Research Roundup

No time to read a year’s worth of studies on nutrition? No problem. Let our expert give you a rundown on some of the most pertinent studies to come out in the last year for competitive athletes.

By Christopher Mohr

Christopher Mohr, MS, RD, LDN, is a Graduate Research Assistant in the Physical Activity & Weight Management Research Center at the University of Pittsburgh. He previously was the Sports Nutritionist for the University of Massachusetts athletic department.

Training & Conditioning, 13.4, May/June 2003, http://www.momentummedia.com/articles/tc/tc1304/research.htm

All too often, athletes receive their nutrition information from unreliable sources. Whether it’s an advertisement from a supplement company or misinformed friends, the amount of unproven information on nutrition for athletes far exceeds the amount of good scientific research on the topic.

This is especially true when it comes to nutritional supplements. For athletic trainers and strength and conditioning coaches, it can be difficult to give athletes the right direction when the research on supplements is all very new. But some good research has been done.

In this article, I’d like to highlight the results from some of the most pertinent studies on nutrition and dietary supplements published over the past year. The studies below were chosen specifically to answer the questions athletes are currently asking about nutrition and enhancing performance. All references are provided to allow those who are interested in obtaining more information to follow up to this article.

Post-Workout Nutrition
In the past few years, sports nutritionists have been concentrating a lot on figuring out what makes the best post-workout snack or meal to help muscles regenerate. Most recommend that athletes ingest a combination of carbohydrates and protein, and a recent study backs up this advice.

The goal of this investigation was to determine the individual and combined effects of amino acids (AA), the building blocks of protein, and carbohydrate (CHO) on muscle protein synthesis. Subjects completed a 40-minute resistance training bout. One hour post-exercise, subjects ingested a CHO-only drink (0.5g CHO/kg bodyweight), a CHO-AA drink (0.5g CHO + 0.087 g/kg AA), or an AA-only drink (0.087g/kg AA). For a 150-pound individual, this is the equivalent of approximately 35g of CHO and 6 g of AA.

It was found that CHO alone positively affected moderate anabolism, but did not affect muscle protein synthesis, which should be a goal of post-recovery nutrition. When the AA was taken alone there was an increase in protein synthesis. However, when the AAs were combined with CHO, there was an interactive effect between the two nutrients. In simple terms, when taken together, the insulin from the CHO facilitated the action of the AA to cause a greater muscle protein response and thus better recovery.

Take-home message: Carbohydrates and protein, together, are ideal for optimizing recovery, which will ultimately lead to enhanced performance. Some suggestions? Fat-free chocolate milk makes a wonderful post-exercise recovery drink, as it contains approximately 35g of CHO and approximately 10g of protein. (The exact serving size needs to be determined on an individual basis according to the athlete’s bodyweight.) If solid food is an option, anything that contains about 3/4 carbohydrate and 1/4 protein is good, such as lowfat yogurt. Some supplements include Go energy drink, Gatorade’s Nutrition Shake, Endurox R4, Hormel’s Great Shake, Distance from GNC, and Performance Bars from PowerBar.

Study Specs: “Independent and combined effects of amino acids and glucose after resistance exercise” in Medicine & Science in Sports & Exercise, 35(3), 449-455, 2003. By Sharon L. Miller, Kevin D. Tipton, David L. Chinkes, Steven E. Wolf, and Robert R. Wolfe.

Creatine Corner
To date, there are over 700 research studies that have been conducted on creatine. However, confusion, misinformation, and rumors about creatine still abound.

Scientific and anecdotal evidence has demonstrated creatine supplementation is beneficial for making gains during short-duration, high-intensity exercise such as weightlifting and sprinting in most individuals. It has also been shown to produce weight gain in those who use it.

A 2002 study wanted to look more closely at why weight gain occurs with creatine supplementation. Specifically, it wanted to see if using creatine results in more carbohydrates or more fat being “burned” for energy.

The trial, which lasted 12 weeks and was double-blind, looked at substrate oxidation in individuals (i.e., what food the body is metabolizing: carbohydrates, proteins, or fats). The method researchers use to determine substrate utilization is the measurement of the respiratory exchange ratio (RER). Values typically range from 0.70 to 1.00. The higher the value, the more carbohydrates are being metabolized. A lower value means fat is the primary fuel.

All 10 subjects participated in a pre-determined strength-training program throughout the study. In addition, the same meals were consumed 12 hours prior to RER testing to reduce potential confounders, and no other food was consumed until post-measurement.

The researchers found that carbohydrate oxidation increased during creatine supplementation (there was a trend for an increase in RER), and thus fat metabolism decreased. In addition, while fat mass did not change with creatine supplementation, it did decrease significantly in those taking the placebo.

