Protein and Amino Acids, 1999
Pp. 331-340. Washington, D.C.
National Academy Press
Dietary Supplements Aimed at Enhancing Performance: Efficacy and Safety Considerations
Timothy J. Maher1
Consumers have used amino acids as dietary supplements for many years in the hope of producing a wide variety of effects, including enhanced physical performance, improved quality of sleep, analgesic relief, and accelerated muscle mass development. Despite continued evidence of the potential for adverse effects associated with imbalances in amino acid ingestion (Benevenga and Steele, 1984), this practice of consuming supranutritional doses (that is, amounts in excess of those believed required to support normal growth and sustain health) of amino acids continues to a significant extent due to the highly effective advertising in the lay literature and press. Although 7 years have passed since the initial outbreak of the L-tryptophan-associated eosinophilia-myalgia syndrome (EMS), little progress has been made in determining the exact cause of this disease (Hertzman et al., 1990; Kamb et al., 1992). The
major research emphasis continues to be placed on one contaminant, the so-called Peak E (1,1'-ethylene-bis[tryptophan]), which has been routinely identified in implicated lots of manufactured trytophan. Interestingly, recent studies have identified a plethora of potentially active compounds including other indole derivatives (e.g., dioxindoylalanine), phenyl derivatives (e.g., anthranilic acid), and 1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid derivatives, some of the latter of which are known to act as benzodiazepine inverse agonists (Simat et al., 1996). Attempts to reproduce in experimental animals the symptomatology associated with EMS in humans have generally failed, and thus, understanding of the mechanisms responsible for EMS associated with contaminated tryptophan products remains elusive.
SAFETY OF AMINO ACIDS AS DIETARY SUPPLEMENTS: THE FASEB/LSRO STUDY
Following the tragic EMS epidemic that resulted from the use of L-tryptophan, the U.S. Food and Drug Administration (FDA) contracted with the Life Sciences Research Office (LSRO) of the Federation of the American Societies for Experimental Biology (FASEB) to perform an extensive review of the extant scientific literature to determine the safety of amine acids used by consumers as dietary supplements (Food and Drug Administration, 1990; FDA Contract No. 223-88-2124, Task Order No. 8). Not only was tryptophan use assessed for safety, but all amine acids identified as being available to consumers were evaluated since prolonged daily ingestion of supranutritional quantities of these compounds as dietary supplements was known to be commonplace.
LSRO initiated their study in the fall of 1990 by first searching the extant scientific literature for reports that related to safety of amine acids. This was followed by an open meeting, in which interested parties presented information and views related to this issue. Additionally, an invitation was extended to the public to submit written materials for consideration (FDA Docket No. 90N-0379). An ad hoc expert panel consisting of nine scientists met subsequently to advise LSRO and prepare a final report. The report, made available in 1992 (FASEB/LSRO, 1992), also contained suggested guidelines for future safety testing (Anderson and Raiten, 1992).
Because consumers primarily used supplemental amine acids presumably to enhance physiological functions or produce pharmacological responses, rather than to affect any nutritional function, a significant dilemma was faced by the expert panel. No credible evidence was available in the scientific literature indicating that a normal, healthy individual would benefit nutritionally in any way from supplementation of the diet with any single amine acid. Furthermore, even in those individuals with a less-than-ideal diet, the practice of supplementing with single amine acids was considered potentially dangerous, since the literature was replete with studies demonstrating ''antinutritional"
effects (i.e., depressed growth and other adverse effects) associated with the intake of imbalanced amino acid diets (Benevenga and Steele, 1984).
A survey of products in the marketplace revealed a wide diversity of label information that generally failed to provide adequate information regarding chemical composition, isomeric identification, purity, shelf life and contraindications to use. While some labels of products containing L-phenylalanine warned patients with phenylketonuria, others failed to do so despite the documented potential for adverse effects associated with the ingestion of this amino acid in subjects with this inherited metabolic abnormality (Matalon et al., 1991). Labeling and advertising carefully avoided legal "drug claim" language, while effectively suggesting that these products provided pharmacological rather than nutritional benefit. The use of D-amino acids as dietary supplements was viewed as an especially dangerous practice since these enantiomers have typically been demonstrated not to provide nutritional support for humans. In fact, in many cases, they are potentially toxic (Friedman, 1991). Concern was also expressed regarding the potential for interaction with numerous over-the-counter and prescription drugs, as there are many documented interactions in the literature (e.g., antidepressants, monoamine oxidase inhibitors, opioid analgesics, and sympathomimetics) (Glassman and Platman, 1969; Hull and Maher, 1990; Hull et al., 1994).
