© Whole Foods Magazine

February 2008


High-Performance Nutrition for Athletes: The Role of carnitine and GPLC.

An interview with Richard J. Bloomer, Ph.D., C.S.C.S.

by Richard A. Passwater, Ph.D.



We have discussed the importance of the nutrients called carnitines and especially the heart and muscle specific GPLC form in a series of chats with cardiologist Dr. Stephen Sinatra. We mentioned that GPLC was also of great importance to athletes.  This month, I am calling upon Sports Physiologist Dr. Richard Bloomer to elaborate on the use of carnitines in high-performance sports.

L-carnitine is often classified as an amino acid, but it isn’t. L-carnitine can be thought of as a close cousin of amino acids, but technically it is a nitrogen-containing, short-chain carboxylic acid.

Carnitine is a key for the production of energy and nitric oxide (NO) in athletes. Previously, Dr. Sinatra discussed why carnitines are so important to the heart and artery lining. These tissues primarily burn fatty acids for their energy source, not glucose (blood sugar). Without carnitine, fats, which are the high-energy fuel for the heart, muscles and certain other body components including the endothelial cells of artery linings, cannot be converted into ATP. ATP is the energy of life. About 60%-70% of the energy used by the heart comes from the breakdown of fatty acids in the mitochondria. Fat is the fuel for the heart, but a lot of people don’t understand this.

Just as important, carnitine also helps carry away toxic waste products.

Yes, the endothelium is more than just a slippery surface to line the arteries and prevent the blood from clotting at the surface interface. The artery lining has four prime functions: 1. to form a barrier to exclude toxic substances from the artery wall; 2.to release factors into the blood to affect blood platelets—to activate them to tend to clump or not; 3. to sense the blood pressure and flow and help the artery adjust; and 4. to sense arterial injury and initiate repair.  The function of adjusting blood pressure involved the production and release of nitric oxide (NO). The importance of NO to high-performance athletes is just now becoming understood and appreciated. Dr. Bloomer’s research examines this role in the athlete. Dr. Bloomer reports that a nutritional supplement in the form of GPLC can increase blood nitrate/nitrite (NO) in human subjects in our chat.


Passwater: Dr. Bloomer, what drew your interest to sports science and physiology?


Bloomer: I’ve been involved with athletics from an early age and played both organized and unorganized baseball, football and hockey through high school, as well as intramurals in college. I began weight training regularly at around the age of 14. I started training for bodybuilding once I began college and I don’t recall having any layoffs (other than planned one- to two-week periods due to vacations, etc.) since that time. With bodybuilding training of course, comes a highly detailed dietary regimen. I learned all I could regarding both training and nutrition and studied these areas as my major while an undergraduate student. Although I learned a good deal through my formal coursework, I would say that I learned much more from my own independent self study, coupled with my “in the gym” and “in the kitchen” real-world application. I cannot stress enough the importance of self study and practical experience outside of the formal classroom setting…textbooks can only provide so much information.

Following my undergraduate work, I completed my Master’s degree in exercise physiology, with my thesis research focused on the impact of macronutrient ratio and composition on the endocrine response following resistance training. This was my initial involvement with “sports nutrition” from a research perspective. After grad school, I worked at Duke University Medical Center for a few years as a research physiologist, working primarily with patients that had cardiovascular disease, which nutrition certainly plays a role. Following this work, I completed my doctorate in exercise physiology with a research focus on antioxidants and oxidative stress, in particular as they related to exercise. These few years allowed me to focus to a greater extent on my now current line of research: antioxidants and oxidative stress. I spent one year at Wake Forest University before coming to the University of Memphis, where I have been since 2004.

In my present position, I direct the Cardiorespiratory/Metabolic Laboratory, where our research is centered on oxidative stress, the role of antioxidant nutrients to attenuate oxidative stress, and clinical and performance outcomes related to the interaction between the two. On a personal note, I continue to maintain a bodybuilding lifestyle, training four times per week and eating six nutrient-balanced meals daily. This is done year round with few exceptions. I believe that it is important to conduct myself in the manner in which I would recommend to others. Anything less than this would be hypocritical.


Passwater: Why is sports nutrition so important to sports physiology and athletic performance?


Bloomer: Athletes and general fitness enthusiasts alike need to understand the absolute importance of optimal nutrient intake. This includes both whole foods and nutritional supplements. Unfortunately, many individuals (even those who are at elite levels) fail miserably when it comes to understanding the fundamental role that nutrients play in optimal physical performance. In this day and age when the science now supports many of the common recommendations, there is no reason why individuals should not have the required information. This is particularly true considering that several of the top teams may have nutrition advisors on the payroll. There are also several excellent books available to guide an individual through independent study.

