Fasting & Muscle Loss

FASTING DOES NOT CAUSE MUSCLE LOSS

The myth about fasting and muscle loss

Most people associate fasting with losing weight, resetting the system, detoxing, or gaining mental clarity. They also share some common concerns. A prevalent myth is that fasting can be dangerous because the body breaks down muscle protein to generate energy. But what if the body is smarter than that?

Humans and wild animals share a genetic programme which allows them to adapt to fasting. In the wild, migratory birds can fly very long distances without eating. Whales can cross the planet while fasting to reach their breeding grounds in tropical regions. Bears and Hedgehogs can hibernate for half a year without eating. Would all these animal species thrive in nature if prolonged fasting was detrimental for their muscles?

We conducted a study using the best technologies available to science to understand how human muscles adapt to long-term fasting. In the following, we take a closer look.

Muscle health during long-term fasting: a natural process

Even if our clinical observations over decades have shown that patients do not lose muscle mass during fasting and can even do some physical activity during their stay at the clinic, we take common concerns about muscle loss seriously. For this reason, we decided to conduct our own scientific studies. For our first study published in 2021, we collaborated with a team at CNRS in France, a prestigious research institution dedicated to exploring how the human body adapts to space travel. In the context of long space missions, understanding how human muscle changes during periods of fasting is particularly important. Through this project, we were able to investigate how fasting influences muscle preservation and regeneration, providing insights that are relevant not only to maintaining health on earth but also to the challenges of life in space.

Among the most surprising findings was the observation that muscle function appeared to remain stable or even improve slightly during fasting interventions. Protein breakdown in muscles, measured by the amount of nitrogen the body loses, gradually slowed down during fasting. This was because the body activates systems to preserve protein. Consequently, the performance of the muscles was maintained during fasting. After reintroducing food, the levels of a protein called myostatin dropped sharply, allowing the muscles to rebuild more efficiently. This suggested that humans also adapt naturally to preserve muscle mass between cyclical periods of eating and fasting.

This study was just a first step for us. Building on these earlier findings, we launched the GENESIS study to delve deeper into the relationship between fasting and muscle health. Conducted in collaboration with Dr. Magalie Viallon and Professor Pierre Croisille, leading researchers from France, this study used MRI technologies to explore how fasting influences muscle function, strength, and cellular health over time.

The GENESIS study: behind the scenes at Buchinger Wilhelmi

Imagine embarking on a scientific expedition that blends data collection with camaraderie and self-discovery. This is what participants in our fasting study experienced. Their adventure required great dedication: They took multiple trips to France to visit Professor Croisille’s laboratory for advanced MRI measurements. Over four weekends – before they started fasting, at the end of the fast, one month after reintroducing food, and again four months later – participants underwent a rigorous schedule of tests involving MRI scans, clinical assessments, and physical performance evaluations.

What might sound like a logistical nightmare turned into something extraordinary: Instead of seeing it as an inconvenience, participants embraced the journey as a shared adventure. A sense of community evolved between them as they laughed, supported one another, and transformed even mundane tasks, like carrying urine collection bottles, into humorous and bonding experiences.

The study also included a two-week stay at Buchinger Wilhelmi Clinic in Überlingen. Here, the participants immersed themselves in a holistic program. They started their days with invigorating morning gym sessions and continued with serene afternoon hikes. Guided meditation sessions, led by Dr. Wilhelmi de Toledo, provided moments of introspection and mental clarity. The evenings were filled with animated conversations, with the participants exchanging insights, sharing struggles, and celebrating milestones together.

By the end of the fasting experience, this mutual scientific journey had evolved into something deeply personal. There were moving moments as participants reflected on how the experience had reshaped their perspectives on life and health. What had begun as a clinical study had transformed into an unforgettable expedition of self-discovery, resilience, and connection – a true testament to the power of science to inspire and transform lives.

When does the body use protein during fasting?

To set the record straight: using protein during fasting does not equal losing muscle. The body has a remarkable ability to adapt and protect essential tissues while meeting its energy needs. Here is a simplified timeline of the body’s fuel usage during fasting:

Intermittent fasting and muscle loss

Intermittent fasting (IF) has gained popularity thanks to its potential benefits for weight management, metabolic health, and longevity. However, concerns are frequently raised about muscle loss during fasting, especially by people who want to build muscle. Research suggests that intermittent fasting, when properly managed, does not inherently lead to muscle loss and may even preserve lean mass under specific conditions. During fasting periods, the body initially relies on glycogen stores for energy. This is reflected in a comprehensive publication on the effects of intermittent fasting, covering the results of all available clinical studies so far. This shows that intermittent fasting can be effective in reducing fat mass while increasing the fat-free mass (i.e. muscle mass). Intermittent fasting is therefore an effective way to improve body composition by reducing body weight, eliminating fat and preserving muscles.

The timing and composition of meals are also crucial during intermittent fasting. Consuming adequate protein within the eating window supports muscle repair and growth, especially if your goal is to build muscle mass. Resistance exercise further enhances the preservation of lean mass by stimulating muscle protein synthesis, even in the absence of frequent meals.

GENESIS study featured in an ARTE documentary

The importance of this research has not gone unnoticed. The GENESIS study was recently featured in a documentary by Sylvie Gilman and Thierry de Lestrade: Fasting: Investigation of a Phenomenon (Le jeûne, enquête sur un phénomène) on ARTE, a television channel. This sequel to their acclaimed 2012 film showcases Stéphane, a French man who transformed his health at Buchinger Wilhelmi during a 21-day fasting programme.

Stéphane arrived at the clinic with non-alcoholic fatty liver disease, obesity, and metabolic syndrome. A Fibroscan confirmed severe liver fat accumulation (CAP 307 dB/m). By the end of the programme, his liver fat levels had normalized (CAP 242 dB/m), and no signs of fibrosis were detected – a remarkable reversal supported by the well-documented benefits of fasting for fatty liver disease.

Stéphane also participated in the physical activity programme at our clinic. In his own words: “Physical activity (hiking, gym, swimming) combined well with my fasting and I did not feel any muscle weakness. On the contrary I had a natural desire to expend this overflowing energy.”

This report underscores the growing interest in fasting as a holistic health intervention and positions the clinic at the forefront of fasting research. For those interested in understanding how fasting impacts muscle health, the documentary offers a compelling introduction.

➥ To the documentation

Stéphane during the recording of the documentary

Interview with Dr Robin Mesnage

Why this matters to you: Protecting your muscle health

So, what does this mean for you? Whether you are an athlete, a health enthusiast, or just concerned about aging, muscle health should be a priority. Incorporating fasting into your lifestyle – under professional supervision – could be a valuable strategy for preserving muscle function and enhancing your overall health.

To support your muscle health during fasting, consider these tips:

• Stay active: Do light to moderate physical activity during fasting to maintain muscle strength.
• Focus on the food reintroduction phase: Proper nutrition is crucial when reintroducing food after your fast. Include protein-rich foods and nutrient-dense meals to support muscle recovery.
• Seek guidance: Always consult a healthcare professional when incorporating fasting into your routine to ensure it is tailored to your individual needs.

The GENESIS publication is citable as:

Naegel A, Viallon V, Ratiney H, Nguyen T, Leporq B, Kennouche D, Grenier T,  Grundler F, Mesnage R, Guy JM, Wilhelmi de Toledo F and Croisille P. Impact of prolonged fasting on skeletal muscle: delving into the relationship between structure, energy metabolism, and function using 31P/1H MRS and MRI. In Press in Journal of Cachexia, Sarcopenia and Muscle. DOI: 10.1002/jcsm.13773