OBJECTIVE - Coffee consumption has been associated with lower risk of type 2 diabetes. We evaluated the acute effects of decaffeinated coffee and the major coffee components chlorogenic acid and trigonelline on glucose tolerance. RESEARCH DESIGN AND METHODS - We conducted a randomized crossover trial of the effects of 12 g decaffeinated coffee, 1 g chlorogenic acid, 500 mg trigonelline, and placebo (1 g mannitol) on glucose and insulin concentrations during a 2-h oral glucose tolerance test (OGTT) in 15 overweight men. RESULTS - Chlorogenic acid and trigonelline ingestion significantly reduced glucose (-0.7 mmol/l, P = 0.007, and -0.5 mmol/l, P = 0.024, respectively) and insulin (-73 pmol/l, P = 0.038, and -117 pmol/l, P = 0.007) concentrations 15 min following an OGTT compared with placebo. None of the treatments affected insulin or glucose area under the curve values during the OGTT compared with placebo. CONCLUSIONS - Chlorogenic acid and trigonelline reduced early glucose and insulin responses during an OGTT. © 2009 by the American Diabetes Association.