Intragastric Lysine Lowers the Circulating Glucose and Insulin Responses to a Mixed-Nutrient Drink without Slowing Gastric Emptying in Healthy Adults.

Background: Lysine is reported to lower the glycemic response to oral glucose in humans and, albeit at high loads, to slow gastric emptying of glucose and decrease food intake in rats. Objective: We investigated the effects of intragastrically administered lysine on early (15 min) and later (60 min) blood glucose and insulin responses to and gastric emptying of a mixed-nutrient drink, and effects on subsequent energy intake. Methods: Twelve healthy volunteers (7 men and 5 women; mean ± SEM age: 24 ± 2 y) received intragastric infusions (200 mL) containing 5 or 10 g l-lysine or a control solution within 2 min on 3 different occasions in randomized order. Fifteen minutes later, participants consumed a mixed-nutrient drink (300 mL, 400 kcal, and 56 g carbohydrates) within 1 min. For the next hour ( t = 0-60 min), we collected blood samples every 15 min (to measure blood glucose, plasma insulin, and plasma glucagon) and breath samples every 5 min (to measure gastric emptying via a 13 C-acetate breath test). We then quantified subjects' energy intake from a buffet-style meal ( t = 60-90 min). Results: There were no differences between the 2 lysine treatments; hence, data were pooled for further analysis. Lysine did not affect blood glucose at 15 min or the blood glucose area under the curve from 0 to 60 min (AUC0-60 min ) but it decreased blood glucose at 60 min compared with the control solution (-9.1% ± 3.1%, P < 0.01). Similarly, the early insulin response and insulin AUC0-60 min were not affected by lysine, but plasma insulin at 60 min was 20.9% ± 5.6% lower than after the control ( P < 0.05). Plasma glucagon at both 15 min (20.7% ± 4.7%, P < 0.001) and 60 min (14.1% ± 5.4%, P < 0.05) and the glucagon AUC0-60 min ( P < 0.01) were greater after lysine than after the control. Lysine did not slow gastric emptying, and there was no effect on energy intake. Conclusion: In healthy adults, lysine slightly reduced the glycemic response to an oral mixed-macronutrient drink, an effect that was apparently independent of insulin or slowing of gastric emptying. This trial was registered at www.anzctr.orgau as 12614000837628.