Wondering If You’re Gaining Muscle or Fat? Look for These Expert-Backed Signs

When you're actively trying to put on muscle, it can be confusing to see the numbers on the scale fluctuate. Whether you've just started strength training or noticed your body changing, it's often tough to tell whether a new weight points to increased muscle mass or fat — especially since body composition changes slowly over time. That said, if you want to know whether you're gaining muscle or fat, there are a few ways to tell the difference.

To help you better understand what might be happening to your body, we asked fitness experts how to tell whether you're gaining muscle or fat. Read on to learn the difference between fat weight gain and muscle weight gain, and the signs of both. Plus, see why you shouldn't rely on the numbers on the scale to track your fitness progress.

Gabbi Berkow, RD, CPT, CDN, is a registered dietitian, exercise physiologist, and certified personal trainer.

Rondel King, MS, CSCS, is an exercise physiologist and founder of sports tech startup WorkRate.

On the most basic level, gaining fat is the result of eating more calories than you burn, says Gabbi Berkow, RD, CPT, CDN. That means anything eaten in excess, whether that's protein, carbs, or fat, can be stored as fat if the calories you eat are greater than the calories you burn. "Let's say, for instance, you're eating an excess of 1,000 calories than your resting metabolic rate is calling for. That needs to go somewhere," explains exercise physiologist Rondel King, MS, CSCS. "As a defense mechanism, [your body] stores those excess calories as fat."

It's also important to note that everyone's body stores fat differently. Based on genetics, some people store more visceral fat (fat around the organs within the abdominal cavity) and others store more subcutaneous fat (the layer of fat between your skin and your muscles).

Gaining muscle is typically harder and requires more work than gaining fat, Berkow notes. "You have to progressively overload your muscles by lifting weights and continually challenging yourself over time," she says. "After every workout, your muscles build more fibers so that they're better equipped to handle the stress of the next workout." But your body eventually gets used to the load, which is why you have to keep increasing the intensity to see progress.

Building muscle is also related to your diet. Protein is necessary because it provides the nutrient building blocks you need to develop more muscle tissue, King explains. That eventually helps you become stronger and better withstand the workout stresses that you place on your body. Since muscle is made of protein, you have to consume plenty of protein — around one gram per pound of body weight every day — for your body to be able to build muscle, Berkow says.

Generally speaking, you'll build the most muscle if you eat more calories than you burn, Berkow says. That means it's possible to gain fat while building muscle. Building muscle without gaining fat is possible, but it requires "strict attention to calories and protein, and you won't put on as much muscle as you would if you ate more calories than you burned," she says. Additionally, you likely won't be able to "bulk up" on muscle if you're focused on losing weight (due to the amount of calories required to build muscle), so be mindful when creating realistic fitness goals.

No, muscle is not "heavier" than fat. A pound of muscle weighs the same as a pound of fat: one pound equals one pound. However, muscle is denser than fat, Berkow says. "It has more water, protein, carbohydrates, and fats in it than fat does, but it takes up less space." Because of that, "the same amount or weight of muscle takes up less space than fat," she says. That's why gaining muscle can result in losing inches on your waist, but not necessarily seeing lower numbers on the scale.

Measuring your body composition — how much of your body is made up of water, muscle, and fat — is the best way to assess whether you're gaining fat or muscle, Berkow says. King notes that many gyms do body composition tests of some sort before people start programs in order to get baseline values and therefore set realistic goals. Some tests include the following:

It's important to note that — for some people — focusing on specific body measurements can lead to an unhealthy preoccupation with exercise, food, or weight loss, and can trigger body image concerns and even disordered eating. If you're predisposed to or have a history of disordered eating, consider skipping any sort of quantitative body measurement. And remember that health cannot be measured solely by the number on a scale or body fat percentage.

If you or someone you know is struggling with disordered eating or an eating disorder, the National Eating Disorder Association (NEDA) has resources available including a 24/7 helpline at 1-800-931-2237 or by texting "NEDA" to 741741.

Aesthetically, it may be difficult to tell if you're gaining muscle or fat. If you gain fat, you'll likely notice more softness, Berkow says. Conversely, when you gain muscle, you may notice that your muscles naturally look more defined and are more visible, she says. They may also look larger in size or feel "harder." Aesthetics aside, a good way to tell if you're gaining muscle is if your workouts feel easier. If you're able to pick up heavier weights, exercise for longer, or move through your sets feels easier, those are all good indicators that you're gaining muscle (and strength).

Even if you're losing fat, the number on the scale may not be going down if you're also gaining muscle, Berkow says. Instead of fixating on the scale, here are some other progress indicators to pay attention to:

If you're frustrated with your weight staying the same for a period of time, Berkow notes that weight-loss plateaus often occur after losing about 10 percent of your body weight. "Your body senses that you're eating less and slows down its metabolism so you burn fewer calories," she explains. And if your journey to bulk up has plateaued, there's a good chance you need to eat more, change your workouts, or amp up the intensity.

Remember that eating nutritiously and exercising will benefit your health in so many ways, from reduced health risks to improved mood. If significantly gaining or losing muscle or fat is your goal, that's up to you — but it's not mandatory. If you're hoping to make a significant change, make sure to speak with your doctor (and/or professionals such as registered dietitians and certified personal trainers) for personalized help.

"Gaining muscle is hard and takes work," Berkow says." You have to lift heavy, eat a lot of protein, and find the balance of lifting enough while allowing for adequate recovery." Maintaining muscle and losing fat is possible, but it's very difficult to gain muscle and lose a significant amount of fat at the same time. It's often best to focus on one at a time, she says.

Samantha Brodsky is a former assistant editor at PS. She uses her gymnast background to inform her sports and fitness coverage, powering through Peloton videos in her free time.

Chandler Plante (she/her) is an assistant health and fitness editor for PS. She has over four years of professional journalism experience, previously working as an editorial assistant for People magazine and contributing to Ladygunn, Millie, and Bustle Digital Group.