Xylitol is a sugar alcohol found naturally in low concentrations in some plant fibres. Xylitol is nutritionally of interest because it is as sweet as sucrose (table sugar) but contains around 30 % fewer calories. In addition, compared to a glycaemic index of 100 for glucose, xylitol has a very low glycaemic index of just 7. Because of this it is a popular sweeteners that is useful; in diabetic foods. Xylitol is naturally found in the diet in low concentrations and consuming xylitol sweetened products increases intake considerably. Even at very high concentrations no toxic effects of xylitol are known. However, xylitol can produce gastrointestinal discomfort and diarrhoea and this might be related to its digestion. In particular xylitol might differ in its transit time through the gut, which may have osmotic consequences and lead to the symptoms associated with its consumption.
Indeed, comparison of glucose to xylitol in human digestion has highlighted specific differences between the compounds with respect transit time. For example, in one study1, researchers fed a single dose of 200 mL water containing either 30 g glucose or 30 g xylitol. The water also contained a tracer in order to allow the researchers to determine gastrointestinal transit. The results showed that addition of xylitol to water slowed gastrointestinal emptying to around half compared to water containing glucose. The authors suggested that this might be the reason for the gastrointestinal symptoms such as diarrhoea associated with xylitol ingestion. In addition, whereas glucose suppressed motilin production xylitol stimulated production. Motilin is a key hormone involved in stimulating gut motility. This suggests that xylitol can increase gut motility and this may also contribute to the gastrointestinal symptoms associated with consumption.
As expected plasma insulin levels increase more rapidly following glucose administration compared to xylitol administration, as has been shown elsewhere. This was reflected in an increase in gastric inhibitory peptide (GIP) following glucose but not xylitol administration. Gastric inhibitory peptide is a hormone believed to be responsible for causing, in part, insulin release. Therefore glucose is more rapidly transported through the gut and causes less gut motility that xylitol. In addition, glucose also causes a more rapid increase in insulin. This explains the perceived benefits of xylitol consumption to diabetics and also explains the gastrointestinal discomfort seen with excessive consumption. Xylitol may have other benefits, perhaps on energy intake and balance, based on its ability to increase gastric transit times. It is thought that this slower digestion rate might account for the weight loss effects of both protein and fibre in the diet.
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