Food Components to Enhance Performance An Evaluation of Potential Performance-Enhancing Food Components for Operational Rations (1994) / Chapter Skim
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17. Carbohydrates, Protein, and Performance
17. Carbohydrates, Protein, and Performance
Pages 321-350
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From page 321... ...
The information presented here suggests that behavioral effects are systematically influenced by the caloric and macronutrient compositions of the meal, especially by its ratio of carbohydrate to protein; by the time of day it is consumed; by individual differences, including the temperament and usual eating habits of the ~ Bonnie J Spring, Department of Psychology, University of Health Sciences, The Chicago Medical School, N
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From page 322... ...
Both folk beliefs share an assumption that fluctuations in plasma glucose levels parallel and mediate the emergence of peaks and troughs in physical and mental performance. Ordinarily, one would cursorily skim over folk wisdoms and proceed rapidly to the scientific theories that have guided research on diet and behavior.
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From page 323... ...
By delaying and blunting both the rise and the fall of the plasma glucose concentration, starches are assumed to ensure a sustained source of metabolic energy, allegedly yielding stabler performance. Unlike the assumption that simple sugars commonly provoke reactive hypoglycemia, folk wisdoms about complex carbohydrates have at least some empirical support.
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From page 324... ...
On the other hand, the nature of military operations has changed so greatly that, especially in combat situations, many contemporary soldiers work not from the trenches but, rather, from the seats of heavily computerized vehicles. Perhaps even more than previously, today's combat environment is as likely to tax mental and emotional wherewithal as it is to strain physical endurance.
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From page 325... ...
Indeed, the experience has been that, whereas mood reliably reflects the effects of caloric deprivation, sensorimotor and cognitive performances are insensitive to caloric restriction, except under conditions that impose an additional burden (Spring et al., 1992~. Two added burdens that make caloric deprivation deficits become visible are stress or demands for continuous performance without allowing recuperative time between tasks.
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From page 326... ...
Subjective fatigue can have profound motivational consequences in the combat environment. CARBOHYDRATES AND FATIGUE The authors' interest in dietary effects on mood stemmed from an initial study that compared the behavioral responses of 184 healthy adult men and women to a sucrose-rich, high-carbohydrate, low-protein meal versus those to a high-protein meal (Spring et al., 19831.
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From page 327... ...
The balanced lunch, offering carbohydate to protein in approximately a 3/1 ratio, supplied 774 kcal, 76.0 g of carbohydrate, 27.7 g of protein, alla 40 g of fat. Self-reported fatigue and plasma glucose, serum insulin, arid plasma amino acid concentrations for each condition are shown in Figures 17-1 to 17-4, respectively.
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From page 328... ...
Furthermore, as Figure 17-2 shows, fatigue after the carbohydrate lunch could not be attributed to hypoglycemia because the plasma glucose level remained elevated at the time when fatigue occurred. The findings do not rule out the possibility that drowsiness after a carbohydrate meal could be triggered by a declining level of plasma glucose rather than by an aberrant insulin response or ail absolute ·30 '20 ILL co ·10 o c, _ J ' c'3loo AS En 90 80 70— ~ CHO O NO-MEAL ~ PROTE IN *
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From page 329... ...
Plasma Amino Acids A final hypothesis was that fatigue after eating carbohydrates results Tom effects on plasma amino acids, which, in turn, influence the synthesis and release of brain serotonin. Consumption of a high-carbohydrate, prote~n-poor meal increases the ratio of plasma tryptophan to other large neutral amino acids, which predicts increased brain tryptophan influx (Fernstrom and Wurtman, 1971~.
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From page 330... ...
, drowsiness is a likely accompaniment of increased serotonin synthesis in a healthy brain. As Figure 17-4 shows, the high-carbohydrate, low-protein lunch did significantly increase the ratio of plasma tryptophan to the other large neutral amino acids that share the same transport system across the blood-brain battier.
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From page 331... ...
In fasted rats, a meal containing 70-75 percent of an insulin-secreting carbohydrate increases the plasma tryptophan ratio, whereas a meal containing 25 percent carbohydrate fails to do so (Yokogoshi and Wurtman, 1986~. In addition to being abundant, a carbohydrate must also be insulin-secreting (e.g., glucose, sucrose, and dextrose)
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From page 332... ...
