>>17643728"Fasting, especially prolonged fasting, can lead to muscle loss because your body needs to find other sources of energy when glucose supplies run low. Your body typically starts by breaking down stored fat, but eventually it will also break down muscle tissue to provide the necessary energy.
The rate of muscle loss during a fast varies greatly depending on many factors such as your starting body composition, physical activity level, age, gender, and the precise composition of your diet.
For example, if you're a male with a relatively high body fat percentage, your body can get most of its energy from stored fat, reducing the need to break down muscle. But if you're a lean individual, the rate of muscle loss might be higher.
Unfortunately, it's not easy to provide a quantitative estimate of muscle loss during fasting because studies on the subject have provided widely varying results. Some studies have found that about 0.5 kilograms (1.1 pounds) of lean mass is lost per week during a fast, but these studies often don't differentiate between losses of muscle tissue and losses of water and glycogen stored in muscle tissue. Other studies have found that muscle loss during fasting is minimal, especially if the individual is also engaging in resistance training
