|
|
|
Refuel
Scientific Support
Chocolate milk and recovery
- One study found that when athletes drank lowfat chocolate milk after an intense bout of exercise they were able to work out longer during a second round of exercise compared to when they drank a carbohydrate replacement beverage.
- Nine healthy, male, endurance athletes participated in this randomized, single-blind crossover study, which showed that chocolate milk was an effective recovery aid between intense exercise sessions. Subjects participated in 3 sets of intense cycling workouts where they biked until their muscles were depleted of energy, rested for four hours, and then biked again until exhaustion. After each initial workout, the cyclists drank about 2 cups of one of three beverages: lowfat chocolate milk, a traditional fluid-replacement drink or a carbohydrate-replacement drink. Time to exhaustion and ratings of total work during the second round of exercise were significantly greater after the chocolate milk trials compared to the carbohydrate replacement drink trials, indicating that chocolate milk may help athletes recover faster after a workout session, which may lead to enhanced performance.
Karp JR, Johnston JD, Tecklenburg S, Mickleborough TD, Fly AD, Stager JM. Chocolate Milk as a Post-Exercise Recovery Aid. International Journal of Sport Nutrition and Exercise Metabolism. 2006; 78-91.
Milk and hydration
- Due to its high water content, milk is inherently a hydration beverage. Additionally, some new research suggests milk may be an optimal post-exercise choice to maintain hydration status.
- In this randomized, crossover study, researchers found that milk may help restore hydration better than some other commonly used post-exercise beverages. Healthy male and female volunteers completed an exercise session in a warm climate. Twenty minutes later, they were given one of four test beverages: water, Powerade, lowfat milk, or lowfat milk with added salt. They repeated the trials with each of the other test beverages, at least seven days apart. Fluid loss to sweat was measured and urine output was monitored for four hours following the experiment. Results showed significantly more urine output after drinking water or sports drink compared to milk or milk with added salt, suggesting that milk may be more effective than water or sports drinks at restoring normal hydration status after exercise. Researchers attribute the results to milkÕs electrolyte content and possibly its energy density. They also speculate that milk is emptied from the stomach at a slower rate than water and sports drinks, which may affect the overall fluid balance.
Shirreffs SM. Watson P. Maughan RJ. Milk as an effective post-exercise rehydration drink. British Journal of Nutrition. 2007;1-8.
Milk and muscle mass
- Some research suggests that proteins in milk may support greater muscle mass buildup after exercise compared to soy-based beverages.
- Canadian researchers found that when men drank milk after resistance exercise, they experienced greater support for muscle mass buildup than after drinking a soy protein beverage. This randomized, single-blind, crossover trial assessed eight healthy men (mean age 21.6 years) who engaged in resistance training at least four days per week. Subjects participated in two trials, in which they completed a standardized resistance workout and then consumed nonfat milk or a soy protein beverage. Both drinks were 500 mL and contained the same amounts of calories, protein, fat and carbohydrate. Results showed that consuming either milk or soy protein beverages after resistance exercise promoted muscle maintenance and gain, but that muscle mass promotion occurred more rapidly and in greater amounts after the subjects drank milk. This led the researchers to conclude that regular consumption of milk protein after resistance exercise may help increase lean muscle mass more rapidly than after consumption of soy protein. This is the first study to show that the source of the proteinÑmilk versus soyÑmay influence muscle development. Although the exact mechanism is unknown, the researchers believe that a difference in digestion patterns between milk and soy may influence muscle protein development.
Wilkinson SB, Tarnopolsky MA, MacDonald MJ, MacDonald JR, Armstrong D, Phillips SM. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. American Journal of Clinical Nutrition 2007;85:1031-40.
- The same researchers conducted a longer term, 10 week study on the effect of reconstituted milk compared to reconstituted soy powder post-exercise found a greater increase in muscle strength after drinking milk compared to soy. In a 12-week study of 56 healthy young men (ages 18-30) at McMaster University, milk drinkers gained 40 percent (2.5 pounds) more muscle than soy protein beverage drinkers and 60 percent (3.3 pounds) more muscle than those who drank a carbohydrate beverage. In addition to building more muscle, milk drinkers lost two pounds of fat at the end of 12 weeks, almost double that of the athletes drinking the carbohydrate beverage. Soy protein beverage drinkers lost no fat.
Hartman JW, Tang JE, Wilkinson SB, Tarnopolsky MA, Lawrence RL, Fullerton AV, Phillips SM. Consumption of fat-free fluid milk following resistance exercise promotes greater lean mass accretion than soy or carbohydrate consumption in young novice male weightlifters. American Journal of Clinical Nutrition, 2007;86:373-381.
- The rate of protein digestion varies depending on the source of amino acid and this difference affects whole-body protein kinetics. Researchers tested the effect of consuming whey or casein proteins on muscle protein synthesis after short, intense bouts of resistance exercise. On three occasions, eight healthy resistance-trained men performed resistance exercises on one leg and then consumed a drink containing 10g of essential amino acids in the form of whey protein, whey and casein (1:1), or casein protein. The pattern of amino acid appearance in the blood after consuming the protein drinks was not affected by the source of amino acids. Rates of muscle protein synthesis were greater in the exercised compared to the non-exercised leg; however, there were no drink-specific differences. The source of amino acids may affect whole-body protein kinetics, but this effect is not apparent in skeletal muscle. Researchers concluded that the ingestion of whey and casein proteins stimulates muscle protein synthesis after resistance exercise.
Tang JE, Kujbida GW, Lysecki PJ, Manolakos JJ, Phillips SM. Effect of whey and casein proteins on muscle protein synthesis after resistance exercise FASEB Journal 2007; 21:A540.7.
