This diet definitely blew up this year, but whether it’s a good idea for your long-term health is still under debate. It involves fasting for a specific amount of hours each day. You might fast for 16 hours, then eat for the other eight hours. "I would not recommend this approach to my clients as I don't think it's sustainable for the long term," Kelly Pritchett , PhD, RD, assistant professor in nutrition and exercise science at Central Washington University, previously told Refinery29 . "You have to ask yourself: Do I want to follow this plan for the rest of my life? If the answer is no, then it's not a sustainable approach to weight loss or healthy eating."