Post-exercise ketosis in post-prandial exercise: effect of glucose and alanine ingestion in humans

This study examined ketosis in response to 90 min of running before and after the ingestion of 50 g glucose or 50 g L-alanine in thirty-three athletes. Everyone ran 20 km at 07.30 h and then rested, while fasting, till 16.00 h. There were four test groups: 'glucose-before', 'glucose-after', 'alanine-before' and 'alanine-after' according to whether glucose or alanine was ingested at 07.00 h, or 09.00 h. Controls did not ingest either test substance. The control 3-hydroxybutyrate concentration rose from 0.23 +/- 0.03 mmol/l (S.E. of mean) at 07.00 h to 0.74 +/- 0.27 mmol/l at 12.00 h, and 0.94 +/- 0.33 mmol/l at 16.00 h. Glucose ingestion before or after exercise did not influence post-exercise ketosis significantly, despite high insulin: glucagon ratios, low free fatty acid concentrations and hyperglycaemia. Alanine significantly lowered the 3-hydroxybutyrate levels, especially after exercise (to 0.14 +/- 0.07 mmol/l at 12.00 h; P less than 0.05) despite reversed insulin: glucagon ratios. This suggests that hepatic responsiveness to portal hyperglycaemia and the main hormones of metabolism is altered immediately after exercise, presumably to promote muscle glycogen synthesis in preference to liver glycogen synthesis.