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用餐时间学问大 吃得健康不发胖

更新时间:2019/4/3 21:54:41 来源:纽约时报中文网 作者:佚名

How meal timings affect your waistline
用餐时间学问大 吃得健康不发胖

When young adults start university, they often gain weight. In the United States, they have a name for this phenomenon: the "freshman 15", referring to the 15lbs typically accrued during students’ first year of living away from home. In part, this weight gain can be explained by the substitution of home-cooked meals for ready meals and fast food, combined with reduction in physical activity.

年轻人在开始上大学时,体重往往会增加。在美国,这种现象叫:“大一新生15磅”,意思是学生第一年离家后体重会增加15磅(约7公斤)。一般的解释是,家常饭被即食食品和快餐所取代,加上体育活动减少所造成。

Increasingly, however, scientists are fingering an additional suspect: circadian disruption, brought about by a culture of late-night eating, drinking, and inconsistent sleep patterns.

然而,越来越多的科学家指出了另一个原因:深夜进食和睡眠不规律,所导致的生物钟紊乱。

For decades, we’ve been told that weight gain, together with associated diseases such as type 2 diabetes and heart disease, are a simple matter of the quantity and type of food we consume, balanced with the number of calories we expend through exercise. But mounting evidence suggests that timing is also important: it’s not just what you eat, but when you eat that matters.

几十年来,我们听到的说法一直是,体重增加能导致各种疾病,比如II型糖尿病和心脏病,这都与吃的多少、食物类型,以及运动消耗的卡路里数量相关。但越来越多的证据表明,吃饭的时间也很重要。重要的不仅仅是吃什么吃多少,还有什么时候吃。

The idea that our response to food varies at different times of day dates back a long way. Ancient Chinese medics believed that energy flowed around the body in parallel with the sun’s movements, and that our meals should be timed accordingly: 7-9am was the time of the stomach, when the biggest meal of the day should be consumed; 9-11am centred on the pancreas and spleen; 11am-1pm was the time of the heart, and so on. Dinner, they believed, should be a light affair, consumed between 5pm and 7pm, which was when kidney function predominated.

我们在一天中的不同时段,对食物的反应是不同的,这个观点可以追溯到很久以前。中国古代中医认为,人体能量的流动与太阳的运行是同步的,我们的进餐时间也与之相对应:早上7点到9点,胃经最旺,这个时候应该吃一天最丰盛的早餐;上午9点到11点,脾经气血最活跃;上午11点到中午1点,心经运行。中医认为,晚餐宜清淡,应在下午5点到7点之间吃,此时肾经占据主导。

Although the explanation is different, modern science suggests that there is plenty of truth in that ancient wisdom.

虽然解释不同,但现代科学表明,这种古老的智慧中蕴含着许多道理。

Consider studies of dieters. Most weight-loss schemes revolve around reducing the overall number of calories consumed – but what if the timing also determined the benefits? When overweight and obese women were put on a weight-loss diet for three months, those who consumed most of their calories at breakfast lost two and a half times more weight than those who had a light breakfast and ate most of their calories at dinner – even though they consumed the same number of calories overall.

以对节食者的研究为例。绝大多数减肥方案,都是围绕着减少卡路里摄入总量来进行的——但如果吃东西的时间也对减肥有影响呢?当超重的肥胖女性吃减肥餐三个月,那些在早餐摄入绝大多数卡路里的人,比早餐简单应付,晚餐摄入绝大多数卡路里的人,减去的体重要多出两倍半,尽管她们摄入的卡路里数量是相同的。

Many people think that the reason you gain more weight if you eat late at night is because you have less opportunity to burn off those calories, but this is simplistic. “People sometimes assume that our bodies shut down when asleep, but that’s not true,” says Jonathan Johnston at the University of Surrey, who studies how our body clocks interact with food.

许多人认为,半夜吃东西体重增加是因为,摄入的卡路里没有机会消耗掉,但这种理解过于简单。萨里大学(University of Surrey)研究生物钟与食物相互作用的约翰斯顿(Jonathan Johnston)说:“人们一般会认为,身体在睡觉的时候会处于停摆状态,但事实并非如此。”

So, what else could be going on? Some preliminary evidence suggests that more energy is used to process a meal when it’s eaten in the morning, compared with later in the day, so you burn slightly more calories if you eat earlier. However, it’s still unclear how much of a difference this would make to overall body weight.

