Human forearm metabolism during progressive starvation.

Area of Science:

• Metabolic studies
• Human physiology
• Obesity research

Background:

• Obesity impacts metabolic flexibility.
• Understanding substrate utilization during fasting is crucial for metabolic health.

Purpose of the Study:

• To investigate forearm muscle metabolism in obese individuals during prolonged fasting.
• To quantify changes in substrate utilization (glucose, fatty acids, ketone bodies) over fasting periods.

Main Methods:

• Studied eight obese subjects under overnight, 3-day, and 24-day fasting conditions.
• Measured arterio-deep-venous differences for key metabolites and forearm blood flow.
• Calculated rates of metabolite utilization and production.

Main Results:

• Oxygen consumption and lactate/pyruvate production remained constant.
• Glucose utilization decreased significantly after 3 and 24 days of fasting.
• Ketone body (acetoacetate, beta-hydroxybutyrate) utilization increased by day 3 but plateaued or decreased by day 24, with preferential acetoacetate uptake.
• Free fatty acids became the primary fuel source by day 24.

Conclusions:

• Obese forearm muscle demonstrates adaptive metabolic changes during prolonged fasting.
• Shift from glucose to fatty acids and ketone bodies highlights fuel flexibility, though ketone utilization may be limited at extreme fasting durations.
• Findings have implications for understanding metabolic adaptation in obesity and starvation.