Eat For 10 Hours. Fast For 14. This Daily Habit Prompts Weight Loss, Study Finds

Dec 8, 2019
Originally published on December 9, 2019 9:54 am

There's a lot of enthusiasm for intermittent fasting — a term that can encompass everything from skipping a meal each day to fasting a few days a week.

Or, how about this approach: Simply limit your daily eating window to 10 hours. This means that if you take your first bite of food at 8 a.m., you'd need to consume your last calorie of the day by 6 p.m.

A new study published in Cell Metabolism offers some evidence that the approach can be beneficial.

Researchers tracked a group of overweight participants who followed this approach for about three months. "Typically, people would go for an 8 a.m. to 6 p.m. eating window," explains Dr. Pam Taub, a cardiologist at the University of California, San Diego's School of Medicine, and an author of the study.

During the fasting period, participants were encouraged to stay hydrated with water. Each day, they logged the timing of their meals and their sleep in an app.

"We saw a 3% reduction in their weight and a 4% reduction in abdominal visceral fat," says Taub.

"We didn't ask them to change what they eat," she explains, though participants consumed about 8.6% fewer calories — likely as a result of the limited eating window.

In addition to the weight loss, "we saw that cholesterol levels improved and blood pressure [levels] also improved," Taub explains. There was also some reported improvement in sleep quality, and many of the participants reported more energy.

"We are surprised that this small change in eating time would give them such a huge benefit," says Satchidananda Panda, a professor at the Salk Institute for Biological Studies and a co-author of the study. Panda and Taub have some theories that may help explain the reduction in belly fat and weight loss.

"When you go into a fasting state, you start to deplete the glucose stores in your body and you start to use fat as your energy source," Taub explains. "You can enter a low-grade state of ketosis."

And once stored fat is fueling your body, "that can lead to a good amount of weight loss," Panda says.

There are still lots of unanswered questions when it comes to fasting, such as: Are shorter windows of fasting effective? "There is recent data to show that time-restricting [eating to] even 12 hours has beneficial effects," says Dr. Phyllis Zee, the director of the Center for Circadian and Sleep Medicine at Northwestern University's Feinberg School of Medicine. She was not involved in the new study, but we asked her to take a look at it. "What is interesting is the result on weight loss within 12 weeks," Zee says.

The study was small, just 19 people. All the participants were overweight and had a cluster of risk factors (elevated blood sugar, elevated cholesterol levels and high blood pressure) that put them at higher risk for Type 2 diabetes and heart disease. A larger study, funded by the National Institutes of Health, is underway to examine daily fasting in people with metabolic syndrome.

For now, the new findings offer some preliminary evidence of the benefits of daily fasting. Taub says you can think of a few extra hours of daily fasting as a way to give your metabolic organs a rest.

"When you're constantly giving the body calories, you're constantly making your cells work," she says. Just as your body and brain feel refreshed after a good night's sleep, the researchers say fasting can help restore and rejuvenate your organs.

This is not the first research to show that the timing of meals can make a difference to our waistlines. As we've reported, a study several years back found that dieters who ate their main meal of the day before 3 p.m. lost about 5 pounds more than people who ate a dinner meal late in the evening.

And as scientists learn more, it's clear that our bodies are timekeeping machines. Not only do we have a master clock in our brains, but there are also clocks in all the organs of our body — from the pancreas to the stomach and liver.

Daylight is a main cue to reset our master clock each day, but it's the first bite of food we take in the morning that may be an important cue to reset other clocks in our organs.

"When the timing of meals does not match with the sleep-wake cycle well, there's a disconnect between the different clocks that we have in basically all the cells of our body," Frank Scheer, director of the Medical Chronobiology Program at Brigham and Women's Hospital, told us several years back.

"When the clocks in our body are out of sync," our bodies don't work as efficiently, and this may lead us to store more fat, explains Panda. "And over a long period of time, that can lead to Type 2 diabetes, obesity and increased risk for heart diseases," Panda says.

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How does intermittent fasting affect your health? By intermittent fasting, we mean people who fast part of the time. Some skip one meal a day; some don't eat at all for several days per week. NPR's Allison Aubrey reports on a study that tracked what happens when people go hungry for 14 hours per day.

ALLISON AUBREY, BYLINE: There are lots of trendy ways to fast. Some people skip multiple meals. Some fast a few days a week. But Pam Taub, a cardiologist at UC San Diego, says there hasn't been a lot of evidence on which strategies are effective.

PAM TAUB: There's a lot of bogus claims out there.

AUBREY: People touting extreme versions, such as two-day fasts, which can be dangerous. Taub and her collaborators decided to test a simple and much more moderate approach. They asked people to restrict their eating to a 10-hour window each day.

TAUB: We didn't ask them to change what they ate. We didn't ask them to change the number of calories that they consumed.

AUBREY: The only instruction was to stick to the 10 hours. So if they ate breakfast at 8 a.m., their last bite of food for the day would need to be eaten by 6:00 p.m., making for a pretty early dinner. The participants followed this diet for three months, and Taub says she really didn't expect the results she found.

TAUB: We saw a 3% reduction in their weight and a 4% reduction in the abdominal visceral fat. So it is surprising to get these types of results.

AUBREY: Especially since all the participants really did was to stop eating a few extra hours each day. It turns out that by shutting off eating early, the participants, all of whom were overweight and at risk of diabetes, ate about 8% fewer calories. But this alone, Taub says, is unlikely to explain the weight loss. She thinks there may be other factors at play.

TAUB: So when you go into a fasting state, typically over 10 hours of fasting, you start to deplete the glucose stores in your body and you start to use fat as your energy source.

AUBREY: In other words, rather than fueling your body on stored sugars, you begin to fuel your body with stored fat. This study was small. Taub and her collaborators have a larger NIH-funded study underway. For now, the new findings offer some preliminary evidence that a 14-hour fast can be beneficial.

TAUB: When you're constantly giving the body calories, you're constantly making your cells work.

AUBREY: Taub says, think of a few extra hours of fasting as a way of giving your metabolic organs some rest.

Allison Aubrey, NPR News. Transcript provided by NPR, Copyright NPR.