount through diet.

Breakfast bowl

Fasting and muscle loss: conclusion

Short fasts don’t affect lean mass. Destruction of lean mass only occurs after fasting from 24-48 hours.

When fasting for less than 24 hours, glycogen, glucose, and circulating fatty acids are used to support the body’s energy demands. In addition, the increase in the production of growth hormones that occurs while fasting helps to maintain muscle mass while stimulating lipolysis.

In conclusion, it’s important to note that exercising while fasting doesn’t produce muscle loss. However, while fasting, keep in mind that your exercise regime should be below 60 percent of your maximum performance in order to reduce the risk of injury.

 
  1. Varady KA., Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?. Obes Rev, 2011. 12 (7): 593-601.
  2. Varady KA., Bhutani S., Church EC., Kiempel MC., Short-term modified alternate-day fasting: a novel dietary strategy for weight loss and cardioprotection in obese adults. Am J Clin Nutr, 2009. 90 (5): 1138-43.