L-Arabinose (CAS: 5328-37-0) is a pentose with a sweet taste and one of the most abundant components released by complete hydrolysis of non-starch polysaccharides (NSP) of vegetable origin. However, NSPs are complicated compounds from the point of view of both physical structure and chemical composition, and they include cellulose, hemicellulose, pectin, and oligosaccharides. It is well-recognized that NSPs are resistant to the digestive enzymes and pass to the hind-gut where microbial degradation takes place. When L-arabinose is ingested in a digestible form, it is absorbed from the intestinal tract at a lower rate than glucose. A portion of the ingested L-arabinose is excreted in the urine. Although widely present in nature, L-arabinose is rarely used, and its physiological effects in vivo have received little attention. L-Arabinose selectively inhibits intestinal sucrase activity in a non-competitive manner and suppresses the plasma glucose increase due to sucrose ingestion. Because the intestinal absorption of sucrose is inhibited in the presence of L-arabinose, the absorption of sucrose should be reduced by arabinose ingestion. Most of the studies reported so far on the absorption and utilization of L-arabinose relate to omnivore animal species other than humans. In a rare case of two autistic brothers that were not associated with any known metabolic disease, it was found the median value for their urine samples was 179 umol/mmol creatinine of L-arabinose, nearly six times greater than normal children. L-Arabinose is found to be associated with ribose-5-phosphate isomerase deficiency, which is an inborn error of metabolism. L-Arabinose is also a microbial metabolite found in Mycobacterium.