By William Misner, Ph.D.
Q: Why should I add protein to post-exercise carbohydrate meals? What does that do and how does it benefit recovery and performance?
I am asked often to support the hypothesis that proposes adding protein to carbohydrates following glycogen-depleting endurance exercise. The actual mechanisms are not (yet) well understood nor explained, but we are beginning to understand partially why it is advantageous to add protein to carbohydrates after exercise. Some research (not listed) reports the immune system is bolstered stronger than if no protein is consumed with carbohydrates. Some research (not listed) supports 1:1 CHO:PRO, while others argue 3:1 or 4:1 CHO:PRO ratio… since glycogen storage is the major endurance-limiting substrate, according to graduate-level sports nutrition texts, there are 5 papers with findings associated with this hypothesis:
Ivy et al, (1) examined the effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Increasing the plasma glucose and insulin concentrations during prolonged variable intensity exercise by supplementing with carbohydrate has been found to spare muscle glycogen and increase aerobic endurance. Furthermore, the addition of protein to a carbohydrate supplement will enhance the insulin response of a carbohydrate supplement. The purpose of the present study was to compare the effects of a carbohydrate and a carbohydrate-protein supplement on aerobic endurance performance.
Nine trained cyclists exercised on 3 separate occasions at intensities that varied between 45% and 75% VO2max for 3 h and then at 85% VO2max until fatigued. Supplements (200 ml) were provided every 20 min and consisted of placebo, a 7.75% carbohydrate solution, and a 7.75% carbohydrate/1.94% protein solution. Treatments were administered using a double-blind randomized design. Carbohydrate supplementation significantly increased time to exhaustion (carbohydrate 19.7 +/- 4.6 min vs. placebo 12.7 +/- 3.1 min), while the addition of protein enhanced the effect of the carbohydrate supplement (carbohydrate-protein 26.9 +/- 4.5 min, p < .05). Blood glucose and plasma insulin levels were elevated above placebo during carbohydrate and carbohydrate-protein supplementation, but no differences were found between the carbohydrate and carbohydrate-protein treatments. In summary, we found that the addition of protein to a carbohydrate supplement enhanced aerobic endurance performance above that which occurred with carbohydrate alone, but the reason for this improvement in performance was not evident.
Miller et al., (2) likewise examined the metabolic response to a provision of mixed protein-carbohydrate supplementation during endurance exercise.
The interaction of substrates and hormones in response to ingestion of intact proteins during endurance exercise is unknown. This study characterized substrate and hormone responses to supplementation during endurance exercise. Nine male runners participated in 3 trials in which a non-fat (MILK), carbohydrate (CHO), or placebo (PLA) drink was consumed during a 2-hour treadmill run at 65% VO2max. Circulating levels of insulin, glucagon, epinephrine, norepinephrine, growth hormone, testosterone, and cortisol were measured. Plasma substrates included glucose, lactate, free fatty acids, and select amino acids. Except for insulin and cortisol, hormones increased with exercise. While post-exercise insulin concentrations declined similarly in all 3 trials, the glucagon increase was greatest following MILK consumption. CHO blunted the post-exercise increase in growth hormone compared to levels in MILK.
Free fatty acids and plasma amino acids also were responsive to nutritional supplementation with both CHO and MILK attenuating the rise in free fatty acids compared to the increase observed in PLA. Correspondingly, respiratory exchange ratio increased during CHO. Essential amino acids increased significantly only after MILK and were either unchanged or decreased in CHO. PLA was characterized by a decrease in branched-chain amino acid concentrations. Modest nutritional supplementation in this study altered the endocrine response as well as substrate availability and utilization following and during an endurance run, respectively.
Tarnopolsky et al., (3) reported post exercise protein-carbohydrate and carbohydrate supplements increase muscle glycogen in men and women. They previously demonstrated that women did not increase intramuscular glycogen in response to an increased percent of dietary carbohydrate (CHO) (from 60 to 75% of energy intake) (M. A. Tarnopolsky, S. A.Atkinson, S. M. Phillips, and J. D. MacDougall. J. Appl. Physiol. 78:1360-1368, 1995).
CHO and CHO-protein (Pro) supplementation post exercise can potentiate glycogen resynthesis compared with placebo (K. M. Zawadzki, B. B. Yaspelkis, and J. L. Ivy. J. Appl. Physiol. 72: 1854-1859, 1992). We studied the effect of isoenergetic CHO and CHO-Pro-Fat supplements on muscle glycogen resynthesis in the first 4 hours after endurance exercise (90 min at 65% peak O2 consumption) in trained endurance athletes (men, n = 8; women, tested in midfollicular phase, n = 8). Each subject completed three sequential trials separated by 3 wk; a supplement was provided immediately and 1-h postexercise: 1) CHO (0.75 g/kg) + Pro (0.1 g/kg) + Fat (0.02 g/kg), 2) CHO (1 g/kg), and 3) placebo (Pl; artificial sweetener). Subjects were given prepackaged, isoenergetic, isonitrogenous diets, individualized to their habitual diet, for the day before and during the exercise trial. During exercise, women oxidized more lipid than did men (P < 0.05). Both of the supplement trials resulted in greater post exercise glucose and insulin compared with Pl (P < 0.01), with no gender differences. Similarly, both of these trials resulted in increased glycogen resynthesis (37.2 vs. 24. 6 mmol . kg dry muscle-1 . h-1, CHO vs. CHO-Pro-Fat, respectively) compared with Pl (7.5 mmol . kg dry muscle-1 . h-1; P < 0.001) with no gender differences. They concluded that post exercise CHO and CHO-Pro-Fat nutritional supplements can increase glycogen resynthesis to a greater extent than Pl for both men and women.
