Users will enter their weight each day. The most important screen will be the graph. There should be on a horizontal line which is the users current average weight and then another horizontal line(their target) which will be one percent lower.
The app has very few screens. The only navigation will be to enter a weight on another screen, settings, and badges. It could use a tab bar at the bottom but would prefer not as Im a little tired of tab bars.
The second screen required is a welcome screen. Something with aspirational images, flat tummies etc. Some possible text "Welcome to the scientifically proven method to lose weight. The app uses proven behaviour change techniques designed to make weight loss easy", and a "Get started now" button