When you’re following a weight-loss plan, few things are more encouraging than seeing the number on the scale go down. Unfortunately, many people who see weight-loss success wind up losing muscle along with fat.
This matters because not only is muscle key for helping you perform everyday tasks (i.e., carrying groceries, putting away heavy bags and boxes overhead), but muscle is also metabolically active tissue; this means muscle burns more calories at rest than fat. Maintaining a good amount of lean muscle mass keeps your basal metabolic rate (i.e., the number of calories your body burns at rest) elevated, which may help you lose fat in the long-term.
So, how do you know if you’re losing fat or muscle? Here are a few ways to tell:
One of the best ways to know whether you’re losing fat or muscle is to examine your exercise routine. If you’re doing a lot of cardio, but you’re not adding strength training, there’s a good chance any weight you lose will be about 50% muscle and 50% fat (though you’ll lose some water weight as well), says Heather Milton, MS, certified strength and conditioning specialist and board-certified clinical exercise physiologist at NYU Langone’s Sports Performance Center.
Assuming you’d like to keep your muscle, make sure to lift weights a minimum of two days per week, and hit all the large muscle groups (e.g., glutes, quads, hamstrings, back and chest). “When you use those muscles, you generate greater recruitment of muscle fibers, and you get a better bang for your buck in terms of energy cost,” Milton says. In other words, prioritizing larger muscle groups over smaller ones (like the biceps and triceps) results in more calories burned — both during and after your workout.
Another way to tell if you’re losing muscle instead of fat is if you notice greater levels of fatigue than usual or if you’re easily tired doing activities that don’t usually make you tired, Milton says.
The only trouble with using energy levels to gauge whether you’re losing fat or muscle is there are many other factors that influence energy, including sleep, diet and medications. Make sure you’re taking other measurements (like those below) into consideration.