If you want to lose weight, your Apple Watch can help you sustain healthy habits, but it can’t actually monitor your progress. For that you need to step onto scales.
Any scale will measure your weight, but that is only part of the story. Whether you are dieting or bulking up, it is just as important to keep track of your body fat. The trouble is, this is notoriously hard to measure accurately. As I discovered when I bought a new Withings Smart Body Analyzer, if you think you already know your body fat percentage, you are probably way off.