Endogenous plasma glucagon-like peptide-1 following acute dietary fibre consumption.

SCFA resulting from the microbial fermentation of carbohydrates have been linked to increased glucagon-like peptide-1 (GLP-1) secretion from the gastrointestinal tract in cell and animal models; however, there is little direct evidence in human subjects to confirm this. The present study was designed to investigate whether endogenous plasma GLP-1 concentrations increase following acute consumption of 48 g dietary fibre (as resistant starch (RS) from high-amylose maize type 2 RS (HAM-RS2)) compared with a matched placebo. A total of thirty healthy males participated in the present randomised cross-over study where HAM-RS2 or placebo was consumed as part of standardised breakfast and lunch meals. Changes to GLP-1, glucose, insulin and C-peptide were assessed half hourly for 7 h. Following the breakfast meal, plasma GLP-1 concentrations were lower with HAM-RS2 compared with the placebo (P = 0·025). However, there was no significant difference between the supplements following the lunch meal. Plasma insulin concentrations were significantly lower following the lunch meal (P = 0·034) with HAM-RS2 than with the placebo, but were not different after breakfast. Plasma glucose and C-peptide concentrations did not differ at any point. These results suggest that increased dietary fibre intake, in the form of HAM-RS2, does not acutely increase endogenous GLP-1 concentrations in human subjects. Further fibre feeding studies are required to determine whether GLP-1 concentrations may increase following longer-term consumption.

Dietary fibre improves first-phase insulin secretion in overweight individuals.

Previous work has shown increased insulin sensitivity, increased hepatic insulin clearance and lower postprandial insulin responses following treatment with resistant starch, a type of dietary fibre. The objective of this study was to further explore the effects of resistant starch on insulin secretion. Twelve overweight (BMI 28.2±0.4 kg/m(2)) individuals participated in this randomized, subject-blind crossover study. Participants consumed either 40 g type 2 resistant starch or the energy and carbohydrate-matched placebo daily for four weeks. Assessment of the effect on insulin secretion was made at the end of each intervention using an insulin-modified frequently sampled intravenous glucose tolerance test (FSIVGTT). Insulin and C-peptide concentrations were significantly higher during the FSIVGTT following the resistant starch compared with the placebo. Modelling of the data showed significantly improved first-phase insulin secretion with resistant starch. These effects were observed without any changes to either body weight or habitual food intake. This study showed that just four weeks of resistant starch intake significantly increased the first-phase insulin secretion in individuals at risk of developing type 2 diabetes. Further studies exploring this effect in individuals with type 2 diabetes are required.

Acute ingestion of resistant starch reduces food intake in healthy adults.

Resistant starch (RS), a non-viscous dietary fibre, may have postprandial effects on appetite regulation and metabolism, although the exact effects and mechanisms are unknown. An acute randomised, single-blind crossover study, aimed to determine the effects of consumption of 48 g RS on appetite compared to energy and available carbohydrate-matched placebo. Twenty young healthy adult males consumed either 48 g RS or the placebo divided equally between two mixed meals on two separate occasions. Effects on appetite were assessed, using an ad libitum test meal and 24-h diet diaries for energy intake, and using visual analogue scales for subjective measures. Changes to postprandial glucose, insulin and C-peptide were also assessed. There was a significantly lower energy intake following the RS supplement compared to the placebo supplement at both the ad libitum test meal (5241 (sem 313) v. 5606 (sem 345) kJ, P = 0.033) and over the 24 h (12 603 (sem 519) v. 13 949 (sem 755) kJ, P = 0.044). However, there was no associated effect on subjective appetite measures. Postprandial plasma glucose concentrations were not significantly different between supplements, but there was a significantly lower postprandial insulin response following the RS supplement (P = 0.029). The corresponding C-peptide concentrations were not significantly different, although the ratio of C-peptide to insulin was higher following the RS supplement compared to placebo (P = 0.059). These results suggest that consumption of 48 g RS, over a 24-h period, may be useful in the management of the metabolic syndrome and appetite. Further studies are required to determine the exact mechanisms.