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研究:吃夜宵,可能比你担心的肥更多

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核心提示:When it comes to weight gain, the timing of your meals may be just as important as what or how much you eat. According to a study of lab animals published online by the journal Obesity, eating during the hours that the body would naturally be sleepi

    When it comes to weight gain, the timing of your meals may be just as important as what or how much you eat. According to a study of lab animals published online by the journal Obesity, eating during the hours that the body would naturally be sleeping may lead to excess weight gain.

    In the first study to associate meal timing with degree of weight gain, sleep scientists at Northwestern University compared two groups of mice, each placed on opposite feeding schedules for a six-week period. Both groups were fed the same high-fat food, and both had the same amount of daily physical activity. The only difference: one group was fed during its normal 12-hour waking period, while the other rodents where fed while they should have been asleep. By the end of the study period, the latter group had gained more than twice as much weight as the mice that ate during active hours: 10.4 g, a 48% increase in body weight, versus 4.4 g, or a 20% gain in baseline weight.

    "For a long time we questioned whether or not eating patterns had anything to do with gaining weight," says obesity expert Dr. Louis Aronne of NewYork-Presbyterian Hospital/Weill Cornell Medical Center. He points to previous observational research suggesting that people who skip breakfast in favor of massive meals in the evening hours tend to be overweight. "We had no proof that it's a real problem," says Aronne, who was not involved in the study. "If an experiment like this is replicated in humans, it might clarify for us just how much time of day matters when it comes to obesity."

    The salient issue, says study co-author Fred Turek, may be the disruption of the body's internal clock, known as the circadian rhythm. Eating at inappropriate times may disturb the body's natural rhythm, setting off a string of metabolic reactions that ultimately lead to weight gain. "Because our bodies are naturally cued to eat at certain times of the day, dining at the wrong time might affect the body's ability to maintain its energy balance," he explains, meaning that our body starts to use its calories differently than it normally would. That in turn could cause fluctuations in numerous hormones, including an increase in ghrelin and a decrease in leptin - the two key hormones that govern appetite and satiety. The hunger hormone ghrelin, which is produced by the stomach, sends a "feed me" message to the brain; leptin, the satiety hormone, signals the brain to stop eating.

    But while these hormones have been successfully manipulated in lab mice to prompt weight gain or loss, the same has not been true in humans. Experiments in which obese human patients were injected with leptin have failed, because the metabolic pathways that control hunger and fullness in people are far more complex than they are in mice. Knocking out one of, say, 50 such pathways through drug treatment just means the other 49 will eventually pick up the slack, says Dr. George Fielding, a bariatric surgeon at the NYU Program for Surgical Weight Loss.

    Although the new findings in Obesity cannot yet be applied outside the lab, other research supports the idea that the disruption of sleep (that includes standing in front of the fridge eating chicken at 2 a.m.) may have something to do with weight gain in humans. Studies of night-shift workers like nurses and factory workers indicate they are at higher risk for being overweight than their daylight counterparts, partly due to poor sleep routines and partly because of their tendency to eat heavy meals late at night, says Aronne. Other studies show that people who get a full eight hours of sleep at night tend to be thinner than those who get less, while numerous epidemiological studies have established a link between short or poor sleeping patterns with overweight-related conditions including diabetes and cardiovascular disease.

    Until future studies in humans bear out Turek's preliminary findings, Aronne suggests that avoiding post-dinner snacking is probably still a good strategy, regardless of size. Not only could it help prevent extra weight gain, it can also lower the risk of gastroesophageal reflux and other digestive problems that may compound sleep problems. Aronne further recommends taking well-balanced and evenly spread meals throughout the day, rather than consuming 50% or more of your daily calories at dinner or afterward, since that may also lead to unwanted pounds.

    当谈到体重增加的问题时,你吃饭的时间和你吃什么或吃多少可能同样重要。根据《肥胖症》周刊在网上公布的一项动物实验表明,在身体本该睡觉的时候吃东西将会导致体重过量增加。

    在首个将吃饭时间和体重增加程度联系起来的研究中,西北大学的睡眠学家比较了六周之内以相反时间喂食的两组老鼠。它们吃同样的高脂肪食物,每天有同样的活动量。唯一的不同之处在于:一组老鼠是在它们正常清醒状态的12小时中喂食的,另一组老鼠则在它们本该熟睡的时候喂食。当研究结束时,后一组老鼠所增加的体重是前一组老鼠增重量的两倍还要多:分别是10.4克、增重48%和4.4克、增重20%.

    纽约-长老会医院、威尔康奈尔医学中心的肥胖问题专家路易·亚隆医生说:"很长一段时间以来,我们都在研究进食方式是否和体重增加有关。"他提到了此前的观测法研究,该研究认为不吃早饭的人更喜欢在晚上饱餐一顿,也更容易体重超标。亚隆本人没有参与到这一研究当中,"我们没有证据证明问题果真如此,"他说,"如果这样一个实验在人群中反复重做,我们就能更清楚在肥胖问题中时间所具有的重要性。"

    该项研究的共同合作者弗雷德·托莱克说,身体生物钟受到扰乱可能是一个突出的问题。身体生物钟又称为生理节律,在不适当的时间进食将会干扰身体的正常节律,并引发一连串终将导致体重增加的代谢反应。"因为我们的身体自然而然地在一天中的特定时间吃东西,如果进食时间不对的话,身体维持能量平衡的能力就会受到影响。"托莱克解释道。这就意味着我们的身体将以有别于正常的方式来消耗卡路里,这反过来又将导致体内荷尔蒙水平的大幅波动,包括饥饿素的增加和瘦体素的减少--它们是掌管饥饿感和饱腹感的两种关键荷尔蒙。饥饿素荷尔蒙由胃部产生,向大脑发送"给我吃东西"的信号;饱腹感荷尔蒙则向大脑发送停止进食的信号。

    但是,虽然科学家们已经成功地通过调节这两种荷尔蒙使试验老鼠的体重增加或减少,但是对于人体来说,这一方法尚不可行。给肥胖症患者注射瘦体素的试验已告失败,因为人体中控制饥饿感和饱腹感的代谢途径比老鼠的要复杂许多。纽约大学手术减重项目的外科手术医师乔治·菲尔丁举例说,通过药物疗法破坏掉50条这样的代谢途径中的其中一条,也仅仅意味着其他49条代谢途径终将补上空缺。

    尽管《肥胖症》周刊的新发现还没能走出实验室投入应用,其他的研究也支持了睡眠紊乱(包括在凌晨2点站在冰箱前面吃鸡)与人体增重可能有关的观点。亚隆医生说,对护士和工人等夜班工作者的研究显示,相比起在白天上班的人来说,夜班工作者体重超标的风险更大。一方面是由于他们糟糕的日常睡眠,另一方面则是因为他们更容易在晚上大吃大喝。还有一些研究表明,晚上睡足八小时的人常常会比睡眠不足八小时的人更瘦一些。另外,大量的传染病研究已经表明,不足或低质睡眠与糖尿病、心血管疾病等肥胖相关病症之间的确存在关联。

    在今后的人体研究证实托莱克的初步发现之前,亚隆医生建议,戒掉饭后点心可能仍旧是个上策,不管点心是多是少。这样做不仅能避免体重额外增加,还能降低食道胃酸逆流的风险和罹患其他加重睡眠问题的消化系疾病的可能。亚隆医生还建议人们在一天当中摄取营养均衡、份量平均的食物,而不是在晚餐或晚餐之后吞下你一天所需热量的一半或更多,因为那也将给你带来多余赘肉。

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关键词: 夜宵 健康 肥胖
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