By Christopher Mohr
Christopher Mohr, MS, RD, LDN, is currently a doctoral student majoring in exercise physiology at the University of Pittsburgh. He previously was a Sports Nutritionist for the University of Massachusetts athletic department.
Training & Conditioning, 13.9, December 2003, http://www.momentummedia.com/articles/tc/tc1309/doesitwork.htm
Whether you are an athletic trainer or a strength and conditioning coach, your athletes are no doubt asking you about the latest supplements on the market. The research claims by manufacturers often sound good, but it’s hard to immediately know whether that research has any merit.
It’s important that those of us advising athletes follow the latest developments in the field. If we shrug our shoulders when asked about a supplement, that may be translated into a “sure, why not” by the athlete. And if we aren’t a good source of knowledge on this topic, athletes may ask those less informed about health and safety for advice.
Granted, it’s not easy to keep up with the latest research in this area—it’s even tough for us nutritionists! That’s why, when the Sports, Cardiovascular, and Wellness Nutritionists (SCAN), a practice group of the American Dietetic Association, put on a symposium in late October, with leaders in the field presenting, I was there. Three of the workshops given related to competitive athletes, and the most important points from these are summarized below.
A common question asked by athletes is, “What is the ideal meal to eat prior to a game or competition?” Ed Coyle, PhD, Professor in the Department of Kinesiology and Health Education at the University of Texas has done extensive research in the area of carbohydrate metabolism and fuel usage during exercise. In his presentation, he updated us on the latest research and recommendations.
To provide some background, Coyle started by covering some basic, but important, information. Glycogen is the form carbohydrates take when stored in our bodies. It is stored in two organs: skeletal muscles and the liver. There are approximately 1,000 to 3,000 kcals of stored glycogen in muscle and 200 to 400 in the liver. Glycogen is broken down into glucose and becomes the primary fuel source used by the body.
Glycogen can fuel our bodies during activity for approximately four hours. After glycogen is used up, our bodies tap into free fatty acid stores for energy. Muscle has about 2,000 to 3,000 kcals of intramuscular triglyceride (IMTG). There are also another 50,000 to 100,000 kcals of stored triglyceride in the body, which is essentially an unlimited supply of energy. Fatty acids are more difficult for the body to break down and utilize for energy, but are still used during exercise. (Protein is used only as a last resort.)
The above covers the basics, but what researchers have been trying to uncover more recently is exactly why and how one fuel source is used over another. Although carbohydrate is used most during exercise, there is never a time that only one fuel source is used. By better understanding how fuel sources are used, the idea is that we can give athletes better advice on what constitutes optimal pregame nutritional intake.
According to Coyle, research still backs up what we’ve been telling our athletes for over a decade: Optimizing glycogen storage is paramount for peak performance. Carbohydrate intake causes an increase in the hormone insulin, which allows the body to take up more glucose and less fat. Therefore, eating a meal that is comprised primarily of carbohydrate to make the glucose more readily available for the working muscles is ideal.
This meal should provide just a moderate amount of protein and be low in fat. While fat itself can be utilized during exercise, Coyle stated that it takes approximately four hours after consumption for fat to be available to the muscles as free fatty acids.
Pregame, it is also best to eat more easily digested foods, such as fruit, rather than non-refined foods such as beans, oatmeal, and whole-grain products. It is also recommended that the stomach be fairly empty during competition so blood can be shuttled to the working muscles instead of being needed in the stomach for digestion to occur.
The best time to figure out what foods work for individuals is prior to practices, not prior to the game itself. Aside from fruit, other foods that work well for many athletes are yogurt, sports bars, the new yogurt drinks, or milk (chocolate milk provides more carbohydrates so it may be useful). But experimenting on the day of a big competition is not the best idea. Athletes should use the guidelines outlined above and then some trial and error.
However, focusing on the pregame meal alone is not sufficient. Optimizing glycogen stores can’t be accomplished immediately prior to competing, and it should be taken care of throughout the days leading up to competition. It takes approximately 20 hours to fill glycogen stores, without interruption from another practice or event, so in addition to the pregame meal, food choices in the days prior to competition are crucial. Again, they should consist of mainly carbohydrates with some fat and protein.
