The problem of Jet Lag is one every international traveller comes across at some time. But do you have to suffer? Understand what it is, and how a careful diet can minimize its worst effects, and your flights will be less stressful.

The effects of rapid travel on the body are actually far more disturbing than we realize. Jet Lag is not a psychological consequence of having to readjust to a different time zone. It is due to changes in the body's physiological regulatory mechanisms, specifically the hormonal systems, in a different environment.

Confused? So was John Foster Dulles, the American Secretary of State, when he flew to Egypt to conduct negotiations on the Aswan Dam. He later blamed his poor judgment on Jet Lag.

The effects can be used to advantage, too. President Johnson once conducted an important meeting in Guam and kept the entire proceedings at Washington DC time. The White House working personnel were as fresh as paint, while the locals, in this case, were jet-lagged. Essentially, they had been instantaneously transported to America.

Now that we understand what Jet Lag is, we can go some way to overcoming it. A great number of the body's events are scheduled to occur at a certain time of day. Naturally these have to be regulated, and there are two regulatory systems which interact.

One timing system comes from the evidence of our senses and stomachs, and the periodicity we experience when living in a particular time zone. The other belongs in our internal clocks (the major one of which may be physically located in a part of the brain called the suprachiasmatic nucleus) which, left alone, would tie the body to a 25 hour - yes, 25 - rhythm. Normally the two timers are in step, and the external cues tend to regularise the internal clocks to the more convenient 24 hour period.

If, however, you move the whole body to a time zone which is four hours different, the two clocks will be out of step, like two alarm clocks which are normally set together, but which have been reset a few hours apart. Whereas the two clocks would normally sound their alarms together, now they ring at different times. Similarly, the body can be set for evening while the sun is rising.

In time the physiological system will reset itself, but it does take time. One easily monitored rhythm is palm sweating. A man flown to a time zone different by 10 hours will take eight days to readjust his palm sweat. Blood pressure, which is also rhythmical, takes four days to readjust.

One reason for this discrepancy is that different bodily events are controlled by different factors. The hormone cortisol, which controls salt and water excretion, is made in the morning, wherever the body is. But the growth hormone is released during sleep, whenever in the day that sleep occurs. Normally these two hormones are separated by seven or eight hours, but if the body arrives at a destination in the early morning (local) and goes to sleep as soon as possible, the two hormones will be released simultaneously.

What can we do about it? It is not feasible to wait four days until the body is used to the new time zone. Fortunately there is a short cut. It relies on two things - the power of the stomach to regulate the timing of other events, and the pharmacological actions of coffee.

The basic assumptions are:

Coffee delays the body clock in the morning, and advances it at night. Coffee at mid-afternoon is neutral.

Protein in meals stimulates wakefulness, while carbohydrates promote sleep.

Putting food into an empty stomach helps synchronize the body clock.

高速飞行时因时差而引起的生理节奏的推敲是每一个跨国旅行者有时会遇到的问题。但你必须得忍受吗？如果你了解它是怎么回事，并且知道如何注意饮食才可以将其最坏影响减到最小程度，你的飞行就不会那么紧张了。

快速旅行对身体的影响实际上比我们所意识到的更加令人不安。调整的习行因时差而引起的生理节奏的破坏不是必须重新调整去适合不同时区的心理影响。它是由人体内的生理调节结构，特别是荷尔蒙系统在不同环境的变化引起的。

感到困惑了吗？美国国务卿约翰·福斯·特杜勒斯飞往埃及进行关于阿斯旺大坝的谈判时也是这样。后来，他把他的不理想的判断归咎于时差反应的不良影响。

时差的影响也可以加以利用。约翰逊总统曾经在关岛召开重要会议，其所有活动都按华盛顿时间进行。白宫工作人员个个精神焕发，而在这种情况下，当地人却受时差反应之苦。实际上，好像他们刚刚被飞机送到美国一样。

既然我们懂得了什么是高速飞行时差综合症。很自然，这些活动不得不加以调节，人体现人有两套相互影响的调节系统。

一个定时系统表现在我们的感觉和胃以及居住在一个特定时区时，我们所经历的周期。另一个定时系统在我们的人体时钟内，这些人体时钟在不受干扰时，会使人体有一个25小时，是的25小时的生理节奏。一般情况下，这两种定时器是步调一致的。外部信号常常调节人体时钟命使之达到更为便利的24小时周期。

然而，如果你将整个身体转移到相差四个小时的时区，这两个小时钟就不协调了。就像两个闹钟通常一起设置，但被重新设置时相差了好几个小时。虽然这两个时钟通常会一起闹时，但现在它们在不同时刻响起。类似的，当太阳升起时身体可能被设定为晚上。

经过一段时间以后，生理系统将会重新调整过来。但这的确需要时间。一个容易监测的节律是手掌出汗的节律。血压也是有节律的，需要四天时间才能得到重新调整。

形成这种差异的百不同的身体活动由不同因素的支配。不管身在何处，控制盐和水分排泄的皮质醇激素是早上产生的。但不论何时睡眠，生长激素是在睡眠中释放的。通常这两种激素相隔七、八个小时释放，但如果人体在一大早到达目的地，并且尽快入睡，这两种激素将同时释放。

关于这点我们能做些什么呢？等待几天直到身体适应新的时区是不可取的。幸好，有一条捷径。它依靠两点――胃调节其他活动定时的能力和咖啡的药物作用。

基本的道理是：

咖啡在早上可以延迟人体时钟，在晚间可以提早人体时钟。咖啡在下午三点左右是中性的。食物中的蛋白质使人不眠，而碳水化合物却使人易于入睡。空腹吃食物帮助人体时钟准时。