To look at things in a simple manner, if you have something on or in your body and you lose it, you lose weight. Then logically, a loss of fat leads to a loss of weight. But it is possible to lose fat and stay the same weight, provided you are replacing that fat with something else: muscle. Mar 27, · Yes, of course two people can be the same height and weight, and have a vastly different body composition. How are we supposed to know if you're going to be lean at 58kg, if we have no idea what your body fat is, or what your idea of lean is? Tracking your body fat in addition to body weight will help to minimize fat gains as you bulk. How to Measure & Track Your Body Fat Percentage. There are several ways to measure your body fat, but not all are created equal. None of the methods are % accurate, but some are far superior to others.