Food Components to Enhance Performance An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations (1994) / Chapter Skim
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1. Introduction and Background
1. Introduction and Background
Pages 3-46
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, to review the potential for specific food components to enhance the performance of military personnel under the stress of field settings. The committee was thus charged with providing a thorough review of the literature in this area and with interpreting these diverse data in terms of military applications.
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Within this context the CMNR was charged with specifically evaluating the potential of selected amino acids, carbohydrates, structured lipids, choline, carnitine, and caffeine to enhance performance. The committee was also asked to provide its recommendations regarding which, if any, of these compounds should be developed further within the current "Soldier as a System" initiative (Army Science Board, 1991~.
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This is followed by a review and interpretation of the available data on the food components proposed for consideration by the Army. Chapter 1 concludes with a discussion of the safety and regulatory aspects of performance-enhancing food components.
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, located at Natick, Massachusetts, share responsibility for implementing the new Science and Technology Objective (STO) that is principally directed at the sustainment or enhancement of soldier performance through the use of performanceenhancing food components (see description of this STO in question 2 on page 41.
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the delivery of the food component to the functional site at a concentration that will be effective and not adversely affect the complex interactions in the overall metabolism. With all of the complexities of human metabolism, it is important to carefully evaluate food components or nutrients as potential performance enhancers (physical and/or cognitive)
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Although experimental studies can focus on measurement of physical performance at levels ranging from the isolated muscle cell to the whole organism, the issue for the military is the performance of the soldier in physically demanding tasks, often under stressful conditions. Review of food components that may enhance physical performance through psychological factors that contribute to performance of all tasks, such as arousal, concentration, and motivation (see Dishman, 1989, for a review)
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The ability to perceive, attend to, and respond appropriately to cues, as well as make appropriate decisions, and to remain vigilant are critical in military combat settings. These areas of cognitive performance also form the basis for many physical performance tasks, such as positioning and loading artillery shells or moving through a mine field.
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The scenarios in Appendix A provide additional direct examples of the types of cognitive performance changes that are of concern in military settings. Reduction in performance degradation through ingestion of food components that may affect neurotransmitters, more general neuronal excitability, or the specific brain regions involved in cognitive activities will be discussed in the sections that follow.
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In addition, physical and cognitive performance measurement need to be well-integrated an area where there is little previous research. In summary, although an individual's food intake in the military is influenced by the same set of factors that influence food intake in nonmilitary settings, the stress of military training or combat settings, the shelf life requirements, the packaging and delivery constraints of military rations, and the added performance capability demands result in a highly complex set of problems for performance enhancement.
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Studies using acute paradigms have examined the behavioral consequences of altered neurotransmitter precursor availability and, hence, neurotransmitter synthesis. Alterations in brain amino acids and neurotransmitter levels are seen within 15-20 minutes after administration of amino acids such as r-tyrosine (TYR)
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Although one cannot determine at present whether DA receptor sensitivity is influenced by chronic stress, administration of TYR should stimulate DA receptor synthesis and release; this is again suggestive of enhanced performance. Although stress does not influence the activity of the serotonin precursor neurons, stress does increase brain concentrations of the essential amino acid tryptophan (TRP - possibly as a consequence of increased serotonin (5HT)
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Typical military stresses generate endocrine responses that tend to be remarkably stereotyped in pattern, although they may vary with the form, duration, and severity of the inciting stress. Hormonal responses may also evolve longitudinally, over time, if stress is protracted.
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Army Ranger trainees were presented at a meeting of the Committee on Military Nutrition Research, Food and Nutrition Board, Institute of Medicine, National Academy of Science, in March 1993.
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These reactions include headaches, myalgia, arthralgia, fever, sleepiness, loss of appetite, loss of muscle protein, and an accelerated metabolism of stored body nutrients, all of which serve to reduce both physical and mental performance. Biochemical components of these cytokine-generated acute-phase reactions include the cellular production of prostaglandins, prostacyclines, leukotrienes, and nitric oxide, which, in turn, generate many of the accompanying symptoms.
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Under resting conditions, glucose uptake is mainly by noninsulin-dependent pathways in the CNS, blood cells, and kidneys, whereas only about onethird is used by insulin-dependent pathways, chiefly in skeletal muscles (which primarily burn fatty acids and some amino acids as their source of metabolic fuels)
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On the other hand, a falling insulin-to-norepinephrine ratio activates lipolysis and mobilizes fatty acids. Pancreatic clamp techniques have demonstrated the effects of individual hormones, with others held constant.
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POTENTIAL PERFOR1\IANCE-ENHANCING FOOD COMPONENTS Physical Performance Enhancement A broad overview of food components that may optimize physical performance is provided by John L Ivy (Chapter 121.
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The prime example of a central stimulant found in food beverages is caffeine, as discussed elsewhere in this report (Chapter 20~. Another example is branched-chain amino acids (BCAAs)
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However, most research with carbohydrate supplementation has been conducted in prolonged continuous moderate exercise such as marathon running or situations that do not readily compare to the exercise demands of military combat. Food Components that May Enhance Mental Performance Various foods and food components have been evaluated for their behavioral effects in animals and humans, including protein and carbohydrate (CHO)
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In particular, concern has been voiced as to the mechanism whereby contextual and sensory differences in food components can be meaningfully separated from macronutrient content. Note is made of the absence of a metabolic/neurochemical mechanism: "Neurochemistry or indeed neuroanatomy, unconnected to any account of how sensory information could be used to direct behavior towards the diets in a manner that achieves nutrient-oriented selection, leaves the feedback idea as a magical incantation, not a scientific hypothesis" (Booth, 1987, pp.