Zawadzki et al., (4) compared carbohydrate, protein, and carbohydrate-protein supplementsto determine their effects on muscle glycogen storage during recovery from prolonged exhaustive exercise. Nine male subjects cycled for 2 h on three separate occasions to deplete their muscle glycogen stores. Immediately and 2 h after each exercise bout, they ingested 112.0 g carbohydrate (CHO), 40.7 g protein (PRO), or 112.0 g carbohydrate and 40.7 g protein (CHO-PRO). Blood samples were drawn before exercise, immediately after exercise, and throughout recovery. Muscle biopsies were taken from the vastus lateralis immediately and 4 h after exercise. During recovery the plasma glucose response of the CHO treatment was significantly greater than that of the CHO-PRO treatment, but the plasma insulin response of the CHO-PRO treatment was significantly greater than that of the CHO treatment. Both the CHO and CHO-PRO treatments produced plasma glucose and insulin responses that were greater than those produced by the PRO treatment (P less than 0.05). The rate of muscle glycogen storage during the CHO-PRO treatment [35.5 +/- 3.3 (SE) mumol.g protein-1.h-1] was significantly faster than during the CHO treatment (25.6 +/- 2.3 mumol.g protein-1.h-1), which was significantly faster than during the PRO treatment (7.6 +/- 1.4 mumol.g protein-1.h-1). The results suggest that post exercise muscle glycogen storage can be enhanced with a carbohydrate-protein supplement as a result of the interaction of carbohydrate and protein on insulin secretion.
Ivy et al., (5) concluded that early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. They tested the hypothesis that a carbohydrate-protein (CHO-Pro) supplement would be more effective in the replenishment of muscle glycogen after exercise compared with a carbohydrate supplement of equal carbohydrate content (LCHO) or caloric equivalency (HCHO). After 2.5 +/- 0.1 h of intense cycling to deplete the muscle glycogen stores, subjects (n = 7) received, using a rank-ordered design, a CHO-Pro (80 g CHO, 28 g Pro, 6 g fat), LCHO (80 g CHO, 6 g fat), or HCHO (108 g CHO, 6 g fat) supplement immediately after exercise (10 min) and 2 h post exercise. Before exercise and during 4 h of recovery, muscle glycogen of the vastus lateralis was determined periodically by nuclear magnetic resonance spectroscopy. Exercise significantly reduced the muscle glycogen stores (final concentrations: 40.9 +/- 5.9 mmol/l CHO-Pro, 41.9 +/- 5.7 mmol/l HCHO, 40.7 +/- 5.0 mmol/l LCHO). After 240 min of recovery, muscle glycogen was significantly greater for the CHO-Pro treatment (88.8 +/- 4.4 mmol/l) when compared with the LCHO (70.0 +/- 4.0 mmol/l; P = 0.004) and HCHO (75.5 +/- 2.8 mmol/l; P = 0.013) treatments. Glycogen storage did not differ significantly between the LCHO and HCHO treatments. There were no significant differences in the plasma insulin responses among treatments, although plasma glucose was significantly lower during the CHO-Pro treatment. These results suggest that a CHO-Pro supplement is more effective for the rapid replenishment of muscle glycogen after exercise than a CHO supplement of equal CHO or caloric content.
SUMMARY: Endurance athletes should experiment with a meal recovery protocol that contains carbohydrate and protein, not simply carbohydrate alone. The best time to consume this meal is the first 30 minutes after exercise to take advantage of the limited post-exercise enzymes & hormonal carrier availability.
References
1) Ivy JL, Res PT, Sprague RC, Widzer MO. Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int J Sport Nutr Exerc Metab. 2003 Sep;13(3):382-95. PMID: 14669937 [PubMed – indexed for MEDLINE]
2) Miller SL, Maresh CM, Armstrong LE, Ebbeling CB, Lennon S, Rodriguez NR. Metabolic response to provision of mixed protein-carbohydrate supplementation during endurance exercise. Int J Sport Nutr Exerc Metab. 2002 Dec;12(4):384-97. PMID: 12500983 [PubMed – indexed for MEDLINE]
3) Tarnopolsky MA, Bosman M, Macdonald JR, Vandeputte D, Martin J, Roy BD. Postexercise protein-carbohydrate and carbohydrate supplements increase muscle glycogen in men and women. J Appl Physiol. 1997 Dec;83(6):1877-83. PMID: 9390958 [PubMed – indexed for MEDLINE]
4) Zawadzki KM, Yaspelkis BB 3rd, Ivy JL. Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. J Appl Physiol. 1992 May;72(5):1854-9. PMID: 1601794 [PubMed – indexed for MEDLINE]
5) Ivy JL, Goforth HW Jr, Damon BM, McCauley TR, Parsons EC, Price TB. Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. J Appl Physiol. 2002 Oct;93(4):1337-44. PMID: 12235033 [PubMed – indexed for MEDLINE]
