Others in this thread have pointed out that diets will fail if you eat too little. If you enter the starvation mode (too few calories to fight disease or maintain a healthy life) your body becomes super efficient. In this survival mode you will always be starving and your basic core instincts will not allow this if there is available food. After a period of starvation, you will gorge yourself and you will not be able stop this eating, no matter your will not too. This type of dieting will fail. It not you, it's a million years of survival training that is buried in your thinking process. It is good.
Solution: Add a couple of hundred calories to your RDI and exercise a couple of hundred less. PLUS, accept this is a long term (Months, repeat, Months) process and a life long plan.
The Perfect Speed
"any number is a limit, and perfection doesn't have limits.
Perfect speed, my son, is being there.”
Chiang from "Jonathan Livingston Seagull