Table 3.
Chemical and physiological characteristics of rare sugars
| Rare sugar | Structure | Caloric content (kcal/g) | Sweetness (compared with sucrose) | Glycemic index | Gut enzymes and metabolic fate |
|---|---|---|---|---|---|
| Allulose |
Monosaccharide (C-3 epimer of fructose) |
0.240 | 70%41 | ND | Transported via GLUT5 in the enterocyte and further transported using GLUT2 (same as fructose)49 |
| L-arabinose |
Monosaccharide (aldopentose) |
050 | ∼50%51 | ND | Inhibited sucrase activity2 |
| D-tagatose |
Monosaccharide (C-4 epimer of fructose) |
(∼1.5–3)43 | 92%42 | 352 | Transported via GLUT5 in the enterocyte, metabolized via glycolytic pathway (same as fructose),2 fermented in the colon53 |
| Trehalose | Dissacharide (2 glucose molecules in an α1,1-glycosidic linkage) | 444 | ∼50%45 | ND | Trehalose broken down by trehalase in the small intestine into 2 glucose molecules, which are then absorbed54 |
| Isomaltulose (palatinose) | Disaccharide (glucose and fructose in an α1-6 glycosidic bond) | 446 | 50%47 | 3252 | Completely but slowly digested by isomaltase37 |
| Kojibiose | Disaccharide (2 glucose molecules connected by an α1-2 glycosidic bond) | ND | ND | ND | ND |
| Sorbose |
Monosaccharide (Ketose) |
ND | 70%48 | ND | ND |
| D-allose |
Monosaccharide (C-3 epimer of glucose) |
ND | 80%48 | ND | Downregulated GLUT1 expression55 |