In a study of the impact of aspartame, fat, and carbohydrate on appetite, we monitored blood glucose continuously for 431 (SE 16) min. Ten healthy males (19-31 years) participated in three time-blinded visits. As blood glucose was monitored, appetite ratings were scored at randomized times. On the first meal initiation, volunteers consumed one of three isovolumetric drinks (aspartame, 1 MJ simple carbohydrate, and 1 MJ high-fat; randomized order). High-fat and high-carbohydrate foods were available ad libitum subsequently. Blood glucose patterns following the carbohydrate drink (+1.78 (SE 0.28) mmol/l in 38 (SE 3) min) and high-fat drink (+0.83 (SE 0.28) mmol/l in 49 (SE 6) min) were predictive of the next intermeal interval (R 0.64 and R 0.97 respectively). Aspartame ingestion was followed by blood glucose declines (40% of subjects), increases (20%), or stability (40%). These patterns were related to the volunteers' perception of sweetness of the drink (R 0.81, P = 0.014), and were predictive of subsequent intakes (R -0.71, P = 0.048). For all drinks combined, declines in blood glucose and meal initiation were significantly associated (chi 2 16.8, P < 0.001), the duration of blood glucose responses and intermeal intervals correlated significantly (R 0.715, P = 0.0001), and sweetness perception correlated negatively with hunger suppression (R -0.471, P = 0.015). Effects of fat, carbohydrate, and aspartame on meal initiation, meal size, and intermeal interval relate to blood glucose patterns. Varied blood glucose responses after aspartame support the controversy over its effects, and may relate to sweetness perception.