The Jaminets in their book 'The Perfect Health Diet' evoke the principle that the provision of what the body needs allows for lower energy intake.
For example, if we have a deficit of carbohydrate, we can eat more protein in an attempt to compensate for the lack, however we will consume more calories than if we had gotten the balance right.
So, if you're having difficulties staying to your diet 1) Did you eat enough? 2) Did what you ate stimulate your appetite? 3) Did what you ate provide what your body needed in the right proportions?
Often low-calorie diets focus on low calorie foods, whereas having a full stomach is the last thing we should aim for.