The important take-home message from these results is that individuals who supplement with creatine may decrease their ability to lose fat after exercise training, potentially due to the RER increase. According to the results from this study only, those attempting to reduce body fat may want to steer away from supplementing with creatine as it may work against them in that regard. (However, as this was the first study of its kind, more research is clearly necessary.)

The strength gains that often accompany creatine supplementation may be beneficial for many athletes, but the subsequent weight gain may not. Especially for those athletes in weight-sensitive sports (wrestlers, lightweight rowers, gymnasts) creatine supplementation may be detrimental. Therefore, it is paramount that athletic trainers educate athletes and coaches on this potential side effect of creatine.

Study Specs: “Creatine supplementation influences substrate utilization at rest” in the Journal of Applied Physiology, 93, 2018-2022, 2002. By M. Erik Huso, Jeffrey S. Hampl, Carol S. Johnston.

Another concern with creatine is whether excess supplementation may put undue stress on both the liver and kidneys. Several small studies in the past have shown that creatine does not harm these vital organs, and this more recent one had similar results.

In a retrospective study of athletes’ self-reported previous (and voluntary) creatine use, it was determined that the 23 volunteers from an NCAA Division II college football team supplemented with an average of 13.9 grams a day. Several analyses were utilized to determine the effects on current kidney and liver function. It was determined that there were no significant differences between kidney or liver function in creatine- and non-creatine-supplemented groups.

We can thus infer that creatine use does not result in any detrimental acute or cumulative effects on liver or kidney function when supplementing for this length of time (average of 2.9 years) and with this amount of creatine (average 13.9g/day).

Study Specs: “Effects of long-term creatine supplementation on liver and kidney functions in American college football players” in International Journal of Sport Nutrition and Exercise Metabolism, 12(4), 453-458, 2002. By David L. Mayhem, Jerry L. Mayhem, and John S. Ware.

Exercise & Fat Loss
Many nutritionists tell athletes that cardiovascular exercise is better for weight loss than resistance training. However, much of the advice is based on anecdotal evidence rather than actual research. Therefore, the primary aim of a study by Edward Melanson, et al., was to compare the effects of aerobic vs. anaerobic training on energy expenditure (EE) and substrate oxidation.

This study measured energy expenditure in 10 non-obese male subjects on four separate occasions using different exercise protocols. Aerobic training was done on an exercise bike while circuit training was used for anaerobic exercise. Subjects expended similar amounts of energy for both types of exercise with no significant differences between exercise conditions.

The results? There were no differences in fat oxidation over 24 hours, but there was an increase in the amount of carbohydrates oxidized during aerobic exercise.

The take-home message from this study: If an athlete’s goal is weight loss, aerobic exercise should be the cornerstone of his or her regimen. This is bad news for the football player attempting to lose weight during preseason workouts, but good news for the long-distance track athlete. Therefore, athletes whose workouts are primarily anaerobic in nature may want to concentrate any weight-loss efforts in the off-season, when it may be more acceptable to incorporate a significant amount of aerobic activities.

Study Specs: “Resistance and aerobic exercise have similar effects on 24-h nutrient oxidation” in Medicine & Science in Sports & Exercise, 34(11), 1793-1800, 2002. By Edward L. Melanson, Teresa A. Sharp, Helen M. Seagle, William T. Donahoo, Gary K. Grunwald, John C. Peters, Jere T. Hamilton, and James O. Hill.

From Ribose to Bovine Colostrum
Providing advice to athletes about nutritional supplements that are very new on the market is sometimes our toughest task. Today’s athletes are eager to try anything that might give them an edge, and simply saying, “There’s not enough research” doesn’t usually satisfy their questions. The next three studies will give you an update on today’s hottest supplements.

Ribose was introduced to the dietary supplement market several years ago with claims of increasing energy and enhancing athletic performance. Its utility in clinical populations has shown promise, but currently there is only a tiny amount of research on ribose among a healthy, athletic population. The problem is, healthy athletes are using ribose based on extrapolated research results from clinical populations, which is like putting bicycle tires on a car with the assumption that a wheel is a wheel.

Earlier this year, a study was published that did use a healthy, athletic population of young men as its subjects in order to examine whether oral ribose supplementation could improve anaerobic performance or recovery. After familiarization with the exercise protocol, eight subjects performed two bouts of repeated cycle sprint performance. After the second bout, subjects received either 32g of ribose or a placebo over a 36-hour period. The authors noted that the typical recommended dose is 3g/day, but had used the 32 grams (8 grams in four doses) due to previous pilot data from their laboratory.

