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多喝水、记得吃饭,头脑就会变好!


2020-06-29


多喝水、记得吃饭,头脑就会变好!

一天究竟该喝多少水,才能维持整体健康与巨复原力,这个问题很难回答。要看你的体重、运动量、身处的气候带,以及其他种种因素。传统说法是大约一天要喝八杯八盎司的水(两公升左右),不过有的人可能需要多喝一点。

我们提出的微复原力观点谈论补充水分时,和传统看法不同的地方在于,除了喝水量很重要,喝水的时机也很重要。当我们压力很大,努力赶上最后期限,劳苦功高的水瓶常被推到桌子远处,接着就被遗忘,然而此时正是我们最需要补水的时候。

研究显示,喝水立刻就能提升表现。英国研究人员证实,在接受具有挑战性的动脑任务之前,受试者先喝一品脱(约500毫升)的白开水,需要的反应时间比没补水的人少14%。[1]同一组科学家也证实,水喝得比同学多的孩童,注意力集中的时间增加,记忆力也增强。

科学显示,如果一忙碌就忘记喝水,不论是忘几小时或忘一整天,达成目标的能力会减弱。

国立卫生研究院(National Institutes of Health, NIH)回顾探讨水、健康与补充水分的研究[2],指出轻微到中等程度的脱水会伤害各种认知领域的表现,包括短期记忆、知觉辨认(perceptual discrimination)、计算能力,以及视觉追蹤的动作协调。[3]

相关研究解释,为什幺水让史坦的日常生活起了很大的变化。记忆力变好,对数字更敏锐,眼睛看得更清楚,手眼协调能力更好,还增强施展人际互动的技巧,打造複杂机械、规画协调的能力等,对他的工作来说全都很重要。他现在能够努力追求高效率与公司利润。

血糖和水分一样,随时影响着我们的复原力。无所不在的杂货店、冰箱和餐厅,让人们随时都能取得食物,但我们依旧有饿肚子的时候。我们可能被卡在迟迟无法起飞的飞机里,困在一场又一场的会议中,或是得接送孩子参加课后活动。现代生活虽然便利,我们还是可能一连几小时吃不到东西。

大脑是新陈代谢的「大户」,明明只占全身重量2%,但每日耗掉我们摄取热量的20~25%。[4]大脑的执行功能,如决策、身心耐力和逻辑推理,比自动发生的认知事件更耗血糖。[5]由于脑中永远只有少量血糖,不补充的话,5~10分钟就会缺糖,执行功能很容易受影响。[6]如果太常忽略进食,就可能头昏脑胀、犹豫不决甚至忧郁沮丧。

血糖下降时,自制能力也会下降。[7]有听过「hangry」(编注:意思是又饿〔hungry〕又气〔angry〕)这个词吗?距离进食时间愈久,就愈难控制情绪,我们会突然暴怒或掉眼泪。此外,血糖低的时候(不正常的低血糖浓度期间)会增加焦虑程度。[8]从前有一句广告台词说:「肚子一饿,你就不是你」(You’re not you when you’re hungry),真是至理名言。

心理学家马修.盖利特(Matthew Gailliot)推测,大脑的複杂高阶执行功能,在演化过程中较晚才出现,因此资源稀缺时会被第一个放弃。大脑採取「后进先出法」(last-in, first-out),情绪控制等进阶的大脑活动早早就遭到抛弃,先保障呼吸、心跳与其他维生功能。血糖低的时候,原始的自我会推开演化后的自我,接掌大局。而自制力需要耗费十分大量的能量,例如:移转进食与性交渴望等原始冲动、战胜惰性,以及化愤怒为力量等。此时,平衡、稳定的血糖浓度,可以替大脑的执行功能助阵,抑制原始的自我。

如果连「正常範围」内的血糖波动也能避免,对我们的好处相当多。[9]自制力或许是最容易受血糖波动影响的大脑执行功能,也有证据显示,良好的自我管理,关係着健康的人际互动、人缘、良好的心理健康、有效的应对技巧、优秀的学业表现,以及比较不容易陷入药物与酒精滥用、犯罪行为或饮食失调。[10]

另一方面,血糖飙高(高血糖)不代表大脑会运转得更顺畅。长期维持高血糖会以各种方式损害全身细胞,包括大脑细胞。血糖状态应该保持得跟三只小熊童话中,金髮女孩(Goldilocks)喜欢的粥一样:不太烫、不太冷、温度刚刚好。[11]

