In the fourth chapter, readers are provided with an overview of the fundamental factors that lead to successful weight loss. In addition to the biologically universal core principle of a negative energy balance, key physiological processes are highlighted. Furthermore, data and facts regarding caloric values are presented, enabling moderate and thus sustainable weight loss—so that every reader understands the basis of successful, long-term weight reduction and what to pay attention to when aiming to lose weight. It is made clear that there is no single “royal road” to weight loss—instead, the focus is on an individualized approach.