Decreased glucose oxidation during short-term starvation

Area of Science:

• Metabolic Physiology
• Human Metabolism

Background:

• Prolonged fasting (days/weeks) is known to alter glucose production and oxidation.
• The effects of short-term starvation (less than 24 hours) on glucose metabolism remain largely uncharacterized.

Purpose of the Study:

• To investigate the impact of short-term fasting (16 and 22 hours) on glucose metabolism in healthy adult males.
• To quantify changes in glucose oxidation and glucose turnover during brief periods of starvation.

Main Methods:

• Indirect calorimetry was used to measure glucose oxidation in 12 healthy men.
• Glucose turnover was assessed using a primed, continuous infusion of 3-3H-glucose in eight volunteers.
• Measurements were taken after 16-hour and subsequently after 22-hour fasting periods.

Main Results:

• After 16 hours, net glucose oxidation was 0.59 ± 0.17 mg·kg−1·min−1 and glucose tissue uptake was 2.34 ± 0.12 mg·kg−1·min−1.
• Extending fasting to 22 hours significantly decreased respiratory quotient, plasma glucose, glucose tissue uptake, net glucose oxidation, and plasma insulin levels (P < .05).
• Net glucose oxidation as a percentage of glucose tissue uptake dropped from 22% to 2% (P < .05), with no net oxidation observed in 7 of 12 subjects.

Conclusions:

• Short-term fasting (22 hours) significantly impairs glucose oxidation and uptake in healthy men.
• The body shifts away from glucose utilization during brief starvation periods.
• These findings highlight substantial metabolic adaptations occurring even with less than 24 hours of fasting.