Metabolic response to small and large C-13-labelled pasta meals following rest or exercise in man

The metabolic response to a 150 or 400 g C-13-labelled pasta meal was studi ed for 8 h following rest or exercise at low or moderate workload (n 6). Fo llowing rest, the 400 g meal totally suppressed fat oxidation (v. 14.1 g fo llowing the 150 g meal) and a small amount of glucose was converted into fa t (4.6 g), but fat oxidation remained high in subjects who had exercised fo llowing both the small (21.8 and 34.1 g) and large meal (14.1 and 32.3 g). Exogenous glucose oxidation was significantly higher in subjects who had re mained at rest both following the small (67.6 g v. 60.4 and 51.3 g in subje cts who exercised at low and moderate workloads) and large meal (152.2 v. 1 23.0 and 127.2 g). Endogenous glucose oxidation was similar in the three gr oups following the 150 g meal (42.3-58.0 g), but was significantly lower fo llowing the 400 g meal in subjects who had exercised at low workload (24.2 v. 72.2 g following rest; P<0.05), and was totally suppressed in those who had exercised at moderate workload. As a consequence, a larger positive gly cogen balance was observed in subjects who exercised before the large meal (182.8-205.1 g v. 92.4 g following rest; P<0.05). Total fat oxidation calcu lated from 08.00 hours to 20.00 hours was similar in subjects who exercised at low and moderate workloads. These results indicate that: (1) de novo li pogenesis, which plays only a minor role for the disposal of an acute dieta ry carbohydrate load, is totally suppressed following exercise, even when a very large carbohydrate load is ingested; (2) the reduction in glycogen tu rnover as well as a preferential conversion of glucose into glycogen are re sponsible for the increase in glycogen stores following exercise; (3) for a similar energy expenditure, exercise at low workload for a longer period d oes not favour fat oxidation when the post-exercise period is taken into ac count.