Amino acid metabolism during prolonged starvation.
Level 4 - case-series / case-control
Uncontrolled physiological case series
PubMed 5773094 · doi:10.1172/JCI106017
What was done
Plasma concentrations, splanchnic and renal exchange, and urinary excretion of 20 amino acids were measured in obese subjects during prolonged (5 to 6 weeks) starvation. Splanchnic amino acid uptake was also evaluated in postabsorptive and briefly (36 to 48 hours) fasted subjects.
What was found
The abstract reports no numerical values or confidence intervals. Splanchnic extraction of alanine was greater than that of all other amino acids combined. Plasma valine, leucine, isoleucine, methionine, and alpha-aminobutyrate increased transiently in the first week, while glycine, threonine, and serine increased progressively after the first 5 days. Thirteen amino acids ultimately decreased, with alanine showing the most rapid and largest diminution. After 5 to 6 weeks of starvation, splanchnic alanine uptake fell markedly due to reduced arterial concentrations. Prolonged fasting also resulted in increased renal glycine utilization and net renal alanine uptake without increased urinary excretion.
Why it matters
This study outlines the regulatory mechanism by which hepatic gluconeogenesis declines during prolonged starvation: preferential splanchnic extraction depletes circulating alanine, curtailing further uptake and sparing body protein.
Limits
The abstract reports no sample size, demographics beyond obesity, or exact numerical values. There is no non-obese control group, and the physiological responses of prolonged total starvation in obesity cannot be assumed for lean individuals or shorter fasts.
Cited by
- contradicts Alanine levels increase significantly during prolonged fasting because it is primarily utilized for gluconeogenesis.