Jennifer Aniston and Reese Witherspoon are both fans of intermittent fasting, in which you increase the daily overnight window where you don’t eat food.

The actors and costars of “The Morning Show,” which launches on Apple TV Plus on November 1, told the UK magazine Radio Times that they shunned solid food for 16 hours every day, leaving them a window of eight hours for eating.

“I do intermittent fasting, so there’s no food in the morning,” Aniston, 50, told the magazine.

“I noticed a big difference in going without solid food for 16 hours.”

While some advocates of intermittent fasting say that all you should consume during fasting hours is water and tea or coffee without milk or sweetener, both Aniston and Witherspoon said they preferred to stick to a liquid diet in the mornings, drinking juice and coffee.

Read more: How calorie-counting actually helped me develop a healthier relationship with food

Aniston said that she's a night owl and usually wakes up at around 8:30 or 9 a.m.

"Today, I woke up and had a celery juice," Aniston said. "Then I started to brew some coffee, but I don't drink coffee that early."

The actor said she fed her dogs, meditated, and worked out before drinking her coffee.

Witherspoon added: "I just have a green juice and a coffee in the morning."

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Her morning routine, however, starts somewhat earlier than Aniston's. She said her 7-year-old son wakes her up at 5:30 or 6 a.m.

Witherspoon, 43, said that she is in fact a morning person but doesn't love exercising early.

"I find it really hard to work out before 7:30 a.m. But that's the time I start one: 7:30 a.m," she said. "I probably do that six days a week."

Though Aniston said she works out one fewer day a week than her costar, Witherspoon said she often asks Aniston for "well-being" advice because she "knows so much" about health and fitness.

"Well, we want to thrive, right?" Aniston said. "We're just beginning."

Intermittent fasting has health benefits

Intermittent fasting has become increasingly popular in recent years, and studies have found a slew of health benefits, from lower blood pressure to increased longevity.

While some people fast to lose weight, many experts agree that the main reason it may lead to weight loss is that having a smaller window of eating means you're likely to eat fewer calories.

"This type of fasting often results in the consumption of fewer calories overall, which contributes to weight loss," Sue Ryskamp, a dietitian at the University of Michigan, said earlier this year.

Rhiannon Lambert, a registered nutritionist, agrees, writing that "the overall picture is that this is most likely due to overall calorie reduction, rather than the results of the fasting diet itself."

Research by Monash University in Melbourne, Australia, published in the British Medical Journal in January found that skipping breakfast could help people lose weight.

Read more: There's even more evidence that skipping breakfast might help you lose weight

David Higgins, a Hollywood personal trainer and physical therapist who has worked with the likes of Margot Robbie, previously told Insider that he thinks breakfast is overrated.

Read more: Margot Robbie's personal trainer thinks breakfast is overrated, and he says there are 2 clear benefits to fasting in the morning

But intermittent fasting doesn't have to mean skipping breakfast: If you prefer to eat in the morning, you can have your final meal earlier in the day and begin your fast after that.

It needn't be a 16-hour fast either - some people start by splitting their day into 12 hours for eating and 12 hours for fasting and then gradually increasing the fasting window.

Intermittent fasting isn't for everyone

Many nutritionists and dietitians have pointed out that intermittent fasting may not work for everyone, as some people simply function better when they eat throughout the day.

"Fasting can be a slippery slope to unhealthy habits and a screwy relationship with food," Jessica Cording, a registered dietitian, wrote for Shape magazine in August.

She added that for most people, it simply isn't a sustainable way to live and eat.

Lambert said that fasting could lead to fatigue, mood changes, low energy levels, and overeating.

"If you enjoy breakfast, then there is no need to fast until lunchtime because someone else lost weight from it," she said.

"There is no 'magic' behind intermittent fasting, and it is not superior as a weight-loss tool, but it is an interesting area of research that may well expand."