The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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14 Amino Acid and Protein Requirements: Cognitive Performance, Stress, and Brain Function
14 Amino Acid and Protein Requirements: Cognitive Performance, Stress, and Brain Function
Pages 289-308
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From page 289... ...
A particular focus will be the possibility that central demands for amino acids may modify nutritional requirements when individuals are exposed to extreme environments and other stressors associated with combat and highintensity military or civilian occupations. To function adequately, the central nervous system (CNS)
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From page 290... ...
Although little information on CNS requirements of specific amino acids is available, results from several lines of related research suggest that the peripheral concentration of particular amino acids can be a factor in the regulation of central neurotransmission, cognitive performance, and mood state. For example, if the amino acid tryptophan is either artificially elevated or lowered, changes in brain function and behavior can occur (Young, 1996~.
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From page 291... ...
At least three active transport mechanisms convey amino acids into the brain (Betz et al., 1994~. Separate mechanisms exist for transport of the large neutral amino acids (LNAA)
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From page 292... ...
Clearly, the Unctions outlined In Table 14-3 are not only critical in a general way for maintaining the normal behavioral status of an organism, but are also closely related to the ability of that organism to function in stressful conditions. In single nonphysiologic doses; or when administered in special diets, all of the amino acid precursors of the transmitter systems shown in Table 14-3 have been found to alter brain activity.
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From page 293... ...
Consistent with the functions of serotonin listed in Table 14-3, the availability of hyptophan to the brain can alter behavioral factors such as alertness, level of depression, aggression, and pain sensitivity (for a recent review, see Young, 19961. The effects of the protein: carbohydrate ratio of meals on brain serotonin is well documented, although the physiologic relevance of the relationship is controversial.
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From page 294... ...
Following consumption of carbohydrate, which elicits the secretion of insulin, the concentration of the branched-chain amino acids in the plasma falls as they move into muscle, while tryptophan levels remain relatively unchanged. Therefore, since more tryptophan is available for transport by the LNAA carrier mechanism, tryptophan transport to the brain increases and more tryptophan is available for the synthesis of serotonin.
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From page 295... ...
on the self-reported fatigue, vigor, and alertness of healthy volunteers as assessed with the Profile of Mood States (POMS) Questionnaire (Panel A)
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From page 296... ...
The changes in aggression and pain induced by artificially altering plasma levels of tryptophan are consistent with data implicating serotonin in the regulation of aggression and pain sensitivity. Overall, there is little doubt that substantial variations in plasma tryptophan levels can have a major impact on the behavior of humans and other animals.
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From page 297... ...
Tyrosine is not typically considered to be an essential amino acid since it can be synthesized by humans Tom phenylalanine; however, it has been suggested by some investigators that the brain may not be able to synthesize sufficient tyrosine from phenylalanine to meet its needs (Pardridge, 1977~. Tyrosine is generally found in larger quantities than Tryptophan in most protein foods.
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From page 298... ...
Exposure to heat, cold, cardiovascular successors, and electric shock all produce significant increases in brain catecholaminergic activity (Stone, 1975~. Central noradrenergic neurons seem to be critical for regulating key behavioral parameters such as attention, arousal level, and mood state (Lieberman, 1994~.
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From page 299... ...
To evaluate the hypothesis that supplemental tyrosine can prevent some adverse behavioral and physiological effects of exposure to various acute stressors, a number of animal and human studies have been conducted (for reviews, see Lieberman, 1994; Owasoyo et al., 1992; Salter, 1989~. In general, the results of these studies suggest that tyrosine administration, particularly when the stress is severe, will have beneficial effects on the ability of the organism to function adequately.
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From page 300... ...
Increased immobility (mean difference in immobility) indicates inability of the animal to respond appropriately to the heat stressor.
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From page 301... ...
The individuals receiving the RLW-30 ration had a substantial daily energy deficit of over 1,300 kcal, while He control group's energy intake was only several hundred kcal below their daily energy expenditure level. At the start and conclusion of the study, two standard tests of cognitive performance previously shown to be sensitive to He effects of nutritional parameters (simple visual reaction time and four-choice visual reaction time)
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From page 302... ...
Although a significant correlation between tyrosine levels and performance was not observed during this field study, the research was conducted in a relatively nonstressful environment, not under conditions where the influence of tyrosine on central catecholamines is likely to be important. ~5 he En O m o cr: I I-1 0 o ~-15 5 ~ , MRE ~ ~ 1 % ~, 5 _ 1 ~LIGHTWEIGHT _~' - ''1' Day O Day 14 TEST DAY Day 31 FIGURE 14-7 Plasma tryptophan levels in soldiers consuming either a lightweight ration or standard field rations (the MRE)
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From page 303... ...
CHOICE VISUAL REACTION TIME · So · ·e ·e Us- ~ ~ ~ -- -- a _~ · . n · :54 · -100 r -0.4~9 ~ I I I I I t -150- 1 1 1 1 1 1 ~.01 0 0.01 0.02 -0.04 ~.02 ~.01 <.01 0 ·0.04 ·0.02 -0.01 0.01 0.02 no lo - OPHAN Redo FIGURE 14-9 Relationship between changes in plasma: tryptophan ratio and two tests of cognitive performance in soldiers consuming either a lightweight ration or standard field rations (the MRE)
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From page 304... ...
Substantial decreases or increases in the typical levels of tryptophan present in the plasma will substantially disrupt normal behavior and brain function. Reduced plasma tryptophan increases depression and aggression, while increases in this amino acid induce drowsiness and decrease pain sensitivity.
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From page 305... ...
1971. Brain serotonin content: Physiological dependence on plasma tryptophan levels.
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From page 306... ...
1996. Report of the working group on protein and amino acid requirements.
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From page 307... ...
Yes? GERALD COMBS: Since tryptophan is the least abundant amino acid in most proteins and would be the most constant, its relationship to total protein would be more nearly the same than any other amino acid.
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