Information about fasting often raises concerns about the risk of muscle breakdown. The belief is that when the body goes without food, it starts breaking down its own protein, primarily from muscles. However, recent studies have challenged this notion and shown that fasting does not necessarily lead to muscle loss.
Therapeutic fasting has been practiced for ages to promote healing and prevent illness. Animals and humans alike instinctively avoid eating when feeling unwell. Despite this, warnings persist about potential muscle breakdown during fasting.
Nonetheless, a study has now demonstrated that these concerns are unfounded. Several other studies support the idea that fasting, especially when done regularly, can reduce the risk of cardiovascular disease and increase life expectancy.
To investigate the effects of prolonged fasting on muscle and protein breakdown, researchers from the University of Strasbourg, Charité University of Berlin, and other institutions in France, Monaco, and the US conducted a study. They published their findings in the Journal of Cachexia, Sarcopenia, and Muscle.
The study involved healthy men aged 30 to 58, some of whom were overweight with an average BMI of 26. They fasted for 10 days, following the Buchinger-Wilhelmi fasting protocol, and engaged in a 3-hour daily moderate exercise program. During fasting, the participants received a daily protein supplement of 200 to 250 kcal in the form of juices and vegetable broth.
The fasting schedule was as follows:
- The day before fasting, participants received three light vegetarian meals, each totaling 200 kcal.
- The fast began by emptying the intestines with 20-40 g of sodium sulfate dissolved in 500 ml of water.
- Each morning, the fasting individuals received a 20 g portion of honey and consumed 2 to 3 liters of water or calorie-free herbal infusions.
- At lunchtime, they drank 250 ml of freshly squeezed fruit juice and 250 ml of vegetable broth at night.
- The total daily calorie intake was 200 to 250 kcal.
- An enema was administered every two days.
- After fasting, there were three days of gradually increasing daily calorie intake, reaching 800 kcal and then 1600 kcal.
The study participants experienced an average weight loss of 5 kg during the fasting period. The weight loss was divided into approximately 40% fat, 35% water, and 25% protein, which came from metabolically active tissues such as the liver, kidneys, spleen, intestinal mucosa, heart, and skeletal muscle, with a small proportion from muscles.
After a few hours of fasting, the body depleted its carbohydrate stores (liver and muscle glycogen) and primarily used fat from its own reserves, along with ketone bodies produced in the liver, as the main sources of fuel for fasting metabolism.
Interestingly, the study revealed that muscle breakdown was minimal. The fasting organism hardly used proteins to generate energy, even though no protein was consumed during the fast. The small amount of protein degradation that occurred seems to be a preliminary stage of accelerated cell and cell structure regeneration.
This means that the body selectively preserves functional muscles and mainly breaks down unnecessary protein structures, such as old or diseased cells. As the fast continued, the body activated protein-sparing mechanisms, leading to even less protein being used for energy production, while more fat was utilized instead.
The researchers concluded that the fear of significant muscle atrophy during fasting is likely unwarranted. Muscle mass was well-preserved, and in some cases, the performance of lower extremity muscles even improved after fasting.
During the fasting period, participants reported increased physical and emotional well-being and reduced feelings of hunger. Levels of leptin, a hormone that stimulates appetite, dropped, as did glucose, insulin, and cortisol levels. At the same time, free fatty acid levels increased, indicating fat loss.
A follow-up examination conducted three months after the fast revealed that the participants’ body weight remained lower than at the beginning of the fast, indicating sustained weight loss.
