Metabolic and structural changes in skeletal muscle during hypocaloric dieting

Area of Science:

• Physiology
• Nutrition Science
• Muscle Biology

Background:

• Hypocaloric dieting and fasting are known to affect skeletal muscle function, leading to low-frequency fatigue.
• Understanding the metabolic and structural adaptations of skeletal muscle during severe caloric restriction is crucial for managing health outcomes.

Purpose of the Study:

• To investigate the metabolic and structural changes in skeletal muscle of morbidly obese women undergoing a hypocaloric diet.
• To identify potential mediators of functional changes in skeletal muscle associated with severe caloric restriction.

Main Methods:

• Gastrocnemius muscle biopsies were obtained from five morbidly obese female subjects.
• Biopsies were performed at baseline (2500 kcal/day) and after 2 weeks of a 400 kcal/day carbohydrate diet.
• Analysis included intracellular calcium, muscle glycogen, lactate, pyruvate, energy stores, enzyme activity, amino acid levels, and histochemistry.

Main Results:

• A significant increase in intracellular muscle calcium content was observed (p < 0.05).
• No significant changes were found in muscle glycogen, lactate, pyruvate, or free energy stores.
• Significant decreases in phosphofructokinase (p < 0.05) and succinate dehydrogenase (p < 0.02) activities, along with reduced glutamine, glycine, and alanine levels, were noted. Muscle histochemistry revealed type II fiber atrophy (p < 0.025).

Conclusions:

• Increased intracellular muscle calcium content is a likely mediator of the adverse functional effects observed during hypocaloric dieting.
• While generalized metabolic and structural changes occur, elevated muscle calcium appears specifically linked to functional impairments.
• These findings highlight the critical role of calcium regulation in skeletal muscle adaptation to severe caloric restriction.