Now playing
01:01
Intermittent fasting may help you live longer
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
PHOTO: Jeenah Moon/Getty Images
NEW YORK, NY - JULY 23: New York Gov. Andrew Cuomo speaks during the daily media briefing at the Office of the Governor of the State of New York on July 23, 2020 in New York City. The Governor said the state liquor authority has suspended 27 bar and restaurant alcohol licenses for violations of social distancing rules as public officials try to keep the coronavirus outbreak under control. (Photo by Jeenah Moon/Getty Images)
Now playing
04:04
NYT: Second former aide accuses Gov. Andrew Cuomo of sexual harassment
PHOTO: CNN Weather
Now playing
02:23
Over 25 million people under threat for severe storms and flash flooding
House Speaker Nancy Pelosi
PHOTO: House TV
House Speaker Nancy Pelosi
Now playing
02:52
House passes Biden's $1.9 trillion Covid-19 relief package
PHOTO: CNN
Now playing
02:54
'Biggest trial of my life': Landlord says eviction moratorium has drained her savings
Jeremy Lin
PHOTO: Getty Images
Jeremy Lin
Now playing
03:40
Ex-NBA star Jeremy Lin says he's been called 'coronavirus' on the court
covid-19 relief package house biden sot malveaux nr vpx _00000000.png
PHOTO: CNN
covid-19 relief package house biden sot malveaux nr vpx _00000000.png
Now playing
02:28
CNN's Joe Johns explains Biden's short speech as relief bill heads to Senate
Misinformation Trump Capitol March rn orig_00004630.png
Misinformation Trump Capitol March rn orig_00004630.png
Now playing
04:08
These Trump supporters are convinced he will be president again on March 4
PHOTO: Isaac Abrack
Now playing
03:00
Hear from schoolgirl who escaped abduction in Nigeria
Saudi Crown Prince Mohammed bin Salman attends a conference in the Saudi capital Riyadh on October 2018.
PHOTO: FAYEZ NURELDINE/AFP/Getty Images
Saudi Crown Prince Mohammed bin Salman attends a conference in the Saudi capital Riyadh on October 2018.
Now playing
02:10
US intel report: Saudi Crown Prince responsible for approving Khashoggi operation
WASHINGTON, DC - JANUARY 17: The U.S. Capitol dome is seen beyond a security fence on January 17, 2021 in Washington, DC. After last week
PHOTO: Michael M. Santiago/Getty Images
WASHINGTON, DC - JANUARY 17: The U.S. Capitol dome is seen beyond a security fence on January 17, 2021 in Washington, DC. After last week's riots at the U.S. Capitol Building, the FBI has warned of additional threats in the nation's capital and in all 50 states. According to reports, as many as 25,000 National Guard soldiers will be guarding the city as preparations are made for the inauguration of Joe Biden as the 46th U.S. President. (Photo by Michael M. Santiago/Getty Images)
Now playing
02:33
This is what's in the $1.9 trillion coronavirus package
PHOTO: CNN
Now playing
09:36
I lost everything: Texas mom's devastating story from winter storm
The Pentagon, the headquarters of the US Department of Defense, located in Arlington County, across the Potomac River from Washington, DC is seen from the air January 24, 2017.  / AFP PHOTO / Daniel SLIM        (Photo credit should read DANIEL SLIM/AFP via Getty Images)
PHOTO: Daniel Slim/Getty Images
The Pentagon, the headquarters of the US Department of Defense, located in Arlington County, across the Potomac River from Washington, DC is seen from the air January 24, 2017. / AFP PHOTO / Daniel SLIM (Photo credit should read DANIEL SLIM/AFP via Getty Images)
Now playing
05:24
US carries out airstrikes on Iran-backed militia groups
(CNN) —  

Abstaining from food for 16 to 18 hours a day could be key to treating a variety of health conditions – even if you’ve got to train yourself to push past the hunger.

A review of past animal and human studies in The New England Journal of Medicine suggests that intermittent fasting can reduce blood pressure, aid in weight loss and improve longevity.

The report functions as a road map of sorts for physicians to prescribe fasting as a method of prevention or treatment for obesity, cancer, diabetes and heart disease.

Study author Mark Mattson, a professor of neuroscience at Johns Hopkins University, hones in on two types: Daily time-restricted feeding (eating 6-8 hours a day and fasting for 16-18 hours) and 5:2 intermittent fasting (fasting two days a week, usually capping a fasting day at 500 calories).

The catch? Most Americans don’t intermittently fast (the norm is three meals a day plus snacks) and thus physicians are less inclined to consider fasting a solution to a broad range of health conditions, according to the review.

Because the research is relatively new, the report advises physicians to monitor their patients throughout intermittent fasting and gradually increase the duration and frequency of fasting to guide their transition.

How it works

Intermittent fasting has been studied in rodents and overweight adults to improve health across the spectrum, though it’s not clear if those benefits are the result of weight loss.

Alternating between fasting and eating can improve cellular health, Mattson said, most likely by triggering metabolic switching. In metabolic switching, cells use up their fuel stores and convert fat to energy – “flipping a switch” from fat-storing to fat-saving.

The benefits

Findings on intermittent fasting range in the diet’s effectiveness, but some studies in animals and humans have linked the practice to longer lives, healthier hearts and improved cognition.

The article points to the residents of Okinawa, known for their extreme longevity and low-calorie, nutrient-rich diet. Their intermittent fasting might contribute to their life spans and keep obesity at bay, the authors posited.

Intermittent fasting is thought to improve insulin resistance, which can stabilize blood sugar levels. Findings from a small 2018 study found that three men with type 2 diabetes, also known as adult-onset diabetes, were able to stop taking insulin after losing weight from intermittent fasting – findings that clash with the widely-held belief that diabetes is incurable.

A previous study (that Mattson co-authored) showed the switch can increase resistance to stress by optimizing brain function and neuroplasticity, or the brain’s ability to adapt to develop throughout one’s life. And older adults who were put on a restricted-calorie diet showed improved verbal memory compared to two other groups who hadn’t fasted, a 2009 study found.

Physical function even improved for some patients. A study of young men who fasted every day for 16 hours lost fat and retained muscle while resistance training for two months.

The limitations

The long-term effects of intermittent fasting require more research that isn’t available yet, and the studies that do exist are narrow. The clinical trials focused on overweight young and middle-age adults, so the benefits and safety can’t be generalized to other groups, the authors said.

Another thing: It’s a difficult diet to stick to, particularly in the United States, where the concept of three meals a day is “so ingrained in our culture” that a change in eating pattern often doesn’t cross doctors’ or patients’ minds, Mattson wrote.

It’ll almost definitely leave participants hungry, irritable and less able to concentrate, the study said.

Almost 40% of people who were assigned to a fasting diet dropped out of a 2017 JAMA study – one of the drawbacks of intermittent fasting as a weight-loss regimen, Dr. Frank Hu, chairman of the Department of Nutrition at Harvard University’s T.H. Chan School of Public Health, noted to Harvard Health Publishing.

“It’s human nature for people to want to reward themselves after doing very hard work, such as exercise or fasting for a long period of time,” he said. “So there is a danger of indulging in unhealthy dietary habits on non-fasting days.”

Get CNN Health's weekly newsletter

Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

When the brain is deprived of food, appetite hormones in the hypothalamus, the brain’s “hunger center,” are released in a flurry and can trigger overeating.

But Mattson said the pain is temporary.

“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,” he said.