Caloric value of inulin and oligofructose.

Dietary carbohydrates, which are absorbed as hexose, (glucose, fructose) have a caloric value of 3.9 kcal/g (16.3 kJ/g), and their cellular metabolism produces approximately 38 mol ATP/mol. However, chicory inulin and oligofructose resist digestion and they are not absorbed in the upper part of the gastrointestinal tract. After oral ingestion, they reach the colon intact where they become hydrolyzed and extensively fermented by saccharolytic bacteria, which produce short-chain carboxylic and lactic acids as electron sinks. Depending on both the degree of their colonic fermentation and the assumptions of the model used, the caloric value of such nondigested but fermented carbohydrates varies between 0 and 2.5 kcal/g. Through the catabolism of the absorbed short-chain carboxylic and lactic acids, they may produce up to 17 mol ATP/mol of fermented sugar moiety. Because the daily intake of these dietary carbohydrates is likely to remain relatively small (<10% and probably often not >5% of total daily calorie intake), it is of low relevance nutritionally to give them a precise caloric value. On the basis of biochemical balance charts for carbon atoms, metabolic pathways and energy yields to the host, the caloric value of a fructosyl residue in chicory inulin and oligofructose has been calculated to be approximately 25-35% that of a fully digested and absorbed fructose molecule. For the purpose of food labeling, it is recommended that chicory inulin and oligofructose, like all the other carbohydrates that are more or less completely fermented in the human colon, should be given a caloric value of 1.5 kcal/g (6.3 kJ/g).