Does intermittent fasting work?

间歇性禁食有效吗？

It does for weight loss. Its other supposed benefits are debatable

对于减肥确实有效。但其宣称的其他健康效益仍有争议

Diets come and diets go. One of the most popular today is “intermittent fasting” in which, as the name suggests, the idea is to limit one’s food intake to certain time windows. One popular variant, the “5-2 diet”, requires people to eat either very small amounts, or nothing at all, on two days a week, but imposes no restrictions on the other five.

减肥方法层出不穷。时下最流行的当属"间歇性禁食"——顾名思义，就是将进食时间限定在特定时段。其中"5-2轻断食法"颇受欢迎，要求每周两天仅少量进食或完全禁食，其余五天则无需限制。

Intermittent fasting is popular. And as a weight-loss strategy, it has several things going for it. One is that it is uncomplicated. There is no need to weigh the ingredients of every meal, as some diets demand, nor to change what you eat drastically. Limiting the restrictions to a couple of days a week, or several hours a day (most of which are spent asleep) also requires less willpower, which might make it easier to stick with.

这种饮食方式大行其道。作为减重策略，它具备多项优势。其一，操作简单。无需像某些饮食法那样精确称量每餐食材，也无需彻底改变饮食结构。每周仅需坚持数天，或每天限制数小时（大部分时间在睡眠中度过），意志力的消耗相对较少，因此更易长期坚持。

Working out whether that actually translates into greater weight loss than other diets is difficult. Most studies find limited data and mixed results. The general consensus, says Nichola Ludlam-Raine, a dietitian and spokeswoman for the British Dietetic Association, is that intermittent fasting seems to work roughly as well for weight loss as traditional calorie-counting does.

但要验证其减重效果是否优于其他饮食法却非易事。多数研究数据有限且结果不一。英国饮食协会发言人、营养学家尼古拉·拉德拉姆-雷恩指出，学界普遍认为间歇性禁食与传统热量控制法在减重效果上大致相当。

Other health benefits might also beckon. Forcing lab animals to fast (albeit not intermittently) can increase their lifespans by up to 40%. It also appears to mitigate the physical decline that comes with old age, boost various markers of metabolic health and even reduce susceptibility to cancer.

该饮食法可能还具备其他健康裨益。实验室动物强制禁食（尽管不是间歇性禁食）可延长寿命达40%，同时能延缓机体衰老、改善代谢指标，甚至降低患癌风险。

Exactly how it does all that is not entirely clear. One important factor seems to be autophagy, the process by which cells break down and recycle parts of themselves. Cells become much keener on autophagy when nutrients are scarce. 

具体作用机制尚未完全阐明。一个重要因素可能是细胞自噬机制——即细胞分解并回收自身部分结构的过程。当营养匮乏时，细胞自噬活动显著增强。

At the same time, autophagy seems to have a preference for attacking damaged and degraded parts of cells—and the accumulation of such cellular detritus is one of several mechanisms thought to underlie the decrepitude that comes with ageing.

同时，这种机制优先清除细胞内的受损老化部分，而此类细胞碎片的堆积正是导致衰老的重要因素。

The hope is that intermittent fasting might provoke a similar response in humans. There are theoretical reasons to think it might: the cellular mechanisms triggered by food shortages seem to have been conserved by evolution in all sorts of different animals. 

人们期待间歇性禁食能在人体引发类似反应。从理论上讲确有可能：食物短缺引发的细胞机制似乎已在各类动物中进化保留。

But running definitive human trials of the sort done on lab animals is impossible. “When we say ‘calorie restriction’ we mean nearly starving [the animals],”says Adam Collins, a nutrition researcher at the University of Surrey.

但要在人体开展实验室动物那种严格试验并不可行。萨里大学营养学家亚当·柯林斯指出："我们所说的'热量限制'对实验动物而言近乎饥饿疗法。"

That leaves scientists reliant, for now, on smallish, short-lived studies that use less drastic diets and which rely on proxy measures of health such as insulin response or cholesterol levels. Their results are mixed. 

目前科学家只能依赖规模较小、周期较短的替代性研究，这些研究采用较温和的饮食方案，并以胰岛素反应或胆固醇水平等替代指标评估健康效益。研究结果同样存在分歧。

Dr Collins’s team, for instance, has published a randomised-control trial (the most rigorous sort) suggesting that intermittent fasting improves the metabolism of fats more than ordinary dieting does. 

柯林斯博士团队发表的随机对照试验（最严谨的研究类型）显示，间歇性禁食比普通节食更能改善脂肪代谢。

A review paper published in April 2024 looked at 23 other studies and concluded that intermittent fasting was slightly better than ordinary dieting for overweight people when it came to improving levels of cholesterol and insulin. A similar article, published in January, found no meaningful difference for either weight loss or cardiovascular health.

2024年4月发表的一篇综述对23项研究进行分析后认为，在改善超重人群胆固醇和胰岛素水平方面，间歇性禁食略胜一筹；但同年1月的另一篇类似论文发现，在减重效果和心血管健康方面两者并无显著差异。

There are also risks. A study in mice published in Nature in October 2024 found that severe fasting (where calories were cut by 40%) had downsides, including muscle mass loss and, possibly, weakened immune systems. Moderation, too, should be taken in moderation.

潜在风险亦不容忽视。2024年10月《自然》杂志刊登的一项小鼠实验表明，严格禁食（热量摄入减少40%）会导致肌肉流失，并可能削弱免疫系统。适度原则本身也需把握分寸。

（红色标注词为重难点词汇）

重难点词汇：

intermittent [ˌɪntərˈmɪtənt] adj. 间歇的；断断续续的

variant [ˈveəriənt] n. 变体；变种 adj.不同的；变化的

drastically [ˈdræstɪkəli] adv. 彻底地；激烈地；极大地

willpower [ˈwɪlpaʊər] n. 意志力；毅力

mitigate [ˈmɪtɪɡeɪt] v. 减轻；缓和；缓解

decrepitude [dɪˈkrepɪtjuːd] n. 衰老；虚弱；老朽

proxy [ˈprɒksi] n. 代理；代表；代理人 v. 代理；代表