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It is also unclear whether CHO cravers prefer sweet CHOs primarily. According to the feedback loop theory, the response of serotoninergic neurons to foodinduced changes in the relative concentration of plasma amino acids allows for a special "sensor" role in nutrient choice (Wurtman, 1983, 1988~.
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SPECIFIC FOOD COMPONENTS Tyrosine Tyrosine is a nonessential dietary amino acid because it can be synthesized in vivo from the essential amino acid phenylalanine and because protein synthesis continues normally even if tyrosine is absent from the diet. However, tyrosine is recognized to be a physiologically important precursor of the catecholamine neurotransmitters dopamine, norepinephrine, alla epinephrine.
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(Banderet and Lieberman, 1989~. Mood and mental performance were assessed using a battery of standardized behavioral tests.
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, an important role has been demonstrated for carbohydrates in sustaining or enhancing physical performance. The role or potential role of dietary carbohydrate in other aspects of performance is considered by Spring and colleagues in Chapter 17.
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The third, or physiological, definition of fatigue can also be a factor of major importance in military stresses involving severe or prolonged muscular exertion. Muscle fatigue, typified, for example, by the performance declines during the last stages of prolonged sprints or marathons, is associated with the buildup of lactic acid and other metabolic products of carbohydrate, amino acid, and fatty acid substrates used by the exercising muscles.
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Structured lipids are defined as fats that are synthesized from mixtures of long- and medium-chain fatty acids. Structured lipids are therefore differentiated from typical dietary fats by the presence of significant amounts of medium-chain fatty acids (i.e., fatty
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. Jandacek reviews the digestion, absorption, and metabolism of long- and medium-chain fatty acids because any possible performance enhancement potential for structured lipids depends on differences in the way long- and medium-chain fatty acids are handled by the body.
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Dietary Choline and Choline Deficiency Free choline or choline-containing esters are present in a wide variety of foods in the diet, and the usual intake of such compounds by humans is probably about 700-1000 mg per day. There is no recommended dietary allowance for choline for humans, but intakes of 500 mg/day result in decreased plasma choline and phosphatidylcholine concentrations.
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Additional placebo-controlled, randomized, double-blind trials are needed to determine whether choline supplementation will enhance the performance of military personnel in the field. Choline supplementation enhances memory and reaction time in animals, particularly aging animals, and enhances memory in humans (Bartus et al., 1980; Meck et al., 1989~.
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To clarify these issues, three doses of caffeine (150, 300, and 600 mg/70 kg of body weight) were assessed among normal healthy males after 2 days of sleep deprivation.
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, blood pressure bears monitoring in any future studies of performance enhancement with caffeine
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These functions have led to the hypothesis that supplementation of free carnitine, acetylcarnitine, or propionylcarnitine theoretically might enhance the oxidation of fatty acids during exercise, thus sparing the use of muscle glycogen, delaying the onset of fatigue, and enhancing exercise performance. Today, research is hindered by the lack of a simple method that permits measurement of the various acylcarnitines in large numbers of samples.
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Human subjects performing maximal exercise tests on bicycle ergometers have been studied with 2g supplements of Carnitine or placebos, and increases in both plasma lactate and pyruvate levels with maximal exercise were lower after carnitine administration throughout the trial, with greater or equal work accomplished, although returns to baseline concentrations of lactate were the same in both groups (Siliprandi et al., 19901. Other evidence in humans suggests that carnitine supplementation may modestly increase the use of fatty acids during exercise.
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The status of carnitine research is such that, at present, no recommendation to increase levels of carnitine in rations are called for. SAFETY AND REGULATORY ASPECTS OF POTENTIAL PERFORMANCE-ENHANCING FOOD COMPONENTS Safety of Amino Acids Military rations exceed the RDAs for protein and the protein source provides an adequate intake of the essential amino acids.
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reviews in detail the literature on animal and human studies that can shed light on the safety of supplements. It is clear from the LSRO report that many amino acids can have toxicological effects, that there is a paucity of information to establish safe use levels for individual amino acid supplements, and that there is adequate evidence to raise concern about certain vulnerable population groups.
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Regulation of Food Components by the U.S. Food and Drug Administration The considerations for the approval of food additives are well developed by John E
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Raiten, eds. 1992 Safety of Amino Acids Used as Dietary Supplements.
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Cerretelli 1992 Muscle carnitine after strenuous endurance exercise.
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1990 Aromatic amino acids and monoamine synthesis in the central nervous system: Influence ofthe diet.
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Garfield 1986a The behavioral effects of food constituents: Strategies used in studies of amino acids, protein, carbohydrate and caffeine.
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Aakvaag, and T.O. Rognum 1980 Altered hormonal response to short-term bicycle exercise in young men after prolonged physical strain, caloric deficit, and sleep deprivation.
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Wahren 1988 Influence of carnitine supplementation on muscle substrate and carnitine metabolism during exercise.
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Links, and H Wagner 1988 Positron emission tomography measurement of human regional cerebral glucose utilization following 48 hours of sleep deprivation.
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