The present disclosure relates to a method of inducing weight loss and/or preventing weight gain in a subject affected by administering certain diets selected based on the fasting blood glucose and/or the fasting insulin of the subject. The present disclosure further provides personalized dietary instruction, based on the fasting blood glucose and/or the fasting insulin of a subject, with the potential to improve the weight loss and prevent weight regain. The present disclosure further relates to methods for predicting weight loss success and classifying responsiveness of a subject to a certain diet as well as methods for selecting a weight loss or a weight gain diet for a subject based on the fasting blood glucose and/or the fasting insulin of the subject.