Purpose: Glucose (Glu) and maltitol (Mal) ingestion affect calciuria and phosphaturia. Renal phosphate leak involving hypophosphatemia is thought to be a mechanism. Inter-race differences in carbohydrate metabolism are known. We investigated the effects of Glu and Mal ingestion on glycaemia and phosphatemia in subjects from two race groups to better understand potential implications for nephrolithiasis.
Methods: Healthy black (B) (n = 8) and white (W) (n = 8) males followed a self-selected standardized diet for 7 days and a strictly controlled standardized diet on Day 8. After an overnight fast, subjects provided blood samples prior to and 30 min after ingestion of a randomly assigned solution of Glu or Mal. Blood Glu and serum phosphate were measured. Protocols were swapped after a 1-week washout period.
Results: Following Glu ingestion, glycaemia increased significantly in W (4.8 vs 6.2 mmol/l) but not in B (4.7 vs 5.3 mmol/l) while phosphatemia decreased significantly in B (1.16 vs 1.01 mmol/l) but not in W (1.24 vs 1.15 mmol/l). After Mal ingestion, glycaemia increased significantly in B (4.7 vs 5.2 mmol/l) but not in W (4.6 vs 5.9 mmol/l), while phosphatemia decreased significantly in W (1.24 vs 1.18 mmol/l) but not in B (1.17 vs 1.06 mmol/l).
Conclusions: Our results suggest that enzymes which regulate glycolysis may be less active in B than in W, or expression of renal transcellular Glu transporters may be relatively inhibited in B. Effects on phosphatemia are carbohydrate- and race-dependent, thereby prohibiting speculation of a general algorithm linking these variables. Inter-race differences in metabolic handling of carbohydrates might impact on respective nephrolithiasis risk factors in such groups.
Keywords: Glycaemia; Nephrolithiasis; Phosphatemia; Polyol ingestion; Racial metabolic differences.