文/邦妮.聖約翰、亞倫.海恩斯

促進大腦運轉,喝水就好

一天究竟該喝多少水,才能維持整體健康與巨復原力,這個問題很難回答。要看你的體重、運動量、身處的氣候帶,以及其他種種因素。傳統說法是大約一天要喝八杯八盎司的水(兩公升左右),不過有的人可能需要多喝一點。

我們提出的微復原力觀點談論補充水分時,和傳統看法不同的地方在於,除了喝水量很重要,喝水的時機也很重要。當我們壓力很大,努力趕上最後期限,勞苦功高的水瓶常被推到桌子遠處,接著就被遺忘,然而此時正是我們最需要補水的時候。

研究顯示,喝水立刻就能提升表現。英國研究人員證實,在接受具有挑戰性的動腦任務之前,受試者先喝一品脫(約500毫升)的白開水,需要的反應時間比沒補水的人少14%。[1]同一組科學家也證實,水喝得比同學多的孩童,注意力集中的時間增加,記憶力也增強。

科學顯示,如果一忙碌就忘記喝水,不論是忘幾小時或忘一整天,達成目標的能力會減弱。

國立衛生研究院(National Institutes of Health, NIH)回顧探討水、健康與補充水分的研究[2],指出輕微到中等程度的脫水會傷害各種認知領域的表現,包括短期記憶、知覺辨認(perceptual discrimination)、計算能力,以及視覺追蹤的動作協調。[3]

相關研究解釋,為什麼水讓史坦的日常生活起了很大的變化。記憶力變好,對數字更敏銳,眼睛看得更清楚,手眼協調能力更好,還增強施展人際互動的技巧,打造複雜機械、規畫協調的能力等,對他的工作來說全都很重要。他現在能夠努力追求高效率與公司利潤。

血糖平衡,心情愈平靜

血糖和水分一樣,隨時影響著我們的復原力。無所不在的雜貨店、冰箱和餐廳,讓人們隨時都能取得食物,但我們依舊有餓肚子的時候。我們可能被卡在遲遲無法起飛的飛機裡,困在一場又一場的會議中,或是得接送孩子參加課後活動。現代生活雖然便利,我們還是可能一連幾小時吃不到東西。

大腦是新陳代謝的「大戶」,明明只占全身重量2%,但每日耗掉我們攝取熱量的20~25%。[4]大腦的執行功能,如決策、身心耐力和邏輯推理,比自動發生的認知事件更耗血糖。[5]由於腦中永遠只有少量血糖,不補充的話,5~10分鐘就會缺糖,執行功能很容易受影響。[6]如果太常忽略進食,就可能頭昏腦脹、猶豫不決甚至憂鬱沮喪。

血糖下降時,自制能力也會下降。[7]有聽過「hangry」(編注:意思是又餓〔hungry〕又氣〔angry〕)這個詞嗎?距離進食時間愈久,就愈難控制情緒,我們會突然暴怒或掉眼淚。此外,血糖低的時候(不正常的低血糖濃度期間)會增加焦慮程度。[8]從前有一句廣告台詞說:「肚子一餓,你就不是你」(You’re not you when you’re hungry),真是至理名言。

心理學家馬修.蓋利特(Matthew Gailliot)推測,大腦的複雜高階執行功能,在演化過程中較晚才出現,因此資源稀缺時會被第一個放棄。大腦採取「後進先出法」(last-in, first-out),情緒控制等進階的大腦活動早早就遭到拋棄,先保障呼吸、心跳與其他維生功能。血糖低的時候,原始的自我會推開演化後的自我,接掌大局。而自制力需要耗費十分大量的能量,例如:移轉進食與性交渴望等原始衝動、戰勝惰性,以及化憤怒為力量等。此時,平衡、穩定的血糖濃度,可以替大腦的執行功能助陣,抑制原始的自我

如果連「正常範圍」內的血糖波動也能避免,對我們的好處相當多。[9]自制力或許是最容易受血糖波動影響的大腦執行功能,也有證據顯示,良好的自我管理,關係著健康的人際互動、人緣、良好的心理健康、有效的應對技巧、優秀的學業表現,以及比較不容易陷入藥物與酒精濫用、犯罪行為或飲食失調。[10]

另一方面,血糖飆高(高血糖)不代表大腦會運轉得更順暢。長期維持高血糖會以各種方式損害全身細胞,包括大腦細胞。血糖狀態應該保持得跟三隻小熊童話中,金髮女孩(Goldilocks)喜歡的粥一樣:不太燙、不太冷、溫度剛剛好。[11]

註釋

  • [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/.

※本文摘自《微復原力》,原篇摘自為〈促進大腦運轉,喝水就好〉、〈血糖平衡,心情愈平靜〉,立即前往試讀►►►

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