那么事实是什么?一些初步证据表明,人在早晨吃东西比在之后的时间吃东西,要消耗更多的能量,如果吃得早一些,身体会燃烧掉更多的卡路里。不过,目前尚不清楚,这会对体重产生多大的影响。

Another possibility is that late-night eating extends the overall window during which food is consumed. This gives our digestive systems less time to recuperate and reduces the opportunity for our bodies to burn fat – because fat-burning only occurs when our organs realise that no more food is coming their way.

另一种可能是,深夜吃东西延长了整体进食时间。消化系统恢复的时间减少,身体燃烧脂肪的机会也减少了——只有当我们的器官得不到食物补充时,才会燃烧脂肪。

Prior to the invention of electric light, humans woke at roughly around dawn and went to bed several hours after the sun set, with almost all food being consumed during daylight hours. “Unless we have access to light, we struggle to stay awake and eat at the wrong time,” says Satchin Panda, a circadian biologist at the Salk Institute in La Jolla, California, and author of The Circadian Code. His own research has revealed that the majority of North Americans eat over the course of 15 or more hours each day, with more than a third of the day’s calories consumed after 6pm, which is very different to how our ancestors must have lived.

在电灯发明之前,人类大约在黎明时分醒来,太阳落山几小时后上床睡觉,因此食物都是在白天吃的。加州拉霍亚(La Jolla)索尔克生物研究所(Salk Institute)研究生物钟的生物学家潘达(Satchin Panda)说:“除非有照明,否则我们就不会熬夜不睡觉、在不该吃东西的时间进食。”他的研究显示,多数北美人每天的进食期达到15个小时甚至更长,三分之一的卡路里是在下午6点之后摄入的,这与我们祖先的生活方式截然不同。

Now consider those college students, eating and drinking long into the night. “A typical college student rarely goes to sleep before midnight, and they also tend to eat until midnight,” Panda says. Yet, many students will still need to get up for classes the next day, which – assuming they eat breakfast – reduces the length of their night-time fast still further.

现在再想想那些晚上还在吃吃喝喝的大学生吧。潘达说:“一个典型的大学生很少在午夜前睡觉,而且往往深夜了还在吃东西。然后,第二天要早起上课,假设他们吃早餐的话,这进一步缩短了夜间空腹的时间。”

It also means that they are cutting short their sleep, and this too could make them more likely to gain weight. Inadequate sleep impairs decision-making and self-control, potentially leading to poor food choices, and it disrupts levels of the “hunger hormones”, leptin and ghrelin, boosting appetite.

这种习惯使他们的睡眠时间变短,可能导致他们容易发胖。睡眠不足会影响决策和自控能力,也可能会导致食物选择不当,还会扰乱饥饿激素、瘦素和胃饥饿素的水平,从而提高食欲。

It is now becoming clear that our circadian rhythms are intimately connected to our digestion and metabolism in many other ways, through the body’s intricate signalling pathways – a new understanding that could explain the long-term effects of jet lag and shift work.

现在越来越清楚的是,我们的生理节律通过身体复杂的信号传输,与我们的消化和新陈代谢密切相关——这是一种新的理解,它可以解释时差和夜班工作对健康的影响。

Inside every cell of your body, there ticks a molecular clock that regulates the timing of pretty much every physiological process and behaviour, from the release of hormones and neurotransmitters, to your blood pressure, the activity of your immune cells, and when you feel more sleepy, alert, or depressed. These clocks are kept in synchrony with each other, and with the time of day outside, through signals from a small patch of brain tissue called the suprachiasmatic nucleus (SCN). And its window on the outside world are a subset of light-responsive cells at the back of the eye called intrinsically photoreceptive retinal ganglion cells (ipRGs).

身体的每个细胞里,都有一个分子时钟在滴答作响,它控制着每一个生理过程和行为的时间,从激素和神经递质的释放,到血压、免疫细胞的活动,以及什么时候感觉困倦、兴奋或抑郁。这些时钟通过一个叫做视交叉上核(SCN)的小块脑组织发出的信号,与外界时间保持同步。它感知外部世界的窗口是位于眼睛后部的一个光敏细胞子集,称为感光性视网膜神经节细胞(ipRGs)。

The point of all these “circadian” clocks is to anticipate and prepare for regular events in our environment, such as the arrival of food. It means that different biochemical reactions are favoured at various times of day, allowing our internal organs to task-switch and recuperate.

