Two of the more well-known IF plans are the 5:2 diet and the alternate-days approach, says Liz Weinandy, a registered dietitian at Ohio State University's Wexner Medical Center in Columbus, OH.
"Under the 5:2 diet, individuals eat normally but healthfully for five days of the week and consume only 500 to 800 calories on two nonconsecutive days," Weinandy said. "On the restricted-calorie days, some might opt to split their calories into two or three mini meals."
Under the alternate-days plan, Weinandy said you would eat normally one day, then fast for part of the day and eat fewer than 600 calories the next day.
A third, though less popular, approach is an everyday method, in which individuals restrict their eating to six to eight hours only, every single day, without altering their caloric intake. A popular option is the 16/8 plan, in which you fast for 16 hours and eat for eight.