Is muscle and protein loss relevant in long‐term fasting in healthy men? A prospective trial on physiological adaptations

Background Fasting is attracting an increasing interest as a potential strategy for managing diseases, including metabolic disorders and complementary cancer therapy. Despite concerns of clinicians regarding protein catabolism and muscle loss, evidence‐based clinical data in response to long‐term fasting in healthy humans are scarce. The objective of this study was to measure clinical constants, metabolic, and muscular response in healthy men during and after a 10 day fast combined with a physical activity programme. Methods Sixteen men (44 ± 14 years; 26.2 ± 0.9 kg/m2) fasted with a supplement of 200–250 kcal/day and up to 3 h daily low‐intensity physical activity according to the peer‐reviewed Buchinger Wilhelmi protocol. Changes in body weight (BW) and composition, basal metabolic rate (BMR), physical activity, muscle strength and function, protein utilization, inflammatory, and metabolic status were assessed during the 10 day fast, the 4 days of food reintroduction, and at 3 month follow‐up. Results The 10 day fast decreased BW by 7% (−5.9 ± 0.2 kg, P