Abstract
Oral fructose decreases fat oxidation and increases carbohydrate oxidation in obese subjects, but the metabolic response to fructose in lean individuals is less well understood. The purpose of this study was to assess the effects of a single fructose-rich mixed meal on substrate oxidation in young healthy nonobese men. We hypothesized that a decrease in fat oxidation and an increase in carbohydrate oxidation would be observed after a fructose-rich mixed meal compared with a glucose-rich mixed meal. Twelve healthy, normal weight to overweight, aged 23 to 31 years participated in a double-blind, crossover study. Each participant completed 2 study visits, eating a mixed meal containing 30% of the calories from either fructose or glucose. Blood samples for glucose, insulin, triglycerides, and leptin as well as gas exchange by indirect calorimetry were measured intermittently for 7 hours. Serum insulin was higher after a fructose mixed meal, but plasma glucose, plasma leptin, and serum triglycerides were not different. Mean postprandial respiratory quotient and estimated fat oxidation did not differ between the fructose and glucose meals. The change in fat oxidation between the fructose- and glucose-rich meals negatively correlated with body mass index (BMI; r = -0.59 [P = .04] and r = -0.59 [P = .04] at the 4- and 7-hour time points, respectively). In healthy nonobese men, BMI correlates with altered postprandial fat oxidation after a high-fructose mixed meal. The metabolic response to a high-fructose meal may be modulated by BMI.