The reproducibility of serial meal and oral glucose tolerance tests in normal subjects

Five normal volunteer subjects within 10% of their ideal body weight received four isocaloric meals per day during two separate study periods. Each study period consisted of two consecutive days one week apart. The plasma glucose and insulin response was determined half-hourly throughout the second day of each of the two study periods. Good reproducibility of the glucose and insulin response to the standardised meals on the two comparative profile days was observed. Only at three points during the day was the plasma glucose significantly different between the profile days while no differences existed for plasma insulin. In addition, a separate group of four healthy normal volunteer subjects within 10% of their ideal body weight received four 50 g oral glucose tolerance tests on each of four days, ie on two consecutive days one week apart. During the second day of each study period half-hourly plasma glucose and insulin concentrations were determined. The within subject reproducibility of the plasma glucose and insulin response to the serial glucose loads was excellent. At one time point only was the mean plasma glucose for the group significantly different between the two study days. No statistically significant difference however was observed for the plasma insulin response between the two days. As the day progressed during both test procedures a small decrease in carbohydrate tolerance was observed. The amplitude of glycaemic excursions in response to the oral glucose tolerance tests was greater than that observed in response to the meal tolerance tests.