That being said, optimal macronutrient intake is likely key, with adequate quantities of carbohydrate, fat and protein consumed in the correct ratios, at the correct times and in the correct amounts throughout the day. In my mind, most athletes should be consuming five to seven nutrient-dense “feedings” per day, every day, with few exceptions. Some of these may come in the form of meal replacement shakes (either commercially available or self made), while most will consist of fresh whole food. Beyond this, micronutrient intake is also very important and sometimes may need to be supplemented in addition to an “adequate” whole food diet. This must be determined through consultation with a qualified sports dietician. Again, several studies have shown the benefits of consuming specific nutrients for the purposes of performance, health and exercise recovery. Interested readers can visit PubMed (www.pubmed.gov) to search for the available studies. The bottom line is that nutrients provide the body with the “fuel” necessary for muscle contraction. Without adequate and appropriate fuel, the body cannot possibly perform at its best.


Passwater: Why did the nutrient carnitine attract your scientific curiosity?


Bloomer: Carnitine is a well-documented antioxidant agent, with other important functions within biological systems (e.g., fatty acid metabolism). Hence, we initially were interested in this aspect of the nutrient. We have been working for the past few years with a novel form of carnitine called propionyl-L-carnitine (PLC). There are multiple studies focused on PLC that document the antioxidant properties of this nutrient. Moreover, other work has indicated significant effects of PLC on vasodilation, leading to decreased symptoms for patients with peripheral vascular disease and coronary artery disease. However, it should be understood by readers that many studies have been conducted in vitro (outside of the body in an artificial environment), using animal models or using humans with known disease. Furthermore, the route of administration in many animal and human studies has been intravenous injection, and the dosages have been high. Hence, individuals need to contemplate these factors when considering whether or not this nutrient will prove beneficial to them (the same applies to all nutritional supplements, by the way).

That being said, we have now completed two human trials using a form of carnitine called glycine propionyl-L-carnitine (GPLC). This molecule is essentially 2/3 PLC and 1/3 glycine (an amino acid precursor to carnitine). We have noted significant effects for blood levels of nitrate/nitrite (a surrogate marker of nitric oxide—a very important signaling molecule in the body that is involved in vasodilation) in both previously sedentary men and women (study 1) and resistance-trained men (study 2). We also have noted potent antioxidant properties of GPLC with regards to decreasing lipid peroxidation in previously sedentary men and women. The findings for nitrate/nitrite agree with animal and human work using PLC, and should be of great interest to both the health and fitness markets. At this point, we are discussing the next step in this line of research.


Passwater: I would bet that most athletes have never heard of carnitine. Briefly, what should they know about carnitine in regards to their health and performance?


Bloomer: Based on our work and the work of others, it is clear that carnitine, in particular GPLC, may be helpful in at least three distinct ways as related to health and performance. However, readers should understand that the effects mentioned below may be specific to certain populations (e.g., those with cardiovascular disease, those who are obese, those who are sedentary) and all effects may not apply to all individuals. So, there appears to be “specificity of effect” for carnitine. This is the same for most nutrients. Of course, the supplement companies don’t like for consumers to know this. That being said, carnitine may provide:

* Antioxidant properties: This may reduce the potentially harmful effects of reactive oxygen species (ROS, sometimes referred to as free radicals). When ROS production overwhelms antioxidant defense, a condition of “oxidative stress” occurs. This can be associated with oxidative modifications to important molecules such as lipids, proteins and DNA. Increased oxidative stress may be associated with impaired performance, although the evidence for this is scarce. Perhaps more importantly, increased oxidative stress is linked to acute illness and most disease states, as well as aging. Therefore, the focus of many has been to decrease oxidative stress. (Note: While this appears to make good sense, readers should understand that some degree of ROS production and a “mild” oxidative stress appears necessary and very beneficial within the body).

* Fatty acid metabolism: Carnitine is essential for the transport of activated fatty acids into the mitochondria matrix to undergo energy production. This is the primary reason why some individuals may feel more “energetic” if using supplemental carnitine, especially if training hard—during which time carnitine concentrations in skeletal muscle may be decreased.

* Vasodilation: Studies have reported improved blood flow with PLC administration. Recently, we have reported increased blood levels of nitrate/nitrite with GPLC. The increase in nitric oxide appears to be one mechanistic link to the improved blood flow, as nitric oxide acts in blood vessel dilation. This is an important initial finding related to GPLC. However, we need to replicate this work in addition to measuring functional parameters that may correlate to the increase in nitric oxide.


Passwater: Are some forms of carnitine better suited for athletes?


Bloomer: Great question. However, few studies have directly compared different forms of carnitine in relation with health and performance parameters. Therefore, it is difficult for me to answer this question. I will say that PLC has been directly compared with L-carnitine related to antioxidant properties, and noted to be superior. Many studies reporting the benefits of carnitine supplementation for the purposes of fatty acid and antioxidant properties have included a variety of types, and I have not seen comparison data. In relation to vasodilation, most work has included PLC as the type of carnitine. As stated previously, we have been using GPLC exclusively in our work.


Passwater: What type of research have you conducted with carnitines?