这些生物钟的意义在于,为生活环境中的常规事件做预测和准备,比如食物的到来。这就意味着,在一天的不同时间段不同的生理反应会受到欢迎,使我们的身体器官能进行任务的切换和恢复。

When we travel abroad, the timing of our light exposure changes, and our body clocks are pulled in the same direction – although the clocks in different organs and tissues adapt at different rates. The result is jet lag, which not only leaves us feeling sleepy or awake at the wrong times, but can also trigger digestive problems and general malaise.

跨时区出国旅行时,我们接受阳光的时间会发生改变,而体内的生物钟会被拉向原来的方向——虽然身体器官和组织里的生物钟会以不同的速度加以调适。结果就是时差反应,使我们在错误的时间感到困倦或者醒来,还会引发消化问题和全身的不适。

However, light isn’t the only thing that can change the timing of our clocks. When we eat our meals can also shift the hands of the clocks in the liver and digestive organs, even though the clocks in our brain cells are unaffected. Recent evidence also suggests that the timing of exercise can tweak the clocks in our muscle cells.

然而,光并不是唯一可以改变生物钟的东西。当我们吃东西的时候,肝脏和消化器官中的时钟也会改变,即使脑细胞中的时钟不受影响。最近还有证据表明,运动的时间可以调整肌肉细胞里的时钟。

When we fly across time zones, or eat, sleep and exercise at irregular times, the various clocks in our organs and tissues fall out of synchrony with one another. This is unlikely to be a problem if you just have the occasional late-night meal or lie-in, but if it’s a regular occurrence this may have longer-term consequences for our health.

当我们飞越时区,或者吃饭、睡觉、运动时间不规律时,我们的器官和组织中的各种时钟就会彼此失去同步。如果只是偶尔宵夜或者偶尔睡懒觉,这可能问题不大,如果经常这样,就会对健康产生长期影响。

Complex processes, such as the metabolism of fats or carbohydrates from the diet, require the coordination of numerous processes occurring in the gut, liver, pancreas, muscle and fatty tissue. If the conversation between these tissues becomes scrambled, they become less efficient, which over the long term may increase our risk of various diseases.

饮食中脂肪和碳水化合物的代谢,是一个复杂的过程,需要肠道、肝脏、胰腺、肌肉和脂肪组织中之间的协调。如果这些组织之间的交流变得混乱,它们的效率就会降低,长期如此,就会增加我们患各种疾病的风险。

In one recent study, researchers compared the physical effects of sleeping for five hours per night for eight days in a row, with getting the same amount of sleep but at irregular times. In both groups, people’s sensitivity to the hormone insulin dropped and systemic inflammation increased, escalating the risk of developing type 2 diabetes and heart disease. However, these effects were even greater in those who were sleeping at irregular times (and whose circadian rhythms were therefore knocked out of alignment): in men, the reduction in insulin sensitivity and increase in inflammation doubled.

在最近的一项研究中,研究人员比较了,连续8天每晚睡5个小时与睡眠时间相同,但睡眠时间不规律对身体的影响。在这两组中,都出现了激素胰岛素的敏感性下降,全身炎症增加,从而也增加了患II型糖尿病和心脏病的风险。然而,在那些睡眠时间不规律,生理节律被打乱的人身上,影响更大,在这一组中胰岛素敏感性指数和炎症反应增加了一倍。

That could be a problem for frequent flyers, students who regularly sleep in, or any shift workers. According to European and North American surveys, some 15 to 30% of the working population is engaged in some form of shift work, which often equates to eating or being active when the body isn’t expecting it. Shift work has been linked to a host of conditions, including heart disease, type 2 diabetes, obesity and depression, and circadian disruption brought about by this irregularity is a prime suspect.

对于经常飞行的人、经常睡懒觉的学生,或者经常倒班的人来说,这是一个问题。根据欧洲和北美的调查,大约15%到30%的就业人员从事倒班工作,这会导致在身体不需要的时候进食或活动。倒班工作与许多疾病有关,包括心脏病、II型糖尿病、肥胖和抑郁症,生活不规律造成的生理节律紊乱,是主要的致病因素。

However, we are all shift workers at least some of the time, says Panda. An estimated 87% of the general population maintains a different sleep schedule on weekdays, compared to weekends, resulting in social jet lag. People also tend to eat breakfast at least an hour later at the weekends, which can result in so-called “metabolic-jetlag”.