The expert panel concluded, based on the scientific evidence available, that the only safe form of amino acid ingestion was via protein in the diet and that there was no evidence to support a safe upper level of any individual amino acid intake in the form of a dietary supplement beyond that found in typical protein foods. Additionally, as a result of the lack of available information bearing on the safety of any of the amino acids used as dietary supplements, it was concluded that a systematic approach to safety testing was required prior to the rational use of such compounds by the general public. Safety testing, which would involve both animal and human studies, would be comprehensive and utilize sophisticated techniques. The effects of both acute and chronic ingestion of amino acids on weight changes, food intake, neurologic and behavioral changes, liver function, routine blood chemistry and hematologic parameters, hormonal changes, and pharmacokinetic profiles following oral administration of the amino acid with and without food in both genders would be determined. Following extensive studies in animals, acute and chronic testing in humans would be required to satisfy additional safety concerns. Growth, neurological and behavioral function, hematologic parameters, pharmacokinetic profiles, and hormonal changes would be monitored following subject's exposure to various doses of the selected amino acids. Careful selection of experimental subjects for these studies was emphasized with specific guidelines set forth.
Despite the findings in the FASEB/LSRO report (1992) the U.S. Congress passed the Dietary Supplement Health and Education Act (DSHEA), which was subsequently signed into law on October 25, 1994. The DSHEA significantly reduced the barriers to the sale of dietary supplements to the general public. On
a promising note, the FDA recently has begun to consider proposed guidelines for the manufacture of dietary supplements. The proposed rule, "Current Good Manufacturing Practice (CGMP) in Manufacturing, Packing, or Holding Dietary Supplements", is currently open for public comment (Food and Drug Administration, 1997). The development of CGMP is critical to ensure some governmental control over the quality of products now more easily available to the general public.
STUDIES ON PERFORMANCE WITH SELECTED AMINO ACIDS AND PROTEIN
Individual amine acids have been administered in supranutritional doses in a variety of studies where effects on performance have been determined. Some of these studies have documented adverse effects with such pharmacological doses, while others failed to document any adverse effects. The difficulty with making decisions regarding the safety of such amine acids from these negative studies may result from the study design, as many of the studies were not carefully designed to detect and monitor adverse effects (Anderson and Raiten, 1992; Bucci, 1989). Similarly, some studies have investigated the effects of enhanced protein intake on physical performance. As reviewed by Hickson and Wolinsky (1989), there is no current consensus on the efficacy of such dietary protein interventions. Carefully designed studies with individual amine acids and protein supplementation should be pursued by the military in their quest to optimize performance. However, careful attention must be paid to the monitoring of adverse effects, realizing that some of these may be subtle or delayed in nature. Although there may be benefits to gain from such dietary approaches, the risks involved must be minimized for the military subjects involved.
ALTERNATIVE PROTEIN SOURCES
While most studies in the past involving manipulations of protein in the diet have utilized very high-quality protein from animal sources, increasing evidence supports the potential benefits from incorporating proteins of vegetable origin. The protein obtained from soybeans (Glycine max) can provide a high- to intermediate-quality protein as determined by growth pattern and nitrogen balance studies (Young, 1991). The use of highly processed soybean protein isolates and concentrates as part of the diet can provide all, or a portion of, the daily protein requirements in an increasingly palatable form. Additionally, differences between countries in the incidence of many diseases including heart disease, hormone-dependent cancers, and osteoporosis have been epidemiologically associated with the degree of dietary soybean protein consumption (Knight and Eden, 1996). For example, Japanese women have approximately one-sixth
the incidence of breast cancer compared with their Western counterparts. Similarly, the incidence of premenstrual symptoms and menopausal complaints is significantly lower in populations where soybeans comprise a significant portion of the daily protein intake.