Carbohydrate-protein content and muscle recovery
- Experts recommend focusing on carbohydrate and protein ratios to ensure muscle recovery. The carb-protein ratio in lowfat chocolate milk is in line with recommendations and research.
| Nutrient Profile of Milk |
| Nutrients per 8 oz serving | Fat free milk | Lowfat chocolate milk |
| Calories | 80 | 160 |
| Carbohydrate | 12.47 g | 26.10 g |
| Protein | 8.26 g | 8.10 g |
| Fat | 0 g | 2.5 g |
- According to the National Athletic TrainersÕ Association, Òpostexercise hydration should aim to correct any fluid loss accumulated during the practice or event,Ó and maintaining hydration is key for health and physical function. According to the Association, rehydration beverages should include water, carbohydrates and electrolytes Ð a nutrition profile that closely matches lowfat milk.
Casa DJ, Armstrong LE, Hillman SK, Montain SJ, Reiff RV, Rich BS, Roberts WO, Stone JA. National Athletic Trainers' Association Position Statement: Fluid Replacement for Athletes. Journal of Athletic Training. 2000;35:212-224.
- Researchers examined whether a carbohydrate-protein supplement would be more effective in replenishing post-exercise muscle glycogen stores compared to a carbohydrate supplement of equal carbohydrate content or caloric equivalent. Participants completed 2.5 hours of intense cycling to deplete muscle glycogen stores. Then, they received one of three test supplements: a carbohydrate/protein supplement (80 g CHO, 28 g Pro, 6 g fat), a carbohydrate supplement without protein (80 g CHO, 6 g fat), or a caloric equivalent of the carbohydrate/protein supplement (108 g CHO, 6 g fat). The carbohydrate-protein supplement yielded significantly greater muscle glycogen storage in the four hours after the exercise, indicating that a carbohydrate-protein supplement is more effective for the rapid replenishment of muscle glycogen after exercise than a carbohydrate supplement of equal carbohydrate or caloric content.
Ivy JL, Goforth HW, Damon BM, McCauley TR, Parsons EC, Price T. Early postexercise muscle glycogen recovery is enhanced with a carbohydrate-protein supplement. Journal of Applied Physiology; 2002:1337-1344.
- Prolonged endurance exercise stimulates whole-body protein turnover (synthesis and degradation) but it remains contentious whether this translates into an increased net protein oxidation or dietary requirement for protein. Skeletal muscle is the major energy consumer during exercise and the oxidation of branched-chain amino acids (BCAA) is increased several-fold, suggesting an increased requirement for fuel. Increased BCAA oxidation has been proposed to impair aerobic energy provision during prolonged exercise, but there is little evidence to support this theory. Endurance training blunts the acute exercise-induced increase in whole-body protein turnover and skeletal BCAA oxidation at a given work intensity. However, training also increases the maximal capacity for skeletal muscle BCAA oxidation, as evidenced by a higher maximal activity of the rate-determining enzyme branched-chain oxo acid dehydrogenase. Exercise-induced changes in protein metabolism are affected by nutritional status, with high carbohydrate availability (as typically practiced by endurance athletes) generally associated with reduced net protein utilisation. Ingestion of protein with carbohydrate improves net protein balance during exercise and recovery compared with carbohydrate alone, but it remains to be determined whether this practice facilitates the adaptive response to chronic training.
Gibala MJ. Protein metabolism and endurance exercise. Sports Medicine. 2007;37:337-40.
- Carbohydrate, protein, and carbohydrate-protein supplements were compared to 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 postexercise muscle glycogen storage can be enhanced with a carbohydrate-protein supplement as a result of the interaction of carbohydrate and protein on insulin secretion.
Zawadzki, K.M., B.B. Yaspelkis, and J.L. Ivy. Carbohydrate-protein complex increases the rate of muscle glycogen storage after exercise. Journal of Applied Physiology. 72(5):1854-1859, 1992.
- This study assessed whether liquid carbohydrate-protein (C+P) supplements, ingested early during recovery, enhance muscle glycogen resynthesis versus isoenergetic liquid carbohydrate (CHO) supplements, given early or an isoenergetic solid meal given later during recovery (PLB). METHODS: Two hours after breakfast (7.0 kcal.kg; 0.3 g.kg P, 1.2 g.kg C, 0.1 g.kg F), six male cyclists performed a 60-min time trial (AMex). Pre- and postexercise, vastus lateralis glycogen concentrations were determined using nMRS. Immediately, 1 h, and 2 h postexercise, participants ingested C+P (4.8 kcal.kg; 0.8 g.kg C, 0.4 g.kg P), CHO (4.8 kcal.kg; 1.2 g.kg C), or PLB (no energy). Four hours postexercise, a solid meal was ingested. At that time, C+P and CHO received a meal identical to breakfast, whereas PLB received 21 kcal.kg (1 g.kg P, 3.6 g.kg C, 0.3 g.kg F); energy intake during 6 h of recovery was identical among treatments. After 6 h of recovery, measurement and cycling protocols (PMex) were repeated. Absolute muscle glycogen utilization was 18% greater (P Berardi JM, Price TB, Noreen EE, Lemon PW. Postexercise muscle glycogen recovery enhanced with a carbohydrate-protein supplement Med Sci Sports Exerc. 2006 Jun;38(6):1106-13.
- 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.
Ivy, J.L., P.T. Res, R.C. Sprague, and M.O. Widzer. Effect of a carbohydrate-protein supplement on endurance performance during exercise of varying intensity. Int. J. Sport Nutr. Exerc. Metab. 13(3):382-395, 2003.
|
|
|
To learn more about milk's role in good nutrition, 
Check out these