Why fasting for 16 hours a day may benefit the brain and body

A review of intermittent fasting studies suggests it's a genuinely healthy lifestyle.


Intermittent fasting could equate to a healthy lifestyle, a review article published this week in The New England Journal of Medicine suggests.

Until recently, most studies on caloric restriction and intermittent fasting focused on aging and life span. But the handful of studies on other potential effects indicate that, overall all, intermittent fasting has “broad-spectrum benefits” for health problems ranging from heart disease to neurologic disorders, the review finds.

But experts caution that intermittent fasting isn’t for everyone — especially those prone to adopting unhealthy eating patterns like emotional eating, binge eating, and eating disorders.

The benefits of intermittent fasting

The review looked at studies involving one of two categories of intermittent fasting diets. One is “daily time-restricted feeding,” which means one eats for six to eight hours a day and fasts for 16 to 18 hours a day. The other is “5:2 intermittent fasting,” which involves eating only one, moderate-sized meal for two days a week, and eating as per usual the rest of the time.

The article cites four studies, conducted in both animals and people, that together suggest intermittent fasting decreases blood pressure, blood lipid levels, and resting heart rates.

Intermittent fasting may also prompt weight loss, suggesting it could help reduce obesity and diabetes. In two studies conducted in the United Kingdom, researchers found that women who on the 5:2 diet lost the same amount of weight as women who simply restricted calories. But the women who fasted had less belly fat and did better on measures of insulin sensitivity.

Evidence suggests that fasting can modify risk factors associated with obesity and diabetes. 

Johns Hopkinds Medicine

Animal studies suggest that intermittent fasting could also enhance cognitive skills, including spatial memory, associative memory, and working memory.

It’s possible that some of the same cognitive benefits may be seen in humans, too. A clinical trial included in this review found that when a group of older adults participated in regimen of caloric restriction, they had improved verbal memory. And a separate, large, randomized clinical trial cited in the review showed that two years of daily caloric restriction led to significant improvement in working memory in adults.

Although these studies evaluated caloric restriction and not intermittent fasting specifically, the review authors say the positive results highlight the need for more targeted research into intermittent fasting and cognition. If similar evidence is found, it could pave the way to new interventions for neurodegeneration and dementia, they say in a statement.

What’s next for intermittent fasting

While the available evidence does hint at a link between intermittent fasting and a healthier life, the review authors — one of whom, Mark Mattson of Johns Hopkins Medicine, has fasted for twenty years — acknowledge that there are impediments to the widespread adoption of the diet. Fasting can make people grumpy (and, in turn, quit fasting), a diet of three meals a day is ingrained into our culture, and most physicians aren’t trained to prescribe intermittent-fasting interventions.

Scientists also don’t fully understand the mechanisms underlying the potential benefits of intermittent fasting. The diet needs to be studied further to truly know what health benefits can emerge, the review authors write. Understanding the effects of fasting on the body could lead to the development of targeted pharmacologic therapies that simply mimic those effects, they suggest.

In a statement, Mattson advised people interested in intermittent fasting to try it out over the course of several months. That way, the hunger pangs that inevitably arise may be easier to bear — and people can suss out whether or not it is really the right lifestyle choice for them.

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