The processes by which dietary carbohydrate is digested to monosaccharides and these are taken up from the gut lumen into cells where they are oxidized to yield energy or consumed in biosynthetic processes are a central part of human metabolism and defects in them can lead to serious disease. Defects annotated here affect saccharide digestion in the gut lumen, fructose metabolism, and the pentose phosphate pathway. In addition, the defect in glucuronate catabolism that leads to essential pentosuria, a benign phenotype that is one of Garrod's original four inborn errors of metabolism, is annotated.