No change in glucose tolerance and substrate oxidation after a high-carbohydrate, low-fat diet

Possible changes in glucose tolerance and substrate oxidation after a high-carbohydrate, low-fat diet were studied in seven healthy volunteers. Each subject consumed two experimental diets for 1 week after 1 week on a stabilization diet; diet no. 1 11% fat and 64% carbohydrates, and diet no. 2 30% fat and 45% carbohydrates. At the end of each experimental week, plasma levels of glucose, insulin, and free fatty acids were measured before and every 30 minutes for 6 hours after a 75-g oral glucose challenge. At the same time, energy expenditure and substrate oxidation were measured by indirect calorimetry. Plasma lipid and lipoprotein levels were measured at the end of one stabilization period and at the end of each diet. Plasma glucose concentrations and areas under the curve of glucose concentrations were identical after the two experimental periods; the means +/- standard deviation for the values at 120 minutes were 6.4 +/- 0.3 and 6.4 +/- 0.6 mmol/L after diets no. 1 and 2, respectively, and areas under the curve were 1,853 +/- 115 and 1,862 +/- 211 mmol.min/L after diets no. 1 and 2, respectively. Similarly, plasma concentrations of insulin and free fatty acids after glucose ingestion were unaffected by the dietary changes. Energy expenditure increased after glucose administration, and this thermic effect of glucose was identical after the two experimental diets at 4.2% +/- 1.4%, and 3.9% +/- 1.4% of ingested energy for diets no. 1 and 2, respectively. Substrate oxidation rates were also identical for both the fasted and post-glucose periods after the two diets.(ABSTRACT TRUNCATED AT 250 WORDS)