Reduced energy diets (REDs) identify ways within a person’s current eating habits to reduce 2000 to 4000 kJ from their usual energy intake each day.
They usually involve swapping energy dense foods for low energy density foods and managing portion sizes. For example, including more fruits and vegetables and less take-away foods is a way to decrease the energy density of your dietary intake.
REDs have the highest adherence in the long term which means more sustainable weight loss however weight loss is slower than when following the other strategies.
For more information on REDs see this: https://theconversation.com/health-check-whats-the-best-diet-for-weight-loss-21557.