By Henry Lukaski
Every four years, sports enthusiasts watch the Olympic Games and seek to learn the secrets of the champion performances.
During the Summer Games in 2004, a sports reporter noted that Michael Phelps, winner of six gold medals in swimming, was seen drinking a milk-based beverage between races. This apparent link between Phelps' world-class performances and milk has launched exciting research to determine the benefits of milk, most recently low-fat chocolate milk, as a recovery beverage for serious athletes as well as for people who regularly exercise to promote health.
Strenuous physical training to increase muscular strength, improve running capacity and boost performance depletes the body of water, electrolytes (sodium and potassium) and minerals (magnesium, calcium, zinc) through sweating, uses up stored sugar or glycogen in muscles and breaks down muscle. The ability to replenish these nutrients and rebuild muscle is fundamental to an exerciser's ability to train hard every day and succeed in competition.
Low-fat milk may be a better choice than sports drinks or soy protein beverages for replacing lost fluids after endurance exercise and for helping to repair and rebuild muscles after strength training. A recent study showed that after exhaustive exercise, athletes who drank low-fat milk compared with those who drank water or a commercial sports drink retained substantially more of the fluid consumed during a two-hour recovery period. Thus, low-fat milk promotes retention of fluid after heavy exercise.
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Other studies have shown that low-fat or fat-free milk compared with a soy protein beverage is an ideal choice for muscle repair and muscle gain after strenuous weight lifting. After one session of weight lifting and 12 weeks of training, consumption of milk increased muscle building and the overall gain of muscle more than the other drinks. The reason for the advantage of milk over the other products may be related to the nutritional content of milk and how the nutrients work together to enable recovery after heavy exercise.
Low-fat milk is a nutritional powerhouse. It consists of 90 percent water, so it is a good source to replace fluid lost in sweat. Low-fat milk also contains calcium, phosphorus and vitamin D to build strong bones and B vitamins to produce energy. Sixteen ounces of low-fat milk provide substantial amounts of potassium and sodium, both of which are lost in sweat during exercise. Low-fat milk also is an important source of the key proteins, whey and casein, which contain leucine, an amino acid (building block) needed to make new protein. Whey is absorbed very quickly and coordinates the process of building muscle protein. Casein plays another essential role by slowing the breakdown of muscle after exercise. Sugar content of low-fat milk also is high.
Low-fat chocolate milk offers additional benefits because it has a greater carbohydrate or sugar content than low-fat milk with slightly more fat. The principal carbohydrate in cow's milk is lactose or milk sugar. Low-fat chocolate milk contains carbohydrates and protein in a proportion greater than 3 to 1, which is the optimal level to refuel tired muscles with carbohydrates after heavy exercise.
The presence of protein in milk is vital because it speeds the uptake of sugar into exhausted muscles by directly increasing insulin levels in blood. A recent study found that men who drank low-fat chocolate milk during the two-hour recovery period after one bout of strenuous exercise improved their time to exhaustion by 52 percent in a second consecutive exercise test as compared with some commercial sports drinks.
Compared with other after-exercise recovery beverages, low-fat chocolate milk provides needed nutrients to refill body fluids, replenish muscle energy stores and rebuild and renew tired muscles. It is unknown whether similar benefits will occur in lactose-intolerant individuals who use lactose-free, low-fat chocolate milk because the carbohydrate content of lactose-free milk is reduced by more than 40 percent with a similar amount of protein.
Because low-fat chocolate milk meets the sport supplement guidelines of the National Collegiate Athletic Association for distribution to college athletes, it is becoming increasingly common in the training facilities of major athletic programs.
Each month, scientists at the Grand Forks Human Nutrition Research Center write a column about their work and how their work affects people's lives on a daily basis. This month's column is written by Henry Lukaski, assistant center director and research physiologist. He received his doctorate from Pennsylvania State University. He also is a Fellow of the American College of Sports Medicine.
