Interaction of training and diet on metabolism and endurance during exercise in man.

Abstract

1. Ten untrained young men ingested a carbohydrate-rich diet (65 energy percent (E %) carbohydrate, T-CHO) and ten similar subjects a fat-rich diet (62 E% fat, T-FAT) while endurance training was performed 3-4 times a week for 7 weeks. For another 8th week of training both groups ingested the carbohydrate-rich diet (T-CHO and T-FAT/CHO). 2. Maximal oxygen uptake increased by 11 % (P < 0 05) in both groups after 7 and 8 weeks.Time to exhaustion at 81 % of pre-training maximal oxygen uptake increased significantly from a mean (± S.E.M.) of 35 + 4 min to 102 + 5 and 65 + 7 min in T-CHO and T-FAT, respectively, after 7 weeks (P < 0 05, T-CHO vs. T-FAT). After 8 weeks, endurance remained unchanged in T-CHO but increased (P < 0 05) to 77 + 9 min in T-FAT/CHO which, however, was still less (P < 0 05) than in T-CHO. 3. Muscle glycogen breakdown rate during exercise was halved by endurance training equally in both T-CHO and T-FAT after 7 and 8 weeks, and muscle glycogen stores at exhaustion were not depleted in any group. 4. During exercise after 7 weeks, the respiratory exchange ratio (RER) was unchanged in T-CHO (0-88 + 0 01) compared with pre-training but decreased (P < 0 05) to 0-82 + 0-02 in T-FAT. After 8 weeks, RER in both T-CHO and T-FAT/CHO was approximately 0-87. 5. During exercise, plasma noradrenaline concentration and heart rate were higher in T-FAT than in T-CHO both at 7 and at 8 weeks. 6. It is concluded that ingesting a fat-rich diet during an endurance training programme is detrimental to improvement in endurance. This is not due to a simple lack of carbohydrate fuel, but rather to suboptimal adaptations that are not remedied by short-term increased carbohydrate availability. Furthermore, the study suggests that the decrease in RER usually seen after training when exercising at the same absolute intensity as before training can be prevented by a carbohydrate-rich diet.Physical endurance training results in marked changes in muscle metabolism and endurance during exercise. Classical adaptations to training include a switch to increased fat metabolism when exercising on the same absolute intensity as before training (

Physical exercise as a modulator of adaptation to low and high carbohydrate and low and high fat intakes

“…Adjustment of macronutrient intakes can elicit shifts in plasma and muscle substrates in as few as 12 h. Starling et al (1997) observed signi®cantly increased concentrations of muscle glycogen and lower concentrations of muscle triglycerides within one day after athletes followed a 120 min cycling bout with a high carbohydrate diet (83% carbohydrate, 5% fat) consumed over 12 h. Conversely, muscle glycogen decreased and intramuscular triglycerides increased in a separate trial when a high fat diet (16% carbohydrate, 68% fat) was consumed following exercise. Interventions in which fat intake comprised between 50 ± 85% of caloric intake for durations of 5 d ± 7 w also showed decreased muscle glycogen and increased muscle triglycerides as well as increased plasma FFA's, increased beta-hydroxy butyrate, and lower plasma lactate levels (Helge et al, 1996;Muoio et al, 1994;Phinney et al, 1983;Starling et al, 1997). Resting blood glucose levels typically did not differ due to diet (Helge et al, 1996;Phinney et al, 1983;Starling et al, 1997).…”

“…These shifts clearly illustrate a decreased reliance on carbohydrate and greater oxidation (Helge et al, 1996;Starling et al, 1997). This observation re¯ects a greater use of lipids during exercise when consuming a high fat diet although this diet-related difference does not persist at higher intensity exercise ( b 90% VO 2 max) (Lambert et al, 1994).…”

“…Interventions in which fat intake comprised between 50 ± 85% of caloric intake for durations of 5 d ± 7 w also showed decreased muscle glycogen and increased muscle triglycerides as well as increased plasma FFA's, increased beta-hydroxy butyrate, and lower plasma lactate levels (Helge et al, 1996;Muoio et al, 1994;Phinney et al, 1983;Starling et al, 1997). Resting blood glucose levels typically did not differ due to diet (Helge et al, 1996;Phinney et al, 1983;Starling et al, 1997). Correspondingly, resting insulin values were not signi®-cantly altered by dietary intervention although insulin action could be expected to vary between individuals consuming a high fat diet vs a high carbohydrate diet (Cutler et al, 1995;Rosholt et al, 1994).…”

“…Substrate shifts observed in response to exercise in trained and untrained subjects eating high fat diets included decreased utilization of glycogen, increased triglyceride utilization, attenuated lactate response, increased plasma FFA, and increased glycerol (Helge et al, 1996;Starling et al, 1997). These shifts clearly illustrate a decreased reliance on carbohydrate and greater oxidation (Helge et al, 1996;Starling et al, 1997).…”

“…Correspondingly, resting insulin values were not signi®-cantly altered by dietary intervention although insulin action could be expected to vary between individuals consuming a high fat diet vs a high carbohydrate diet (Cutler et al, 1995;Rosholt et al, 1994). Few studies report profound hormonal shifts in response to dietary intervention, although one investigator noted an enhanced norepinephrine response to exercise in high fat trials (Helge et al, 1996).…”