The influence of high-carbohydrate meals with different glycaemic indices on substrate utilisation during subsequent exercise.

The present study was designed to examine the effects of mixed high-carbohydrate meals with different glycaemic indices (GI) on substrate utilization during subsequent exercise. Nine healthy male recreational runners (age 26.8 (sem 1.1) years, body mass 74.7 (sem 2.4) kg, VO2max 58.1 (sem 1.7) ml/kg per min) completed three trials: high-glycaemic-index meal (HGI), low-glycaemic-index meal (LGI) and fasting (FAST), separated by 7 d. The test meals contained 2 g carbohydrate/kg body mass, they were isoenergetic and the GI values were 77.4, 36.9 and 0.0 respectively. In each trial, subjects consumed the test meal 3 h before performing a 60 min run at 65 % VO2max on a motorized treadmill. Ingestion of the HGI and LGI resulted in hyperglycaemia and hyperinsulinaemia during the postprandial period compared with the FAST (P<0.05). The incremental area under the curve for plasma glucose was 2-fold higher for HGI compared with LGI (108.7 v. 48.9 mmol/l per min). In contrast, plasma non-esterified fatty acid concentrations were significantly lower following HGI and LGI compared with FAST (P<0.05). During the subsequent submaximal exercise, plasma glucose declined to below the fasting value in HGI compared with LGI and FAST (P<0.05). The estimated total fat oxidation was significantly higher for the LGI than the HGI during exercise (P<0.05). In summary, both pre-exercise carbohydrate meals resulted in lower rates of fat oxidation during subsequent exercise than when subjects performed exercise in the fasting state. However, the LGI resulted in a higher rate of fat oxidation during exercise than following the consumption of the HGI.