By Staff
Training & Conditioning, 13.8, November 2003, http://www.momentummedia.com/articles/tc/tc1308/nutritionroundup.htm
With all the research being done in nutrition, it can be difficult to provide athletes the most up-to-date advice. Therefore, to help facilitate understanding of this constantly evolving subject, Nutrition Roundup will be presented three times a year, devoted to research studies of nutrition, dietary supplements, and athletic performance. References are provided for those who want to obtain more information on specific studies.
Amino Acids & Performance
The first study we’ll look at examined the effects of amino acid supplementation on muscular strength, power, and high-intensity endurance. Seventeen previously trained subjects were randomly assigned to either a placebo or amino acid supplement group. Subjects underwent four weeks of a periodized resistance training program specifically designed to allow the researchers to effectively measure the outcomes of the study.
Subjects in the test group received an amino acid supplement that provided 0.4 grams of amino acids per kilogram of body weight divided into three daily doses. To reduce the confounding factor of energy differences between groups, all subjects were instructed to follow a calculated isocaloric diet throughout the study. However, the researchers noted that subjects in the amino acid supplement group consumed an additional 25 to 55 grams protein per day through the supplement.
There were no significant changes in any of the physiological variables measured, such as weight. But there were some significant performance changes among the experimental group. For example, one-repetition maximum squat and bench press increased significantly during the final three time points of the study. There were also trends towards significance in improvement of other variables. The authors noted that these gains may be attributed to the fact that amino acid supplementation increases protein synthesis, enhances glycogen resynthesis, and reduces muscle damage.
Take home message: While the results of this study demonstrate that supplementing with amino acids may benefit individuals in very specific aspects of training, getting adequate amounts of protein should suffice. Remember, those in the amino acid group consumed an extra 25 to 55 grams of protein per day. If individuals were to consume this additional protein without adding amino acids, more than likely they would receive the same benefit as with a supplement. A study comparing the effects of an amino acid supplement versus those consuming the same amount of extra protein through foods would be interesting.
Study Specs: “The effects of amino acid supplementation on muscular performance during resistance training overreaching” in The Journal of Strength and Conditioning Research, 17(2), 250-258, 2003. By Nicholas A. Ratamess, William J. Kraemer, Jeff S. Volek, Martyn R. Rubin, Ana L. Gomez, Duncan N. French, Matthew J. Sharman, Michael M. McGuigan, Timothy Scheett, Keijo Haakkinen, Robert U. Newton, and Francesco Dioguardi.
Recovery Drinks Go Head to Head
Carbohydrate drinks are often recommended as a way for athletes to replenish glycogen stores. The hope is that athletes will recover quicker and thus perform better at their next practice or competition. However, research is emerging that indicates carbohydrate isn’t the only nutrient necessary during recovery and that protein may be just as important for optimal results.
Researchers compared a carbohydrate-electrolyte beverage to a carbohydrate-protein beverage. It was hypothesized that the addition of protein would enhance the insulin response that occurs with the consumption of carbohydrates, subsequently enhancing the restoration of muscle glycogen, since insulin helps facilitate the storage of glycogen.
The study was broken up into two segments. The first part, which determined the actual outcome of supplementing with the two drinks, will be covered here. The second part examined why this outcome happened.
Eight male cyclists were recruited for this study and after initial testing, were asked to cycle for two hours at 65 to 75 percent VO2max on a cycle ergometer. This protocol was designed with the intention of depleting muscle glycogen. Subjects consumed either 355 mL of the carbohydrate-only beverage or 355 mL of the carbohydrate-protein beverage immediately post-exercise and again two hours later. After the two-hour rest, each subject then completed another exercise bout and their time to fatigue was determined. Time to fatigue was significantly greater when subjects consumed the carbohydrate-protein supplement versus the carbohydrate-only supplement (31.1 minutes and 20.0 minutes, respectively).
While I agree that protein should be added to post-workout recovery food or beverage, the results of this particular study are difficult to interpret because the carbohydrate-protein drink also provided an additional 205 calories and 32 grams of carbohydrate in each 355 mL portion. Considering the subjects ingested this twice before their performance test, those in the carbohydrate-protein group each consumed an additional 64 grams of carbohydrate and 410 calories.
Take home message: Although the design of this study does not fully explain the mechanism, the results support the notion that protein should be added to recovery drinks. Future studies should use isocaloric beverages to examine the mechanisms of the increased glycogen resynthesis.
Study Specs: “Effects of recovery beverages on glycogen restoration and endurance exercise performance” in The Journal of Strength and Conditioning Research, 17(1), 12-19, 2003. By Michael B. Williams, Peter B. Raven, Donovan L. Fogt, and John L. Ivy.
Alcohol & Recovery
The question at hand was to see if acute alcohol consumption, as may occur among athletes, particularly after a game or event, would affect glycogen storage. This is important because glycogen is the primary source of energy during exercise.
The 15 subjects in the 24-hour study (the researchers also conducted a similar, 8-hour study, but only results from the 24-hour study will be presented here) were all trained cyclists. The participants first performed cycling bouts intended to deplete glycogen stores. They were then fed various diets during the 24-hour recovery phase. The different diets were a control diet (which provided 60 percent of energy from carbohydrate), a second diet with 37 percent of energy from carbohydrate and 22 percent from alcohol, and a third diet with 49 percent of energy from carbohydrate and 18 percent from alcohol. Each subject performed the cycling procedure three times, so the researchers could determine the effects of each of the experimental diets. Each diet and exercise bout was separated by one week to reduce potential carryover from the previous experimental bout.
The researchers found that when alcohol was consumed, there was a trend for lower glycogen storage despite equal dietary carbohydrate. While the exact mechanism is unclear, the researchers concluded that alcohol can have an indirect effect on post-exercise glycogen resynthesis, if it displaces carbohydrate consumption.
Take home message: Emphasize the importance of consuming adequate post-exercise nutrients (carbohydrates and some protein) prior to consuming any alcohol, if at all. Alcohol should not be recommended to athletes in general, but on the practical side, athletes don’t always know what’s best for them and sometimes partake in unhealthy activities. Providing scientific evidence that consuming alcohol may negatively affect their performance may sway them from these behaviors.
Study Specs: “Effect of alcohol intake on muscle glycogen storage after prolonged exercise” in Journal of Applied Physiology 95, 983-990, 2003. By Louise M. Burke, Greg R. Collier, Elizabeth M. Broad, Peter G. Davis, David T. Martin, Andrew J. Sanigorski, and Mark Hargreaves.