Off the topic of pregame meals, Coyle also discussed the hot topic of tinkering with macronutrient combinations to enhance performance. There is a lot of talk, and some recent research, about the effect of high-fat diets on performance. Increasing fat intake does in fact spare glycogen usage. While this may seem like a good thing, the only effect high-fat diets actually seem to have on performance is that they change the fuel mixture used during activity. Increasing fat doesn’t appear to positively or negatively affect performance.
Key points from this lecture:
• Carbohydrates are the primary fuel source during exercise.
• The pre-competition meal should focus mainly on easily digested carbohydrates and be low in fat.
• High-fat, low-carbohydrate diets do not enhance performance.
• The meals leading up to competition will do more for performance than one single pregame meal.
Today’s athletes often look to the shelves of their local GNC for a competitive edge. Unfortunately, the research does not happen as fast as manufacturers issue new claims, so we need to stay on the forefront in giving our athletes the most up-to-date advice. In the next seminar, Douglas Kalman, MS, RD, FACN, the Director of Nutrition at Miami Research Asso-ciates, discussed a variety of popular dietary supplements on the market.
Creatine: Consumers in the U.S. currently spend more than $200 million on creatine per year. Creatine is produced endogenously and stored in the muscles as phosphocreatine. During the early stages of high-intensity activity, phosphocreatine is dephosphorylated (loses a phosphate) and donates this phosphate to adenosine diphosphate to produce adenosine triphosphate (ATP, the energy currency of the body). Therefore, it is thought that increasing the intramuscular stores of phosphocreatine, via exogenous supplementation, will allow the body to continue this cycle and increase the available ATP.
Creatine is one of the most widely researched dietary supplements, and studies have shown its consumption to benefit approximately 75 percent of the users. Benefits to athletes include getting stronger, recovering more quickly, and potentially decreasing sprint times. Kalman quickly reviewed many of the activities creatine has been tested in, and offered the following synopsis:
• Creatine has been shown to be effective in short-duration, high-intensity sports (weight lifting, sprinting, etc.).
• Creatine has shown no positive effect on endurance.
• Creatine has shown no positive effect on swimming performance.
It also appears that creatine is safe. While there are many reports of increased rates of cramping, dehydration, and strains/pulls, these anecdotal claims have not been duplicated in research settings.
One side effect of creatine is weight gain, which is often what people hope to accomplish via supplementation. At this time, it is unclear whether this weight gain is solely from increased water retention or increased protein synthesis within muscle.
Glutamine: Next up was glutamine, an amino acid that constitutes about 60 percent, and sometimes more, of the intramuscular amino acid pool. Glutamine is used often in patients with muscle wasting diseases, such as HIV and cancer. As little as two grams of glutamine per day has been shown to improve nitrogen retention, a marker of muscle breakdown, in muscle wasting diseases.
Because of the research in diseased patients, companies promote this dietary supplement as an anti-catabolic agent, meaning it will prevent, or at least reduce, muscle breakdown. However, like many other dietary supplements introduced with a lot of promise, glutamine has not panned out with athletes. The few studies that have been conducted on glutamine use with athletes have shown no effect on muscle recovery.
HMB: Beta-hydroxy beta-methylbutyrate, better known as HMB, has been shown to improve nitrogen balance in lab rats, indicating it may more quickly reverse muscle damage. Similarly, supplementing horses with HMB has been shown to improve their performance.
However, horses and rats don’t have the same exact metabolic mechanisms as humans, and the few small studies of HMB conducted on humans have shown no benefits. The two studies Kalman discussed were six days and eight weeks long, respectively. In both, when individuals were supplemented with HMB, there was no positive (or negative) effect on muscle damage.
Protein: Although there are several different protein supplements on the market, Kalman concentrated specifically on amino acid (AA) supplementation. Amino acids are the building blocks of protein. There are 20 different amino acids, and nine of them are essential, meaning they cannot be produced by the body. Some of the most recent studies suggest that supplementing the body with essential amino acids can help muscles recover more quickly.
