Molecular formula: C5H12O5
Molecular weight: 152.15
Xylitol has water solubility of about 0.64 g per mL.
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) has determined the "Laxative Threshold Value" (LTV) for a number of polyols and low-digestible sugars. Xylitol has an LTV of 20 grams per meal. See my essay "Polyols--Digestive Issues" for a discussion of the potential gastrointestinal effects of polyol consumption.
Xylitol is absorbed by passive diffusion (most sugars are actively transported into the body). It is therefore absorbed more slowly, and absorption is usually incomplete. This can be an advantage in terms of calorie reduction, but it can cause adverse effects if large quantities (over 50 grams) are consumed. First, bacteria in the colon may ferment xylitol, producing gas and acids. Second, the acids and the undigested xylitol can osmotically draw water into the colon, leading to diarrhea. Over time, people who consume large quantities of xylitol may develop different populations of bacteria and adapt to these effects.
Xylitol has been shown to reduce incidence of dental caries [ Maguire, A.; Rugg-Gunn, A.J. Xylitol and caries prevention - is it a magic bullet? Brit. Dental J. 194:429-436 (2003)]. Bacteria in the mouth normally utilize sugars to make insoluble glucan, which adheres to teeth. They also produce acids, which can dissolve calcium and phosphate in tooth enamel. Xylitol is not efficiently used by bacteria, so it slows their growth and inhibits acid production. It also appears to prevent adhesion, either by decreasing production of insoluble glycan, or by preventing the adhesion of the glycan. Finally, when used in chewing gum, xylitol stimulates saliva flow, and increased saliva flow also inhibits carie formation.
Recent studies suggest that xylitol may facilitate remineralization of teeth. Combining a calcium source with xylitol in a chewing gum provided better effects than the xylitol alone [Suda, R.; Suzuki, T.; Takiguchi, R.; Egawa, K.; Sano, T.; Hasegawa, K. The effect of adding calcium lactate to xylitol chewing gum on remineralization of enamel lesions. Caries Res. 40:43-46 (2006)].
Xylitol seems to be particularly toxic for dogs--it rapidly raises insulin levels and causes liver damage [Dunayer, E.K.; Gwaltney-Brant, S.M. Acute hepatic failure and coagulopathy associated with xylitol ingestion in eight dogs. J. Amer. Vet. Med Assoc. 229:1113-1117 (2006)]. So keep xylitol-sweetened gum and candy out of reach of your pets!