Body weight can be a difficult issue to grapple with. But we're software engineers—what if we approached it as an engineering problem? Our bodies have inputs (food) and outputs (water and waste). The difference between the two dictates weight changes.
It's a simplification, but it gives us a good starting point to model the system. When we understand the system, we can adjust inputs to affect desired changes.
We'll learn about concepts introduced in The Hacker's Diet such as running averages of weight to “hack” ourselves not to read too much into scale readings, managing and adjusting calories to our activity levels, and exercising not to lose weight but to be healthier.