Saccharides that cannot be absorbed from the small intestine and do not increase blood glucose have not been considered useful for human health. However, we have demonstrated that intestinal bacteria can play an important role in the metabolism of non-digestible and/or non-absorbable saccharides, and that the concept of fermentation and absorption is essential when considering the value of foodstuffs for human health. It has also been demonstrated experimentally that non-digestible and/or non-absorbable saccharides are metabolized by intestinal bacteria to short-chain fatty acids (SCFAs), carbon dioxide, hydrogen and methane, and that SCFAs can be a source of available energy in the host. Non-digestible and/or non-absorbable saccharides have a calorific value of 2kcal/g. Ingestion of a sufficiently high amount of non-digestible and/or non-absorbable saccharides can cause overt diarrhea in humans. The maximum permissive dosage of non-digestible and/or non-absorbable saccharides for producing transitory diarrhea was 0.3-0.4g/kg body weight. The value increases with repeated ingestion and can be a valuable component of the diet.