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Many health care professionals are practicingwhat they preach daily-exercise forcardiovascular health. And an increasingnumber of patients are taking the exercisemessage to heart.
Many health care professionals are practicing what they preach daily-exercise for cardiovascular health. And an increasing number of patients are taking the exercise message to heart. Marketing companies have caught on to this trend, and numerous “sports drinks” are now available to the enthusiast. Most of the drinks are advertised by sports figures who themselves are epitomes of conditioning. Do these products add evidence-based benefits to endurance exercise?
SPORTS DRINK VS CEREAL AND NONFAT MILK
Researchers from the University of Texas at Austin recently addressed this question.1 They observed that endurance exercise drains muscle glycogen stores and that this substrate is the rate-limiting factor in exercise. In addition, muscle protein breakdown is accelerated by exercise. During recovery from exercise, muscles require both glucose for glycogen replenishment and amino acids for protein synthesis. Most sports drinks address the need for glucose effectively but not the need for protein.
In the Texas study, 12 cyclists and triathletes (8 men and 4 women) performed scientifically quantifiable cycling exercises of 120 minutes’ duration. After the glycogen-depleting exercise, the participants were then replenished according to a crossover design. They (n =6) received two 20-oz bottles of a 6% carbohydrate sports drink after the first bout of exercise and 73 g of 100% whole grain cereal with 350 mL of nonfat milk following the second bout several days later, or vice versa (n = 6). A muscle biopsy was performed immediately after exercise, followed by replenishment with either sports beverage or cereal and another biopsy (1 hour later).
The biopsy specimens were evaluated for glycogen content, critical enzymes required for new protein synthesis in muscle, and the volume of the muscle proteins themselves. In addition, insulin, glucose, and lactate levels were measured by taking blood samples. After ingestion of cereal in nonfat milk, plasma insulin levels were higher (probably as a result of the amino acids in milk) and lactate levels were lower (perhaps because of enhanced muscle uptake of glucose). Although muscle glycogen content increased with both the sports drink and cereal after exercise, phosphorylation of 2 muscle enzymes necessary for protein synthesis-mTOR and protein kinase B-was increased significantly only after the cereal phase of replenishment.
BOTTOM LINE FOR ENDURANCE ATHLETES
The study would have more impact if the sports drink contained a protein as an amino acid precursor in addition to a carbohydrate source. However, many marketed sports drinks contain only carbohydrate.
The bottom line is that it appears recovering muscles require both glucose and protein for optimal function. Cereal in nonfat milk provides both and may give the bona fide as well as the weekend athlete an advantage.
Kammer L, Ding Z, Wang B, et al. Cereal and nonfat milk support muscle recovery following exercise.
J Int Soc Sports Nutr.