Severe energy deficit, such as would occur during dieting or prolonged hospitalization, promotes skeletal muscle losses. A recent study demonstrated that exercise mitigates some of these losses by inhibiting the induction of autophagy.
Autophagy is a highly conserved cellular defense mechanism that sequesters protein aggregates, pathogens, and damaged or dysfunctional organelles into vesicles called autophagosomes and then delivers them for destruction. The primary goal of autophagy is to allow the cell to adapt to changing conditions and external stressors, including energy deficit.
The study involved 15 overweight or obese men between the ages of 30 and 50 years. In the first phase of the study, the participants ate a very low-calorie diet consisting solely of sucrose or whey protein and engaged in endurance exercise consisting of 45 minutes of arm exercises and eight hours of walking for four days. This diet/exercise protocol created an energy deficit of approximately 5,500 calories per day. In the second phase, they ate a control diet and engaged in limited exercise for three days.
At the end of each phase, participants provided muscle biopsies for analysis, which revealed that severe energy deficit induced autophagy in skeletal muscle, but endurance exercised inhibited this induction, especially in the lower extremities. Interestingly, dietary intake of protein had little effect in preserving muscle mass.
The authors of the study proposed that exercise may sensitize the skeletal muscle to the anabolic signals that inhibit autophagy induction during energy deficit. These findings underscore the importance of exercise during dietary restriction, especially during prolonged hospital stays, to prevent or reduce skeletal muscle losses.