Clients often tell me they just want to lose 5 or 10 pounds to “lean out.” (Sound familiar?) But you’ve probably heard the old “muscle weighs more than fat” line. While that’s not technically true (a pound is a pound), it is true that a pound of muscle is denser and takes up less space than a pound of fat. So if your goal is to shed pounds, you really should be aiming to lose body fat and gain (or retain) muscle. Essentially, you’re hoping to shift your body composition and lower your body fat percentage. You can measure this in a number of ways: You can ask a trainer at your gym to test it using skinfold calipers, you can try a body-comp scale or monitor that uses bioimpedance (where you stand on or hold metal pads and a current determines your body composition), or you can go to a special lab for a more accurate (though pricier) air- or water-displacement test. Keep in mind that the first two options aren’t 100-percent accurate, but as long as the measurements are done under the same general conditions, you’ll be able to get a pretty good look at your progress.