Contained within raw soybeans, and carried through intact in the processing of protein concentrates/isolates and flours, are a group of compounds chemically classified as isoflavones (Wang and Murphy, 1994). Among the isoflavones are the phytoestrogenic glucosides, genestein and daidzein, along with their corresponding aglycones, genestein and daidzein, respectively. These weakly estrogenic compounds are approximately .001 to .0001 as potent as estradiol. However, in a typical Eastern soy-based diet, the levels of circulating genestein and daidzein are approximately 1,000 to 10,000 times higher than usual estradiol levels. Thus, as supported by many recent studies, the dietary consumption of such phytoestrogens could favorably influence the incidence of estrogenic-mediated processes. More recently, reports have demonstrated the association between estrogen replacement therapy and the decreased incidence of certain dementias. Much more research is needed to explore fully the utility of soybean and alternate protein sources on the performance and overall health of subjects in the general public, as well as in the military.
DIETARY SUPPLEMENTS AND PREMENSTRUAL SYNDROME
Numerous studies have demonstrated the ability of serotoninergic agonists to affect somatic, appetitive, behavioral, and cognitive changes that recur monthly in many women during the late luteal phase of the menstrual cycle (Brzezinski et al., 1990; Wood et al., 1992). Although administration of L-tryptophan, the precursor of serotonin, has been shown to increase serotonin in the brain of experimental animals and affect numerous serotonergic-mediated behaviors, this amino acid is no longer available for unrestricted use due to the above described association with the EMS epidemic. However, another approach to increasing central serotonergic function without the exogenous administration of the individual amino acid precursor involves the consumption of carbohydrate which, by virtue of its ability to increase insulin release, enhances the uptake from the circulation of large neutral amino acids (LNAA) that compete with L-tryptophan for transport into the brain (Fernstrom and Wurtman, 1972). Studies have demonstrated that carbohydrate ingestion enhances the synthesis of serotonin in the brain of experimental animals and alters serotonin-mediated behaviors. Similarly, studies in humans have also demonstrated that various carbohydrate meals enhance the serum tryptophan: LNAA ratio (a predictor of tryptophan entry into the brain) and affect behavior (Lieberman et al., 1986b; Maher et al., 1984).
This approach was recently used in a study to determine the influence of a dietary supplement to alter premenstrual symptoms in women (Sayegh et al., 1995). Three isocaloric beverages were formulated and administered in a
double-blind crossover fashion to 24 women confirmed to suffer from premenstrual symptoms. One beverage containing 47.5 g of a mixture of dextrose and maltodextrin led to a 29 percent increase in the serum tryptophan:LNAA ratio and significantly decreased (as determined by an abbreviated Profile of Mood States test) self-reports of tension, anger, depression, confusion, and increased cognitive performance in recognition memory measures (as determined by the Auditory Consonants Trigrams Recognition test). The other beverages tested (15 g casein with 32.5 g dextrose; and 47.5 g galactose plus dextrose) did not significantly alter the serum tryptophan:LNAA ratio or the behavioral and cognitive performance parameters monitored. The ability of this dietary supplement to alter the mood and performance decrements associated with the premenstrual period in some women may offer an alternative strategy to addressing this syndrome with a relatively benign intervention.
CHOLINE AND ENDURANCE PERFORMANCE
Although it is not an amine acid or protein, choline has recently been demonstrated to enhance certain types of endurance performance. Initial studies in subjects completing the Boston Marathon demonstrated a decrease in plasma choline levels of approximately 40 percent from prerace values (Conlay et al., 1986). Subsequent studies (Sandage et al., 1992) demonstrated the ability of supplemental choline administration in the form of a beverage to prevent the dramatic decrease in plasma choline following a similar physical endurance event (20-mi run). Additionally, the performance of individuals was significantly increased as indicated by reduced time required to complete the run when subjects consumed the choline-containing beverage versus the placebo, choline-free beverage. This double-blind, crossover study has led to numerous other trials that may help to further characterize the potential beneficial effects of this dietary supplement in a variety of other physical endurance activities. The use of choline in endurance events should be investigated in greater detail by the military.
