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, VO(2)max 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 % VO(2)max 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 (1087 v. 48.9 mmol/1 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.