A number of gut peptides are known to be involved in inducing a feeling of satiety and reducing further food intake. Many of theses act locally on the gastrointestinal tract, but others enter circulation and act on the central nervous system. The exact mechanism of action and interaction of many of the peptide hormones is not known, but researchers are interested in understanding their effects because of a possible role in the development of obesity. Soluble fibres such as guar gum, pectin, β-glucan and psyllium are known to slow gastric emptying and lower the blood glucose and insulin responses following a carbohydrate meal, perhaps by altering gut peptide secretion. Research suggests that one of the key property of fibre that allows regulation of satiety and gut peptides is its viscosity. A higher viscosity is known to delay gastric emptying after both solid and liquid meals.
Researchers1 have used oat bran enriched beverages to investigate the effects of fibre viscosity on the feeling of satiety and the release of various gut hormones. Following a 12 hour fast, 20 healthy volunteers ingested 2 isocaloric 300mL oat bran drinks with either a lower or higher viscosity. Each drink contained 57.9 g carbohydrate, 7.8 g protein, 3.3 g fat and 10.2 g fibre. The viscosity of the lower viscosity drink was reduced by enzymatically treating the drink with β-glucanase. Satiety in the subjects was greatest after consumption of the lower viscosity drink. In addition, blood samples taken up to 3 hours after consumption of the drinks showed that the lower viscosity drink produced a greater increases in plasma glucose, plasma insulin, cholecystokinin, glucagon-like peptide 1 and peptide YY. Ghrelin levels decreased the most after the lower viscosity oat bran beverage. Gastric emptying was faster in the lower viscosity drink as would be expected.
The lower secretions of cholecystokinin, peptide YY and glucose-like peptide 1 with ingestion of the high viscosity drink are interesting in that they suggest that the fibre may in some way inhibit interaction of nutrients with the gut mucosa and so reduce peptide secretions. Ghrelin is inhibited by cholecystokinin and the larger increase in cholecystokinin levels after the lower viscosity drink may therefore explain the greater decrease in ghrelin. The greater effects on satiety with the lower viscosity drink would at first appear to suggest that fibre is not beneficial in inducing satiety, but this may in fact be due to the shot term nature of the blood samples taken. Fibre can be hydrolysed by gut bacteria where it is known to contribute to energy requirements and it may therefore require longer term analysis to accurately assess the effects of fibre on appetite.
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