Impaired Jejunal Absorption Rates of Essential Amino Acids Induced by Either Dietary Caloric or Protein Deprivation in Man

Abstract

The alteration in transport specificity and jejunal absorption rates of essential amino acids before and after 2 weeks of either total starvation or isocaloric protein-free dieting were determined by an in vivo perfusion technique in 7 normal and 7 obese human volunteers. In addition, the possible change in the intestinal mucosal morphology during these dietary deprivations was investigated by light and electron microscopic examination of the tissue specimens obtained by peroral jejunal biopsy in 4 subjects. Both starvation and protein depletion resulted in the reduction of amino acid absorption rates in 12 subjects (normal as well as obese). However, the specificity of preferential amino acid absorption from equimolar mixtures of all eight essential amino acids was not affected by these dietary manipulations. Moreover, there was a decrease in the absorption rates of amino acids with high (leucine) as well as low (threonine) affinity for the amino acid carrier systems. The evidence for a reduction in the capacity of intestine to transport leucine after starvation was further supported by the demonstration of a lower rise in the plasma concentrations of leucine during the perfusion studies in starved subjects. In the face of reduced amino acid absorption rate, the jejunal mucosal histology and cell organelles appeared intact.