The main regulators of gastric emptying of nutrient solutions appear to be the total gastric volume and the energy density of ingested solutions. A high gastric volume increases the rate of emptying while a high energy content decreases gastric emptying. The present study examined the interaction of repeat ingestion of solutions with low or high carbohydrate (CHO) content on gastric emptying rate. Following ethics committee approval, eight (4 male, 4 female) healthy subjects gave written informed consent before being enrolled in the study. The subjects’ mean (S.D.) age was 25 ± 3 years, height was 172 ± 13 cm and body mass was 69.8 ± 19.7 kg. The low CHO test drink was a 2 % glucose (0.34 kJ ml^-1) solution with a mean (S.D.) osmolality of 112 ± 3 mosmol kg^-1 and the high CHO drink contained 10 % carbohydrate (1.70 kJ ml^-1), as a mixture of glucose monomer and polymer, with an osmolality of 115 ± 8 mosmol kg^-1. After an overnight fast, subjects undertook four trials, each separated by 7 days. In two trials, subjects ingested a single 600 ml bolus of either the 2 % (2S) or 10 % (10S) CHO test solution. In the repeat ingestion trials, an additional 100 ml volume of the same test drink was instilled into the stomach using a gastric aspiration tube at 15 min intervals after the initial intake of 600 ml of either the 2 % (2R) or 10 % (10R) test drink. All drinks contained a known amount of phenol red as a non-absorbable marker. Gastric emptying was measured using a modified double sampling aspiration method (Reher et al. 1990). All subjects were familiarised with the study procedures before undertaking any trial; the treatment order was carried out using a Latin square design. Statistical significance (P < 0.05) was determined using one-way ANOVA with Tukey’s post-hoc analysis or Kruskal-Wallis and Mann-Whitney tests as appropriate.

The rate of gastric emptying of the 2 % glucose drink was faster than that of the 10 % CHO solution. The mean (S.D.) volume of test drink emptied into the small intestine over the 60 min measurement period was greater (P = 0.001) in trial 2R (829 ± 104 ml) than in trials 2S (580 ± 44 ml), 10S (486 ± 87 ml) or 10R (575 ± 136 ml). Although a greater volume of test drink was ingested in the repeat filling trials (900 ml) than in the single bolus trials (600 ml), similar volumes were emptied over 60 min in trials 2S, 10S and 10R (P = 0.11). Over 60 min, the median (range) amount of CHO delivered to the small intestine was less (P < 0.005) in trial 2S (12 (9.5-12) g) than in trials 2R (17.6 (12-18) g), 10S (46.8 (37.7-60) g) or 10R (60.7 (37.9-74.5) g). Overall CHO delivery was less (P = 0.001) in trial 2R than in trials 10S and 10R, which were similar to each other (P = 0.21).

In the present study, the highest rate of gastric emptying was promoted with repeated ingestion of the 2 % CHO solution, while increasing the intake of the 10 % CHO solution had little effect on emptying. This may indicate an upper limit of CHO delivery to the intestine in some individuals. The volume of fluid delivered to the duodenum was greater from the 2 % CHO solution, but the 10 % CHO solution promoted greater energy delivery.