To optimize the postexercise insulin response and to increase plasma amino acid availability, we studied postexercise insulin levels after the ingestion of carbohydrate and wheat protein hydrolysate with and without free leucine and phenylalanine. After an overnight fast, eight male cyclists visited our laboratory on five occasions, during which a control drink and two different beverage compositions in two different doses were tested. After they performed a glycogen-depletion protocol, subjects received a beverage (3.5 mL · kg-1) every 30 min to ensure an intake of 1.2 g · kg-1 · h-1 carbohydrate and 0, 0.2 or 0.4 g · kg-1 · h-1 protein hydrolysate (and amino acid) mixture. After the insulin response was expressed as the area under the curve, only the ingestion of the beverages containing wheat protein hydrolysate, leucine and phenylalanine resulted in a marked increase in insulin response (+52 and + 107% for the 0.2 and 0.4 g · kg-1 · h-1 mixtures, respectively; P < 0.05) compared with the carbohydrate-only trial). A dose-related effect existed because doubling the dose (0.2-0.4 g · kg-1 · h-1) led to an additional rise in insulin response (P < 0.05). Plasma leucine, phenylalanine and tyrosine concentrations showed strong correlations with the insulin response (P < 0.0001). This study provides a practical tool to markedly elevate insulin levels and plasma amino acid availability through dietary manipulation, which may be of great value in clinical nutrition, (recovery) sports drinks and metabolic research. Chemicals/CAS: Amino Acids; Blood Glucose; Dietary Carbohydrates; Dietary Proteins; Insulin, 11061-68-0; Leucine, 61-90-5; Phenylalanine, 63-91-2; Protein Hydrolysates; Tyrosine, 55520-40-6