It is understood that weight lifting is a critical part of most athletes’ training, but weight lifting itself is really a double-edged sword. It is necessary to gain muscle strength and size, but the act of weight lifting actually promotes muscle breakdown, making it necessary to consume adequate calories, including protein, to provide muscles with the necessary nutrients to recover and grow. With this basic physiology in mind, researchers have begun to assess whether providing essential AA before, during, and after a workout would help restore muscles more quickly.
Previous studies have shown that consuming protein in a one-to-three or one-to-four ratio to carbohydrate im-mediately after a workout is beneficial. In this seminar, Kalman updated us on research conducted on supplementation prior to and during the workout.
Several recent studies on humans have demonstrated that approximately six grams of the essential amino acids taken before and during the workout help enhance protein utilization. This small amount of AA provides the body with the necessary fuel to enhance muscle protein synthesis and decrease the breakdown of muscles.
Researchers are still determining the proper dose, and some claim that the actual dose should be six grams AA for every 70 kg of body weight (approximately 150 lbs). Research is underway to determine if in fact AA intake is dose dependent.
While the focus of these studies was on taking a supplement, consuming food with similar amounts of protein should have the same positive effect. Taking in approximately 10 grams of a complete protein provides approximately six grams of essential amino acids so, theoretically, this should be just as effective. Ideally, the food should also have some carbohydrate in it, for the reasons mentioned in Coyle’s seminar. One cup of low-fat or fat-free chocolate milk before, during and after exercise may go a long way in preventing or slowing muscle breakdown and enhancing recovery.
Green Tea: Researchers have long known about the antioxidant properties of green tea. Recently, some have begun to measure its role in weight loss as well, and athletes looking to lose weight have become interested in its effects.
Green tea is high in certain compounds called catechins. The specific catechin of interest is known as epigallocatechin (EGCG), which is found in very high doses in green tea. A few studies, mainly in rats, have shown high doses of this compound may inhibit the enzyme lipase, which is necessary in fat metabolism. This, in turn, may reduce fat digestion.
Research in humans is in its infancy and studies that have been conducted have not shown EGCG to have a positive effect on weight loss itself. One study did demonstrate that those taking EGCG increased their resting metabolic rate by four percent, but this did not correlate to any significant changes in bodyweight and body fat.
More research is definitely needed in this area, as it does show some promise. However, it’s too early to recommend EGCG as a weight loss supplement. Companies have begun to include EGCG in their products, but there is not enough research at this time to support its inclusion.
Ever since home run slugger Mark McGuire admitted he used androstenedione (andro), the interest in prohormones, also called prosteroids, has increased. Andro was one of the first supplements of its kind in this category, and after andro proved to be ineffective and have some negative side effects, supplement makers began producing other prohormones.
Although these types of supplements are banned by the NCAA and many professional sports leagues, athletes may still be interested in them. Whether banned in your level of play or not, understanding the mechanisms, science, and safety behind these products is warranted.
In this seminar, Tim Ziegenfuss, PhD, CSCS, Chief Scientific Officer for Phoenix Laboratories, discussed his research in this category of supplements. The basic premise is that supplementing with prohormones will increase testosterone levels, subsequently increasing lean body mass.
Ziegenfuss first discussed the difficulty in measuring hormone levels in subjects because of the inter- and intra-subject variability with regard to hormone levels. For example, the time of day, previous exercise, sleep patterns, and meals all affect these levels. Therefore, careful consideration must be taken when attempting to assess and scientifically measure hormone levels.
With that said, some of the newer prohormones do in fact show promise in transiently increasing testosterone levels. But the most important consideration is still whether this transient increase correlates to lean body mass gains or any positive effects. This research has not yet been performed.
The bad news here is in the supplements’ side effects. Studies have revealed several negative side effects, such as decreases in HDL (the good cholesterol), increased estrogen levels, and potential increases in fatty tissue. It’s best to urge athletes to leave these products on the store shelves, no matter how promising they sound.
There are a myriad of dietary supplements available. In fact, there are more than 29,000 products available to date. With this in mind, it’s always best to educate athletes so that they can make informed decisions as to what they are considering putting into their bodies. This works better than solely trying to steer them away from all products.