The branched-chain amino acids, leucine and isoleucine, have been shown to lower blood glucose (BG). Moreover, in our recent study, intraduodenal infusion of leucine decreased energy intake in healthy, lean men. We have now investigated the effects of intragastric administration of leucine and isoleucine on gastric emptying of, and the blood glucose responses to, a mixed-nutrient drink, and subsequent energy intake. In two separate studies, healthy, normal-weight subjects (each n=12) received, on three separate occasions, intragastric infusions of either leucine or isoleucine (5 g or 10 g) or control. 15 min later, subjects consumed a mixed-nutrient drink (400 kcal, 56 g carbohydrates), and gastric emptying (¹³C-acetate breath test) and BG were measured for 60 min. Immediately afterwards, ad-libitum energy intake was assessed. For leucine, there was a trend for an effect of treatment on BG AUC (P=0.076). There was no significant difference between treatments for peak BG (t=15 min, mmol/l; control: 7.2±0.3, 5 g: 6.6±0.2, 10 g: 6.4±0.2). Leucine had no significant effects on gastric emptying or energy intake, however, BG AUC correlated with gastric emptying (r=0.46, P<0.05). For isoleucine, 10 g significantly reduced BG AUC compared with control (P<0.01), and both loads reduced peak BG (mmol/l; control: 7.3±0.2, 5 g: 6.7±0.2, 10 g: 6.2±0.3; P<0.05 for both). Gastric emptying was slower after 10 g isoleucine compared with control (P<0.05), but did not correlate with AUC BG. Isoleucine did not affect energy intake. In conclusion, our data suggest that despite their structural similarity, leucine and isoleucine differentially affect BG and gastric emptying. The effects of these amino acids on BG in patients with type 2 diabetes warrant evaluation. It is unclear why intraduodenal, but not intragastric, leucine reduces energy intake. Further studies need to investigate the underlying mechanisms, including differential effects on plasma leucine concentrations and/or gut hormone release.