Everyone from Silicon Valley executives like Twitter CEO Jack Dorsey to Hollywood stars like Jennifer Aniston talked about "intermittent fasting" this year. Given the diet's popularity among high-profile individuals, it's no surprise that "intermittent fasting" was the top-trending diet search in Google in 2019, according to Google Trends data.
So what exactly is intermittent fasting and what is it supposed to do?
The eating method involves eating meals within a specific time frame and fasting for another period, according to the National Institute of Health.
Some people choose to restrict their meals to several hours during the day, for instance, eating normally from 9 a.m. to 5 p.m. (eight hours) and then having nothing but water, coffee or plain tea for the other 16 hours.
Another method of intermittent fasting entails alternating full days of fasting and full days of eating normally.
The so-called benefits of intermittent fasting are plenty. Some studies suggest that intermittent fasting could lead to weight loss, slow the effects of aging and even improve your cardiovascular health. But so far, these studies have been limited to mice or very small groups of people, so it's too soon to say whether it works in humans and whether the protocol would be safe for people to use outside of a lab and for the long-term.
As for the claims that intermittent fasting helps your brain perform? More mice studies suggest that intermittent fasting could improve cognition and even have a protective effect on the brain against neurodegenerative diseases such as Alzheimer's. However, experiencing hunger during fasting periods could significantly impact your ability to make decisions, think and concentrate.
Weight loss is another big draw. However, a 2018 study found that people who intermittent fasted for 50 weeks lost about the same amount of weight as those who followed a traditional diet that restricted their calories.
Ultimately, while intermittent fasting might be trendy and sound promising right now, it's not for everyone. It's not clear whether intermittent fasting is sustainable to follow long-term, or if it's safe for people above age 60 or those who take diabetes medications, according to the Mayo Clinic. Intermittent fasting could put people at risk of developing nutrient deficiencies, for example. For some who have a history of disordered eating, intermittent fasting could lead to increased binge-eating, or harm their relationship to food.
Even though the research on intermittent fasting is hazy, that hasn't stopped big names from adopting their own intermittent fasting routines.
Twitter and Square CEO Dorsey, for example, fasts all day and only eats dinner between 6:30 p.m. and 9 p.m. He claims that he's able to focus better when he's not being interrupted to eat, he told Ben Greenfield on his Ben Greenfield Fitness: Diet, Fat Loss and Performance podcast in April. On the weekends, Dorsey said that he'll go from Friday evening to Sunday evening without eating.
"I just found that I got so much more done during those fasting periods because I was so focused and it just felt like I had much more time to really think and to work in that moment," Dorsey said.
Actor Jennifer Aniston does a 16:8 intermittent fasting protocol, which means she eats for an eight-hour window during the day. She told RadioTimes.com in October that she wakes up at at 8:30 a.m or 9 a.m. and doesn't eat all morning.
"I noticed a big difference in going without solid food for 16 hours," she said.
Kourtney Kardashian has also experimented with intermittent fasting and the ketogenic diet, another hugely popular low-carb high-fat diet, a few years ago.
"I wouldn't eat past 7 p.m. at night, and then I would wait to eat the next day until after my morning workout, which would be around 10:30 a.m. or 11 a.m," she recalled on her website Poosh. Once a week, she would fast for 24 hours and only drink bone broth, water, and green tea.
Actor and fitness aficionado Chris Hemsworth told Men's Health UK in January that he only eats between 12 p.m. and 8 p.m.
"I've found that it dramatically increased my energy levels," he said. "I've found that once you get over the initial shock in the first week or two of not eating [as regularly], your body kicks into a different state."
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