The truth is, the most effective diet is the one you can stick to for a long time. Making a lasting change takes time, and bouncing from diet to diet, losing and gaining the same five pounds over and over, isn’t going to get you anywhere. If having a cookie every night after dinner helps you finally reach your goal weight, that’s significantly better than trying to cut out all sweets and resorting to binge eating every weekend, making no long-term progress.