不过,潘达表示,我们都是倒班工作者,至少在某些时候。据估计,87%的人群在工作日和休息日睡眠时间不同,导致社交时差综合症。人们也倾向于在周末晚一小时吃早餐,这可能导致所谓的“代谢时差”。

It’s not only consistency in the timing of meals, but in the amount of food we eat at each meal that seems to be important.

不仅进餐时间很重要,每餐吃的食物量也很重要。

Gerda Pot is a nutrition researcher at King’s College London, investigating how day-to-day irregularity in people’s energy intake affects their long-term health. She was inspired by her grandmother, Hammy Timmerman, who was rigorous about routine. Each day she’d eat breakfast at 7am; lunch at 12.30pm, and dinner at 6pm. Even the timing of her snacks was intransigent: coffee at 11.30am; tea at 3pm. When Pot came to visit, she soon learned that sleeping in was a mistake: “If I woke up at 10am, she’d still insist I ate breakfast, and then we’d be having coffee and a cookie half an hour later,” she says. Increasingly, though, she is convinced that her grandmother’s rigid routine helped keep her in good health until she was almost 95.

波特(Gerda Pot)是伦敦国王学院(King's College London)的营养研究员,研究人们日常能量摄入的不规律如何影响长期健康。她的灵感来自祖母蒂默曼(Hammy Timmerman),祖母的生活作息非常严格。每天早上7点吃早餐,中午12点半吃午餐,下午6点吃晚餐。甚至连吃零食的时间也是固定的:上午11点半喝咖啡,下午3点喝茶。波特去看她的时候,很快就意识到在她那里睡懒觉是个错误。波特说:“如果我早上10点醒来,她仍然坚持让我吃早餐,过半小时后喝咖啡,吃饼干。”不过,波特越来越相信,是严格的作息习惯让祖母保持了一直健康,直到她快95岁的时候。

There are some good reasons why this might be. Our sensitivity to the hormone insulin, which enables the glucose from the food we eat to enter our cells and be used as fuel, is greater during the morning than at night. When we eat late (as Hammy Timmerman never did), that glucose remains in our blood for longer, which over the long term can increase the risk of developing type 2 diabetes, where the pancreas no longer produces enough insulin. It can also damage tissues elsewhere, such as blood vessels or nerves in the eyes and feet. In the worst cases, this can result in blindness, or amputations.

这其中的道理是。我们对胰岛素的敏感性早上比晚上高,胰岛素能使血液中的葡萄糖进入细胞并被身体利用。如果吃的太晚(蒂默曼就从不这样做),葡萄糖在血液中停留的时间增长,长此以往,就会增加患II型糖尿病的风险;得了糖尿病,胰腺就无法产生足够的胰岛素。糖尿病还会损害身体其它组织,比如眼睛和脚上的血管和神经。严重的情况,还可能导致失明或者截肢。

Using data from a UK national survey which has tracked the health of more than 5,000 people for over 70 years, Pot found that, even though they consumed fewer calories overall, people who had a more irregular meal routine had a higher risk of developing metabolic syndrome – a cluster of conditions, including high blood pressure, elevated blood sugar levels, excess fat around the waist and abnormal fat and cholesterol levels in their blood, which together increase the risk of cardiovascular disease and type 2 diabetes.

英国进行了一项全国性的调查,对5000多人的健康状况跟踪了70多年,波特从调查数据中发现,经常吃饭不规律的人,尽管总体摄入的卡路里会少一些,但患上代谢综合征的风险更高。代谢综合征,是指一系列紊乱症候群,包括高血压、高血糖、腰部脂肪堆积以及血液中的脂肪和胆固醇水平异常等等,增加了患心血管疾病和II型糖尿病的风险。

So, what should we do about it? Striving for greater consistency in the timing of our sleep and meals is a good first step, and ideally, all our clocks should be operating on the same time zone. When we open the curtains and see bright light in the morning, this resets the master clock in the brain, so by eating breakfast soon afterward, this reinforces the message that its morning to the clocks in our liver and digestive system. Eating a good breakfast may therefore be essential to keeping our circadian clocks running in synchrony.