AUTHOR'S SUMMARY AND RECOMMENDATIONS
The FASEB/LSRO report on the safety of amine acids as dietary supplements concluded the following:
There is no nutritional rationale for the use of amine acids as dietary supplements, and such a practice can be dangerous.
Supplemental amine acids should be used for pharmacological rather than nutritional purposes.
The extant scientific literature fails to support a safe upper limit for supplementation of any amino acid beyond that found in dietary protein.
Appropriate testing in animals and humans is required before the safety of supplemental amino acids can be adequately assessed. Several additional recommendations may be made:
Alternative proteins of vegetable origin should be considered when designing long-term studies.
Manipulation of serotonergic function with carbohydrate may constitute a relatively benign intervention for lessening the symptoms of the premenstrual period in some women.
Choline supplementation for endurance activities should be considered and requires careful investigation under a variety of applicable military conditions.
It is therefore recommended that approaches to fortify military rations with supplemental amino acids, protein, or additional compounds be initiated. However, appropriate safeguards for the welfare of subjects must be treated as such interventions may result in adverse effects, especially if individual amino acids are used at supranutritional doses over a long period of time.
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ROBERT NESHEIM: Any questions for Dr. Maher? Yes?
ROBERT WOLFE: It seems like you are always better safe than sorry, but I guess I have a little problem with the conclusion that that entire list of tests should be run for testing safety of any amino acid given orally.
In light of the practicality of any studies actually being completed, and in light of most of the data you showed—and I did review that Document 12 for the NIH symposium on protein supplements that was held, and I was not impressed that there was really much evidence of detrimental effects, and with the layers of proposed tests that would be run before any studies would be done, I am concerned that any further investigation would be precluded without a sufficient basis in many cases for implementing these additional screening tests.
TIMOTHY MAHER: I think that we have the two extremes. On the one hand, we have the FASEB-LSRO study that suggests treating these compounds similar to pharmacological agents, and performing extensive safety testing, as you would with any other chug.
On the other hand, we can go down the street to any of the health food stores, and we can buy many of these things, and there has been no testing done whatsoever.
I think it is important to find a happy medium somewhere in between, maybe not as extensive as the FASEB-LSRO study but definitely more than what is currently known about these compounds.
I would hope that whoever decides to investigate amino acids as performance-enhancing strategies would at least do some of those studies. I don't know that the financial impetus is there on the part of the health food industry, but I hope that the military or whatever other organization wants to look at this in a proper way will do some of those studies.
ROBERT NESHEIM: Any other questions for Tim, or questions on anything that was covered today?
MARITZA RUBIO-STIPEC: I just had a minor question. I just wanted to know, all of the studies you mentioned except one were done only on men?
TIMOTHY MAHER: Are you referring to studies of individual amino acids or protein? The PMS studies were obviously with women.
MARITZA RUBIO-STIPEC: Yes, I know. What about the others.
TIMOTHY MAILER: With studies of choline, we have used both men and women.
MARITZA RUBIO-STIPEC: Do you have the distribution by gender?
TIMOTHY MAHER: No. But, most of the studies of the individual amine acids have been in men, especially the ones that have dealt with athletics and performance.
ROBERT NESHEIM: A question?
MACKENZIE WALSER: I wanted to comment. I was on that same committee that Dr. Maher was on, and I think one point that you did not bring out was that we were concerned about quality control. You can put sugar on the shelf in a grocery store, and it is going to have to meet certain standards. I have no idea what they are, but it does have to meet certain standards, or the FDA will impound it.
On the other hand, you can put lysine on the shelf, and it can actually be sodium cyanide. I am not kidding. There is absolutely no control of quality.
I will never forget that while working in this committee, we got some table—not sodium cyanides—but we did get some tablets of lysine and put them in a beaker of water to see what the dissolution time was. Three days later, they were still there, intact.
So there are no criteria, either, for dissolution, which is a minimum requirement for any capsule that is sold as a drug.
So I don't understand why the FDA, cannot design standards for quality control, at least for amine acids, before we have these tremendous studies of efficacy.