Imagine yourself lying in bed, your mind in turmoil. You toss and turn, but sleep won't come. Maybe a bedtime snack would help. What should you choose? If you think first of toaster waffles or popcorn, some experts would say you're on the right track. Foods high in complex carbohydrates-such as cereals, potatoes, pasta, crackers, or rice cakes-make many people relaxed and drowsy.
　　Missed that one? Try again. Suppose the weather's rotten, you forgot your homework, and your best friend's mad at you. What's good medicine when you're feeling low? A sugary cola or candy may give you a quick lift, but you'll crash just as quickly. Better choices may be Brazil nuts (for selenium), skim milk (for calcium), or a spinach salad (for folic acid). In research studies, all three of those nutrients have been shown to lift spirits and battle the blues.
　　Try one more. You have a math test coming up in the afternoon. You want to be sharp, but you usually feel sleepy after lunch. Is your best choice an energy fix of fries and a shake or a broiled chicken breast and low fat yogurt? If you pick the high fat fries and shake, you may feel sluggish and blow that test. The protein rich chicken and yogurt are better choices. Protein foods energize, some experts say.
　　How does food affect mood and mind? The answer may lie in the chemistry of the brain and nervous system. Molecules called neurotransmitters are chemical messengers. They carry a nerve impulse across the gap between nerve cells. The release of neurotransmitter molecules from one neuron and their attachment to receptor sites on another keep a nerve impulse moving.
　　Nerve impulses carry messages from the environment to the brain, for example, the pain you feel when you stub your toe. They also carry messages in the other direction, from the brain to the muscles. That's why you back away from the obstacle that initiated the pain signal and exclaim, "Ouch!"
　　"Many neurotransmitters are built from the foods we eat," says neuroscientist Eric Chudler of the University of Washington. Too little or too much of a particular nutrient in the diet can affect their production, Chudler says. For example, tryptophan from foods such as yogurt, milk, bananas, and eggs is required for the production of the neurotransmitter serotonin. Phenylalanine from beets, almonds, eggs, meat, and grains goes into making the neurotransmitter dopamine.
　　Dozens of neurotransmitters are known; hundreds may exist. Their effects depend on their amounts and where they work in the brain. The neurotransmitter serotonin, for example, is thought to produce feelings of calmness, relaxation, and contentment. Drugs that prevent its reuptake (into the neuron that released it) are prescribed to treat depression. In at least some healthy, nondepressed people, carbohydrate foods seem to enhance serotonin production and produce similar effects. "It is the balance between different neurotransmitters that helps regulate mood," Chudler says.
　　Proper nutrition may also enhance brainpower. Choline is a substance similar to the B vitamins. It's found in egg yolks, whole wheat, peanuts, milk, green peas, liver, beans, seafood, and soybeans. The brain uses it to make the neurotransmitter acetylcholine. To test the effects of choline on memory and learning, researchers at the Massachusetts Institute of Technology gave memory tests to college students before increasing the amount of choline in their subjects diets. Later, they retested. On the average, memories were better, and the students learned a list of unrelated words more easily.

　　设想一下你躺在床上，脑子里一片混乱。你辗转反侧，但总也睡不着。也许睡觉时吃点零食会有帮助。你应当吃什么呢？如果你的首选是威化饼或爆米花，那么一些专家就会说你选对了。麦片、土豆、面食、饼干或米糕这些富含复合碳水化合物的食品会使人感到放松和困倦。
　　你选错了吗？再试一次。假如天气很糟，你忘了做家庭作业，而你的好朋友又对你大发雷霆。在你情绪低落之时，对你来说什么是一剂良药呢？一杯甜可乐或一块糖可能会使你情绪很快高涨，但你的情绪又会很快地进入低潮。更好的选择是吃一些巴西胡桃（获得更多的硒），脱脂牛奶（获得更多的钙），或菠菜沙拉（获得更多的叶酸）。研究表明，上述三种营养素都会使人们情绪高涨，摆脱忧虑。
　　再试一次吧。下午你有数学测验。你想要精力充沛，可你总是在午饭后感到昏昏欲睡。能使你精神饱满地面对考试的最佳食品是炸薯条和奶昔，还是鸡胸肉和低脂酸奶？如果你选中了高脂肪的炸薯条和奶昔，你就会感到非常懒散，很可能考砸了。高蛋白的鸡肉和酸奶是较好的选择。有些专家说蛋白质食品给人们提供能量。
　　食物如何影响情绪和思维？答案可能要到大脑和神经系统的化学结构中去找。被称为神经递质的分子是化学信使。它们把神经冲动带到神经细胞之间的空隙中。神经递质分子从一个神经原释放后，附着到另一个接受点，令神经冲动保持运动的状态。
　　神经冲动能够把周边环境的信息带到大脑中--例如，当你脚趾被绊了一下时，你会感到疼。它们也能从反方向传递信息，比如说从大脑到肌肉。这就是为什么当障碍物产生疼痛的信号时，你就会躲开障碍物，并且喊：哎哟！
　　华盛顿大学的神经科学家埃里克•查德勒说：许多神经递质是靠我们所吃的食物形成的。 查德勒指出过多或过少地通过饮食摄入一种营养素可以影响这些神经递质的形成。例如，来自诸如酸奶、牛奶、香蕉和鸡蛋的色氨酸会产生神经递质的血清素。来自甜菜、杏仁、鸡蛋、肉和谷物中的苯基丙胺酸会形成神经递质的多巴胺。
　　我们已知的神经递质有几十种，实际存在的可能有几百种。它们产生的效果取决于本身的数量和它们在大脑中工作的位置。例如，神经递质血清素被认为会产生平静、放松和满足的感觉。治疗情绪低落时，大夫就开出一些能够防止它返回（即进入到释放出它的神经元中）的药。至少在一些健康和情绪不低落的人当中，碳水化合物食物似乎能够促进血清素的生成并能产生类似效应。查德勒说：不同神经递质之间的平衡帮助调节人的情绪。
　　恰当的营养能提高人的大脑思考能力。胆碱是一种类似于维生素B的物质。它存在于蛋黄、全麦、花生、牛奶、菜豆、肝、蚕豆、海鲜和黄豆中。大脑利用这种物质生成神经递质的乙酰胆碱。为了检测胆碱对记忆和学习的影响，麻省理工学院的研究者们对大学生进行了记忆测验。随后，他们在被试验者的饮食中增加胆碱的量，重新做了实验。从总体上来看，学生的记忆力有所提高，能够更加容易地学会一系列不相关的单词。