Accelerated oligosaccharide absorption and altered serum metabolites during oral glucose tolerance test in young Japanese with impaired glucose tolerance

AIMS/INTRODUCTION: Impaired glucose tolerance (IGT) is a subtype of prediabetes, a condition having high risk for development to diabetes mellitus, but its pathophysiology is not fully understood. In the present study, we examined metabolic changes in IGT by using two types (D‐glucose [Glc] and partial hydrolysate of starch [PHS]) of oral glucose tolerance tests (OGTTs), with emphasis on serum incretins and metabolites. MATERIALS AND METHODS: We carried out the two types of OGTT (Glc/OGTT and PHS/OGTT) in 99 young Japanese individuals who had tested either positive (GU (+); n = 48) or negative (GU (−); n = 51) for glycosuria. After OGTT, they were sub‐grouped into five categories: normal glucose tolerance (NGT) in the GU (−) group (GU (−)/NGT; n = 49), NGT in the GU (+) group (GU (+)/NGT; n = 28), IGT (n = 12), diabetes mellitus (n = 1) and renal glycosuria (n = 9). Serum incretin and metabolites of GU (−)/NGT and IGT were then measured. RESULTS: When the serum insulin level at each time‐point during PHS/OGTT was expressed as its ratio relative to Glc/OGTT, it was increased time‐dependently in GU (−)/NGT, but not in IGT. Such an increase in the ratio was also detected of serum incretin levels in GU (−)/NGT, but not in IGT, suggesting a lack of deceleration of oligosaccharide absorption in IGT. Metabolome analysis showed a difference in the serum levels of two metabolites of unknown function in mammals, methylcysteine and sedoheptulose 1,7‐bisphosphate, between GU (−)/NGT and IGT. CONCLUSIONS: Comparison of PHS/OGTT and Glc/OGTT showed that oligosaccharide absorption was accelerated in IGT. Methylcysteine and sedoheptulose 1,7‐bisphosphate could be novel markers for dysregulated glucose metabolism.