限时饮食可以预防甚至逆转肥胖

Scientists, like mothers, have long suspected that midnight snacking is inadvisable. But until a few years ago, there was little in the way of science behind those suspicions. Now, a new study shows that mice prevented from eating at all hours avoided obesity and metabolic problems — even if their diet was sometimes unhealthful.

长期以来，母亲们都认为不宜在半夜吃零食，科学家们对此也持有相同的看法。但直到几年前，人们也只是有此怀疑，却没有多少科学证据可以支持它。现在，一项在小鼠中进行的新研究显示，即使有时候它们的饮食不够健康，但只要不是一天到晚吃个不停，就可避免肥胖和代谢问题。

Researchers at the Salk Institute for Biological Studies in San Diego and elsewhere began experimenting with the eating patterns of laboratory mice in a previous study. On that occasion, some mice consumed high-fat food whenever they wanted; others had the same diet but could eat only during an eight-hour window. None exercised. The mice that ate at all hours soon grew chubby and unwell, with symptoms of diabetes. But the mice on the eight-hour schedule gained little weight and developed no metabolic problems. Those results were published in 2017.

在此前的一项研究中，美国圣地亚哥索尔克生物研究所(Salk Institute for Biological Studies)和其他机构的研究人员们开始对实验室小鼠的饮食模式进行实验。在该研究中，有一部分小鼠可以依自己的喜好，随时食用高脂肪食物，而其他小鼠虽然也可以享用完全相同的饮食，但它们每天可以进食的时间限制在八小时。两组小鼠都未进行任何运动。全天均可进食的小鼠很快就胖得圆滚滚的，健康也发生了问题，出现了糖尿病的症状。但是严格遵照八小时时间表进食的小鼠体重几乎没有增加，而且也未出现代谢问题。上述研究结果在2017年发表。

For the new study, which appeared in the journal Cell Metabolism in December, Salk scientists fed groups of adult males one of four diets: high-fat, high-fructose, high-fat and high-sucrose, and regular mouse kibble. Some of the mice in each dietary group were allowed to eat whenever they wanted throughout their waking hours; others were restricted to feeding periods of nine, 12 or 15 hours. The caloric intake for all the mice was the same.

而在去年12月发表于《细胞-代谢》(Cell Metabolism)杂志上的新研究中，索尔克生物研究所的科学家们分别以四种不同的饮食喂养四组成年雄性小鼠：高脂肪、高果糖、高脂肪兼高糖以及普通鼠粮。在每个饮食组中，又允许一部分小鼠在清醒状态下的任何时候进食，其他小鼠每天的进食时间则分别限制在9、12或15小时。所有小鼠摄入的热量卡路里数均相同。

Over the course of the 38-week experiment, some of the mice in the time-restricted groups were allowed to cheat on weekends and eat whenever they chose. A few of the eat-anytime mice were shifted to the restricted windows midway through the study.

在为期38周的实验过程中，限时进食的小鼠中又有一部分获准在周末“放纵一下”，随心所欲地在任何时间进食。在研究的中途，还有几只原本随时可以进食的小鼠被转移入限时进食组。

By the end, the mice eating at all hours were generally obese and metabolically ill, reproducing the results of the earlier study. But those mice that ate within a nine- or 12-hour window remained sleek and healthy, even if they cheated occasionally on weekends. What’s more, mice that were switched out of an eat-anytime schedule lost some of the weight they had gained.

在研究结束时，随时可以进食的小鼠普遍都变得肥胖，并患上了代谢疾病，这印证了早期的研究结果。但相比之下，即使周末偶有放肆，那些平时每天只有9或12小时可以进食的小鼠体型保持得很好，身体也很健康。更重要的是，从随时进食组转入限时进食组的小鼠原本增加的体重也有一定程度的减轻。

“Time-restricted eating didn’t just prevent but also reversed obesity,” says Satchidananda Panda, an associate professor at the Salk Institute who oversaw the studies. “That was exciting to see.” Mice that consumed regular kibble in fixed time periods also had less body fat than those that ate the same food whenever they chose.

“限时饮食不仅可以预防肥胖，还可以逆转肥胖，”该研究的负责人，索尔克生物研究所的副教授萨特旦安达·潘达(Satchidananda Panda)说，“这样的发现真令人兴奋。”此外，与在一天的任何时间都可以食用鼠粮的小鼠相比，每天只能在固定时段食用相同食物的小鼠的体脂肪量也较低。

Precisely how a time-based eating pattern staved off weight gain and illness is not fully understood, but Dr. Panda and his colleagues believe that the time at which food is eaten influences a body’s internal clock. “Meal times have more effect on circadian rhythm than dark and light cycles,” Dr. Panda says. And circadian rhythm in turn affects the function of many genes in the body that are known to involve metabolism.

目前尚不完全清楚基于时间的进食模式是如何避免体重增加和疾病的，不过，潘达博士及其同事们认为，进食的时间影响了身体内部的生物钟。潘达博士指出：“进食时间对昼夜节律的影响比光暗周期更大。”反过来，昼夜节律又可以影响体内许多已知与新陈代谢有关的基因的功能。

To date, Dr. Panda’s studies have been conducted with only mice, but he says the results seem likely to apply to humans. The upshot: Contain your eating to 12 hours a day or less. And pay attention to when you begin. The clock starts, Dr. Panda says, with “that first cup of coffee with cream and sugar in the morning.”

迄今为止，潘达博士仅在小鼠身上进行了研究，但他相信这些结果有可能同样适用于人类。因此我们最好将一天中的饮食时间限制在12小时或12小时之内，并留心每天开始进食的时间。“当你早上饮用第一杯加了奶油和糖的咖啡时”，计时就开始了，潘达博士说。