News Release 25-Dec-2019

Johns Hopkins Medicine

For many people, the New Year is a time to adopt new habits as a renewed commitment to personal health. Newly enthusiastic fitness buffs pack into gyms and grocery stores are filled with shoppers eager to try out new diets.

But, does scientific evidence support the claims made for these diets? In a review article published in the Dec. 26  issue of The New England Journal of Medicine, Johns Hopkins Medicine neuroscientist Mark Mattson, Ph.D., concludes that intermittent fasting does.

Mattson, who has studied the health impact of intermittent fasting for 25 years, and adopted it himself about 20 years ago, writes that “intermittent fasting could be part of a healthy lifestyle.” A professor of neuroscience at the Johns Hopkins University School of Medicine, Mattson says his new article is intended to help clarify the science and clinical applications of intermittent fasting in ways that may help physicians guide patients who want to try it.

Intermittent fasting diets, he says, fall generally into two categories: daily time-restricted feeding, which narrows eating times to 6–8 hours per day, and so-called 5:2 intermittent fasting, in which people limit themselves to one moderate-sized meal two days each week.

An array of animal and some human studies have shown that alternating between times of fasting and eating supports cellular health, probably by triggering an age-old adaptation to periods of food scarcity called metabolic switching. Such a switch occurs when cells use up their stores of rapidly accessible, sugar-based fuel, and begin converting fat into energy in a slower metabolic process.

Mattson says studies have shown that this switch improves blood sugar regulation, increases resistance to stress and suppresses inflammation for various periods of time. Because most Americans eat three meals plus snacks each day, they do not experience the switch, or the suggested benefits.

In the article, Mattson notes that four studies in both animals and people found intermittent fasting also decreased blood pressure, blood lipid levels and resting heart rates.

Evidence is also mounting that intermittent fasting can modify risk factors associated with obesity and diabetes, says Mattson. Two studies at the University Hospital of South Manchester NHS Foundation Trust of 100 overweight women showed that those on the 5:2 intermittent fasting diet lost the same amount of weight as women who restricted calories, but did better on measures of insulin sensitivity and reduced belly fat than those in the calorie-reduction group.

More recently, Mattson says, preliminary studies suggest that intermittent fasting could benefit brain health too. A multicenter clinical trial at the University of Toronto in April found that 220 healthy, nonobese adults who maintained a calorie restricted diet for two years showed signs of improved memory in a battery of cognitive tests.
While far more research needs to be done to prove any effects of intermittent fasting on learning and memory, Mattson says if that proof is found, the fasting — or a pharmaceutical equivalent that mimics it — may offer interventions that can stave off neurodegeneration and dementia.

“We are at a transition point where we could soon consider adding information about intermittent fasting to medical school curricula alongside standard advice about healthy diets and exercise,” he says.

Mattson acknowledges that researchers do “not fully understand the specific mechanisms of metabolic switching and that “some people are unable or unwilling to adhere” to the fasting regimens. But he argues that with guidance and some patience, most people can incorporate them into their lives. It takes some time for the body to adjust to intermittent fasting, and to get beyond initial hunger pangs and irritability that accompany it. “Patients should be advised that feeling hungry and irritable is common initially and usually passes after two weeks to a month as the body and brain become accustomed to the new habit,” Mattson says.

To manage this hurdle, Mattson suggests that physicians advise patients to gradually increase the duration and frequency of the fasting periods over the course of several months, instead of “going cold turkey.” As with all lifestyle changes, says Mattson, it’s important for physicians to know the science so they can communicate potential benefits, harms and challenges, and offer support.

Rafael de Cabo, Ph.D., of the Translational Gerontology Branch of the National Institute on Aging Intramural Research Program, is a co-author of the published review.

This work was supported by the Intramural Research Program of the National Institute on Aging, National Institutes of Health.

Disclosure forms provided by the authors are available with the full text of this article at NEJM.org.

间歇性禁食已成为过去20年来最受欢迎的健康和健身趋势之一，据信其可以减肥、增强精力和延长寿命。

但这种饮食主张是否有科学依据呢？在《新英格兰医学杂志》（The New England Journal of Medicine）上发表的一篇综述中，约翰霍普金斯医疗集团的神经学家Mark Mattson博士得出结论认为该饮食主张有科学依据。 Mattson对间歇性禁食的健康影响进行了25年的研究，在大约20年前他自己也采用了这种饮食方式，他写道，间歇性禁食可成为健康生活方式的一部分。约翰霍普金斯大学医学院的这位神经学教授表示，他的新文章旨在帮助阐明间歇性禁食的科学和临床应用，以帮助医生指导想要尝试该饮食方式的患者。

他表示，间歇性禁食饮食方式通常分为两类：每日限时进食，每天进食时间缩窄至6-8小时；以及所谓的5:2间歇性禁食，即每周有两天仅吃一顿中等量的餐食。

一系列动物和一些人类研究表明，交替禁食和进食有利于细胞健康，可能的机制是激发了一种古老的对食物稀缺时期的适应（称之为代谢转换）。当细胞耗尽其可快速获得的糖类能源储存并通过较慢的代谢过程开始将脂肪转化为能量时，就会发生这种转换。 Mattson表示，研究还表明，这种转换可以改善血糖调节，增加抗压性，并在不同时间段内抑制炎症。由于大多数美国人每天进食三餐外加点心，因此他们不会发生该转换或获得其带来的益处。

Mattson在文章中指出，四项动物和人类研究发现，间歇性禁食还会降低血压、血脂水平和静息心率。 越来越多的证据表明间歇性禁食可以改变与肥胖和糖尿病相关的风险因素，Mattson说道。南曼彻斯特大学医院NHS信托基金会对100名超重女性开展的两项研究显示，采用5:2间歇性禁食饮食方式的女性的体重减轻量与采用卡路里限制的女性相同，但在胰岛素敏感性和腹部脂肪减少指标上禁食组比卡路里限制组表现更好。

Mattson最近表示，初步研究表明间歇性禁食也有益于大脑健康。4月在多伦多大学进行的一项多中心临床试验发现，220名保持卡路里限制饮食达两年的健康、非肥胖成年人在一系列认知测试中显示出记忆力改善的迹象。

Mattson表示，尽管需要开展更多的研究来证明间歇性禁食对学习和记忆力的影响，但如果发现这种证据，该饮食方式（或有类似作用的药物）可提供一种能防止神经变性和痴呆的干预措施。

我们正处于一个转折点，我们可能很快就会考虑将有关间歇性禁食的信息添加到医学院课程中，同时提供有关健康饮食和运动的标准建议。

Mattson承认研究人员尚不完全了解代谢转换的具体机制，并且有些人不能或不愿意遵守禁食方案。但他认为，在耐心指导下，大多数人可以在日常生活中坚持该饮食方式。身体需要一段时间才能适应间歇性禁食，并摆脱伴随禁食的最初饥饿感和烦躁不安。他说，

应该告知患者饥饿感和烦躁不安最初很常见，但随着身体和大脑习惯这种新饮食方式，这些现象会在两周到一个月后消失。

为了克服这个障碍，Mattson建议医生指导患者在几个月的时间内逐渐增加禁食期的持续时间和频率。Mattson表示，与所有生活方式的改变一样，医生有必要了解科学依据，这样他们就可以告知潜在的利益、危害和挑战，并提供支持。

国家老龄化研究所转化老年学分所院内研究项目的Rafael de Cabo是本综述的共同作者。

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