那么我们应该怎么做呢?定时睡觉、吃饭是良好的第一步,尽量保持生物钟在同一时区运行。我们早上拉开窗帘时,明亮的光线会重置大脑里的时钟,在起床后不久吃早餐,是在强化肝脏和消化系统中的时钟接收早晨的信息。因此,吃一顿丰盛的早餐对于保持体内生物钟同步运转是非常重要的。

Indeed, a recent study involving 18 healthy individuals, and 18 with type 2 diabetes, found that skipping breakfast led to disrupted circadian rhythms in both groups, as well as greater spikes in blood glucose levels when they finally did eat.

最近一项对18名健康人和18名II型糖尿病患者的研究发现,事实上,不吃早餐对健康人和糖尿病患者生理节律都有影响,当他们最终开始吃东西的时候,体内血糖水平会大幅飙升。

However, regularising our schedules shouldn’t come at the expense of missed sleep. Although it’s unlikely that the occasional lie-in will cause you any harm, we should generally be striving to go to bed at a time that will allow us to get adequate sleep – the recommended amount is seven to eight hours for most adults – on every day of the week. Here, light exposure could help. Dimming the lights in the evenings and getting more exposure to bright light during the day time has been shown to shift the timing of the master clock in the brain (the SCN) several hours earlier, making people more lark-like.

然而,调整生活作息不应该以牺牲睡眠时间为代价。偶尔睡个懒觉不会带来任何伤害,但我们还是应该尽量不熬夜,保证睡眠充足。对多数成年人来说,推荐的睡眠时间是7到8个小时。这个方面光照会对人有所影响,晚上调暗灯光,白天更多地暴露在明亮的光线下,大脑时钟会提前几个小时,让人像鸟儿一样早睡早起。

Some are advocating a more hardcore approach of forgoing all food for at least 12 hours, and possibly for as long as 14-16 hours overnight. In a landmark study published in 2012, Panda and his colleagues compared one set of mice that had access to fatty and sugary foods at any time of day or night, with another group that could only consumed these foods within an eight to 12-hour window during their “daytime”. Even though they consumed the same number of calories, the mice whose eating window was restricted appeared to be completely protected from the diseases that began to afflict the other group: obesity, diabetes, heart disease and liver damage. What’s more, when mice with these illnesses were placed on a time-restricted eating schedule, they became well again.

有人采取偏激的方式,每天至少禁食12个小时,晚上则长达12至16个小时。在2012年进行的一项有重大意义的研究中,潘达和同事对两组老鼠进行了比较,其中一组在白天和晚上任何时候,都能获得高脂肪和含糖的食物;另一组只能在白天8至12小时的窗口期,吃到这些东西。虽然卡路里摄入量相同,但进食时间受到限制的那组并没有另一组老鼠所患的疾病:肥胖、糖尿病、心脏病和肝损害。更重要的是,当患有这些疾病的老鼠进食时间受到限制后,它们又恢复了健康。

“Almost every animal, including us, evolved on this planet with a very strong 24-hour rhythm in light and darkness, and the associated rhythms in eating and fasting,” explains Panda. “We think a major function [of these cycles] is to enable repair and rejuvenation each night. You cannot repair a highway when the traffic is still moving.”

潘达解释说:“几乎所有的动物,包括人类在内,在这个星球上以严格的昼夜节律演化而来,这种节律也与进食和禁食的节奏有关。我们认为这个节律的主要功能,就是每晚都要修复和恢复活力。如同高速路不封闭,是没有办法修路。”

Human trials of time-restricted eating are just beginning, but some of the early results look promising – at least in certain groups. For instance, when eight men with prediabetes were randomised to eat all their meals between 8am and 3pm, their sensitivity to insulin improved and their blood pressure dropped by 10-11 points on average, compared to when they consumed the same meals within a 12-hour period.

限时饮食的试验才刚刚开始,但一些早期的结论,在特定人群中很有价值。例如,随机安排8名患有前驱糖尿病的男性,在早上8点到下午3点之间吃完一日三餐时,他们对胰岛素的敏感性得到了改善,与那些在12个小时内吃完三餐的人相比,血压平均下降了百分之十左右。

Quite what this means for the rest of us is unclear at this point, but the adage that you should breakfast like a king, lunch like a prince and dine like a pauper has never seemed truer. And it’s almost certainly worth fitting a padlock on the fridge overnight.

这对于正常人群意味着什么,目前还不清楚,但“早餐吃得像皇帝,中午吃得像平民,晚餐吃得像乞丐。”这句老话可谓无比正确。而且可以肯定的是,晚上锁紧冰箱,是值得做的事情。

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