[1] C. J. Edmonds, R. Crombie, and M. R. Gardner, “Subjective Thirst Moderates Changes in Speed of Responding Associated with Water Consumption,” Frontiers in Human Neuroscience 7 (2013): 363.[2] B. M. Popkin, K. E. D’Anci, and I. H. Rosenberg, “Water, Hydration, and Health,” Nutrition Reviews 68, no. 8 (2010): 439–458.[3] C. Cian et al., “Effects of Fluid Ingestion on Cognitive Function after Heat Stress or Exercise-Induced Dehydration,” International Journal of Psychophysiology 42 (2001): 243– 251; C. Cian et al., “Influence of Variations of Body Hydration on Cognitive Performance,” Journal of Psychophysiology 14 (2000): 29–36; P. M. Gopinathan, G. Pichan, and V. M. Sharma, “Role of Dehydration in Heat Stress-Induced Variations in Mental Performance,” Archives of Environmental Health 43 (1988): 15–17; K. E. D’Anci et al., “Voluntary Dehydration and Cognitive Performance in Trained College Athletes,” Perceptual and Motor Skills 109 (2009): 251–269. [4] R. I. Dunbar, “The Social Brain Hypothesis and Its Implications for Social Evolution,” Annals of Human Biology 36, no. 5 (2009): 562–572; John J. Ratey, MD, A User’s Guide to the Brain: Perception, Attention, and the Four Theaters of the Brain (New York: Pantheon, 2001). [5] M. T. Gailliot, “Unlocking the Energy Dynamics of Executive Functioning: Linking Executive Functioning to Brain Glycogen,” Perspectives on Psychological Science 3 (2008): 245. [6] John J. Ratey, MD, A User’s Guide to the Brain: Perception, Attention, and the Four Theaters of the Brain (New York: Pantheon, 2001). [7] M. T. Gailliot et al., “Self-Control Relies on Glucose as a Limited Energy Source: Willpower Is More than a Metaphor,” Journal of Personality and Social Psychology 92 (2007): 325–336. [8] Daniel G. Amen, MD, Change Your Brain, Change Your Life: The Breakthrough Program for Conquering Anxiety, Depression, Obsessiveness, Lack of Focus, Anger, and Memory Problems. (New York: Harmony, 2015). [9] M. T. Gailliot et al., “Self-Control Relies on Glucose as a Limited Energy Source: Willpower Is More than a Metaphor,” Journal of Personality and Social Psychology 92 (2007): 325–336. [10] C. N. DeWall et al., “Violence Restrained: Effects of Self-Regulation and Its Depletion on Aggression,” Journal of Experimental Social Psychology 43 (2007): 62–76; A. L. Duckworth and M. E. P. Seligman, “Self-Discipline Outdoes IQ in Predicting Academic Performance of Adolescents,” Psychological Science 16 (2005): 939–944; E. J. Finkel and W. K. Campbell, “Self-Control and Accommodation in Close Relationships: An Interdependence Analysis,” Journal of Personality and Social Psychology 81 (2001): 263–277; M. T. Gailliot, B. J. Schmeichel, and R. F. Baumeister, “Self-Regulatory Processes Defend against the Threat of Death: Effects of Self-Control Depletion and Trait Self-Control on Thoughts and Fears of Dying,” Journal of Personality and Social Psychology 91 (2006): 49–62; Michael R. Gottfredson and Travis Hirschi, A General Theory of Crime (Stanford, CA: Stanford University Press, 1990); D. Kahan, J. Polivy, and C. P. Herman, “Conformity and Dietary Disinhibition: A Test of the Ego-Strength Model of Self-Regulation,” International Journal of Eating Disorders 32 (2003): 165–171; T. C. Pratt and F. T. Cullen, “The Empirical Status of Gottfredson and Hirschi’s General Theory of Crime: A Meta-Analysis,” Criminology 38 (2000): 931–964; Y. Shoda, W. Mischel, and P. K. Peake, “Predicting Adolescent Cognitive and Self-Regulatory Competencies from Preschool Delay of Gratification: Identifying Diagnostic Conditions,” Developmental Psychology 26 (1990): 978–986; J. P. Tangney, R. F. Baumeister, and A. L. Boone, “High Self-Control Predicts Good Adjustment, Less Pathology, Better Grades, and Interpersonal Success,” Journal of Personality 72 (2004): 271–322; K. D. Vohs and T. F. Heatherton, “Self-Regulatory Failure: A Resource-Depletion Approach,” Psychological Science 11 (2000): 249–254. [11] Larry Husten, “Lancet: Researchers Find Goldilocks Effect in Glucose Control for Diabetes,” Cardio Brief (blog), January 26, 2010, http://cardiobrief.org/2010/01/26/lancet-researchers-find-goldilocks-effect-in-glucose-control-for-diabetes/.

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