Ribose supplementation did not result in statistically significant increases in mean or peak power (which were the outcome parameters utilized in this protocol). They failed to show any significant benefit with 32g over a 36-hour period and thus concluded that the 3g/day would not produce results either.

The practical application of this study is that ribose supplementation does not appear to be effective for performance enhancement in a healthy, athletic population. Moreover, oral ribose supplements are extremely expensive (approximately $60 for a one-month supply of 3g/day), which adds up to a lot of wasted dollars.

Study Specs: “Effects of ribose supplementation on repeated sprint performance in men” in the Journal of Strength and Conditioning, 17(1), 47-52, 2003. By John M. Berardi and Tim N. Ziegenfuss.

HMB (beta-hydroxy beta-methylbutyrate) supplementation is purported to enhance lean-body mass gains during resistance training and stimulate fat oxidation. Therefore, researchers recently conducted a study designed to measure the effects of HMB on muscular strength and body composition.

The subjects in this study were 35 NCAA Division I collegiate football players with at least four years of strength-training experience. The study was double-blind placebo controlled. One group of athletes was supplemented with 3g of HMB (manufacturer-recommended dose) for four weeks, followed by a washout week with no supplement, and then four weeks of taking a placebo. The second group followed the opposite pattern of intake. The nine-week exercise program consisted of workouts four to five days a week for approximately 20 hours/week, under the supervision of a strength coach.

The authors of this study found no significant differences for muscular strength (measured by bench press, power cleans, and squats). Nor did they find any differences for body composition, body fat, or weight.

Some research has suggested HMB may be beneficial in an untrained population initiating an exercise program. However, the take-home message with this study is that HMB supplementation doesn’t seem to be beneficial for enhancing muscular strength, decreasing body fat, or positively altering body composition in a previously trained athletic population.

Study Specs: “The effect of beta-hydroxy beta-methylbutyrate on muscular strength and body composition in collegiate football players” in the Journal of Strength and Conditioning, 17(1), 34-39, 2003. By Jack Ransone, Kerri Neighbors, Robert Lefavi, and Joseph Chromiak.

Bovine colostrum is the first milk secretion (often known as “pre-milk”) from the mammary glands of a cow after she gives birth. The concentrations of protein, immunoglobulins, insulin-like growth factors, and many vitamins and minerals are higher in colostrum than they are in normal milk. Animal studies using colostrum have demonstrated an increase in protein synthesis, which may correlate to increases in lean body mass and, subsequently, enhanced performance.

To investigate this hypothesis, 35 elite male and female field hockey players participated in an eight-week study to determine the effects of 60g/day of bovine colostrum supplementation, compared to 60g/day of whey protein, on body composition (skinfold measurement) and exercise performance. The exercise tests included a 50-meter sprint, suicide (subject had to run as fast as possible between six markers with a total distance of 300m), a shuttle run, and a vertical jump.

After the eight-week protocol, which occurred during the first half of the athletes’ competitive season, there was a significant improvement for both groups in the sprint test (reduction in sprint time from baseline to week eight), with a significant difference between the two groups as well. The subjects in the colostrum-supplemented group decreased their sprint time -0.64 seconds ±0.09 seconds. In the whey group, subjects improved -0.33 seconds ±0.09 seconds. This is considered significant. There were no significant changes in any other aforementioned exercise tests.

Lean body mass significantly improved in both groups, with no differences between groups. This is not surprising, since both supplements provided just under 400kcal of additional energy to their normal diets, which could correlate to an increase in lean body mass.

The take-home message here is that bovine colostrum may be beneficial for increasing straight-ahead speed, but the results from this study alone do not warrant supplementing with bovine colostrum, especially since it comes with an extremely hefty price tag (approximately $12/day for 60g dose). In addition, some vegetarians might be hesitant to use this supplement.

Study Specs: “The effect of bovine colostrum supplementation on exercise performance in elite field hockey players” in International Journal of Sport Nutrition and Exercise Metabolism, 12(4), 461-469, 2002. By Zandrie Hofman, Rolf Smeets, George Verlaan, Richard van der Lugt, and Peter A. Verstappen.

Conclusion
In the year 2000, sales of dietary supplements reached 16.8 billion dollars. It is impossible for research to keep up with the plethora of products available, and unfortunately, the untested claims of these supplements are persuasive.

In response, it’s important that coaches and athletic trainers stay updated so they can give athletes the latest scientifically sound advice and so that athletes see them as knowledgable on the subject. This is the best way to steer our young athletes to the products that show promise and steer them away from the ineffective or dangerous ones.