On the other hand, breakfasts, including Danish pastry, that contained at least 8 percent protein actually lowered the tryptophan ratio slightly. Overview of Studies on Carbohydrates and Fatigue If increased brain tryptophan influx and serotonin synthesis is the mechanism that causes drowsiness after a high-carbohydrate meal, then carbohydrate meals that actually increase the tryptophan ratio should be the ones most likely to induce fatigue.
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From page 333... ...
. lithe data revealed that only Me 0 percent protein meal caused a significant change in We t~yptophan ratio (q = 4.73, p < 0.05)
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From page 334... ...
Studies are arrayed according to percent protein in Me carbohydrate test meal and the time of the test meal. Findings are categorized according to whether carbohydrateinduced fatigue was greater than that in the control condition (Yes)
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From page 335... ...
· Individual differences characterize the affective response to carbohydrate. In certain clinical conditions characterized by dysphoric mood, weight management difficulties, and heightened snacking on carbohydrate-rich foods, carbohydrate has activating, antidysphoric effects.
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From page 336... ...
Second, skipping breakfast is more likely to impair the performance of those who usually eat breakfast (Richards, 1971, 1972~. Third, emotional and/or physical stress and continuous time pressure increase the likelihood that late-morning impairments will appear on tests of complex cognitive functions.
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From page 337... ...
The macronutrient composition of the meal also influences the likelihood that a lunch will elicit a postlunch dip and affects the magnitude of performance deterioration that will be observed. Carbohydrate-rich, protein-poor meals elicit greater performance deterioration than do isocaloric protein-rich
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From page 338... ...
(pm) FIGURE 17-6 Postlunch percent omission errors on a sustained attention task relative to the undifferentiated prelunch covariate as a function of whether the subject usually eats a light (L)
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From page 339... ...
Smith and colleagues reported that higher-carbohydrate meals containing either starch or sugar slowed reactions to peripheral visual stimuli, whereas higher-protein meals enhanced susceptibility to distraction. There are also individual differences in susceptibility to the postlunch dip as a function of personality.
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From page 340... ...
, yet no data characterize their effects on performance at that time of day. Snacks are one of the few eating vehicles likely to supply less than 5 percent protein.
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From page 341... ...
They interpret their data to suggest that aging is associated with impaired brain uptake of glucose from blood, which can be attenuated by increasing circulating blood glucose levels in these subjects. It is possible that relatively pure carbohydrate solutions have unique effects in young and elderly individuals.
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From page 342... ...
Not only is a low-fat, high-carbohydrate diet needed to bolster glycogen supplies, but there is also a need to replenish plasma glucose levels during the activity, preferably via solutions comprising glucose polymers. Wright et al.
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From page 343... ...
Both because of their appeal and because of their positive effects on performance, snacks warrant additional research. Virtually nothing is known about what macronutrient composition would make an ideal snack, and there are conflicting interpretations of the potential cognitive benefits of pure carbohydrate (glucose)
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From page 344... ...
Brain serotonin content: Physiological regulation by plasma neutral amino acids. Science 178:414-416.
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From page 345... ...
Garf~eld 1986a The behavioral effects offood constituents: Strategies used in studies of amino acids, protein, carbohydrate and caffeine.
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From page 346... ...
Gessa 1972 Changes in brain serotonin metabolism associated with fasting and satiation in rats.
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From page 347... ...
Wurtman 1986 Meal composition of plasma amino acid ratios: Effect of various proteins or carbohydrates, and of various protein concentrations. Metabolism 35:837-842.
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From page 348... ...
There may also be independent reasons why carbohydrate loading benefits endurance performance. For example, carbohydrates may exert pain-suppressing effects, by enhancing brain tryptophan influx.
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From page 349... ...
When performance deficits appear as a result of caloric deprivation, for example, after skipping breakfast, those effects show up most clearly when an individual is under stress. The point has been made repeatedly that in the laboratory you do not come near the level of stress you are going to find in the field.
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From page 350... ...
They are going to test what I guess Steve Ahlers was talking about. The evidence that when you run a marathon, the plasma choline level before the marathon and of course the original concern that it might impair neuromuscular transmission might diminish acetylcholine production in muscles, but if you are creating plasma choline, you are also affecting brain acetylcholine levels.
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