She was right. You generally cannot win a battle against a defective weight-regulating gizmo by having good intentions or thinking good thoughts. You must have a biological strategy that gets the gizmo working again. Spontaneous Normal weight regulation is surprisingly stable, maintaining body weight within a 5-10 lb. range even with major changes in activity, and food supply. If you are lucky, modest changes in food intake do not change body weight, but rather change body heat and activity level.
Efficiency factors change the balance between energy utilization and storage.
A key concept in weight management is that appetite and weight regulation is largely determined by the adequacy of the incoming nutrient set. These food qualities influence the set point and eating behaviors. Nutrient density is the nutrient to calorie ratio of the food supply. You can only reduce calories if you increase the nutrient density of the food you eat. This is most easily accomplished by adding an appropriate complete nutrient formula to the day's food supply.