The engine behind getting healthy is you and then metabolism, which is the burning of the foods ingested and determined by how quickly and efficiently the body can use up the calories. With respect to weight loss it is about burning the accumulated fat reserves then building up the body with nutrients. For developing health, muscle, and overall well being it is about efficiency of breaking down food and assimilating the nutrients.
The calories written on a food label are determined by actually burning the food in a bomb calrimeter that measures the amount of heat to fully consume an item. In the body though hydrochloric acid is made by the stomach to break the food down into its usable ingredients and then move it to the intestines to be absorbed through the intestinal wall and processed to the cells. This is why it is critical that a person stays away from junky food and gets plenty of vitamins and minerals from a nutritious lifestyle. You want to use the best materials to build yourself up right?
The trick is to achieve your goal is to maintain the balance that brings you to your goal. Get your calories from a nutritious lifestyle and you can eat greater quantities without guilt, actually be less hungry, and receive more energy. The vitamins and minerals that you eat will maximize the efficiency along with probiotics that maximize the nutrient processing.
Nutrition + Fitness = Health