The latest diet trend in America is also an ancient human activity. The activity is fasting, or not eating food for a set amount of time.
Social media apps and Facebook groups are appearing for people who do "intermittent fasting," or fasting on a part-time basis.
Like other diets, intermittent fasting helps you lose weight by setting limits on eating. But instead of limiting what you eat, it limits when you eat.
One of the more popular approaches to intermittent fasting is called "time-restricted feeding." It is not as difficult as some of the other approaches, since the fasting period can include the time you are sleeping.
The basic idea of time-restricted feeding is to limit eating to an eight-hour period. You then fast during the day's other 16 hours.
Many people make the eating period shorter or longer. Some eat just one meal a day.
In other approaches, people fast several days during a week. On fasting days, some people may permit themselves around 600 calories.
Whatever the approach, people are not supposed to overeat when they stop fasting.
Supporters and critics
Melissa Breaux Bankston is a Crossfit instructor in New Orleans, Louisiana. She tried intermittent fasting as a way to reduce her snacking. "I wanted to limit the amount of time that I was eating," she said.
Studies on the potential health benefits of intermittent fasting are still limited, including for its effectiveness with weight loss.
For now, limited research suggests it may not be any better for weight loss than reducing calorie intake over the long term.
"It's really another way of fooling your body into eating less calories," said Krista Varady, who studies intermittent fasting at the University of Illinois at Chicago.
Courtney Peterson, of the University of Alabama at Birmingham, also studies intermittent fasting. She suggested the benefits of intermittent fasting are not as great as some might suggest. "Unfortunately, intermittent fasting gets a little hyped," she said.
Is intermittent fasting right for you?
Some health experts say intermittent fasting might be too difficult for many people. They point to a study of 100 people where those placed in a fasting group lost about the same amount of weight as those on diets that restricted calories. The fasting group had a dropout rate of 38 percent, compared with 29 percent for the caloric-restriction diet group.
But intermittent fasting may be easier for people who already skip meals when they are too busy, said Varady.
People interested in intermittent fasting should talk to their doctor before trying it. Health experts do not recommend intermittent fasting for children, people on some medications and people with a history of eating disorders.
I'm John Russell.