Impact of Long-Term Fasting on Skeletal Muscle: Structure, Energy Metabolism and Function Using ³¹P/¹H MRS and MRI

Area of Science:

• Human physiology
• Metabolic studies
• Nutritional science

Background:

• Fasting shows public health benefits but raises concerns about muscle loss, especially in the elderly.
• This study investigated the effects of prolonged fasting on muscle health.

Purpose of the Study:

• To explore the impact of long-term fasting (12 days, 250 kcal/day) on muscle structure, metabolism, and performance.
• To assess muscle changes in a diverse group including older adults.

Main Methods:

• Prospective assessment of muscle volume, composition, and lipid metabolism using high-resolution MRI and MR spectroscopy.
• Measurements included maximal voluntary contraction (MVC) and exercise testing (VO2peak).
• Evaluations were conducted before, during, and after the fasting period.

Main Results:

• Body weight loss averaged 7.4%, with a 5.4% decrease in skeletal muscle volume, largely attributed to glycogen and water loss.
• Muscle strength (MVC) and aerobic capacity (VO2peak) remained unchanged.
• Fasting induced intracellular fat redistribution within muscle, enhancing lipid utilization and mitochondrial function, particularly in females.

Conclusions:

• Long-term fasting does not impair muscle metabolism or performance, nor cause structural or inflammatory damage.
• Observed muscle volume reduction is minor and reversible.
• Muscles demonstrate adaptability to fasting, similar to animal models, by optimizing fuel utilization and maintaining metabolic pathways.