Definition of body composition may be deceptive in the type of actions you should take.
As a fitness component, body composition defines the percentages of water, muscle, bone and fat. To determine obesity and weight loss goals, the focus becomes the percentage of fat without the body. To increase metabolism, the focus shifts to percentage of muscle tissue that burns hotter.
In theory, a fit body has less fat in relation to muscle tissue. However, a slim person may pass this criterion and still fail other health related tests including high blood pressure and high cholesterol. Define body composition in relation to your health rather than your look.