It's a pretty well known fact that, when trying to lose weight, you have to create a caloric deficit -- for every 3500 calories burned, that's one pound of weight lost. Thus, it takes a combination of diet and exercise to create said deficit. However, it is exceedingly difficult to keep track of your caloric intake, as well as calculate the calories burned for various activities. If you're serious about getting in shape, though, there is a solution: using an automatic body monitoring system like BodyMedia's FIT Armband.
So, what does this have to do with Android, you ask? The BodyMedia FIT has a corresponding app in which it communicates with via Bluetooth, making it even easier to monitor where you're at for the day.