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.

    當談到體重增加的問題時，你吃飯的時間和你吃什么或吃多少可能同樣重要。根據(jù)《肥胖癥》周刊在網(wǎng)上公布的一項動物實驗表明，在身體本該睡覺的時候吃東西將會導致體重過量增加。

    在首個將吃飯時間和體重增加程度聯(lián)系起來的研究中，西北大學的睡眠學家比較了六周之內以相反時間喂食的兩組老鼠。它們吃同樣的高脂肪食物，每天有同樣的活動量。唯一的不同之處在于：一組老鼠是在它們正常清醒狀態(tài)的12小時中喂食的，另一組老鼠則在它們本該熟睡的時候喂食。當研究結束時，后一組老鼠所增加的體重是前一組老鼠增重量的兩倍還要多：分別是10.4克、增重48%和4.4克、增重20%.

    紐約-長老會醫(yī)院、威爾康奈爾醫(yī)學中心的肥胖問題專家路易·亞隆醫(yī)生說："很長一段時間以來，我們都在研究進食方式是否和體重增加有關。"他提到了此前的觀測法研究，該研究認為不吃早飯的人更喜歡在晚上飽餐一頓，也更容易體重超標。亞隆本人沒有參與到這一研究當中，"我們沒有證據(jù)證明問題果真如此，"他說，"如果這樣一個實驗在人群中反復重做，我們就能更清楚在肥胖問題中時間所具有的重要性。"

    該項研究的共同合作者弗雷德·托萊克說，身體生物鐘受到擾亂可能是一個突出的問題。身體生物鐘又稱為生理節(jié)律，在不適當?shù)臅r間進食將會干擾身體的正常節(jié)律，并引發(fā)一連串終將導致體重增加的代謝反應。"因為我們的身體自然而然地在一天中的特定時間吃東西，如果進食時間不對的話，身體維持能量平衡的能力就會受到影響。"托萊克解釋道。這就意味著我們的身體將以有別于正常的方式來消耗卡路里，這反過來又將導致體內荷爾蒙水平的大幅波動，包括饑餓素的增加和瘦體素的減少--它們是掌管饑餓感和飽腹感的兩種關鍵荷爾蒙。饑餓素荷爾蒙由胃部產(chǎn)生，向大腦發(fā)送"給我吃東西"的信號；飽腹感荷爾蒙則向大腦發(fā)送停止進食的信號。

    但是，雖然科學家們已經(jīng)成功地通過調節(jié)這兩種荷爾蒙使試驗老鼠的體重增加或減少，但是對于人體來說，這一方法尚不可行。給肥胖癥患者注射瘦體素的試驗已告失敗，因為人體中控制饑餓感和飽腹感的代謝途徑比老鼠的要復雜許多。紐約大學手術減重項目的外科手術醫(yī)師喬治·菲爾丁舉例說，通過藥物療法破壞掉50條這樣的代謝途徑中的其中一條，也僅僅意味著其他49條代謝途徑終將補上空缺。

    盡管《肥胖癥》周刊的新發(fā)現(xiàn)還沒能走出實驗室投入應用，其他的研究也支持了睡眠紊亂（包括在凌晨2點站在冰箱前面吃雞）與人體增重可能有關的觀點。亞隆醫(yī)生說，對護士和工人等夜班工作者的研究顯示，相比起在白天上班的人來說，夜班工作者體重超標的風險更大。一方面是由于他們糟糕的日常睡眠，另一方面則是因為他們更容易在晚上大吃大喝。還有一些研究表明，晚上睡足八小時的人常常會比睡眠不足八小時的人更瘦一些。另外，大量的傳染病研究已經(jīng)表明，不足或低質睡眠與糖尿病、心血管疾病等肥胖相關病癥之間的確存在關聯(lián)。

    在今后的人體研究證實托萊克的初步發(fā)現(xiàn)之前，亞隆醫(yī)生建議，戒掉飯后點心可能仍舊是個上策，不管點心是多是少。這樣做不僅能避免體重額外增加，還能降低食道胃酸逆流的風險和罹患其他加重睡眠問題的消化系疾病的可能。亞隆醫(yī)生還建議人們在一天當中攝取營養(yǎng)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熱量的一半或更多，因為那也將給你帶來多余贅肉。