Bloomer: As mentioned previously, we have now completed two human trials using GPLC. The first study involved sedentary subjects who were assigned to supervised aerobic exercise with or without GPLC treatment for eight weeks. We noted significant increases in resting levels of blood nitrate/nitrite, as well as potent antioxidant properties of GPLC as compared to placebo. We found no significant differences in relation to exercise performance, however. It should be noted that most studies reporting exercise performance benefits with carnitine supplementation have included older, deconditioned and often times diseased adults as test subjects. For these individuals, performance appears to be improved with carnitine supplementation. The same may not appear true for young, otherwise healthy individuals; at least with regards to our findings. Although, a few studies using younger, healthy subjects have noted improved performance with carnitine supplementation. The results are certainly mixed.


To follow up on this research, we decided to determine if GPLC can promote the same increase in blood nitrate/nitrite in well-trained subjects, as in our sample of previously sedentary subjects. This is because sedentary individuals generally experience a much more pronounced effect in relation to several health variables. We wanted to determine if our initial work could be replicated in a sample of exercise-trained subjects. Therefore, in this study we used healthy, young, resistance-trained men. Here, we noted a similar increase in blood nitrate/nitrate in response to isometric forearm exercise (used to stimulate an increase in blood flow). This was an interesting finding that we believe will receive considerable attention in the months ahead. This is especially true considering the incredible hype over “nitric oxide stimulating products.” Despite the craziness of these supplement ads for nitric oxide products, to our knowledge there exist no published reports in scientific format indicating an increase in blood nitric oxide with any of these products. We now have two peer-reviewed manuscripts in which we report that a nutritional supplement in the form of GPLC can increase blood nitrate/nitrite in human subjects. The findings agree with animal and human work using PLC, and should be of great interest to fitness market. At this point, we are discussing the next step in this line of research.

It can be noted that data from our first study with GPLC will be published in early 2008 in The International Journal of Vitamin and Nutrition Research (nitrate/nitrite and antioxidant data) and The International Journal of Sport Nutrition and Exercise Metabolism (exercise performance data). Data from study 2 using GPLC is now published in the Journal of the International Society of Sports Nutrition.


Passwater:  This is an interesting study. I attended one of your lectures discussing your research findings while the article was “in press.” Please help our readers interpret your findings. What is the “take home message” for athletes?


Bloomer: Nitric oxide is a very important signaling molecule in the body that is involved in vasodilation. In other words, it may improve blood flow. For athletes, this is important because greater blood flow is associated with greater oxygen and nutrient delivery to skeletal muscle. This may be important both during the exercise bout (to aid in performance), as well as during the acute recovery period (to aid in nutrient delivery to help facilitate recovery). While this is theoretically true, I must admit that we have not studied these functional outcomes in our previous investigations. Indeed, future work is needed related to these issues.


Passwater: Well, if GPLC is so helpful for athletes, are there health benefits for non-athletes as well?


Bloomer: As stated earlier, we noted similar effects for blood nitrate/nitrite, as well as potent antioxidant properties of GPLC in our first study using previously sedentary subjects. So, yes, GPLC appears to be beneficial for non-athletes. Likewise, most previous reports indicating antioxidant benefits and increased blood flow with PLC have included sedentary subjects exclusively. Therefore, sedentary (often times older) adults may benefit from GPLC supplementation; in particular for the antioxidant properties and potential positive effects related to blood flow. However, as with all dietary supplements, individual response will vary. Some may experience extraordinary benefits while others note little benefit. Experimentation, coupled with approval and supervision by a qualified health care professional is always necessary.


Passwater: Do some forms of carnitines provide more health benefits than others in non-athletes?


Bloomer: Again, head-to-head comparisons are sparse in the scientific literature. That being said, it should be noted that certain forms of carnitine appear better for certain conditions. For example, much of the work related to cardiovascular disease (ischemic heart disease and peripheral artery disease) has involved PLC. In these instances, the dietary supplement GPLC may be appropriate. In relation to cognitive function, memory, mood, etc., much of the work has involved acetyl-L-carnitine. So, there does exist some specificity. Readers are encouraged to review the scientific literature on the subject by visiting PubMed.com. Here they can search and read hundreds of scientific abstracts, as well as some full text articles—free of charge. This can be done without the marketing hype seen on so many websites and in so many magazines.

In addition to the type of carnitine, potential users should always pay attention to the dosage used in the studies. Readers should understand that very often the effective dosage used in the studies is FAR greater than the dosage recommended by the manufacturer. The bottom line is that the cost would be too great for users to actually afford taking the product as provided in the research study. Unfortunately, taking 1/10th of the effective dosage (of any supplement) will likely yield little to no benefit. Therefore, readers should pay very close attention to dosage and always consult with a qualified health care professional before starting a new supplementation protocol.


Passwater: Thank you, Dr. Bloomer, for sharing your research findings with our readers. WF


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