Ingestion of CHO and PRO following intense exercise has been reported to increase insulin levels, optimize glycogen resynthesis, enhance PRO synthesis, and lessen the immuno-suppressive effects of intense exercise [2
]. Since different forms of CHO have varying glycemic effects [28
], the purpose of this study was to determine whether the type of CHO ingested with PRO following resistance-exercise affects blood glucose availability, insulin levels, markers of anabolism and catabolism, and/or general immune markers during the first two hours of recovery. The major findings of this study were: 1.) ingesting CHO with PRO following resistance-training promoted significant increases in insulin levels; 2.) no significant differences were observed among the forms of CHO ingested on insulin levels suggesting that each of these types of CHO can be an effective source of CHO for post-exercise CHO/PRO supplements; 3.) that glucose levels were maintained to a greater degree in subjects ingesting honey as the source of CHO; and, 4.) post-exercise nutritional supplementation did not significantly affect the time course of testosterone, cortisol, the ratio of testosterone to cortisol, muscle and liver enzyme efflux, or general markers of immunity during the first two hours of recovery following resistance-exercise. These findings add to a growing body of literature indicating that ingestion of CHO and PRO following exercise can stimulate insulin levels and thereby anabolic processes [3
]. Moreover, they extend our understanding of how different sources of CHO with differing glycemic responses influence glucose availability, insulin levels, and recovery indices. The following provides additional insight into the results observed.
Results from the present study indicate that glucose and insulin concentrations peaked 30-min following ingestion of CHO/PRO and then proceeded to decline for 120-min. This finding is of interest from a nutrient delivery and timing standpoint in that it has been suggested that athletes should ingest CHO and PRO within two hours following intense exercise in order to optimize the hormonal effects of intense exercise and recovery [1
]. It has typically been thought that glucose and insulin levels increase the greatest following ingestion of a high GI form of CHO and that combining high GI carbohydrates with PRO would optimize the insulin and glucose response following exercise. For this reason, post-exercise CHO/PRO supplements often contain dextrose, sucrose, or maltodextrin as the source of CHO. However, it is well known that the GI profile of CHOs may be altered when co-ingesting CHO with PRO, fat, and/or other nutrients due to influences on the energy density, osmolality, and/or gastric emptying rates GI of the meal [30
]. Consequently, one can not assume that adding a high GI CHO to a PRO supplement will yield the most advantageous glucose and insulin response. In support of this contention, glucose levels were increased to the greatest degree when ingesting honey as the source of CHO rather than sucrose or maltodextrin. As noted previously, the honey powder used in this study contained fructose (31.5%), glucose (26%), wheat starch (25.3%), and maltose (4.7%). These findings suggest that it may be more advantageous to ingest a mixture of CHO's with PRO following exercise in order to promote a more sustained increase in blood glucose response. However, although ingesting CHO with PRO significantly increased insulin levels in comparison to controls, no significant differences were observe among types of CHO ingested in peak insulin levels (C 8.7 ± 2.9 u
IU/mL; S 136.2 ± 15.6 u
IU/mL; H 150.1 ± 25.3 u
IU/mL; M 154.8 ± 18.9 u
IU/mL) or AUC values in insulin observed after ingestion of the supplements (C -243 ± 162 u
IU/mL; S 7,527 ± 883 u
IU/mL; H 8,656 ± 1,758 u
IU/mL; M 10,016 ± 974 u
It is also interesting to note that glucose values in the H group stayed above baseline throughout recovery while values fell below baseline in the S and M groups. Consequently, this form of CHO may help maintain glucose levels and prevent incidents of hypoglycemia that some individuals may experience when ingesting large amounts of CHO and PRO. Although we did not measure glycogen uptake at the muscle, previous research has shown that ingesting CHO with higher GI following exercise promotes a more rapid resynthesis of muscle glycogen [28
]. Additionally, that ingesting CHO and PRO following exercise increases muscle glycogen replenishment [6
]. Since co-ingesting CHO with other nutrients influences the energy density, osmolality, gastric emptying rates, and the GI of the meal [32
], additional research should evaluate the effects of ingesting different forms of CHO with PRO on muscle glycogen resynthesis following intense exercise.
Post-exercise ingestion of PRO and amino acids have been reported to stimulate PRO synthesis [3
]. Additionally, insulin has been reported to be a potent stimulator of PRO synthesis [3
]. While there is some debate whether provision of CHO with PRO and/or amino acids enhances the effects on PRO synthesis [43
] as well as whether adding PRO or amino acids to CHO promotes greater glycogen resynthesis [44
], it is clear that individuals engaged in intense training need to ingest these nutrients in order to optimize recovery [1
]. In the present study, we examined the influence of ingesting different forms of CHO with PRO on a number of markers of anabolism and catabolism during recovery in an attempt to determine whether these nutritional strategies influenced the acute phase of recovery. Previous research has indicated that resistance-trained men consuming a CHO:PRO supplement for one week were found to have lower cortisol concentrations during supplementation, as well as higher levels insulin-like growth factor-I following several days of heavy-resistance exercise [15
]. Chandler et al. [14
] also demonstrated that insulin and growth hormone concentrations during recovery from a single heavy-resistance training session were significantly higher and testosterone concentrations were lower when subjects consumed a CHO:PRO supplement immediately before and 2 h after the workout. The supplements had no effect on IGF-1 but testosterone concentrations decreased and were interpreted by the authors to be the result of increased testosterone clearance [14
]. In our trial, testosterone concentrations and the ratio of testosterone to cortisol significantly increased in response to resistance-exercise and then declined during the recovery period. However, the nutritional intervention did not significantly influence this response. Interestingly, cortisol levels increased to the greatest degree in response to exercise in the non-supplemented control group while decreasing in the supplemented groups. However, these apparent differences were not statistically significant. Likewise, significant time effects were observed in creatinine, BUN, the BUN/creatinine ratio, CK, ALT, and AST. However, no significant differences were observed among groups with the exception that the BUN/Creatinine ratio increased significantly during recovery following nutritional supplementation in comparison to the non-supplemented control. The BUN/Creatinine ratio is a general marker of whole body catabolism. Higher levels typically are indicative of greater PRO degradation. However, the increased BUN/Creatinine levels observed following supplementation in the present study were most likely due to the ingestion and utilization of supplemental PRO.
Finally, research has shown that intense exercise causes an acute immuno-suppression for several hours after exercise. For this reason, a number of nutritional countermeasures including CHO and PRO have been proposed to lessen the immunosuppressive effects of intense exercise [1
]. In this study, we examined whether different forms of CHO influenced general markers of immunity. We found that WBC, neutrophils, and the total neutrophil to total lymphocyte ratio were significantly increased in response to exercise and throughout recovery. These findings support prior findings that intense resistance-training can promote an immune challenge. However, ingestion of CHO and PRO had no influence on these responses during the acute phase of recovery. Whether, ingestion of CHO and PRO may influence markers of immunity during a more prolonged period of recovery remains to be determined.
In conclusion, CHO and PRO ingestion following exercise significantly influences glucose and insulin responses without significantly altering markers of anabolism, catabolism or immunity during the first two hours of recovery. Although ingesting honey as the source of CHO with PRO tended to maintain blood glucose levels to a greater degree, no significant differences were observed among the types of CHO ingested in terms of insulin response to supplementation. These findings suggest that each of these types of CHO can serve as effective sources of CHO to ingest with PRO following intense resistance-exercise in an attempt to optimize CHO availability as well as post-exercise anabolism.